spectra of nanoparticles

[7]. Particle size obtained in microreactors has smaller and narrow particle size distribution than batch process due to better mixing and mass transfer in microfluidic devices [5]. Microreactor devices offer higher surface to volume ratio compared to the batch reactors hence the removal of heat is effectively carried out for exothermic reactions. Microfluidics has been used not only for synthesis of inorganic, organic and biological materials but also for synthesis of the janus, polymeric nanoparticles and hybrid materials. In microreactor systems, reaction takes place in small reaction volume, hence there is less heat and mass transfer resistances which help in safe handling of exothermic reactions. Rapid mixing of reactants and control of reagent concentration can produce precise conditions which are required for nanoparticle synthesis. Mixing of reactants in microreactor takes place very rapidly and control of reagent concentration can produce precise conditions which are required for nanoparticle synthesis. Hybrid nanoparticles are also synthesized by microreactor technology and particle size can be manipulated at the fluid–fluid interfaces in microreactors [8–16]. Boleininger et al. [17] synthesized the gold/silver metal nanorods using ascorbic acid, CTAB solution and precursor such as HAuCl4 /AgNO3 . In presence of CTAB, prepared micelles were used as template for anisotropic growth of particles. In batch synthesis

ORIGINAL PAPERSilicon-hybrid carbon dots strongly enhance the chemiluminescence of luminolZhen Lin&Xiangnan Dou&Haifang Li&Qiushui Chen&Jin-Ming LinReceived:3October2013/Accepted:18December2013#Springer-Verlag Wien2014Abstract We report on a4-min microwave pyrolytic meth-od for the preparation of fluorescent and water-soluble silicon-hybrid carbon dots(C-dots)with high fluorescent quantum yield.The material is prepared by preheating aminopropyltriethoxysilane and ethylene diamine tetraacetic acid for1min,then adding a mixture of poly(ethylene glycol)and glycerin to the solution and heating for another 3min.It is found that the hybrid carbon dots strongly enhance the chemiluminescence(CL)of the luminol/N-bromosuccinimide system.A study on the enhancement mechanism via CL,fluorescence and electron paramagnetic resonance spectroscopy showed that the effect most proba-bly is due to electrostatic interaction between the C-dots and the luminol anion which facilitates electron transfer from luminol anion to the N-bromosuccinimide oxidant.CL in-tensity is linearly related to the concentration of the C-dots in the range between1.25and20μg mL−1.The detection limit is0.6μg mL−1(at an S/N of3).Keywords Carbon dots.Chemiluminescence.Luminol. Bromosuccinimide IntroductionFluorescent carbogenic nanoparticles hardly photobleach and display low toxicity to living cells and tissue[1].They have attracted tremendous attentions recently and could be an al-ternative for traditional heavy metal contained nanoparticles. Carbon dots is a kind of a new emerging star among various fluorescent carbogenic nanoparticles.Since the first report in 2004[2],the preparation method and their luminescence mechanism have gained great attentions[3].The methods for the preparation of carbon dots consist of “bottom up”and“top down”methods.In“top down”method, materials such as graphite[4],multiwalled carbon nanotubes [5],candle soots[6]were oxidized or exfoliated into carbon nanoparticles with diameter in the range of2to10nm.In “bottom up”route,small chemical compounds,such as citrate acid[7],ascorbic acid[8],were pyrolized to produce fluores-cent carbon dots.The quantum yields of the carbon dots and the surface modification were challenging and worthwhile.In the present work,we report an economic and fast microwave pyrolysis method to prepare luminescence carbon dots