Activated Carbons from Crosslinked Novolac Resin

Chemical Engineering Journal 156 (2010) 146–156Contents lists available at ScienceDirectChemical EngineeringJournalj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c ejHeavy metals uptake from aqueous solutions and industrial wastewaters by humic acid-immobilized polymer/bentonite composite:Kinetics and equilibrium modelingT.S.Anirudhan ∗,P.S.SuchithraDepartment of Chemistry,University of Kerala,Kariavattom,Trivandrum 695581,Indiaa r t i c l e i n f o Article history:Received 27January 2009Received in revised form 3October 2009Accepted 6October 2009Keywords:Humic acidPolymer/clay composite Heavy metal ion Adsorption Wastewater Regenerationa b s t r a c tThis study explored the feasibility of utilizing a novel adsorbent,humic acid-immobilized-amine-modified polyacrylamide/bentonite composite (HA-Am-PAA-B)for the adsorption of Cu(II),Zn(II)and Co(II)ions from aqueous solutions.The FTIR and XRD analyses were done to characterize the adsorbent material.The effects of pH,contact time,initial adsorbate concentration,ionic strength and adsorbent dose on adsorption of metal ions were investigated using batch adsorption experiments.The optimum pH for Cu(II),Zn(II)and Co(II)adsorption was observed at 5.0,9.0and 8.0,respectively.The mechanism for the removal of metal ions by HA-Am-PAA-B was based on ion exchange and complexation reactions.Metal removal by HA-Am-PAA-B followed a pseudo-second-order kinetics and equilibrium was achieved within 120min.The suitability of Langmuir,Freundlich and Dubinin-Radushkevich adsorption models to the equilibrium data was investigated.The adsorption was well described by the Langmuir isotherm model.The maximum monolayer adsorption capacity was 106.2,96.1and 52.9mg g −1for Cu(II),Zn(II)and Co(II)ions,respectively,at 30◦C.The efficiency of HA-Am-PAA-B in removing metal ions from dif-ferent industry wastewaters was tested.Adsorbed metal ions were desorbed effectively (97.7for Cu(II),98.5for Zn(II)and 99.2%for Co(II))by 0.1M HCl.The reusability of the HA-Am-PAA-B for several cycles was also demonstrated.© 2009 Elsevier B.V. All rights reserved.1.IntroductionHeavy metals contained in industrial effluents,constitute a major source of metal pollution of the environment,since they are persistent and cannot be degraded or destroyed and can be bio-magnified by aquatic organisms.Main industries containing heavy metals in its effluents are mining,metallurgical,nuclear power plants,metal coating,and battery production [1].Cu(II),Zn(II)and Co(II)ions are among the most common heavy metal ions in indus-try effluents.The accumulation of these contaminants in human body can cause severe health risk.According to U.S.Environmental Protection Agency (EPA)and WHO,the permissible limit of cop-per in drinking water is 1.3and 2.0mg dm −3,respectively [2].The WHO recommended tolerance limit for Zn(II)is 5.0mg dm −3[3]while that of Co(II)is limited to 0.05mg dm −3[4].Removal of these toxic contaminants is essential for environmental pollution con-trol and many researchers demand a cost effective yet recyclable process such as ion exchange and adsorption for removing heavy metal ions from wastewater.In recent years,solid adsorbents such∗Corresponding author.Tel.:+914712418782.E-mail address:tsani@ (T.S.Anirudhan).as clays,agricultural residues and industrial waste products have been widely used for the removal of heavy metals in low-cost wastewater treatment [5].Polymer/clay composites have been regarded as promising materials for many applications due to their unique properties,which include high particle dispersion,gas permeability,structural flexibility,fire retardance and thermal and mechanical stability.Although earlier workers [6]have investigated the adsorption per-formance of polymer/clay composites;a few studies are reported on the recovery of heavy metal ions by using polymer/clay com-posites.The removal of humic acids (HAs)from water suppliers has demonstrated great attention because (1)they are precursors of potentially calcinogenic chlorinated disinfective by-products in chlorine disinfection process [7]and (2)their high affinity for adsorbing various pollutants including heavy metals and pesticides.Adsorption is an effective and versatile method for the removal of HAs,when combined with an appropriate desorption step solving the problem of sludge disposal.The literature [8]contains several references to the adsorption of HA by various adsorbents which include:activated carbons,zeolites,clay minerals,alumina,resins,chitosan,fly ash,amino polyacrylonitrile fibers and hydrotalcites.In many cases after four or five cycles of repeated use,the adsor-bent materials cannot be reused and causes a disposal problem.The1385-8947/$–see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.cej.2009.10.011T.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156147Scheme1.Preparation route of HA-Am-PAA-B.disposal of the spent adsorbent in an economically sound manner is very important.This study follows from our previous investiga-tion[8],where a polyacrylamide/bentonite composite(PAA-B)with amine functionality(Am-PAA-B)was evaluated as an adsorbent for the removal of HA from aqueous solutions.HA is one of the major components of humic substances which contain both hydrophilic and hydrophobic molecules as well as many functional groups such as phenolic,carboxylic and hydroxyl groups connected to a skeleton of aliphatic and aromatic units. Because of the deprotonation of carboxylic and phenolic groups in weakly acidic to basic media,HA has negative charge and enhances the adsorption of cations through electrostatic interactions and/or complexation reactions.The acid dissociation constants(p K a’s)for various carboxylic groups have been reported to be3.0–5.0.[9]. Lower pH(<3.0)will cause the carboxyl functional groups of HA to be protonated to a higher extent and result in a stronger repulsion for a positively charged cations in the solution.However,at pHs greater than4.0,the carboxyl groups are deprotonated and favor the adsorption of positively charged cations.Metal ions bind to the carboxyl groups through ion exchange followed by a complexation reaction.The use of HA-immobilized ion exchange resin for the adsorption of uranium from aqueous solutions was investigated by Ho and Miller[10].Previously in our groups,we have demonstrated that HA-immobilized bentonite and HA-immobilized zirconium pillared clay can be used as good adsorbents for the removal of some heavy metals and some cationic dyes,respectively,from aqueous solutions[11,12].The objective of this study is to investigate the efficiency of spent adsorbent,i.e.,HA-immobilized Am-PAA-B(HA-Am-PAA-B)for the removal of Cu(II),Zn(II)and Co(II)ions from wastewaters.2.Experimental2.1.MaterialsThe bentonite(B),NNN N N N -hexamethylenediamine(HMD) and metal salts(CuCl2,ZnCl2and CoCl2)were obtained from Fluka,Switzerland.Analytical-grade acrylamide(AA),N,N -148T.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156methylenebisacrylamide(MBA),K2S2O8and ethylenediammine (en)were supplied by E.Merck(India)Ltd.Sodium salt of HA was purchased from Sigma–Aldrich(Germany).2.2.Preparation of Am-PAA-BAbout10g of the raw bentonite was stirred for12h with1L of 1.0M NaCl solution to replace all exchangeable cations with Na+, then centrifuged and washed several times with distilled water until Cl−was free.The product,Na-saturated bentonite(Na-B)was dried at105◦C,ground and sieved to obtain−80+230mesh size particles.To a homogenous suspension of10g of Na-B with250mL distilled water,20g of AA in50mL distilled water was added and stirred for2h and then1.6g MBA and500mg K2S2O8followed by0.5mL HMD was added to propagate the polymerization and heated in a water bath at60◦C.The polyacrylamide–bentonite composite obtained was then washed with hot water to eliminate homopolymer.It was dried at60◦C for24h and the product here-after designated as PAA-B.To introduce the amine functionality in PAA-B,10g of PAA-B was heated with50mL en at80◦C and pH11.0 for4h.The product amine-modified PAA-B(Am-PAA-B)was sep-arated from the solution and washed with water until thefiltrate was free from en,as indicated by the absence of any blue colour with ninhydrine reagent.The product,Am-PAA-B was dried at70◦C and sieved to80–230mesh size of particles(average diameter of 0.096mm).2.3.Preparation of HA-Am-PAA-BOur earlier work showed that maximum loading of HA onto Am-PAA-B from aqueous solution occurred at an initial pH of4.0.In order to prepare HA-immobilized Am-PAA-B(HA-Am-PAA-B),10g Am-PAA-B was suspended in100mL distilled water and500mL of 1.25mmol L−1HA was subsequently added to the suspension.The reaction mixture was then adjusted to pH4.0using NaOH and HCl solutions and then stirred continuously for24h at room temper-ature.The product,HA-Am-PAA-B wasfiltered and washed with water to remove any residual HA and dried at50◦C and sieved for particle size of80–230mesh.Scheme1represents the preparatory route of HA-Am-PAA-B.2.4.Characterization methods of the adsorbentThe X-ray powder diffraction patterns(XRD)of the samples were taken in a Rigaku diffractometer using Cu K␣radiation at a scanning speed of2◦min−1.The FTIR spectra were recorded with a Nicolet Protege460spectrophotometer between4000and 450cm−1using the KBr pellet technique.The cation exchange capacity was determined by ammonium acetate method[13].The total number of acidic groups and carboxylic groups present in the adsorbent sample was estimated using conductometric titra-tion methods proposed by James et al.[14].The surface area of the adsorbent was determined using methylene blue adsorption isotherm method.Apparent density of the adsorbent was deter-mined by pycnometric method using nitrobenzene as a displacing liquid using specific gravity bottle.A potentiometric method[15] was used to determine the pH of point of zero charge(pH pzc).The pH of the solution was measured with a Systronic microprocessor pH meter(model␮-362).2.5.Metal adsorption procedureA stock solution of1000mg L−1of Cu(II),Zn(II)and Co(II)ions was prepared in distilled water and corresponding concentration ranges for the experiments were obtained by diluting the stock solution with distilled water.A batch equilibrium techniquewas Fig.1.FTIR spectra of Na-B,Am-PAA-B,HA-Am-PAA-B and Cu(II)-loaded HA-Am-PAA-B.employed for the investigation of metal uptake by the HA-Am-PAA-B.Fifty milliliter of metal solution containing0.1g of the adsorbent in a100mL Erlenmeyerflask was agitated at200rpm in a temper-ature controlled water bath shaker(Labline Instruments Pvt.Ltd., Kochi,India)at30◦C.The initial pH of the solution was adjusted to a definite value using0.1M HCl or0.1M NaOH solutions.After attaining equilibrium,two phases were separated by centrifuga-tion at600rpm for5min and an aliquot of the supernatant was analyzed for metal by atomic absorption spectrometry(AAS).A GBC Avanta(A5450)AAS was used to determine the concentra-tion of Cu(II),Zn(II)and Co(II)ions in aqueous solutions.pH studies were carried out with an initial metal concentration of25mg L−1 in a pH range2.0–10.0for Zn(II)and Co(II)and2.0–6.0for Cu(II). The effect of ionic strength on metal ion adsorption was studied by conducting batch experiments at different ionic strengths of 0.001,0.005,0.01,0.05and0.1M NaCl and CaCl2.To determine the effect of contact time and adsorbate concentration,0.1g adsor-bent was added to50mL of different metal concentrations ranging from25to100mg L−1and equilibrated for4h.Isotherm experi-ments were performed using different metal concentrations ranged between10and300mg L−1.For desorption studies0.1g HA-Am-PAA-B equilibrated with50mL of10mg L−1metal solution and after the adsorption process,the adsorbed metal ions were eluted with different reagents.The eluted adsorbent was then washed thoroughly with distilled water to remove any residual desorb-ing reagents and placed into metal solution for the subsequent adsorption–desorption cycle.3.Results and discussion3.1.Adsorbent characterizationThe FTIR spectra of Na-B,Am-PAA-B and HA-Am-PAA-B and Cu(II)-loaded HA-Am-PAA-B are shown in Fig.1.The spectrum ofT.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156149Fig.2.XRD patterns of Na-B,Am-PAA-B,HA-Am-PAA-B and Cu(II)-loaded HA-Am-PAA-B.Na-B shows the basic characteristic peaks at3650and3410cm−1 (O–H stretching),1020cm−1(Si–O–Si bonds),760cm−1(deforma-tion Si–O bond)and534and423cm−1(bending modes of the Si–O bond).The shifts or change in peaks observed in the spectrum of Am-PAA-B compared to Na-B particularly for asymmetric stretch-ing(from1024to1045cm−1),deformation(from760to771cm−1) and bending(from534to543cm−1)of Si–O–Si bands indicate the interaction of Na-B with PAA.The broader band at3490cm−1for the Am-PAA-B spectrum may be due to the N–H stretching vibrations. The presence of two peaks near1574and1030cm−1was due to N–H bending and C–N stretching provides strong evidence for the presence of amino groups in the Am-PAA-B,while IR spectrum of Na-B did not exhibit these peaks.The formation of a chemical bond between the amino groups on the Am-PAA-B and HA being loaded is indicated by the IR spectrum of HA-Am-PAA-B when N–H bond vibrations(stretching and bending)were formed being shifted to 3976and1553cm−1due to HA immobilization.In addition,the spectrum of HA-Am-PAA-B shows new bands at 1720cm−1( c o)and1458cm−1( c–o)which are characteristics of the carboxyl(COOH)groups from the immobilized HA from the sur-face of Am-PAA-B.Moreover,the appearance of four peaks in the region600–900cm−1,which can be attributed to the polyphenyl groups of HA,is another evidence of the loading of HA onto Am-PAA-B.The characteristic carboxyl bands at1720and1458cm−1 are shifted to1706and1443cm−1after Cu(II)adsorption.This shifts in peaks observed after metal adsorption,indicate a chemical inter-action occurred between Cu(II)ions and carboxylate groups on HA. Moreover the peak at1368cm−1is indicative of C–O stretching at the benzene ring when Cu(II)gets coordinated with oxygen.The presence of Cu(II)ions due to adsorption can be confirmed by the band at517cm−1of Cu–O stretching vibration in the spectrum of Cu(II)-loaded HA-Am-PAA-B.The XRD patterns of Na-B,Am-PAA-B,HA-Am-PAA-B and Cu(II)-loaded HA-Am-PAA-B are shown in Fig.2.The XRD pattern showed that Na-B sample is rich in montmorillonite showing areflectionFig.3.Surface charge density as a function of pH.at2Â=5.14◦,which indicates a basal spacing of1.43nm.Besides, XRD pattern of Na-B showed the characteristic d values0.45,0.37, 0.26and0.15nm.The reflection