with high quantum yield within4min.The carbon dots contain silicon related group on the surface and are water-soluble, which are convinient for surface modification and their po-tential applications in many fields.Some new properties of carbon dots,such as enzy-matics mimetics[9,10],flurescent probe[11,12]and photocatalyst[13,14],have been reported recently by several groups.Our group firstly used chemiluminescence(CL)gen-erated through a chemical reaction to study the optical proper-ties of carbon dots.Their CL properties in the prescence of oxidant,such as KMnO4,Ce(IV)[15]as well as peroxynitrous acid(ONOOH)[16]have been found.Radiative recombina-tion of the injected electrons and holes was supposed to con-tribute to the CL emission.The exploring of new CL properties of carbon dots is still an interesting and challengingwork. Electronic supplementary material The online version of this article(doi:10.1007/s00604-013-1153-x)contains supplementary material,which is available to authorized users.Z.LinDepartment of Pharmaceutical Analysis,Faculty of Pharmacy,Fujian Medical University,Fuzhou350004,ChinaZ.Lin:X.Dou:H.Li(*):Q.Chen:J.<M.Lin(*)Department of Chemistry,Beijing Key Laboratory for MicronalyticalMethods and Instrumentation,The Key Laboratory of BioorganicPhosphorus Chemistry&Chemical Biology,Tsinghua University,Beijing100084,Chinae-mail:lihaifang@e-mail:jmlin@Microchim ActaDOI10.1007/s00604-013-1153-xLuminol(3-aminophthalhydrazide)is a famous CL re-agent,which has been successfully utilized in bioanalysis or sensitive detectors for high-performance liquid chromatogra-phy or capillary electrophoresis.The effective catalysts for this reagent include metal ions,metal nanoparticles,and en-zymes[17,18].The CL enhanced property of the carbon dots in luminol system has been firstly found in the present study, which extends the range of the enhancer for the luminol CL system.Futhermore,the CL emission spectra,fluorescence spectra and electron paramagnetic resonance(EPR)spectra were employed to investigate the CL enhancement mecha-nism,which provided us new insight into the CL properties of carbon dots.Experimental sectionReagents and materialsAll chemicals used were of analytical grade and used as received.Ethylene diamine tetraacetic acid(EDTA)and glyc-erin was from Sinopharm Chemical Reagent Co.,Ltd(Shang-hai,China,).(3-Aminopropyl) triethoxysilane(APTES),luminol and N-bromosuccinimide were obtained from Alfa Aesar China Ltd(China,www. ).Polyethylene glycol1500(PEG1500)were purchased from Merck Company(Darmstadt,Germany, ).ApparatusThe CL kinetic curves were recorded by a BPCL lumines-cence analyzer(Institute of Biophysics,Chinese Academy of Sciences,Beijing,China).CL signal from the flow injection was measured with a LumiFlow LF-800detector(NITI ON, Funabashi,Japan).Transmission electron microscopy image was recorded by a JEM2010electron microscope(JEOL, Japan).The CL spectra and fluorescence spectra were mea-sured with a fluorescence spectrophotometer(F7000,Hitachi, Japan).EPR spectra were measured on a Bruker spectrometer (ESP300E,Bruker,Germany).Fourier transform infrared (FTIR)spectrum was recorded on a PerkinElmer100FTIR spectrometer(Massachusetts,USA).The zeta potential was performed by Zetasize3000HSa(Malvern UK).The X-ray photoelectron spectrum(XPS)was measured by a PHI Quantera SXMTM Scanning X-ray MicroprobeTM using Al-Kαas the exciting source(1486.6ev)and binding energy calibration was based on C1s at284.8eV.Synthesis of silicon-hybrid carbon dotsFive hundredμL APTES were preheated with0.1g EDTA for 1min by mircowave-heating.The amino group on the APTES was conjugated with the carboxylic group on the EDTA,then mixture of PEG1500(1mL)and glycerin(1mL)was injected into the solution.The microwave treatment for3min caused the dehydration and pyrolysis of the mixture,and then made them broken into small luminescent carbon dots.PEG1500 and glycerin provided high boiling media for the reaction. Carbon dots were dialyzed against pure water before the experiment.CL systemCL kinetic curves were obtained by batch experiments,which were carried out in the glass cuvette.The CL profiles were displayed and integrated for0.1s interval.A microliter sy-ringe was used for the injection of the solution from the upper injection port.The effect of the carbon dots on the CL from luminol-N-bromosuccinimide system has been investigated by both batch experiment and flow injection system.The manifolds of the flow injection system were shown in Fig.S1.H2O was used as the carrier for carbon dots solution. Carbon dots were firstly mixed with luminol at the three-way channel.The mixture finally mixed with N-bromosuccinimide at the flow cell,where the CL signal was collected by the LF-800detector.The peak height of the signal recorded was measured as CL intensity.Results and discussionSynthesis and characterization of carbon dotsThe microwave-heating of APTES and EDTA induced the amino group on the APTES to be conjugated with the carbox-ylic group on the EDTA.After the injection of the mixture of PEG1500and glycerin into the solution,the further micro-wave treatment for3min caused the dehydration and pyroly-sis of the mixture,and then made them broken into small luminescent carbon dots.Transmission electron microscopy(TEM)image showed that the carbon dots had an average diameter of3nm(Fig.1a). The carbon dots showed excitation wavelength-dependence fluorescence emission with the excitation wavelength higher than360nm.Different from previously reported carbon dots [19],the emission wavelength of the silicon hybrid carbon dots did not shift with the excitation wavelength lower than360nm (Fig.1b),which may be because that the surface energy traps for the carbon dots were modified by the silicon element. Furthermore,the quantum yield of the silicon-carbon dots was calculated as24%with quinine sulfate as the reference, which was higher than some water-soluble carbon dots.The microwave heating time has some influence on the size and the fluorescence of the carbon dots.3min heating could make the carbon dots own the suitable structure with highestZ.Lin et al.fluorescence intensity.Heating time longer than 3min caused little effect on the size of the carbon dots,which was con-firmed by the TEM image.The effect of the weight ratio between APTES and EDTA on the fluorescence of the carbon dots has been investigated.Five hundre μL APTES and 0.1g EDTA could obtain the homogenous carbon dots with high fluorescence intensity.X-ray photoelectron spectroscopy (XPS)spectrum (Fig.2a )showed that the prepared carbon dots contained C,N,O and Si in a weight ratio of 61.11:5.77:24.62:8.50.Fourier trans-form infrared spectroscopy (FT-IR)(Fig.2b )revealed func-tional groups,such as ≥C-OH (hydroxyl),≥C-O-C ≤(ether),=C=O,≥Si-OH and ≥Si-O-Si ≤,could be formed on the car-bon dots.Hydroxyl group and silicon hydroxyl group on the carbon dots are beneficial for their conjugation with biomol-ecules.The X-ray diffraction pattern indicated that the carbon dots were amorphous (Fig.S2).The enhanced CL from luminol-N-bromosuccinimide system by carbon dotsIn alkaline media,N-bromosuccinimide could hydrolyze into HBrO and oxidize luminol to excited 3-aminophthalate dianion,which returned to basic state with CL emission (Fig.3a (1)).The injection of N-bromosuccinimide into the mixture of carbon dots and luminol brought in almost ten fold enhancement compared with the CL from luminol-N-bromosuccinimide system (Fig.3a (2)).The CL reaction between N-bromosuccinimide and car-bon dots in the absence of luminol was also investigated to get further insights into the interaction of the reagent.It was found