at0.45nm further implied2:1 mineral type.The XRD pattern of Na-B was clearly affected by poly-mer insertion,as observed by the change of the(001),(002)and (003)reflections.The basal reflection was shifted from1.53to 2.49nm.This increase in basal spacing indicated intercalation of the matrix polymer.The broadening of the(001)reflection indi-cated that the ordered structure of the layers is disrupted due to the intercalation of the polymer.Loading of HA leads to a considerable decrease in crystallinity in comparison to Am-PAA-B indicated by the decreased number and intensity of reflection.The basal spac-ing of3.85nm in HA-Am-PAA-B suggested the presence of HA.The XRD pattern of Cu(II)-loaded HA-Am-PAA-B shows an increase in 2Âvalue and a decrease in basal spacing.The diffraction at2Â=5.6◦with a basal spacing of2.9nm in Cu(II)-HA-Am-PAA-B suggested the presence of Cu(II)ions.Fig.3represents the pH dependent surface charge of Na-B,Am-PAA-B and HA-Am-PAA-B.As shown,the Na-B,Am-PAA-B and HA-Am-PAA-B display point of zero charge at pH pzc3.0,7.0and 4.8,respectively,suggesting that HA-Am-PAA-B surface is more positive than that of Na-B and more negative than Am-PAA-B sur-face,since pH above the value of pH pzc the surface charge of the adsorbent has a negative charge,below that pH the clay has a positive charge.The apparent density of Na-B,Am-PAA-B and HA-Am-PAA-B was found to be1.19,1.59and1.71g mL−1,respectively. The total acidity and cation exchange capacity were found to be 0.43and0.39meq g−1for Na-B,and1.28and0.83meq g−1for HA-Am-PAA-B,respectively.The carboxylate group for HA-Am-PAA-B was found to be0.66meq g−1.The surface area of Na-B,Am-PAA-B and HA-Am-PAA-B was found to be150.3,203.5and336.3m2g−1, respectively.3.2.Effect of pH on metal adsorptionSince the surface charge of an adsorbent could be modified by changing pH of the solution,pH is one of the most important param-eters affecting the metal adsorption process.The effect of initial pH on the adsorption of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B is shown in Fig.4.The results presented show excellent removal capacities for Cu(II),Zn(II)and Co(II)ions by using HA-Am-PAA-B,where a similar profile of removal was observed.For comparison,metal hydroxide precipitation by NaOH is also given in Fig.4.It can be seen that at any pH,metal removal by adsorption on HA-Am-PAA-B is very much greater than the removal by hydrox-ide precipitation observed in the absence of adsorbent.With an increase of pH of the solution from2.0to6.0,Cu(II)removal capacity increased from30.0to99.0%at an initial concentration of25mg L−1. Similarly,when the initial pH of suspension increased from2.0to150T.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156Fig.4.Effect of pH on the removal of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B.10.0,the removal capacity increased from27.1to99.0%for Zn(II) and22.7to95.4%for Co(II)at an initial concentration of25.0mg L−1. It has been shown that thefinal pH is always less than the initial pH(Fig.4).In the case of Cu(II),when the initial pH of the reaction mixture varied between3.0and6.0,thefinal pH of the reaction mixture remained between2.7and4.7for an initial concentra-tion of25mg L−1.The possible sites on HA-Am-PAA-B for specific adsorption in acidic pH include H+ions in–COOH functional groups. Divalent Cu(II)ions displaced two protons from–COOH groups for each metal cations adsorbed while one proton is exchanged for each of the monovalent(Cu(OH)+)species adsorbed.At higher pH values(>5.5),the solubility product of Cu(OH)2is exceeded,there-fore,Cu(II)is removed from the solution by adsorption as well as by precipitation.Thus to correlate Cu(II)removal with adsorption(ion exchange),an optimum initial pH of5.0was chosen for performing all subsequent adsorption experiments.For Zn(II)and Co(II),pH9.0 and8.0,respectively,was selected to be the optimum initial pH for further studies.The decreased metal adsorption at low pH can be explained as follows:(i)in acidic region both the adsorbent(since pH pzc of the adsorbent is4.8,below which the adsorbent surface is positive) and adsorbate are positively charged and the net interaction is that of electrostatic repulsion and(ii)the positively charged metal ions faces a good competition with the higher concentration of H+ions present in the reaction mixture and(iii)generally,the carboxyl groups presented a p K a value between3.0and5.0[16].At pH lower than p K a,carboxylate groups carried positive charge,restricting access sites to metal ions as a result of repulsive forces and result-ing in a low uptake.At pH<5.0,the linked H+is released fromthe Fig.5.Effect of ionic strength on the removal of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B.active sites and adsorbed amount of metal ions is increased.In this pH range,it is believed that the ion exchange and complex for-mation process are the major mechanism for removal of metal ions from solution.The amount of metal ions adsorbed by HA-Am-PAA-B increased in the order of Cu(II)>Zn(II)>Co(II).3.3.Effect of ionic strengthFig.5shows the effect of ionic strength on the adsorption behav-ior of HA-Am-PAA-B towards heavy metal ions.As shown,in the presence of Na-and Ca-electrolyte there was a decrease in adsorp-tion capacity of HA-Am-PAA-B towards metal ions.When ionic strength of both electrolyte increased from0.001to0.1M,the total decrease in percentage removal of25mg L−1Cu(II),Zn(II)and Co(II)was20.7,24.5and26.3,respectively,for Ca-electrolyte and 16.4,18.2and19.8,respectively,for Na-electrolyte.This suggests that with increase in the concentration of chloride anions in metal ion solution,there is a possibility for the formation of uncharged species(CuCl2,ZnCl2and CoCl2)and negatively charged chloride complexes(CuCl3−,CuCl42−,ZnCl3−,ZnCl42−,CoCl3−and CoCl42−) that will invariably reduce the adsorption capacity of the adsor-bent[17]for positively charged cations.The adverse effect of ionic strength on metal uptake suggests the possibility of ion exchange mechanism being in operation in the adsorption process.Ca2+andT.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156151Na+ions can compete with metal ions for the same binding sites on the HA-Am-PAA-B surface and thus negatively affect the removal efficiency.3.4.Adsorption kineticsKinetic behavior of the adsorbent,towards Cu(II),Zn(II)and Co(II)ions,was examined by monitoring the extent of adsorption with respect to contact time and the time profiles are given in Fig.6. The adsorption was rapid for all the three metal ions;an interaction period30min supplied about73%adsorption where as the equi-librium was reached in approximately120min.After this period, the amount of adsorbed metal ions did not change significantly with time.The rapid uptake of metal ions onto HA-Am-PAA-B may indicate that most of reaction sites of the adsorbent are exposed for interaction with metal ions.The equilibrium time is indepen-dent of initial concentrations.The time profile of metal uptake is a single,smooth and continuous curve leading to saturation,suggest-ing the possible monolayer coverage of metal ions on the surface of the adsorbent.Due to the presence of MBA crosslink units in polymer/clay composite,the adsorbent possesses a high swelling capacity in water[18]and,consequently its network is sufficiently expanded to allow a fast diffusion process for the metal ions.This expanded network of the adsorbent favors the interaction between the cations and the most favorable adsorption sites(carboxylic groups)on the adsorbent surface.Furthermore,this may indi-cate that there is an ion exchange/complexation reaction between HA from adsorbent surface and metal ions because these ion exchange/complexation reactions are usually very fast as indicated by complexation studies of HA with metal ions[19].With increase in metal concentration from25to100mg L−1,the amount of metal adsorbed increased from11.47to47.31mg g−1for Cu(II),11.15to 44.71mg g−1for Zn(II)and10.98to34.37mg g−1for Co(II)indi-cating that the Cu(II)removal by adsorption on HA-Am-PAA-B is concentration dependent.Also,the amount of metal ions adsorbed by the adsorbent is of the following order:Cu(II)>Zn(II)>Co(II)for the concentrations studied.Two generally applied simplified kinetic models,i.e.,pseudo-first-order and pseudo-second-order equations are analyzed to model the adsorption kinetic data[20,21].The pseudo-first-order model is given by:q t=q e(1−e−k ad t)(1) where k1is the pseudo-first-order rate constants(min−1)and q e (mg g−1)is the pseudo-equilibrium adsorption corresponding to the initial metal ion concentration C0and q t(mg g−1)is the amount of metal adsorbed at any time t.On the other handpseudo-second-Fig.6.Adsorption kinetics of Cu(II),Zn(II)and Co(II)ions uptake onto HA-Am-PAA-B.order model is expressed asq t=k2q2e t1+k2q e t(2)where k2(g mg−1min−1)is the pseudo-second-order rate con-stant.The values of q e,k1and k2for different concentrations andTable1Kinetic parameters for the adsorption of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B.Metal ion C0(mg L−1)q e(exp)Pseudo-second-order Pseudo-first-orderk2(g mg−1min−1)q e(cal) 2R2k1(min−1)q e(cal) 2R2Cu(II)2511.47 6.83×10−211.580.060.9990.41510.790.560.994 5022.52 4.02×10−222.430.040.9990.31620.960.870.987 7536.980.71×10−237.010.070.9990.16434.74 1.670.983 10047.310.39×10−247.770.940.9950.11745.67 1.540.967Zn(II)2511.15 2.56×10−211.380.020.9990.15910.130.810.982 5021.23 1.06×10−222.110.420.9950.11220.56 2.570.959 7535.580.32×10−236.550.890.9970.07331.23 5.760.969 10044.710.28×10−245.18 1.660.9930.05741.34 4.470.968Co(II)2510.98 1.06×10−211.070.070.9990.07510.020.430.961 5017.880.43×10−218.130.590.9970.06416.760.720.944 7525.370.28×10−225.780.150.9990.03424.47 1.910.984 10034.370.21×10−235.170.760.9970.04633.38 1.800.931152T.S.Anirudhan,P.S.Suchithra/Chemical Engineering Journal156 (2010) 146–156 temperatures were calculated using non-linear regression analy-sis and the results are shown in Table1.As shown,on comparisonwith pseudo-first-order,pseudo-second-order kinetic expressionyielded the best results for experimental kinetic data with highervalues of R2and lower 2values.As shown in Table1,the valueof rate constant k2decreases with increasing initial concentrationand surface loading.Higher surface loadings would result in lessdiffusion efficiency and a high competition of metal ions for afixedreaction sites,consequently a lower k2values were observed.More-over,Fig.6also represents the best agreement of the experimentalkinetic data with the pseudo-second-order kinetic model.3.5.Adsorption isothermThe relation of metal ion concentration in the bulk and theadsorbed amount at the interface is a measure of the positionof equilibrium in the adsorption process and can generally beexpressed by one or more of a series of isotherm models.Theinterpretation of adsorption data through theoretical or empiricalequations is essential for the quantitative estimation of the adsorp-tion capacity or amount of the adsorbent required to remove theunit mass of pollutant from wastewater.Fig.7shows adsorptionisotherms of Cu(II),Zn(II)and Co(II)ions at30◦C.All the threemetals’adsorption onto HA-Am-PAA-B was found to be concen-tration dependent.As calculated from adsorption data,the amountof Cu(II),Zn(II)and Co(II)increased from4.37to107.85,4.25to96.75and4.13to52.15mg g−1,respectively,when the initial con-centration increased for all the three from10to300mg L−1.Inthis study the experimental data were correlated by the non-linearforms of Langmuir,Freundlich and Dubinin-Radushkevich adsorp-tion isotherm equations:Langmuir:q e=Q0bC e1+bC e(3)Freundlich:q e=K F C1/ne(4) Dubinin-Radushkevich:q e=q m(ε2)−ˇ(5) where q e is the quantity of metal adsorbed at equilibrium over the mass of adsorbent material(mg g−1)and C e is equilibrium concen-tration(mg L−1)of the adsorbate species in solution.Q0and b are Langmuir constants related to the monolayer adsorption capacity (mg g−1)and energy or intensity of adsorption(L mg−1).The Fre-undlich constants K F and1/n are related to the adsorption capacity and heterogeneity factors related to binding strength,respectively. q m is D-R constant related to theoretical saturation capacity andεis the Polanyi potential,equal to RT ln(1+1/C e),where R is the gas constant(kJ mol−1K−1)and T is the temperature(K).A detailed analysis of the correlation coefficients obtained for these isotherms by using non-linear optimization method for Cu(II), Zn(II)and Co(II)adsorption,showed that all the three isotherm equations adequately describe the adsorption data,but are bet-terfitted to Langmuir,from which we can assume that adsorption of Cu(II),Zn(II)and Co(II)onto HA-Am-PAA-B would not take place beyond a monolayer coverage and all adsorption sites are equivalent with uniform energies of adsorption with out any interaction between the adsorbed molecules.Fig.7also shows a comparison between the theoretical Langmuir,Freundlich and D-R isotherms and the experimental data.The resulting parameters for all the three isotherms are tabulated in Table2.As shown,Q0 which is indicative of adsorption capacity changed in the order of Cu(II)>Zn(II)>Co(II).Similar results are also reported by earlier workers[22].The Freundlich exponent1/n gives an indication of the favorability of adsorption.Values of1/n<1.0represent favor-able adsorption condition.The values of1/n obtained in the present study for all the three metal ions are less than unity,indicatethe parison of the experimental and modelfits of the Langmuir,Freundlich and D-R isotherms for the adsorption of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B.favorable adsorption of Cu(II),Zn(II)and Co(II)ions onto HA-Am-PAA-B.The value of D-R constantˇis related to the adsorption free energy E(kJ mol−1),which is defined as the free energy change required to transfer1mol of ions from solution to the solid sur-face.From theˇvalues the values of E can be calculated as E=(2ˇ)−1/2.The magnitude of E is useful to determine the type of adsorption reaction.Physisorption processes have adsorption energy in the range1–8kJ mol−1,while chemisorption processes have adsorption energy in the range20–40kJ mol−1.On the other hand,adsorption can be explained by ion exchange if E values lie between8.0and16.0kJ mol−1[23].The calculated E values (Table3)for Cu(II),Zn(II)and Co(II)adsorption onto HA-Am-PAA-B are ranged between7.87and8.46kJ mol−1indicating an ion exchange reaction,which support the idea,that the adsorption of metal ions onto HA-Am-PAA-B mainly proceeds by binding surface functional groups,as stated earlier.。

Application of Fenton Õs reagent to regenerate activatedcarbon saturated with organochloro compoundsLuciana C a ssia Toledo,Ana Cl a udia Bernardes Silva,Rodinei Augusti,Rochel Montero Lago *Departamento de Qu ımica––ICEx,Universidade Federal de Minas Gerais,Av.Ant ^o nio Carlos 6627,Belo Horizonte,Minas Gerais 31270-901,Brazil Received 5December 2001;received in revised form 25September 2002;accepted 25September 2002AbstractIn this work Fenton Õs reagent was used to treat activated carbon saturated with organochloro compounds for the oxidation of the adsorbed contaminants and the regeneration of the carbon adsorbent.Activated carbon containing adsorbed chlorinated model substrates such as chlorobenzene,tetrachloroethylene,chloroform or 1,2-dichloropropane was treated with Fenton Õs reagent at room temperature resulting in a rapid consumption of the organochloro com-pounds.Thermogravimetric,infrared,BET surface area and MIMS adsorption studies showed that Fenton Õs treatment has no significant effect on the physico-chemical properties of the activated carbon.The used carbon adsorbents can be efficiently regenerated and recycled with no loss of its adsorption capacity even after five consecutive treatments with Fenton Õs reagent.Ó2002Elsevier Science Ltd.All rights reserved.Keywords:Activated carbon;Regeneration;Fenton;Organochloro compounds;MIMS1.IntroductionActivated carbon is extensively used as an adsorbent.Due to its high surface area and porous structure it can physically adsorb gases and compounds dispersed or dissolved in liquids (Matson and Mark,1971).When activated carbon is used to adsorb toxic compounds or to decontaminate effluents,it becomes a hazardous waste that should be treated or disposed properly.In-cineration,which can be used to eliminate the solid waste material,has the disadvantage of not recycling the activated carbon.Moreover,the incineration of acti-vated carbon saturated with organochloro compounds might produce and release to the air compounds withgreater toxicity,such as chlorodioxines and chloro-dibenzofuranes (Buser et al.,1978).Economical application of activated carbon as an adsorbent depends on an efficient means of regenerating and recycling after its adsorptive capacity has been reached.Several methods have been studied for the treatment and regeneration of activated carbon satu-rated with organic compounds,e.g.biological treatment (Scholz and Martin,1997;Tanaka and Miyake,1999),solvent extraction (Ruthven,1984),thermal regenera-tion (Mishra et al.,1995;Yustratov et al.,1998),wet oxidation (Ding et al.,1987;Lee et al.,1999),electro-chemical treatment (Clifford et al.,1997)and the use of radiation (Borong et al.,1997).Biological treatment is not efficient and shows several limitations concerning the non-biodegradability and the toxicity of some con-taminants to microorganisms (Scholz and Martin,1997;Tanaka and Miyake,1999).The cost and toxicity of some common solvents make the solventextractionChemosphere 50(2003)1049–1054/locate/chemosphere*Corresponding author.Tel.:+55-31-3499-5719;fax:+55-31-3499-5700.E-mail address:rochel@dedalus.lcc.ufmg.br (go).0045-6535/03/$-see front matter Ó2002Elsevier Science Ltd.All rights reserved.PII:S 0045-6535(02)00633-1method prohibitive.Moreover,a further treatment to destroy the extracted contaminants is necessary.During thermal regeneration and wet oxidation the organic contaminants are destroyed concomitantly with the re-generation of the activated carbon.In thefirst method the organics decompose thermally;in wet oxidation, oxidation in aqueous solution and in air via a free rad-ical mechanism occurs(Lee et al.,1999).However,the high temperatures necessary for both processes are very energy demanding,requiring special installations and frequently leading to loss of carbon surface area mainly by destruction of micropores.Moreover,organochloro contaminants are not efficiently destroyed by these thermal technologies.In this work,FentonÕs reaction at very mild condition was used to destroy adsorbed organochloro contami-nants and to regenerate the activated carbon.FentonÕs reagent is one of the most promising systems to treat aqueous effluents containing organic contaminants(Clif-ford et al.,1997).This system is based on hydrogen peroxide,a clean oxidizer,and a ferrous salt to generate hydroxyl radicals HOÅ(Eq.(1)),which are very active to oxidize organic molecules in aqueous medium(Haber and Weiss,1934;Goldstein and Meyerstein,1999).Fe2þþH2O2!Fe3þþHOÀþHOÅð1ÞFentonÕs reaction has been extensively studied and has shown high efficiency to destroy most classes of organ-ics,even the more refractory organochlorinated com-pounds,in aqueous solution(Clifford et al.,1997).On the other hand,no work has been carried out yet on its use for the oxidation of adsorbed organic molecules and regeneration of adsorbents.2.ExperimentalThe chemicals were purchased from Aldrich or Merck and were used without any additional treatment. Experiments with FentonÕs reagent were carried out with 11mmol of H2O2(30%),0.27mmol of ferrous ammo-nium sulfate and sulfuric acid.For the reactions,50mg of activated carbon(Aldrich with BET surface area of 720m2gÀ1,100mesh)were impregnated by direct addition of50mg of the organochloro compound (chlorobenzene,tetrachloroethylene,1,2-dichloropro-pane,chloroform).In a typical experiment,the impregnated activated carbon was mixed with10ml of water,the pH was ad-justed to3with a H2SO4solution and the H2O2and Fe2þsalt added(molar ratio organochloro/H2O2/Fe2þof ap-proximately1/25/0.6).The reactionflask was kept at room temperature and after the reaction,40ml of etha-nol were added for extraction of the reaction mixture and analysis by gas chromatography(Shimadzu17A,FID detector,Carbowax20M capillary column).The total organic carbon(TOC)measurements were carried out in a5000A Shimadzu instrument calibrated with glucose.For the recycling studies,the activated carbon was consecutively submitted tofive cycles of impregnation with chlorobenzene and treatment with FentonÕs re-agent.After each cycle the carbon was analyzed by IR spectroscopy(Mattson Instruments FTIR),thermo-gravimetry(Mettler TA4000,TG50H Shimadzu,N2flow,10°C minÀ1)and by membrane introduction mass spectrometry(MIMS)(Lauritsen and Kotiaho,1996; Augusti et al.,1998;Silva et al.,1999)adsorption ex-periments.In the adsorption experiments an aqueous solution of the organic compound,with concentration of30mg lÀ1, was passed through the activated carbonfilter and then through the MIMS membrane probe in order to moni-tor adsorption(Fig.1).Theflow rate was5.0ml minÀ1. In a typical MIMS adsorption experiment(see in Fig.2 the adsorption of chlorobenzene on activated carbon)a high intensity m/z112(C6H5Clþ)signal can be observed initially as the solution is pumped directly to the mem-brane probe.When the4-way valve is switched the so-lution passes through the activated carbonfilter and the chlorobenzene is adsorbed resulting in a decrease of the m/z112signal.As the activated carbon becomes satu-rated,the adsorption of the chlorobenzene decreases and the signal m/z112increases.After complete saturation of the activated carbon no chlorobenzene is adsorbed and the MIMS m/z112signal returns to its original intensity.From the integrated area over the MIMS ad-sorption profiles(Fig.2)the adsorption capacity of the activated carbon can be obtained.Chloride was deter-mined by precipitation with AgNO3and analysis of the excess silver by atomic absorption(Hitachi Z-8200). 3.Results and discussion3.1.Application of Fenton’s reagent to oxidize adsorbed organochloro compoundsAlthough FentonÕs reaction has been extensively studied little work(L€u cking et al.,1998)has been done on its use for the oxidation of adsorbed organic mole-cules.In this work,it was observed that FentonÕs reagent was very efficient to oxidize organochloro compounds adsorbed on the surface of activated carbon.Under the reaction conditions(organochloro/H2O2/Fe2þmolar ratio of1/25/0.6at room temperature)the following conversions were observed after2h reaction:%100% tetrachloroethylene(below the detection level),99% chloroform,99%1,2-dichloropropane and90%chloro-benzene.Blank experiments using only H2O2and acti-vated carbon without Fe2þshowed chlorobenzene conversion lower that5%.1050L.C.Toledo et al./Chemosphere50(2003)1049–1054Although high conversions were produced,the or-ganochloro was not completely mineralized under the reaction conditions employed.Fig.3shows chloroben-zene consumption and chloride production during Fen-ton Õs reaction.It can be observed that chlorobenzene was rapidly consumed with 84%conversion after 30min,but chloride formation reaches only 45%.These results suggest that the mineralization of chlorobenzene to HCl,CO 2and H 2O is not complete and part of the chlorine is still in the form of organic intermediates.TOC measurements indicated the presence of 5.4mg l À1of organic carbon after the reaction.Further optimiza-tion studies are necessary to completely mineralize the organochloro compounds.3.2.Effect of Fenton’s treatment on the physico-chemical properties of activated carbonThe effect of Fenton Õs treatments on the physico-chemical characteristics of the activated carbon was alsoinvestigated.The activated carbon was subjected to five consecutive Fenton reactions and after eachtreatmentFig.1.Scheme of MIMS adsorption experiments.L.C.Toledo et al./Chemosphere 50(2003)1049–10541051was analyzed by IR spectroscopy,TG and MIMS ad-sorption of chlorobenzene.For these experiments all the samples were exhaustively washed after each FentonÕs treatment and carefully dried at100°C under vacuum. For comparison,the untreated original activated carbon was also washed with water and dried under vacuum.TG analyses(Fig.4)showed for the untreated carbon a weight loss of approximately8%at the on-set tem-perature of610°C probably related to the decomposi-tion of more stable surface oxygen groups such as ketones,ethers and hydroxyls originally present in the structure of the activated carbon(Fisher,1991).It can be observed that after1,2,3,4and5FentonÕs treat-ment,the activated carbon shows constant weight losses of approximately13–15%setting on at%440°C.Blank experiments,treating the carbon only with H2O2/Fe2þwithout chlorobenzene showed similar TG results,sug-gesting that the weight losses observed are probably related to the decomposition of more reactive surface oxygenated groups such as hydroxylic,generated by FentonÕs reagent.The IR spectra of activated carbon samples after the third and thefifth treatment are shown in Fig.5.The appearance of absorption in the range3300–3600cmÀ1 for the carbon treated with Fe2þ/H2O2can be observed. This IR broad band is probably related to the presence of O–H surface groups or OH–H2O surface association (Zawadzki,1989).The MIMS adsorption studies of the activated car-bons treated with FentonÕs reagentfive times are dis-played in Fig.6.It can be observed that the adsorption capacity for chlorobenzene on the activated carbon does not decrease after FentonÕs treatments.Moreover,the measured BET surface area and pore size distribution after FentonÕs treatment(718m2gÀ1)was very similar to that measured for the original activated carbon(720 m2gÀ1).Several studies in the literature(Gomez-Serrano et al., 1996;Koizumi,1996;Oosawa,1996;L€u cking et al., 1998;Shinmyou and Yang,1998)show that activated carbon promotes the H2O2decomposition,probably via the formation of radicals of the hydroxyl and hydro-peroxyl types.Probably,these radicals can also promote the oxidation of the organochloro compounds.The TG and IR data discussed above suggest that radicals,es-pecially the hydroxyl HOÅ,produced by FentonÕs re-agent are to some extent hydroxylating the activated carbon surface.The hydroxylation appears to be much more pronounced in thefirst treatment,since no sig-nificant increase in TG weight loss was observed for the subsequent reactions(Figs.4and6).On the other hand,FentonÕs reagent is not affecting significantly the porous structure,the surface area or the surface chemical properties of the activated carbon sinceno change in the adsorption capacity for chlorobenzene was observed.3.3.Application of Fenton’s reagent in solution versus on activated carbonThe efficiency of Fenton Õs for the oxidation of chlo-robenzene system was compared for the reaction carried out in solution and on activated carbon.The results are displayed in Table 1.The study in solution was carried out with 50mg chlorobenzene dissolved in 1L of water and the reaction was monitored by MIMS (Silva et al.,1999).The chlo-robenzene conversion after 30min was 66%and no significant increase was observed for longer reaction times (Fig.7).On the other hand,in the presence of activated carbon,using 10ml reaction volume and the same amounts of Fe 2þand H 2O 2,higher organochloro conversions (84%)are obtained after 30min.On both cases the initial TOC of 32mg was reduced to approx-imately 6mg.From Table 1it can be observed that the smaller reaction volume (10ml)required approximately100times less sulfuric acid necessary to adjust the pH in the process.The use of Fenton Õs reagent to treat large volumes of contaminated aqueous effluents with low concentration of organic contaminants shows several drawbacks such as:(i)large amounts of Fe 2þ,H 2O 2and H 2SO 4are necessary for the process,(ii)after the treatment the effluent must be neutralized to pH 7which leads to the (iii)formation of large amounts of sludge (Tedder and Pohland,1993;Benitez et al.,1999;Kuo and Lo,1999).A process,which can potentially deal with these draw-backs,is a combination of two processes:adsorption and Fenton Õs treatment.In this combined process the organic compound is first adsorbed from a large volume of effluent and pre-concentrated on an adsorbent such as activated carbon.The saturated adsorbent is then trea-ted with Fenton Õs reagent for the destruction of ad-sorbed contaminant and regeneration of the adsorbent.4.ConclusionsAlthough Fenton Õs reagent has been extensively studied in the past decades this work is the first attempt to use it to regenerate activated carbon saturated with organic contaminants.Fenton Õs reagent was very effi-cient to destroy organics adsorbed on activated carbon,even the more refractory organochloro compounds.The activated carbon can be efficiently regenerated and re-cycled with no loss of its adsorption capacity or surface area.AcknowledgementsThe authors wish to acknowledge the financial sup-port from CNPq and FAPEMIG.ReferencesAugusti,R.,Dias, A.O.,Rocha,L.L.,Lago,R.M.,1998.Kinetics and mechanism of benzene derivatives degradation with Fenton Õs reagent 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10.5666On activated carbon0.010.005845aAfter 30min reaction.bTOC expressed in mg ofcarbon.L.C.Toledo et al./Chemosphere 50(2003)1049–10541053Ding,J.,Snoeyink,V.L.,Larson,R.A.,Recktenwalt,M.A., Wedeking, C.A.,1987.Effects of temperature,time and biomass on wet air regeneration of carbon.Journal of Water Pollution Control Federation59(3),139–144. 