that the CL reaction between N-bromosuccinimide and carbon dots could be observed in the absence of luminol in alkaline media (Fig.3b )under high recording voltage (−1.2kv),although its CL intensity was much lower com-pared with the CL from carbon dots-luminol-N-bromosuccinimide system.The CL emission arousedfromFig.1a TEM image of the carbon dots and b fluorescence spectra for carbon dots excited at wavelengths from 280nm to 460nm with 20nmincrementFig.2a X-ray photoelectron spectrum and b the IR spectrum of the silicon hybrid-carbon dotSilicon-hybrid carbon dots strongly enhance the chemiluminescencethe injection of N-bromosuccinimide to carbon dots-NaOH solution had the similar intensity compared with that from the injection of carbon dots to the mixture of NaOH and N-bromosuccinimide (Curve 1and 2in Fig.3b ).The injection of N-bromosuccinimide to carbon dots in the absence of NaOH only resulted in low CL emission (Curve 3in Fig.3b ).NaOH herein was to adjust the pH value of the system for the hydration of the N-bromosuccinimide to HBrO that acted as the oxidant in the CL reaction.It is suspected that the CL between the carbon dots and N-bromosuccinimide is similar with previous research which used KMnO 4,Ce(IV)as well as peroxynitrous acid as the oxidant [15,16],except that the CL reaction should take place in alkaline media.The CL mechanism illustrationThe enhancement role of the nanoparticle in the CL system has gained great attentions in recent years.Nanoparticle could act as catalyst that facilitated the generation CL related spe-cies,as the energy acceptors receiving the energy releasing from the excited species,or as participator that is involved in the oxidation or reduction reaction.In the presence of oxidant,such as acidic potassium per-manganate and cerium(IV),carbon dots acts as the electron acceptor.The radiative recombination of oxidant-injected holes and electrons in the carbon dots accounts for the CL emission [15].In order to verify the role of carbon dots in the N-bromosuccinimide-luminol system,EPR was utilized to investigate the ground-state properties of luminescent species in the carbon dots.The EPR signal of carbon dots at g =1.9990revealed singly occupied orbital in ground-state carbon dots.The EPR spectra of the carbon dots after their reaction with N-bromosuccinimide in the absence of luminol were presented in Fig.4and the g value of the carbon dots shifted from 1.9990to 1.9982,which suggested the electron transfer between the carbon dots and N-bromosuccinimide in the absence of luminol.While in N-bromosuccinimide -luminol-carbon dots system,the g value of the carbon dots presented little shift,which indicated that new role rather than electron donor of the carbon dots.Luminol with low reductant potential is reason-able to serve as the electron donor in N-bromosuccinimide-luminol-carbon dots system.The fluorescence of the carbon dots exhibited severely decreased after their reaction with N-bromosuccinimide.The pr ese nce of lum inol with c arb on d ots a nd N-bromosuccinimide alleviated the decreasing of the fluores-cence of carbon dots,which also indicated that luminol com-peted with carbon dots to react with N-bromosuccinimideandFig.3CL profiles in the batch system:a (1)50μL of 10−6M luminol+50μL of H 2O+N-bromosuccinimide;(2)(1)50μL of 10−6M luminol+50μL of carbon dots+N-bromosuccinimide;b (1)injection of N-bromosuccinimide into the mixture of NaOH and carbon dots;(2)injec-tion of carbon dots into the mixture of NaOH and N-bromosuccinimide;(3)injection of N-bromosuccinimide into carbon dots;(4)The mixture in (3)+NaOH.a and b were recorded with PMT voltage of −0.9kV and −1.2kV ,respectivelyFig.4The EPR signal of the carbon dots before and after CL reaction with N-bromosuccinimideZ.Lin et al.confirmed the role of electron donor of luminol on