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Journal of Hazardous Materials 181 (2010) 535–542Contents lists available at ScienceDirectJournal of HazardousMaterialsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /j h a z m atAdsorptive removal of methyl orange from aqueous solution with metal-organic frameworks,porous chromium-benzenedicarboxylatesEnamul Haque a ,Ji Eun Lee a ,In Tae Jang b ,Young Kyu Hwang b ,Jong-San Chang b ,Jonggeon Jegal c ,Sung Hwa Jhung a ,∗aDepartment of Chemistry,Kyungpook National University,Daegu 702-701,Republic of KoreabResearch Center for Nanocatalysts,Korea Research Institute of Chemical Technology,P.O.Box,107,Yusung,Daejeon 305-600,Republic of Korea cMembrane and Separation Research Center,Korea Research Institute of Chemical Technology,P.O.Box 107,Yusung,Daejeon 305-600,Republic of Koreaa r t i c l e i n f o Article history:Received 8February 2010Received in revised form 8May 2010Accepted 10May 2010Available online 16 May 2010Keywords:Porous chromium-benzenedicarboxylates MOFsMethyl orange DyeAdsorption Removala b s t r a c tTwo typical highly porous metal-organic framework (MOF)materials based on chromium-benzenedicarboxylates (Cr-BDC)obtained from Material of Institute Lavoisier with special structure of MIL-101and MIL-53have been used for the adsorptive removal of methyl orange (MO),a harmful anionic dye,from aqueous solutions.The adsorption capacity and adsorption kinetic constant of MIL-101are greater than those of MIL-53,showing the importance of porosity and pore size for the adsorption.The performance of MIL-101improves with modification:the adsorption capacity and kinetic constant are in the order of MIL-101<ethylenediamine-grafted MIL-101<protonated ethylenediamine-grafted MIL-101(even though the porosity and pore size are slightly decreased with grafting and further protonation).The adsorption capacity of protonated ethylenediamine-grafted MIL-101decreases with increasing the pH of an aqueous MO solution.These results suggest that the adsorption of MO on the MOF is at least partly due to the electrostatic interaction between anionic MO and a cationic adsorbent.Adsorption of MO at various temperatures shows that the adsorption is a spontaneous and endothermic process and that the entropy increases (the driving force of the adsorption)with MO adsorption.The adsorbent MIL-101s are re-usable after sonification in water.Based on this study,MOFs can be suggested as potential re-usable adsorbents to remove anionic dyes because of their high porosity,facile modification and ready re-activation.© 2010 Elsevier B.V. All rights reserved.1.IntroductionRecently,considerable amount of waste water having color has been generated from many industries including textile,leather,paper,printing,dyestuff,plastic and so on [1].Removal of dye mate-rials from water is very important because water quality is greatly influenced by color [1]and even small amount of dyes is highly visible and undesirable.Moreover,many dyes are considered to be toxic and even carcinogenic [1–3].It is difficult to degrade dye materials because they are very sta-ble to light and oxidation [3].For the removal of dye materials from contaminated water,several methods such as physical,chemical and biological methods have been investigated [1,3].Among the proposed methods,removal of dyes by adsorption technologies is regarded as one of the competitive methods because adsorption does not need a high operation temperature and several color-ing materials can be removed simultaneously [1].The versatility∗Corresponding author.Fax:+82539506330.E-mail address:sung@knu.ac.kr (S.H.Jhung).of adsorption,especially with activated carbons,is due to its high efficiency,economic feasibility and simplicity of design [3].Methyl orange (MO)is one of the well-known acidic/anionic dyes,and has been widely used in textile,printing,paper,food and pharmaceutical industries and research laboratories [2].The struc-ture of MO is shown in Scheme 1and the removal of MO from water is very important due to its toxicity [2,3].Harmful MO is selected in this study as a representative acidic dye.Several adsorbents such as ammonium-functionalized MCM-41and layered double hydroxides (LDH)have been studied for the removal of MO dye [4,5].Adsorbents,including activated carbon,made from wastes attract attention to decrease the cost of adsorp-tion [2,6].Agricultural wastes such as lemon [7],banana and orange peel [8]and biopolymers [9]like alginate have also been used.Functionalized adsorbents such as hyper-crosslinked polymers [10]and diaminoethane sporollenin [11]have also been studied.For efficient separation of adsorbent from liquid after adsorption,magnetic particles have also been dispersed/incorporated in the adsorbent [9,12].The thermodynamics parameters of MO adsorption have been studied over various adsorbents [2,5–7,10].In every case,the G0304-3894/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2010.05.047536 E.Haque et al./Journal of Hazardous Materials181 (2010) 535–542Scheme1.is negative for spontaneous adsorption;however H depends on adsorbents[2,5–7,10]and S is generally positive[2,5–7]. The adsorption kinetics has been interpreted with various models [2–10]and the adsorption of MO over MCM-41illustrates that the adsorption process is composed of complex processes like diffusion in surface or mesopore and adsorption on mesopore[4].Moreover, the kinetic constants vary widely depending on the adsorbents [2–10].Metal-organic frameworks(MOFs)are crystalline porous mate-rials which are well known for their various applications[13–20]. The particular interest in MOF materials is due to the easy tunability of their pore size and shape from a microporous to a mesoporous scale by changing the connectivity of the inorganic moiety and the nature of organic linkers[13–15].MOFs are especially inter-esting in thefield of adsorption,separation and storage of gases and vapors[16,19].For example,the storage of hydrogen[16]and carbon dioxide/methane[21]using MOFs has been extensively investigated.The removal of hazardous materials such as sulfur-containing materials has also been studied[22,23].Among the numerous MOFs reported so far,two of the most topical solids are the porous chromium-benzenedicarboxylates (Cr-BDCs)namely MIL-53[24](MIL stands for Material of Insti-tute Lavoisier)and MIL-101[25,26],which are largely studied for their potential -53with a chemical formula of Cr(OH)[C6H4(CO2)2]·n H2O,has an orthorhombic structure and pore volume of0.6cc/g[24].MIL-101,Cr3O(F/OH)(H2O)2[C6H4(CO2)2], has a cubic structure and huge pore volume of1.9cc/g[25,26].The pore sizes of MIL-53and MIL-101are around0.85and2.9–3.4nm, respectively[24–26].MIL-53is very interesting due to the breath-ing effect[27],and has been widely studied for adsorption[23]and drug delivery[20,28].MIL-101is a very important material due to its mesoporous structure and huge porosity,and is widely studied for adsorption[29],catalysis[30]and drug delivery[20,28].However,so far,there has been no report of the use of MOFs including Cr-BDCs in the removal of dye materials.In this work,we report,for thefirst time,the results of the adsorption of MO over MOFs,especially well-studied Cr-BDCs,to understand the charac-teristics of adsorption and possibility of using MOFs as adsorbents for the removal of dye materials from waste water.2.ExperimentalThe Cr-BDCs such as MIL-53and MIL-101were prepared follow-ing the reported methods[24–26,31,32].Ethylenediamine-grafted MIL-101(ED-MIL-101)was obtained by grafting ethylenediamine according to the method reported earlier[26,30].The protonated ED-MIL-101(PED-MIL-101)was obtained by acidification of ED-MIL-101with0.1M HCl solution at room temperature for6h. Activated carbon was purchased from Duksan chemical company (granule,size:2–3mm).The textural properties of the adsor-bents were analyzed with a surface area and porosity analyzer (Micromeritics,Tristar II3020)after evacuation at150◦C for12h. The surface area,pore volume and average pore size were calcu-lated using the nitrogen adsorption isotherms.An aqueous stock solution of MO(1000ppm)was prepared by dissolving MO(molecular formula:C14H14N3NaO3S,molecu-lar weight:327.34,Daejung Chemicals co.Ltd.,Korea)in deionized water.Aqueous MO solutions with different concentrations of MO (5–200ppm)were prepared by successive dilution of the stock solution with water.The MO concentrations were determined using the absorbance(at464nm)of the solutions after getting the UV spectra of the solution with a spectrophotometer(Shimadzu UV spectrophotometer,UV-1800).The calibration curve was obtained from the spectra of the standard solutions(5–50ppm)at a specific pH5.6.Before adsorption,the adsorbents were dried overnight under vacuum at100◦C and were kept in a desiccator.An exact amount of the adsorbents(∼10mg)was put in the aqueous dye solutions (50mL)havingfixed dye concentrations from20ppm to200ppm. The MO solutions(pH:5.6)containing the adsorbents were mixed well with magnetic stirring and maintained for afixed time(10min to12h)at25◦C.After adsorption for a pre-determined time,the solution was separated from the adsorbents with a syringefil-ter(PTFE,hydrophobic,0.5␮m),and the dye concentration was calculated,after dilution(if necessary),with absorbance obtained using UV spectra.The adsorption rate constant was calculated using pseudo-second or pseudo-first order reaction kinetics[33–35]and the maximum adsorption capacity was calculated using the Lang-muir adsorption isotherm[33,36]after adsorption for12h.To get the thermodynamic parameters of adsorption such as G(free energy change), H(enthalpy change)and S(entropy change) the adsorption was further carried out at35and45◦C.To determine the adsorption capacity at various pHs,the pH of the MO solution was adjusted with0.1M HCl or0.1M NaOH aqueous solution.The used adsorbent was activated with deion-ized water(0.05g adsorbent in25ml water)under ultrasound (Sonics and Materials,USA;Model:VC X750,power:750W,ampli-tude;35%)at room temperature for60min(temperature raised to 65◦C–70◦C after sonification).After separation,the adsorbent was dried and reused for the next adsorption.3.Result and discussion3.1.Adsorption kineticsTo understand the adsorption kinetics,MO was adsorbed at var-ious times up to12h,and the quantity of adsorbed MO is displayed in Fig.1when the initial MO concentration is30-50ppm.As shown in Fig.1,the adsorbed quantity of MO is in the order of acti-vated carbon<MIL-53<MIL-101<ED-MIL-101<PED-MIL-101for the whole adsorption time from any initial MO concentration.The adsorbed MO slightly increases with the initial MO concentration, showing the favorable adsorption at high MO concentration.The adsorption time needed for saturation of the adsorbed amount is in the order of activated carbon>MIL-53>MIL-101>ED-MIL-101>PED-MIL-101(Supplementary data Fig.S1).The adsorption over modified MIL-101s is practically completed in2h,showing the rapid adsorption of MO over the modified MIL-101s.However, the adsorbed amount increases steadily with time over the acti-vated carbon.To compare the adsorption kinetics precisely,the changes of adsorption amount with time are treated with the versa-tile pseudo-second-order kinetic model[33–35]because the whole data during adsorption time can be treated successfully:dq tdt=k2(q e−q t)2(1) or,tq t=1k2q2e+1q et(2)where q e:amount adsorbed at equilibrium(mg/g);q t:amount adsorbed at time t(mg/g);t:adsorption time(h).E.Haque et al./Journal of Hazardous Materials181 (2010) 535–542537Fig.1.Effect of contact time and initial MO concentration on the adsorption of MO over thefive adsorbents:(a)C i=30ppm;(b)C i=40ppm;(a)C i=50ppm.Therefore,the second-order kinetic constant(k2)can be calcu-lated byk2=slope2int erceptwhen the t/q t is plotted against t.Fig.2shows the plots of the pseudo-second-order kinetics of the MO adsorption over thefive adsorbents at threeinitial Fig.2.Plots of pseudo-second-order kinetics of MO adsorption over thefive adsor-bents:(a)C i=30ppm;(b)C i=40ppm;(a)C i=50ppm.dye concentrations.The calculated kinetic constants(k2)and cor-relation coefficients(R2)are shown in Table1.The adsorption kinetic constants for MO adsorption are in the order of activated carbon<MIL-53<MIL-101<ED-MIL-101<PED-MIL-101,similar to the adsorbed quantity(Fig.1).Therefore,PED-MIL-101is the most effective adsorbent for MO removal in the viewpoint of adsorption amount and rate.538 E.Haque et al./Journal of Hazardous Materials181 (2010) 535–542 The adsorption kinetic constants over activated carbon and Cr-BDCs are larger than those over crosslinked polymer[10]andactivated carbon(obtained from agricultural product,Phragmitesaustralis)[3].On the contrary the constants are smaller than theconstants over NH3+-MCM-41,activated carbon(entrapping mag-netic cellulose bead)[12],lemon peel[7]and alginate bead[9].The kinetic constants over activated carbon and Cr-BDCs increaseslightly with increasing the initial MO concentration,showingrapid adsorption in the presence of MO in high concentration.Theincrease of the kinetic constant with increasing initial adsorbateconcentration has been reported too[33,37,38].The kinetic con-stants of adsorption over Cr-BDCs show that the adsorption overPED-MIL-101is the fastest and the adsorption kinetics increaseswith modification of virgin MIL-101.The kinetic constant over PED-MIL-101is around10times greater than that of the activated carbonunder the experimental conditions.The adsorption data were also analyzed using the pseudo-first-order kinetic model[33]:ln(q e−q t)=ln q e−k1t(3)Therefore,thefirst order kinetic constant(k1)can be calculatedbyk1=−slope when the ln(q e−q t)is plotted against t.The plots of the pseudo-first-order kinetics of the dye adsorp-tions over thefive adsorbents at the initial MO concentrations of30–50ppm are shown in Fig.S2(adsorption time is only0–1hfor good linearity[33])and the kinetic constants are displayed inTable S1.Similar to the second-order kinetic constants,the rateconstant generally increases in the order of activated carbon<MIL-53<MIL-101<ED-MIL-101<PED-MIL-101,confirming once againthe most rapid adsorption over PED-MIL-101.However,the lin-earity of thefirst order kinetics is relatively poor(low correlationcoefficients R2).The fast adsorption of MO over MIL-101,compared with theadsorption over MIL-53,is probably due to the large pore size ofMIL-101as the kinetic constant of adsorption generally increaseswith the increasing pore size of a porous material not only inliquid-phase adsorption[39,40]but also in gas phase adsorption[41].However,the kinetic constants of the MIL-101s show that thepore size of the MIL-101s(Table1)does not have any effect on thekinetics of adsorption,suggesting the presence of a specific inter-action between PED-MIL-101or ED-MIL-101and MO because theadsorption kinetic constant increases with increasing pore size ifthere is no specific interaction between adsorbate and adsorbent[39–41].3.2.Adsorption thermodynamicsThe adsorption isotherms were obtained after adsorption forsufficient time of12h,and the results are compared in Fig.3a.Theamount of adsorbed dye is in the order of PED-MIL-101>ED-MIL-101>MIL-101>MIL-53>activated carbon for the experimentalconditions,suggesting the efficiency of the Cr-BDCs,especially PED-MIL-101.As shown in Fig.3b,the adsorption isotherms have beenplotted to follow the Langmuir equation[33,36]:C e q e =C eQ0+1Q0b(4)where C e:equilibrium concentration of adsorbate(mg/L) q e:the amount of adsorbate adsorbed(mg/g)Q0:Langmuir constant(maximum adsorption capacity)(mg/g) b:Langmuir constant(L/mg or L/mol)So,the Q0can be obtained from the reciprocal of the slope of a plot of C e/q e against C e.The Q0for all of the samples is determined from Fig.3b and the values are summarized in Table1.Generally the Q0increases inthe Fig.3.(a)Adsorption isotherms for MO adsorption over thefive adsorbents and(b) Langmuir plots of the isotherms(a).The arrows in(b)show that the y-axis scale of activated carbon is different to that of MOFs.order of activated carbon<MIL-53<MIL-101<ED-MIL-101<PED-MIL-101,and the adsorption capacity of PED-MIL-101is194mg/g. The large adsorption capacity of MIL-101for MO,compared to that of MIL-53,is probably due to the large porosity of MIL-101as the adsorption capacity generally increases with increasing the poros-ity of adsorbents[42,43].So far many adsorbents have been evaluated as candidates for the removal of MO from water and their adsorption capacities have varied widely from2.1to about366mg/g depending on the adsor-bent[1–12].Even though the adsorption capacity of Cr-BDCs is less than that of NH3+-MCM-41[4],LDH[5]and activated carbon(made from an agricultural product,Phragmites australis)[3],its capacity is relatively greater than that of the most adsorbents[1,2,6–12].To shed light on the MO adsorption over Cr-BDCs,the adsorp-tion free energy,enthalpy and entropy change were calculated from the adsorption of MO over PED-MIL-101at various temperatures. Fig.4a shows the adsorption isotherms at the temperature of25, 35and45◦C,and the Langmuir plots are displayed in Fig.4b.The adsorption capacity increases with increasing adsorption temper-ature,suggesting endothermic adsorption.The Gibbs free energy change G can be calculated by the fol-lowing Eq.(5)[5,6,10,35]:G=−RT ln b(5)(where R is the gas constant)The Langmuir constant b(dimension:L/mol)can be obtained from the slope/intercept of the Langmuir plot of Fig.4b.The negative free energy change( G)shown in Table2suggests spontaneous adsorption under the adsorption conditions.E.Haque et al./Journal of Hazardous Materials181 (2010) 535–542539Fig.4.(a)Adsorption isotherms for MO adsorption over PED-MIL-101at25,35and45◦C;and(b)Langmuir plots of the isotherms(a);(c)Adsorption isotherms for MO adsorption over MIL-101at25,35and45◦C;and(d)Langmuir plots of the isotherms(c).The enthalpy change H can be obtained by using the van’t Hoffequation[5,44]:ln b= SR− HRT(6)The calculated H,obtained from the(−slope×R)of the van’tHoff plot(Fig.5),is29.5kJ/mol,confirming endothermic adsorp-tion in accord with the increasing adsorption capacity associatedwith increasing adsorption temperature(Fig.4a).The endothermicTable1Textural properties,the pseudo-second-order kinetic constants(k2)with correlation constants(R2)at various MO concentrations and the maximum adsorption capacities (Q0)of thefive adsorbents.Adsorbent(pore size,nm)BET surfacearea(m2/g)Total porevolume(cm3/g)Pseudo-second-order kinetics constants k2(g/(mg min))Maximum adsorptioncapacity,Q o(mg/g) 30ppm40ppm50ppmk2R2k2R2k2R2Activated carbon(<1.0)10680.50 2.17×10−40.987 2.34×10−40.981 2.59×10−40.97811.2MIL-53(<1.0)14380.557.23×10−40.9997.70×10−40.9997.84×10−40.99957.9MIL-101(1.6,2.1)3873 1.709.01×10−40.9999.19×10−40.9969.29×10−40.998114ED-MIL-101(1.4,1.8)3491 1.37 1.06×10−30.998 1.19×10−30.999 1.27×10−30.999160PED-MIL-101(1.4,1.8)3296 1.18 2.75×10−3 1.00 2.95×10−3 1.00 3.04×10−30.999194Table2The maximum adsorption capacity and thermodynamic parameters of MO adsorption over PED-MIL-101and MIL-101at different temperatures.Adsorbent Temp.(◦C)Q o(mg/g) G(kJ/mol) H(kJ/mol) S(J/mol/K)PED-MIL-10125194−32.535219−34.529.520945241−36.6MIL-10125114−31.935121−33.1 4.0012045140−34.3540 E.Haque et al./Journal of Hazardous Materials 181 (2010) 535–542Table 3The equilibrium adsorbed amount (q e )and pseudo-second-order kinetic constant (k 2)of fresh and reused PED-MIL-101s and ED-MIL-101s (Temperature:25◦C,C i :50ppm).Adsorbent Items Fresh 1st reuse 2nd reuse PED-MIL-101q e (mg/g)187186181k 2(g/mg min) 3.04×10−3 1.87×10−3 1.18×10−3ED-MIL-101q e (mg/g)130127123k 2(g/mg min)1.27×10−31.07×10−37.62×10−4Fig.5.van’t Hoff plots to get the H and S of the MO adsorption over the MIL-101and PED-MIL-101.adsorption may be due to a stronger interaction between pre-adsorbed water and the adsorbent than the interaction between MO and the adsorbent.However,further work is necessary to clarify this suggestion.The entropy change S can be obtained from the (intercept ×R )of the vant’t Hoff plot (Fig.5),and the obtained entropy change S is 208J/(mol K).The positive S means the increased randomness with adsorption of MO probably because the number of desorbed water molecule islarger than that of the adsorbed MO molecule (MO is very bulky compared with water;therefore several water may be desorbed by adsorption of a MO molecule).Therefore,the driving force of MO adsorption (negative G )on PED-MIL-101is due to an entropy effect (large positive S )rather than an enthalpy change ( H is positive).Fig.6.Effect of pH of MO solution on the adsorbed amount of MO over activated carbon and PED-MIL-101(C i :50ppm,adsorption time:4h).The thermodynamic properties were also determined for the case of MIL-101using the adsorption isotherms (Fig.4c)and the Langmuir plots at different temperatures (Fig.4d).Generally,the isotherms and Langmuir plots are similar to those of PED-MIL-101(Fig.4a and b).However,it should be mentioned that the adsorbed amount of MO over PED-MIL-101is high at very low concentra-tion (especially at 45◦C),which is very helpful to remove MO even at a low concentration.The adsorption free energy,enthalpy and entropy change over MIL-101,obtained from Fig.4d and Fig.5,are displayed in Table 2.Similar to PED-MIL-101,the adsorption of MO over MIL-101is a spontaneous process (negative G ).However,the absolute value of H is very small for the case of MIL-101.This may be due to a physical adsorption of MO and little desorption of pre-adsorbed water.The small free energy change ( S )sup-ports this assumption (small number of desorbed water molecules).However,a more detailed study will be necessary to understand the difference between MIL-101and PED-MIL-101in terms of the adsorption enthalpy and entropy changes.3.3.Effect of pH and regeneration of MOFsThe adsorption of a dye usually highly depends on the pH of the dye solution [2,6].MO adsorption at various pH values was mea-sured after equilibration withPED-MIL-101and activated carbon.As shown in Fig.6,the adsorbed amounts decrease with increas-ing the pH of the MO solution,which is quite similar to previously reported results [2,6].The decreasing of adsorbed MO with increas-ing pH might be due to the fact that the concentration of positive charge of adsorbents is decreased with increasing pH.Scheme 2.E.Haque et al./Journal of Hazardous Materials181 (2010) 535–542541Fig.7.(a)Effect of contact time on the MO adsorption and(b)Pseudo-second-order plots to show the re-usability of the spent PED-MIL-101.Even though more detailed work is necessary to clearly under-stand the mechanism of MO adsorption on Cr-BDCs,the mechanism may be explained with electrostatic interaction between MO and adsorbents(as proposed in Scheme2).MO usually exists in the sulfate form;therefore,there will be a strong electrostatic inter-action with an adsorbent having a positive charge.The positive charge distribution increases in the order of MIL-101<ED-MIL-101<PED-MIL-101as suggested in Scheme2.On the other hand the positive charge of PED-MIL-101will be decreased with increasing the pH of the solution due to the deprotonation of the proto-nated adsorbent.Therefore,the increase of adsorption capacity and kinetic constant with modification(MIL-101<ED-MIL-101<PED-MIL-101)or increasing acidity may be explained with the increased positive charge of the adsorbent,especially PED-MIL-101in a low pH condition.A similar adsorption mechanism of anionic dyes via electrostatic interaction has been reported in the case of chitosan [44]and NH3+-MCM-41[4].Facile regeneration of an adsorbent is very important for commercial feasibility.The re-usability of spent adsorbent(PED-MIL-101)is shown in Fig.7a.Even though the adsorption kinetic constants(shown in Table3which are derived from Fig.7b) decrease noticeably with the cycle of adsorption,the amount of adsorbed MO does not decrease much,suggesting the applicabil-ity of Cr-BDCs in the adsorptive removal of anionic dye materials from waste water.Similar re-usability of ED-MIL-101has also been observed(Table3,Supporting Fig.3).4.ConclusionThe liquid-phase adsorption of MO over MOF-type materials has been studied to understand the characteristics of dye adsorption on these materials.The adsorption capacity and adsorption kinetic constant of MIL-101are greater than those of MIL-53,showing the importance of porosity and pore size for adsorption,which is sim-ilar to reported -101,after being modified to have a positive charge,can be efficiently used to remove MO via liquid-phase adsorption.Based on the rate constant(pseudo-second or pseudo-first-order kinetics for adsorption)and adsorption capac-ity,it can be suggested that there is a specific interaction like electrostatic interaction between MO and the adsorbent for rapid and high uptake of the dye.The adsorption of MO over PED-MIL-101 at various temperatures shows that the adsorption is spontaneous and endothermic and the randomness increases with the adsorp-tion of MO.The driving force of MO adsorption over PED-MIL-101 is mainly due to an entropy effect rather than an enthalpy change. From this study,it can be suggested that the MOF-type materials may be applied in the regenerable adsorptive removal of anionic dye materials from contaminated water.AcknowledgementsThis work was supported by the National Research Founda-tion of Korea(NRF)grant funded by the Korea Government(MEST) (2008-0055718,2009-0083696).Appendix A.Supplementary dataSupplementary data associated with this article can be found,in the online version,at doi:10.1016/j.jhazmat.2010.05.047. References[1]G.Crini,Non-conventional low-cost adsorbents for dye removal:a review,Bioresour.Technol.97(2006)1061–1085.[2]A.Mittal,A.Malviya,D.Kaur,J.Mittal,L.Kurup,Studies on the adsorptionkinetics and isotherms for the removal and recovery of Methyl Orange from wastewaters using waste materials,J.Hazard.Mater.148(2007)229–240. [3]S.Chen,J.Zhang,C.Zhang,Q.Yue,Y.Li,C.Li,Equilibrium and kinetic studies ofmethyl orange and methyl violet adsorption on activated carbon derived from Phragmites australis,Desalination252(2010)149–156.[4]Q.Qin,J.Ma,K.Liu,Adsorption of anionic dyes on ammonium-functionalizedMCM-41,J.Hazard.Mater.162(2009)133–139.[5]Z.-M.Ni,S.-J.Xia,L.-G.Wang,F.-F.Xing,G.-X.Pan,Treatment of methyl orangeby calcined layered double hydroxides in aqueous solution:adsorption prop-erty and kinetic studies,J.Colloid Interface Sci.316(2007)284–291.[6]K.P.Singh,D.Mohan,S.Sinha,G.S.Tondon,D.Gosh,Color Removal fromWastewater Using Low-Cost Activated Carbon Derived from Agricultural Waste Material,Ind.Eng.Chem.Res.42(2003)1965–1976.[7]A.Bhatnagar,E.Kumar,A.K.Minocha,B.-H.Jeon,H.Song,Y.-C.Seo,Removalof anionic dyes from water using Citrus limonum(lemon)peel:equilibrium studies and kinetic modeling,Sep.Sci.Technol.44(2009)316–334.[8]G.Annadurai,R.-S.Juang,D.-J.Lee,Use of cellulose-based wastes for adsorptionof dyes from aqueous solutions,J.Hazard.Mater.92(2002)263–274.[9]V.Rocher,J.-M.Siaugue,V.Cabuil,A.Bee,Removal of organic dyes by magneticalginate beads,Water Res.42(2008)1290–1298.[10]J.-H.Huang,K.-L.Huang,S.-Q.Liu,A.-T.Wang,C.Yan,Adsorption of rhodamineB and methyl orange on a hypercrosslinked polymeric adsorbent in aqueoussolution,Colloid Surf.A:Physicochem.Eng.Aspects330(2008)55–61. [11]A.Ayar,O.Gezici,M.Küc¸ükosmano˘g lu,Adsorptive removal of methyleneblue and methyl orange from aqueous media by carboxylated diaminoethane sporopollenin:on the usability of an aminocarboxilic acid functionality-bearing solid-stationary phase in column techniques,J.Hazard.Mater.146(2007) 186–193.[12]X.Luo,L.Jhang,High effective adsorption of organic dyes on magnetic cellulosebeads entrapping activated carbon,J.Hazard.Mater.171(2009)340–347. [13]G.Férey,Hybrid porous solids:past,present,future,Chem.Soc.Rev.37(2008)191–214.[14]S.Kitagawa,R.Kitaura,S.-I.Noro,Functional porous coordination polymers,Angew.Chem.Int.Ed.43(2004)2334–2375.[15]O.M.Yaghi,M.O’Keeffe,N.W.Ockwig,H.K.Chae,M.Eddaoudi,J.Kim,Reticularsynthesis and the design of new materials,Nature423(2003)705–714.。