N-bromosuccinimide-luminol-carbon dots system.CL spectrum of one CL reaction is beneficial for us to get further insight into the CL emitters in the system.CL spectrum was measured by a fluorescence spectrometer with the xenonlamp turned off.In view of the weak CL emission from N-bromosuccinimide-carbon dots system,high-energy cutoff filters of various wavelengths were also used to determine the CL spectrum of the system (Blue line in Fig.5).Both methods showed that the maximum CL emission for carbon dots-N-bromosuccinimide CL system located in 550nm (Fig.5a ),which could be attributed to the oxidation of carbon dots by N-bromosuccinimide.However,the maximum CL emission for the luminol-carbon dots-N-bromosuccinimide system was around in 425nm,which was characteristic wave-length of excited 3-aminophthalate (Fig.5b ).The shift of g value of carbon dots and the sharply decrease of fluorescence indicated the reaction between carbon dots and N-bromosuccinimide.The CL emission spectra further confirmed that carbon dots acted as CL emitter in carbon dots-N-bromosuccinimide system,which was similar with the sit-uation that carbon dots reacted with some other oxidant [15].The coexistence of luminol in carbon dots-N-bromosuccinimide system not only reduced the shift of g value of carbon dots,but also reduced the decrease of FL.In addition,the CL spectra revealed the CL emitter in luminol-carbon dots-N-bromosuccinimide system was excited 3-aminophthalate,which indicated that carbon dots played a new role rather than the CL emitter in the luminol-carbon dots-N-bromosuccinimide system.pH value has significant effect on the CL emission of the CL system.The highest CL emission for carbon dots-luminol-N-bromosuccinimide system is observed in the solution with a pH value of 7.0(Fig.S3).Under the pH condition,the Zeta value of the carbon dots is 14.7mV .The pKa for luminol is 6and 13[20].Luminol is negatively charged in media with a pH value of 7.0.Therefore,it is reasonable to assume electro-static interaction between the carbon dots and luminol anion,which facilitates the electron transfer from luminol anion to the N-bromosuccinimide oxidant.As a result,the carbon dots enhance the CL intensity of thesystem.Fig.5The CL spectra of the carbon dots-N-bromosuccinimide system (a )and carbon dots-luminol-N-bromosuccinimide system (b)Fig.6Schematic illustration of CL mechanism of carbon dots-N-bromosuccinimide-luminol systemSilicon-hybrid carbon dots strongly enhance the chemiluminescenceThe contribution of 1O 2to the CL emission was excluded by investigating effects of different radical scavengers on the CL system.4-Diazabicyclo [2,2,2]octane (DABCO)was known to be a quencher of 1O 2,which could deactivate O 2(1Σg +)through electronic-to-vibrational (e-v)process [21].0.01M DABCO showed no inhibition of the CL.NaN 3,as a specific scavenger for 1O 2[22,23],with a concentration of 0.001M still could not decrease the CL signal.Based on the discussion above,the enhancement of the carbon dots on N-bromosuccinimide-luminol system could be explained as follows.The carbon dots with positive zeta potential resulted in the concentrating of the luminol anion (Fig.6),which facilitated the oxidation of luminol by HBrO that hydrolyzed from the N-bromosuccinimide.Luminol was oxidized by HBrO to excited 3-aminophthalate,which turned to its basic state by CL emission in 425nm.The application of the systemIn carbon dots-N-bromosuccinimide and carbon dots-luminol-N-bromosuccinimide systems,the CL intensity showed a linear relationship with the concentration of the carbon dots (Fig.7)in the range from 1.25×10−3to 2.00×10−2mg mL −1(Fig.4b )with a correlation coefficient of 0.9985.The detection limit was as low as 6.00×10−4mg mL −1(S /N =3).The CL system could be developed as a method for the determination of carbon dots.The carbon dots prepared by the present method contained hydroxyl group and silicon hydroxyl group on the surface that were easy for modification.It is expected that carbon dots could be conjugated with various biomolecules,such as protein,or DNA via covalent bond.These biomolecules could be quan-tified through the concentration of carbon dots.ConclusionsIn summary,microwave pyrolysis method has been developed for the preparation of silicon-hybrid carbon dots with quantum yield as high as 24%.The silicon modified carbon dots are convenient for labeling.Furthermore,the carbon dots could act as CL enhancer for luminol,which extended the range of the enhancer for luminol.The linear relationship between the CL intensity and the concentration of carbon dots has been found and could be further developed as determination meth-od for carbon dots or their biomolecule conjugates.Acknowledgments This work was supported by National Nature Sci-ence Foundation of China (Nos.20935002,21305015,21275088).References1.Baker SN,Baker GA (2010)Luminescent carbon nanodots:Emergent nanolights.Angew Chem Int Ed 49(38):6726–67442.Xu X,Ray R,Gu Y ,Ploehn HJ,Gearheart L,Raker K,Scrivens WA (2004)Electrophoretic analysis and purification of fluorescent single-walled carbon nanotube fragments.J Am Chem Soc 126(40):12736–127373.Esteves da Silva JC,Gonçalves HM (2011)Analytical and bioanalytical 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ORIGINAL CONTRIBUTIONBimetallic palladium–gold nanoparticles synthesized in ionic liquid microemulsionGuoping Zhang&Haihui Zhou&Chunling An&Dan Liu&Zhongyuan Huang&Yafei KuangReceived:12October2011/Revised:23March2012/Accepted:22April2012#Springer-Verlag2012Abstract The palladium and gold precursors were dissolved in dispersive and continuous phase of ionic liquid microemul-sion(H2O/Triton X-100(TX-100)/1-butyl-3-methylimidazo-lium hexafluorophosphate),respectively.[PdCl6]2−ions were reduced in situ by TX-100in dispersive phase(H2O)to prepare Pd nanoparticles(NPs)and then[AuCl4]−crossed through the interface film and reacted with the as-prepared Pd NPs to form Pd4Au NPs.The as-prepared Pd4Au NPs were characterized by transmission electronic microscopy,energy dispersive X-ray spectroscopy,X-ray diffraction,and ultravi-olet–visible spectroscopy.The as-prepared Pd4Au NPs sus-pension and carbon nanotubes(CNTs)suspension were vigorously stirred to prepare the electrocatalyst supported on the CNTs with a total metal loading of20wt.%(denoted by Pd4Au/CNTs).Cyclic voltammetry and chronoamperometry tests show that the Pd4Au/CNTs are very promising for the oxidation of ethanol in alkaline medium.The result can be attributed to the synergistic effect between Pd and Au during the catalytic process.Keywords Ionic liquid.Microemulsion.Bimetallic nanoparticle.Ethanol.ElectrooxidationIntroductionMicroemulsions are thermodynamically stable,isotropic, optically transparent dispersions of two immiscible liquids stabilized by a surfactant and occasionally a surfactant/co-surfactant mixture[1].Currently,room temperature ionic liquids(RTILs)have been used as one of the three compo-nents required to form IL microemulsions[2],which were developed as interesting media for preparing some predom-inant nanomaterials[3–16].Compared with volatile organic solvents,RTILs possess special solubility to inorganic salts [17,18].Therefore,two metal precursors can be dissolved in dispersive and continuous phase of water/surfactant/IL microemulsion simultaneously to prepare prospective bimetallic pared with the bimetal syn-thesized in solution,the bimetal prepared in water/surfac-tant/IL microemulsion would possess special microstructure and excellent properties.Direct alcohol fuel cells(DAFCs)have been widely recog-nized as attractive power sources for portable electronic devi-ces and other