注：括号内数字为对应题的答案所在原文的位置Unit 1Passage One针对大气中氟氯化碳的研究工作最终促使全球氟氯化碳禁令的实施，将我们从臭氧层消耗中挽救出来。

我们是否有时间去做一个关于碳排放量的类似研究工作，从而改变气候变化以挽救我们自己？根本没有任何希望。

大多数“绿色”的东西都几乎是一个大骗局。

获得庞大的政府补贴的碳交易只是金融和工业界所需要的。

（57）它跟气候变化的事情没有关系，但他会让不少人挣很多钱，并推迟人们算账的日子。

（58）我不反对可再生能源，但让我无法容忍的是风力发电厂对英国城郊环境的破坏。

这绝对没有必要，而且还要占用2500平方公里的面积——这可是极大的乡村面积——去发十亿瓦特的电。

将二氧化碳从空气中隔离的工作也是在在浪费时间。

这是一个疯狂的想法——而且很危险。

这要用很长时间和很多能源，最终不会成功。

（59）对英国而言，核能是解决能源问题的一个办法，但他不能改善全球性的气候变化。

实施削减排放量的措施为时已晚。

但是我们并非就走到了绝路。

有这样一种方法可以自救，那就是通过大规模的木炭掩埋。

（60）这将意味着农民将他们所有的农业废弃物——它们含有植物在夏季通过吸收合成的碳——转化为木炭，然后埋入土壤中。

然后你就可以真正的开始大量减少大气中的碳。

并快速降低二氧化碳含量。

（60）我们能做的是让农民在低氧状态下燃烧农作物尾料，将其转变为木炭，然后农民将这些木炭犁入农田。

在这个过程中释放了少量的二氧化碳，但大部分都被转化成了碳。

你还能获得小部分作为燃料过程副产品的生物燃料，农民可以将这些燃料出售。

（61）这项计划将不需要任何补助：因为农民将会获利。

通过这样的方式，我们可以真正地让世界有所改变。

56——61：BACDCPassage Two几年前，将巴恩斯——美国一个令人尊敬的艺术结构——从其当时所在的宾夕法尼亚洲郊区城梅尼昂迁到费城博物馆区的决定引起了争议，不仅是因为这一决定无耻地违背了建立者阿尔伯特C巴恩斯的意愿。

Technical Data Sheet Laboratory-Scale Depth FiltrationBECO MiniCap TM ACFDisposable Filter Unit with BECO CARBON TMActivated Carbon Depth Filter SheetsBECO MiniCap ACF disposable filter units withBECO CARBON activated carbon depth filtersheets are ready-to-use for the filtration of smallvolumes for laboratory applications, scale-uptrials, and sample preparation.The depth filter sheets of BECO MiniCap ACFdisposable filters have a high adsorptive capacitydue to the use of immobilized activated carbon andare used for decolorization as well as for theremoval of undesired by-products or for taste andodor correction.The specific advantages of the BECO MiniCap ACFrange:- The disposable filter unit is autoclavable and thereis no cleaning effort required.- Due to the dust-free handling, the application is simple and clean.- BECO MiniCap ACF disposable filter units with activated carbon types of different porosity meetthe requirements of a broad range of applications. -Filtration-active and adsorptive properties are ideally combined in the BECO MiniCapACF 07.10.-The adsorption performance in the BECO MiniCap ACF 02 and ACF 03 is maximized through acarbon content of up to 1000 g/m² and the lowendotoxin content ensures high product safety. AValidation Guide for the activated carbon depthfilter sheet of BECO MiniCap ACF 03 is availableon request.Application Examples-Decolorization and removal of organic impurities from active pharmaceutical ingredients (API)solutions:-Decolorization of antibiotic solutions-Protein and endotoxin removal-Purification of blood plasma products-Treatment of contrast media-Decolorization of natural extracts and cosmetics -Removal of unwanted by-products from food or dietary supplements, e.g., decolorization ofglucose, enzyme and vitamin solutions-Correction of taste and color of beverages (Spirits, fruit juices, hard seltzer etc.)-Decolorization and removal of organic impurities from chemicals, organic solvents and syntheticoils, e.g., removal of …off-flavor“ and unwanted by-products from silicone oils Selection Guide for BECO MiniCap ACF Disposable Filter Units with BECO CARBON Activated Carbon Depth Filter SheetsThe activated carbon of the BECO MiniCap ACF filter is a microporous, inert material with a very large inner surface of up to 2000 m²/g of activated carbon. The activated carbon used can be divided into different porosity ranges:Macroporous (∅ >50 nm)Decolorization of dark discolorations (brown to yellow) and for the separation of large molecules(e.g., protein separation).Mesoporous (∅ 2-50 nm)Decolorization of medium discoloration (yellow to yellowish) and impurities, as well as for correcting the taste of food.Microporous (∅ <2 nm)Decolorization of light discolorations (yellowish to whitish-gray), for odor correction and for the separationof smaller molecules (e.g., endotoxins).Physical DataThis information is intended as a guideline for the selection of BECO MiniCap disposable filter units. The water throughput is a laboratory value characterizing the different BECO CARBON activated carbon depth filter sheets. It is not the recommended flow rate.22ACF 07.10 19607 15 >11.6 (80) 34.7 (1415) - 420 ACF 02 19602 2.5 >11.6 (80) 6.75 (275) < 0.125 1000 ACF 03 19603 5 >11.6 (80) 7.4 (300) < 0.125 1000* 100 kPa = 1 bar** Endotoxin content analysis after rinsing with 1.23 gal/ft² (50 l/m²) of WFI (Water for Injection)Technical Data3.3 in² (21.2 cm²)2.9 in (74 mm)Polypropylene according to FDA CFR § 177.1520Hose connections 0.24–0.47 in (6–12 mm) in diameter44 psi (300 kPa/3 bar) at 77°F (25°C)0.44 fl oz (13 ml)4.40.17 fl oz (5 ml)0.08–0.14 gal/h (85–145 gfd)5–8 ml/min (150–250 l/m²/h)0.05–2.6 gal (0.2–10 l)Ordering InformationF071C300 BECO MiniCap ACF 07.10 kit*F002C300 BECO MiniCap ACF 02 kit*F003C300 BECO MiniCap ACF 03 kit** One package contains three individually packed BECO MiniCap disposable filter units. The carton label shows the following information: article description, article, and lot numbers.Compliance NoticeBECO CARBON activated carbon depth filter sheets meet the requirements of the Regulation (European Commission) 1935/2004 and the LFGB standard (German Food, Commodity and Feed Act) as well as the test criteria of FDA (U.S. Food and Drug Administration) Directive 21 CFR § 177.2260.The polypropylene components comply with regulation (EU) 10/2011 and meet the requirements of FDA,21 CFR § 177.1520.BECO CARBON ACF 03 and the polypropylene components of the BECO MiniCap ACF 03 disposable filter unit also meet the requirements of the USP Class VI tests.For further details on individual components and materials see the declaration of conformity.ComponentsBECO CARBON activated carbon depth filter sheets are made from particularly pure materials. Finely fibrillated cellulose fibers and cationic charge carriers are used. The materials for each filter type in particular are as follows:-BECO CARBON ACF 07.10(S):acid-washed, steam-activated carbon and high-quality diatomaceous earth-BECO CARBON ACF 02:chemically activated carbon-BECO CARBON ACF 03:acid-washed, steam-activated carbonInstruction for CorrectDepending on the filtered liquids, the operating temperature should not exceed 176°F (80°C). Please contact Eaton regarding filtration applications at higher temperatures.Sterilization (optional)The wetted BECO MiniCap ACF disposable filter units can be sterilized one time in an autoclave as follows: Preparation: Rinsing with minimum of 1.7 fl oz (50 ml)for optimum wettingTemperature: M ax.250 °F (121 °C)Duration: Approx. 30 minutesRinsing: After sterilizing with 3.4 fl oz (100 ml)/1.23 gal/ft² (50 l/m²) at 1.25 times theflow rate Filter Preparation and FiltrationUnless already completed after sterilization, Eaton recommends pre-rinsing the closed filter with 3.4 fl oz (100 ml)/1.23 gal/ft² (50 l/m²) of water or in exceptional cases with product appropriate solution at 1.25 times the flow rate prior to the first filtration. Depending on the application, this usually equals a rinsing time of 10 to 20 minutes.Only in exceptional cases which, for example do not allow rinsing with water, product or product appropriate solution should be circulated for 10 to 20 minutes and disposed after rinsing.Test the entire filter for leakage at maximum operating pressure.Filtration SpeedAdsorption processes are decisively affected by the contact time between the product and the adsorbing substance. The adsorption performance can thus be controlled by the speed of filtration. Slow filtration speeds 0.08 – 0.14 gal/h (85 – 145 gfd)/5 – 8 ml/min (150 – 250 l/m²/h) respectively extended periods of contact result in optimum utilization of the adsorption capacity.Inlet and Differential PressureTerminate the filtration process once the limit of adsorption capacity or the maximum permitted inlet or differential pressure of 43.5 psi (300 kPa, 3 bar) is reached. A higher inlet and differential pressure could damage the depth filter sheet material.SafetyWhen used and handled correctly, there are no known unfavorable effects associated with this product. Further safety information can be found in the relevant Material Safety Data Sheet, which can be downloaded from our website.Waste DisposalDue to their composition, BECO MiniCap ACF disposable filter units can be disposed of as harmless waste. Comply with relevant current regulations, depending on the filtered product.StorageBECO MiniCap ACF disposable filter units must be stored in a dry, odor-free, and well-ventilated place, ideally in their original packaging.Do not expose the BECO MiniCap ACF disposable filter units to direct sunlight.BECO MiniCap ACF disposable filter units are intended for immediate use and should be used within 36 months after production date.Quality Assurance According to DIN EN ISO 9001 The Quality Management System of Eaton Technologies GmbH has been certified according to DIN EN ISO 9001.This certification verifies that a fully functioning comprehensive Quality Assurance System covering product development, contract controls, choice of suppliers, receiving inspections, production, final inspection, inventory management, and shipment has been implemented.Extensive quality assurance measures incorporate adherence to technical function criteria and chemical purity and quality recognized as safe under the German legislation governing the production of foods and beverages.All information is given to the best of our knowledge. However, the validity of the information cannot be guaranteed for every application, working practice and operating condition. Misuse of the product will result in all warrantees being voided.Subject to change in the interest of technical progress.North America44 Apple StreetTinton Falls, NJ 07724Toll Free: 800 656-3344 (North America only)Tel: +1 732 212-4700Europe/Africa/Middle EastAuf der Heide 253947 Nettersheim, Germany Tel: +49 2486 809-0 Friedensstraße 4168804 Altlußheim, Germany Tel: +49 6205 2094-0An den Nahewiesen 2455450 Langenlonsheim, Germany Tel: +49 6704 204-0 Greater ChinaNo. 7, Lane 280,Linhong RoadChangning District, 200335Shanghai, P.R. ChinaTel: +86 21 2899-3687Asia-Pacific100G Pasir Panjang Road#07-08 Interlocal CentreSingapore 118523Tel: +65 6825-1620For more information, pleaseemail us at ********************or visit /filtration© 2023 Eaton. All rights reserved. All trademarks andregistered trademarks are the property of their respectiveowners. All information and recommendations appearing inthis brochure concerning the use of products describedherein are based on tests believed to be reliable. However,it is the user’s responsibility to determine the suitability forhis own use of such products. Since the actual use byothers is beyond our control, no guarantee, expressed orimplied, is made by Eaton as to the effects of such use orthe results to be obtained. Eaton assumes no liabilityarising out of the use by others of such products. Nor is theinformation herein to be construed as absolutely complete,since additional information may be necessary or desirablewhen particular or exceptional conditions or circumstancesexist or because of applicable laws or governmentregulations.EN1 A 4.2.8.503-2023。