mobile applications[19].Considerable efforts have been made to develop catalytic materials with high activity for DAFCs.The bimetallic materials have attracted a great interest in scientific research and industrial applications due to their predominant catalytic properties different from those of the corresponding monometallic counterparts[20, 21].It is acknowledged that Au and Pd catalysts are very efficient for different reactions involved in fuel cells[22, 23].Nowadays,the addition of Au to Pd to form bimetallic catalyst not only improves catalytic activity but also reduces the cost and enhances the resistance to poisoning in fuelcells G.Zhang:H.Zhou:C.An:D.Liu:Z.Huang:Y.Kuang(*)College of Chemistry and Chemical Engineering,Hunan University,Changsha410082,People’s Republic of Chinae-mail:yafeik@G.ZhangShenzhen Institutes of Advanced Technology,Chinese Academy of Sciences,Xueyuan Avenue1068,Shenzhen518055,ChinaH.Zhou(*)State Key Laboratory for Chemo/Biosensing and Chemometrics,College of Chemistry and Chemical Engineering,Hunan University,Changsha410082,People’s Republic of Chinae-mail:haihuizh@Colloid Polym SciDOI10.1007/s00396-012-2670-6[24].Most of the studies concerning the bimetallic systems were confined in solution and employed a successive[25,26] or coreduction[27,28]approach.Here,we dissolved Pd and Au precursors in dispersive phase(water)and continuous phase(1-butyl-3-methylimida-zolium hexafluorophosphate([BMIM]PF6))respectively and prepared Pd–Au nanoparticles(NPs)by in situ reduction and replacement reactions in H2O/Triton X-100(TX-100)/ [BMIM]PF6microemulsion for the first time.The resultant Pd–Au NPs were supported on carbon nanotubes(CNTs)for ethanol electrooxidation under alkaline condition. ExperimentalChemicalsThe ionic liquid[BMIM]PF6was prepared according to the literature[29]and dried under vacuum at70°C for12h before use.Its purity was checked by applying the AgNO3 test,1H and31P NMR,and cyclic voltammetry[30].Pristine multiwalled CNTs were purchased from Shenzhen Nano-tech Port Co.Ltd.,China and purified by being refluxed in concentrated nitric acid for12h.(NH4)2PdCl6and HAuCl4·4H2O were purchased from Aldrich Chemicals, Co.TX-100(chemically pure),ethanol(analytical reagent), and KOH(analytical reagent)were obtained from Shanghai Chemical Reagent Factory(China).The water used in the experiments was deionized and double distilled.Catalyst preparationThe H2O/TX-100/[BMIM]PF6microemulsion was prepared according to previous work[2].(NH4)2PdCl6and HAuCl4·4H2O were dissolved respectively in H2O and [BMIM]PF6before the preparation of H2O/TX-100/ [BMIM]PF6microemulsion[31].The procedure was carried out as follows:4.90g TX-100and2.72g[BMIM]PF6 (containing0.0015mmol[AuCl4]−)were added into a three-necked flask,and then the mixture was vigorously magnetically stirred in N2atmosphere.The resultant solu-tion was heated to45°C with0.5mL(NH4)2PdCl6aqueous solution injected into the solution([Pd IV]/[Au III]04),and the reaction time was2h.During this process,the mixture turned from light yellow to dark gray.The monometallic Pd or Au NPs were prepared by adding(NH4)2PdCl6or HAuCl4·4H2O singly into the dispersive phase(H2O)of [BMIM]PF6microemulsion.Unless otherwise stated,the Au NPs were synthesized at the condition of60°C for 2h.The as-prepared Pd and Pd–Au NPs were collected by means of centrifugation.The metal NPs suspension and CNTs suspension were vigorously stirred to prepare electro-catalyst with a total metal loading of20wt.