Synthesis and evaluation of biochar-derived catalysts for removal of toluene(model tar)from biomass-generated producer gasPushpak N.Bhandari a,Ajay Kumar b,*,Danielle D.Bellmer b,Raymond L.Huhnke ba Agricultural&Biological Engineering,Purdue University,West Lafayette,IN47907,USAb Biobased Products and Energy Center,Department of Biosystems&Agricultural Engineering,Oklahoma State University,Stillwater,OK74078,USAa r t i c l e i n f oArticle history:Received2July2013Accepted17December2013 Available online11January2014Keywords:BiocharActivated carbonBiomass gasificationTarToluene a b s t r a c tChallenges in removal of contaminants,especially tars,from biomass-generated producer gas continue to hinder commercialization efforts in biomass gasification.The objectives of this study were to synthesize catalysts made from biochar,a byproduct of biomass gasification and to evaluate their performance for tar removal.The three catalysts selected for this study were original biochar,activated carbon,and acidic surface activated carbon derived from biochar.Experiments were carried out in afixed bed tubular catalytic reactor at temperatures of700and800 C using toluene as a model tar compound to measure effectiveness of the catalysts to remove tar.Steam was supplied to promote reforming reactions of tar. Results showed that all three catalysts were effective in toluene removal with removal efficiency of69 e92%.Activated carbon catalysts resulted in higher toluene removal because of their higher surface area (w900m2/g compared to less than10m2/g of biochar),larger pore diameter(19A compared to15.5A of biochar)and larger pore volume(0.44cc/g compared to0.085cc/g of biochar).An increase in reactor temperature from700to800 C resulted in3e10%increase in toluene removal efficiency.Activated carbons had higher toluene removal efficiency compared to biochar catalysts.Ó2013Elsevier Ltd.All rights reserved.1.IntroductionGasification is a thermochemical conversion process in which carbonaceous materials(such as natural gas,naphtha,residual oil, petroleum coke,coal and biomass)react with a gasification me-dium(such as air,oxygen and/or steam)at high temperatures (600e1000 C)to produce a mixture of gases called producer gas[1e4].The major components of producer gas are carbon monoxide(CO),carbon dioxide(CO2),nitrogen(N2),and hydrogen (H2).Producer gas also contains methane(CH4),water,some higher hydrocarbons,various inorganic and organic contaminants like char,ash,tar,ammonia(NH3),hydrogen sulfide(H2S),sulfur diox-ide(SO2),and nitrogen dioxide(NO2)[1,5,6].The impurities in producer gas can cause serious problems with downstream appli-cations of the gas by clogging the process lines,deactivating cata-lysts,and acting as precursors for toxic emissions[7,8].Tar can be defined as all organic contaminants having molecular weights higher than benzene[9,10].Tar contents in producer gas are as high as0.22kg/kg biomass[13].Scrubbers and electrostatic precipitators are effective in reducing the levels of tars.However,these techniques are inefficient because they result in reducing the gas energy content and require disposal of solvents.Catalysts offer a more cost-efficient and an equally effective approach to removal of contaminants[11,12].Biochar is naturally produced during biomass gasification. Adding value to low-value biochar by using it in applications such as soil amendment,carbon sequestration and gas upgrading has shown researching interest in recent times.Studies have shown that low-cost biochar is a potential catalyst for tar removal[1].The surface area of biochar is generally low;ranging from5m2/g to around65m2/g depending on the type of biomass and gasification operating conditions[14e18].Effectiveness of the biochar to remove tar can be drastically increased by increasing its surface area and improving its chemical properties.Several studies suggest that increasing surface area of catalyst is critical to efficient tar removal.Seshadri and Shamsi[19].concluded that a char and dolomite mixture and calcined dolomite were not as active as ze-olites and other catalysts evaluated for tar conversion in coal gas streams due to their low surface acidity and low surface area. Donnot et al.[20].found that the residence time for efficient tar removal is inversely proportional to char surface area.They also investigated the carbon deposition phenomena on the char catalyst and found that at temperatures below750 C,a decrease in activity*Corresponding author.Tel.:þ14057448396.E-mail address:ajay.kumar@(A.Kumar).Contents lists available at ScienceDirect Renewable Energyjournal ho me page:www.elsevier.co m/locate/renene0960-1481/$e see front matterÓ2013Elsevier Ltd.All rights reserved./10.1016/j.renene.2013.12.017Renewable Energy66(2014)346e353occurs after a short time due to coking.Hence,to understand the effect of coking in our study,experiments were carried out at two temperatures:700and800 C.Activated carbon is a highly porous material with high surface area.Generally,activated carbon can be synthesized by either chemical activation,physical activation,or a combination of chemical and physical activation of a carbon precursor[21].This activation process gives rise to a highly porous carbon material with high adsorptive properties.The carbon precursor can be any ma-terial with carbon as its primary constituent.Various agricultural waste precursors like wheat[22],rice husks[23],sugarcane bagasse [23],corn stover[24],hazelnut[25],tobacco stems[30]and biochar [14]have been used to synthesize this activated carbon.Little data is available in literature on the properties and use of biochar,a by-product from gasification of switchgrass,for the production of activated carbon.Also,activated carbon remains untested as a po-tential catalyst for tar reduction.Azargohar and Dalai[14]carried out a study to synthesize activated carbon from biochar derived from fast pyrolysis of wood.For this study,we evaluated biochar derived from gasification of switchgrass as a precursor for the synthesis of activated carbon.The effect of ultrasonic impregnation of potassium hydroxide(KOH)onto biochar on the change in the properties of the activated carbon product was also studied. Further,the activated carbon was evaluated for removal of toluene (model tar compound).Previously,a review of carbon-based cata-lysts for removal of various producer gas contaminants such as ammonia,H2S,tar,and CO2was made[26].Based on the review,it was concluded that increased surface area of carbon-based cata-lysts may improve the catalyst performance for removal of con-taminants.To validate some of thefindings of the review, performance of selected biochar-based catalysts for toluene(model tar compound)removal was evaluated in this study.No studies have been reported previously for synthesis of acti-vated carbon from biochar derived from gasification of switchgrass. Also,in the present paper,we are investigating the synthesis of activated carbon from biochar using ultrasonication to improve the surface area of the synthesized catalysts.Ultrasonication helps in synthesis of high surface area catalysts[26]and also helps improve particle dispersion[27].We hypothesize that acidic surface catalyst may help react with a basic contaminant in the producer gas,such as ammonia.However,the acidic surface should not decrease tar removal efficiencies.Acidic surface activated carbon,previously untested for toluene removal,was evaluated in this study.The three synthesized catalysts(biochar,activated carbon,and acidic surface activated carbon)are characterized and evaluated for toluene (model tar compound)removal infixed-bed reactor experiments. Finally,the effect of reaction temperatures(800 C and900 C)and reaction gas medium(N2and producer gas)on toluene removal is also included in this paper.The specific objectives of this study were to a)synthesize acti-vated carbon from biochar precursors derived from switchgrass gasification and evaluate the effect of ultrasonic potassium hy-droxide(KOH)impregnation onto biochar for change in the prop-erties of the activated carbon,b)compare the activated carbon synthesized using biochar fromfluidized bed gasification and downdraft gasification,and c)evaluate the effectiveness of biochar and biochar-based activated carbon and acidic surface activated carbon catalysts on the removal of toluene as a model tar compound.2.Material and methodsThe experimental design for catalyst synthesis and selection is shown in Fig.1.Biochar was synthesized in downdraft gasifier and fluidized bed gasifier from gasification of switchgrass.The biochar from both the gasifiers was impregnated with KOH,with and without ultrasonication,and further carbonized to form activated carbons.Biochar and activated carbon derived from downdraft gasifier were selected for further studies because of their higher surface areas than those of biochar and activated carbon derived fromfluidized bed gasifier.Further,the activated carbon from downdraft gasifier was coated with dilute ascorbic acid to syn-thesize acidic surface activated carbon.Finally,the three downdraft gasifier derived catalysts i.e.biochar,activated carbon,and acidic surface activated carbon,were evaluated for their toluene removal efficiency infixed-bed reactor experiments.2.1.Catalyst preparationBiochar was generated in a downdraft gasifier[16]andfluidized bed gasifier[17]using switchgrass as a biomass feedstock.The details of the gasifier have been described elsewhere[16,17].The procedure for the synthesis of the activated carbon was based upon a previous study by Azargohar and Dalai[14].The biochar was sieved to get the sample with particle size between150and 600m m.Ten grams of sieved biochar was mixed with10g of KOH pellets(Fisher Scientific,Hampton,NH)and100mL distilled water to obtain1:1mass ratio of KOH to biochar.A1:1mass ratio of KOH to biochar is used based upon promising results obtained previ-ously[14].This mixture was stored overnight to allow sufficient time for KOH to access biochar pores.To synthesize activated car-bon using an ultrasonication method,the mixture was sonicated (Fisher Scientific550Sonic Disembrator,Pittsburgh,PA)for0.25 and0.5h at30%power.The mixture was then dried at110 C overnight in an oven(Vulcan3-550,Neycraft).The biochar was carbonized[14,28,29]in a tubular catalytic reactor made of quartz glass with22mm inner diameter and914mm length(schematic shown in Fig.2)with nitrogenflow.The temperature of the reactor bed was raised from25to200 C at3 C/min and held for1h.This was followed by ramping up the temperature at10 C/min to700 C and held at that temperature for2h.The reactor temperature was controlled by a heating jacket(Carbolite furnace model TVS12/600, WI,USA).The bed temperatures were monitored using thermo-couples and a constant temperature zone was identified before carrying out any experiments.The inlet lines of the reactor were heated and kept at200 C using heat tapes(model STH051-020, Omega Engineering INC,Stamford,CT)to preheat the nitrogen gas supply.After carbonization,the bed temperature was decreased from700 C to25 C overnight under nitrogenflow in the reactor. The cooling procedure was done to prevent combustion of biochar upon immediate exposure to air.The heat treatment was followed by washing with distilled water and further with0.1M HCl,to help develop the pore structure.The samples were dried overnight at 120 C.Activated carbon derived from downdraft gasifier biochar was selected for synthesis of acidic surface activated carbon due to its higher surface area.Acidic surface activated carbonwas Fig.1.Design of experiments for catalyst development.Gray blocks indicate catalysts selected for toluene removal study.P.N.Bhandari et al./Renewable Energy66(2014)346e353347synthesized by stirring the activated carbon with10%dilute citric acid(1:1volumetric ratio).The coated activated carbon was further dried at110 C for4h in a furnace oven to give acidic surface activated carbon.2.2.Catalyst characterizationCharacterization was carried out on downdraft gasifier biochar and downdraft gasifier activated carbon.The downdraft gasifier catalysts were selected for characterization and testing because they had a higher surface area than those offluidized bed gasifier catalysts.The catalysts were characterized before and after use in the catalytic reactor experiments.Analysis of Brunauer e Emmett e Teller(BET)surface area and pore diameter and volume was done using a surface area analyzer(Quantachrome model1-C,Boynton Beach,FL).Nitrogen isotherms were measured at77K for relative pressure(P/P0)values ranging from0.1to0.3.The catalysts samples were outgassed for24h at300 C before calculating their surface areas.Temperature programmed oxidation(TPO)was carried out using5%O2in helium gas;whereas chemisorption experiments were carried out using CO2gas using the same Quantachrome equipment.X-ray diffraction(XRD)imaging was performed using Bruker D-8Advanced X-ray powder diffractometer(Bruker AXS, Madison,WI).Scanning electron microscopy(SEM)images were captured using a JEOL JSM-6360and FEI Quanta600F Scanning Electron Micrographs at magnifications of100e1000Â.The cata-lysts were placed in the multi-specimen holder of the scanning electron microscope without gold sputtering.Different magnifica-tions were used at accelerating voltages of15kV and20kV.Energy-dispersive X-ray spectroscopy(EDS)spectra were taken using EVEX EDS(Princeton,NJ)at different magnifications with accelerating voltages of20kV.2.3.Toluene removal with catalystsToluene was selected as a model tar compound because toluene is the largest component of the tar(13%w/w of tar)other than benzene and has been used previously as a model tar compound[28,29,31].Biochar and synthesized activated carbon catalysts derived from downdraft gasifier were evaluated for their effectiveness to decompose toluene in a high-temperature tubular reactor.Based on the surface area results obtained(Sec-tion3.1),three catalysts were selected as catalysts for toluene removal(Fig.1).The catalysts selected were downdraft gasifier biochar,activated carbon derived from downdraft gasifier bio-char,and acidic surface activated carbon,because their surface areas were greater thanfluidized bed gasifier biochar andfluid-ized bed gasifier biochar-derived activated carbon respectively. The reactor(Fig.2)consisted of a stainless steel reactor tube (0.0127m inner diameter,0.91m length).This tube was placed in the tube furnace used for carbonization.Experiments were car-ried out in two sets.Thefirst set of experiments consisted of toluene in nitrogenflow to observe gas formation and reactions. The second set of experiments was carried out with gas mixture with a composition similar to producer gas(5.15%H2,7.49%CH4, 16.79%CO2,19.30%CO,and balance N2)so as to observe the effect of producer gas components on the toluene removal process.The temperature of the bed was monitored using a K-type thermo-couple placed in the middle of the catalytic bed.Liquid syringe pumps(KD Scientific,Holliston,MA)were used to inject toluene into the reactor.The toluene was vaporized before mixing with the gas stream.Gas samples were collected in syringes and analyzed using gas chromatograph(Agilent5890Series II,Santa Clara,CA)calibrated for all the producer gas components using various calibration mixture cylinders purchased from Stillwater Steel Inc.(Stillwater,OK).The analysis was carried out using two columns in series:HP Plot Q(Agilent Technologies,Santa Clara, CA)and HP Molsieve column.The gases were detected using two detectors i.e.aflame ionization detector(FID)used to detect toluene and methane and a thermal conductivity detector(TCD) to detect the remaining gases.Argon was used as the carrier gas; air and hydrogen were used for the FIDflame.Proper operation of the GC was ensured using a column isolation technique.One gas sample was taken every20min.Toluene removal efficiency was defined asX¼ðC inÀC outÞC inÂ100where,X is the percent removal of toluene,and C in and C out are the concentrations of toluene(%volume)at the inlet and outlet, respectively.The gas residence time,s(kg m3hÀ1),was defined as s¼wv0where,w is the weight of the catalyst(kg)and v0is theflow rate of the gas mixture at the catalyst bed(m3/h).The gas residence time was approximately0.035kg h mÀ3for biochar and0.123kg h mÀ3 for activated carbons.Quantities of catalysts used for the experi-ments were1g of biochar obtained from downdraft gasification of switchgrass and0.35g of activated carbon and acidic surface acti-vated carbon,synthesized using ultrasonication from the same downdraft gasifier char as used in these experiments.A lower quantity of activated carbon was used since activated carbon has lower density than biochar.Different catalyst quantities were used to ensure same bed height(0.014m)and bed volume (4.39Â10À8m3)for all the experiments.2.4.Statistical analysisStatistical analysis of the data was carried out with the help of SAS9.3(Carey,NC)statistical software.Surface area data was643To GCN2TI PI2 Toluene178TIPI95Producer gas6Fig.2.Process schematic of reactor(1.Ball valve;2.Rotameter;3.Temperature indi-cator;4.Pressure indicator;5.Heated line;6.Catalyst bed;7.Tubular reactor;8.Tubular furnace;9.Water condenser).P.N.Bhandari et al./Renewable Energy66(2014)346e353 348analyzed using two-sample t-test assuming a¼1%.Quality of data obtained from toluene removal with catalysts experiments was confirmed by checking normality of data from comparison of data histogram with a normal probability curve.A bell-shaped curve was obtained for the data.General linear model(GLM)procedure was used to analyze the data further.Post-hoc multiple comparisons were performed using LSD and Duncan’s tests.Finally,correlations among the variables were also evaluated.3.Results and discussion3.1.Synthesis and surface characterization of fresh catalystsThe area e volume e pore size summaries of activated carbon and biochar derived from the two types of gasifiers are shown in Table1. The biochar obtained from the downdraft gasifier had a higher surface area(900m2/g)than that obtained from thefluidized bed gasifier(200m2/g).This is primarily due to the different configu-rations of the two gasifiers which result in differences in gasifica-tion conditions[16e18].A significant increase in surface area(p<0.01)was observed upon ultrasonication of the biochar obtained from downdraft gasifier(Table1).Also,the increase in surface area with increase in ultrasonication time was found to be significant(p<0.01).On the other hand,very little increase in surface area was observed (Table1)for the activated carbon synthesized using ultrasonication fromfluidized bed gasifier compared to that without using ultra-sonication(p>0.01).Ye at al.(2004)reported that ultrasonication resulted in homogeneous dispersion of catalyst particles[32]which may have played a role in improving contact of catalyst with the gas stream.Increase in contact of contaminants with the catalyst sur-face may lead to increase in tar removal efficiencies.3.2.Surface characterization of used catalystsThe surface characteristics of used catalysts(Table2)show a significant decrease(p<0.01)in surface area.A decrease of25.6% was observed in surface area of the used activated carbons(about 700m2/g)as compared to that of the fresh activated carbon(about 900m2/g).The pore radius decreased from15to18A to around 11A for all the catalysts.There was an88%decrease in the pore volume of biochar,possibly due to coking of the catalyst.Coke formation usually occurs due to deposition of graphitic carbon on the surface of biochar-based catalysts and is well documented in literature[33e36].These decreases in pore radius and pore volume may prove to be a barrier for commercialization of biochar as cat-alysts.Regeneration of the catalysts might be needed to improve its performance over longer time on stream[37].The decrease in surface area of activated carbons(25.6%)was comparatively lesser than that of biochar(75%)when used as catalyst for toluene removal.3.3.Proximate and elemental analyses of catalystsElemental analysis(Table4)shows that biochar obtained from thefluidized bed gasifier contained low amounts of total carbon (1.4%)and total nitrogen(0.05%);whereas biochar from the downdraft gasifier contained high amount of total carbon(64.8%). Both the activated carbons contained high amounts of total carbon (64e73%)and nitrogen(0.7e0.8%)because the ash content was lowered due to several wash cycles during their synthesis.These results imply that not all biochar generated from biomass gasifi-cation may be suitable for use in specific applications such as producer gas contaminant removal or as gasification in-bed cata-lysts.Biochar consists of ash(minerals)and char(carbon)as its primary constituents;generally,high carbon content seems promising for tar removal as ash has been found to be ineffective for tar removal[38].Hence,only biochar and activated carbon from downdraft gasifier(with much lower ash content)were selected for further study on toluene removal.X-ray diffraction(XRD)images(Fig.5)show that silica was the only easily identifiable element in fresh biochar(2Q¼28.8 ); whereas several elements were identifiable in used biochar due to its higher mineral content.In fresh activated carbon,not many el-ements can be easily identified due to its low ash content after several wash cycles.However,silica oxide was identified in the used activated carbon due to its lower carbon content(2Q¼21.6 ).Energy-dispersive X-ray spectroscopy(EDS)spectra were ob-tained for fresh and used catalysts.The elements observed in the samples(Table5)showed that silica content was the highest in fresh biochar catalyst(82.5%).Minerals such as magnesium,po-tassium were not as easily identified in the used biochar sample as compared to those in the used activated carbon.This may be a result of the high silica content in the fresh biochar to begin with. Silica,calcium,potassium,and iron were the major elements found in activated carbon samples.3.4.Microscope analysis of catalystsAs shown in Scanning Electron Microscopy(SEM)images of fresh catalysts(Fig.3),biochar consisted of background materials, which were possibly the solid residues present in the biochar sample.Solid residues may contain unburnt biomass particles during the gasification process.Also,the ends of the biochar par-ticles were observed to be closed and not porous.On the other hand,the activated carbon showed clear pore developments that may have resulted in larger surface area.When the volatiles from the char leave the char particle,they generate pores in the carbonTable1Effect of ultrasonication on surface and pore characteristics of activated carbons obtained from downdraft andfluidized-bed biochars.Gasifier Catalyst BETsurfacearea(m2/g)Averageporeradius( A)Total porevolume(cc/g)Downdraft gasifier Biochar6415.50.09 Activated carbon88918.90.42 Activated carbon(15min ultrasonication)91118.90.44 Activated carbon(30min ultrasonication)94419.10.45Fluidizedbed gasifier Biochar215.00.02Activated carbon20018.90.43Activated carbon(15min ultrasonication)21019.00.42Activated carbon(30min ultrasonication)20719.00.43Table2Surface and pore characteristics of downdraft-gasifier derived catalysts after use infixed-bed reactor experiments.Catalyst BET surfacearea(m2/g)Pore radius(A)Pore volume(cc/g)Used biochar16.711.20.01Used activatedcarbon702.411.20.39Used acidic surfaceactivated carbon632.811.10.35P.N.Bhandari et al./Renewable Energy66(2014)346e353349particle.These can clearly be observed in the images of activated carbon.The thermal treatment and several wash cycles of biochar cause the solid residues to volatilize or wash out and hence,no background matter was observed in the images of activated carbon.Scanning electron microscopy (SEM)images of the used cata-lysts (Fig.4)show high amount of coking in the biochar as evident from the round structures blocking the pores of the carbon fila-ment.Images of the used activated carbons show changes in catalyst structure.This could also be the result of coking of the catalysts.Decreases in surface area,pore volume and pore diameter of the activated carbon were observed (Table 2)due to blocking of the pores also seen from the SEM images.3.5.Toluene decomposition study3.5.1.Toluene in nitrogenToluene removal ef ficiencies of both activated carbon catalysts were signi ficantly higher than that of biochar at 800 C (Table 3).The toluene removal ef ficiencies for both activated carbons were not signi ficantly different at 700 C.Also,at 700 C,activated car-bon showed the highest toluene removal ef ficiency (86.3%),whereas at 800 C,acidic surface activated carbon showed the highest removal ef ficiency (92.1%)among all the catalysts.Biochar showed the highest average standard deviation of toluene removal ef ficiency among all the catalysts indicating that biochar perfor-mance was variable during the 4h experiment,possibly due to coking of the catalyst.It was observed that toluene removal ef fi-ciencies decreased with time on stream (results not shown)for all the catalysts at 800 C.This was con firmed by observing the ana-lyses of covariances plot that had a decreasing linear trend as well as from the Pearson ’s correlation coef ficient ‘r ’that was À0.27at 800 C.The Pearson ’s value (r ¼À0.27)at 800 C indicates thatthere is weak negative correlation between time on stream and toluene removal ef ficiency.This further implies that the catalysts deactivate slowly during the time period the catalysts were tested.Toluene removal ef ficiencies were as high as 92.1and 86.3%for activated carbons and biochar,respectively.These values are com-parable with those of commercial catalysts such as fluid catalytic cracking catalysts and transition metal (Ni)based catalysts reported in previous studies [38,39].The commercial catalysts are more expensive and are easily deactivated [43]by coking and poisoning by other gasi fication contaminants such as H 2S.Gases evolved during the tests (results not shown)indicate that concentration of CO,CO 2,and H 2were the highest at 800 C for activated carbon among the three catalysts.The methane concen-tration remained relatively constant for all catalysts and tempera-tures.Formation of methane indicates that methane reforming reactions may be occuring [35].The reaction mechanism for methanation is as follows:CO þ3H 24CH 4þH 2OThe gas concentration for biochar did not change with tem-peratures;whereas an increase in gas evolution with temperature was observed for the two activated carbons.3.5.2.Toluene in producer gasNo signi ficant difference was observed in the toluene removal ef ficiencies for the two activated carbons at both 700and 800 C in producer gas medium (Table 3).However,the toluene removal ef-ficiency of biochar was signi ficantly different than those of acti-vated carbon catalysts.Activated carbons exhibited better performance (79e 88%)in toluene removal ef ficiency from pro-ducer gas (Table 3)compared to biochar.For all the catalysts,the toluene removal ef ficiencies in the presence of producer gas were lesser than those obtained in the presence of nitrogen gas.This indicates that producer gas components decrease toluene removal ef ficiency possibly due to their adsorption on the catalysts [36].Also,the toluene removal ef ficiency of acidic surface activated carbon (about 79%)was less than that of activated carbon (about 82%)at 700 C;although the mean toluene removal ef ficiencies of the two catalysts were not signi ficantly different.The removal of other producer gas contaminants,such as NH 3which are basic inTable 4Elemental analysis of biochar and activated carbon derived from fluidized bed gasi fier (FBG)and downdraft gasi fier (DDG).Element Unit FBG biochar DDG biocharDDG activated carbon FBG activated carbon Totalnitrogen %db a 0.050.690.820.69Totalcarbon %db a 1.3864.8073.1064.10P %0.040.270.030.03Ca %0.13 2.810.060.11K %0.170.730.030.05Mg % 2.650.450.060.15Na %0.030.130.010.01S %0.010.040.010.01Fe %0.780.290.040.09Zn ppm 79.497.8 4.7 5.9Cu ppm 5.78.8 2.8 2.6Mn ppm 130.1394.512.871.3Ni ppm 303.7 4.6 1.3 1.8Alppm426.01408.080.2675.3adb ¼dry basis.Table 5EDS spectra findings for fresh and used catalysts.Elements Fresh biochar Used biochar Fresh activated carbon Used activated carbon Mg (%wt)0.50.770* 2.19Si (%wt)82.5563.5756.6845.58K (%wt)13.8413.7413.69 4.66Ca (%wt) 3.1111.629.6327.83Fe (%wt)0*10.320*14.43Weight percent values are relative to total elements observed.0*:Elements that are not identi fied.Table 3Mean toluene removal for biochar and activated carbon catalysts at toluene flow rate of 2ml/h and N 2/producer gas flow rate of 1scfh,(standard deviation for 2experiments).CatalystMean Toluene removal*(%)Toluene with N 2Toluene with producer gas 700 C800 C700 C800 C Biochar78.65a *Æ12.0581.01b *Æ11.8369.18b$Æ11.8978.83b *Æ4.74Activated carbon86.28a$Æ7.791.69a *Æ4.982.08a&Æ7.7388.55a$Æ6.62Acidic surface activated carbon80.78a$Æ7.792.09a *Æ8.479.13a$Æ7.7888.14a *Æ7.89*Means followed by same letter (a or b)within a column or followed by same symbol (*,$or &)within a row are not signi ficantly different (a ¼0.05).P.N.Bhandari et al./Renewable Energy 66(2014)346e 353350。

基于炭浆的氧传感器空气孔道制备宋斌，曹文杰，尤庆亮（江汉大学化学与环境工程学院，湖北武汉430056）摘要：为了制备平整的氧传感器芯片空气孔道，采用了丝网印刷的方法。

相应配制了一种适印性的炭浆，优化的条件为：优选了活性炭和松油醇、最佳的球磨级配为m Φ6.5∶mΦ3=1∶2、球磨时间为12h 、分散剂含量为30%、胶含量为5%。

在优化的条件下制备的空气孔道平整稳定，该制备方法具有精度高、形状平整可控、成本低以及操作简便等优点。

关键词：空气孔道；氧传感器；炭浆；活性炭中图分类号：O646.7文献标志码：A 文章编号：1673-0143（2018）03-0231-07DOI ：10.16389/42-1737/n.2018.03.006Preparation of Air Pore Canal of Lambda Sensor Based on Activated Carbon SlurrySONG Bin,CAO Wenjie,YOU Qingliang （School of Chemistry and Environmental Engineering,Jianghan University,Wuhan 430056,Hubei,China ）Abstract ：In order to prepare the flat air pore canal of the lambda sensor chip,the method of screen printing was used.A suitable carbon slurry was prepared,and the optimum conditions were as follows:activated carbon and terpineol were chosen,the grading was m Φ6.5∶m Φ3=1∶2,ball milling time was 12h,dispersant content was 30%,rubber content was 5%.Under the optimal conditions,the smooth and sta⁃ble air duct was prepared.The method has the advantages of high precision,controllable shape,low cost and simple operation.Key words ：air pore canal,lambda sensor,carbon slurry,activated carbon据中国汽车工业协会数据显示，2017年全年汽车产销2901.5万辆和2887.9万辆。