%(denoted by Pd/CNTs and Pd4Au/CNTs).The resultant electrocatalyst was washed with anhydrous ethanol,dried under reduced pressure.The black powder was redissolved in water to prepare the sample(0.5mg mL−1)for the TEM analysis.Instruments and measurementsThe morphologies of Pd and Pd4Au NPs were investigated by transmission electron microscopy(TEM JEOL3010) operating at300kV.The compositions of the nanomaterials were analyzed by energy dispersive X-ray spectroscopy (EDS).The X-ray diffraction(XRD)patterns were obtained with a Bruker D8Advance Diffractometer.The ultraviolet–visible(UV-vis)spectra were preformed on the TechLab UV-2100ultraviolet and visible spectrophotometer.All electrochemical measurements were carried out with a CHI660C electrochemistry workstation(Shanghai Chenhua Instrument Factory,China)at room temperature. The Pd/CNTs-and Pd4Au/CNTs-modified glassy carbon electrodes(GC,s00.1256cm2)were used as working electrodes.A Pt wire and a saturated calomel electrode (SCE)were used as counter and reference electrode,re-spectively.The electrolyte was a1.0M KOH solution containing1.0M ethanol,which was deaerated by N2 (99.99%)for30min in advance.Results and discussionCharacterization of the Pd–Au bimetallic NPsPd–Au nanomaterials with promising properties were pre-pared by the aid of superior solubility of water and IL to metal precursors in the H2O/TX-100/[BMIM]PF6microe-mulsion.(NH4)2PdCl6and HAuCl4·4H2O were dissolved in H2O and[BMIM]PF6,respectively.Although the standard reduction potential of[AuCl4]−/Au(1.00V vs.standard hydrogen electrode(SHE))is lower than that of[PdCl6]2−/ Pd(1.88V vs.SHE)and the reduction by Triton X-100is an alcohol reduction in the microemulsion system[32],the [PdCl6]2−ions were in situ reduced preferentially by the interface film(TX-100)in the water phase to form Pd NPs at45°C.However,[AuCl4]−ions were dissolved in the [BMIM]PF6phase to form a carbine complex[33],which could not be reduced by[BMIM]PF6or TX-100at the condition of45°C.With the reaction proceeding,the com-plex crossed slowly through the interface film and entered into the water phase to get in contact with the as-prepared Pd NPs.Because of a large standard reduction potential gap between Pd2+/Pd(0.83V vs.SHE)and[AuCl4]−/Au (1.00V vs.SHE),the replacement reactions between Pd NPs and[AuCl4]−ions take place to form core(Pd)–shell (Au)bimetallic nanomaterial and Pd2+ions[34].Then,theColloid Polym Sciresultant Pd 2+ions were reduced by TX-100,and the newly obtained Pd NPs covered on the surface (Au)of Pd –Au NPs.Furthermore,the [AuCl 4]−ions were reduced by as-prepared Pd NPs.The synthetic process cycled continuouslyuntil the irregular Pd 4Au NPs with Pd core,middle Au,and outermost Pd were obtained as shown in Fig.1.The UV-vis spectra of Pd,Au,and Pd 4Au NPs are shown in Fig.2.It can be observed that a pronouncedgoldFig.1Schematic illustration showing the synthesis of Pd 4Au NPs in H 2O/TX-100/[BMIM]PF 6microemulsionFig.2UV-vis absorption spectra of Au,Pd,and Pd 4AuNPs Fig.3XRD patterns of Pd,Au,and Pd 4Au NPsColloid Polym Scicharacteristic peak is obtained and ascribed to the surface plasmon resonance (SPR)of Au NPs.Pd NPs are known to absorb in the UV region with virtually no structure [35].However,the UV-vis spectrum of Pd 4Au is similar to that of pure Pd NPs,and the SPR does not show any absorption peak in the investigated region.This may be attributed to that the Pd 4Au NPs are totally encapsulated by the sur-rounding Pd atoms and the Pd atoms layer in the Pd 4Au nanostructure is thick enough to hide the characteristic SPR peak of Au [36].Figure 3shows the XRD patterns of Au,Pd,and Pd 4Au NPs.The diffraction peak of Pd 4Au NPs shifted to a lower 2θangle than that of pure Pd,indicating the increase in lattice constant of Pd due to the incorporation of Au atoms [37].Compared with the XRD pattern of pure Au,no diffraction peak assigning to Au is evident in that of Pd 4Au NPs,suggest-ing the absence of large isolated Au particles.This finding further demonstrates that [AuCl 4]−mainly reacted with Pd to form Pd 4Au rather than forming a new nucleus.Figure 4shows the high-resolution TEM (HRTEM)images of Pd and Pd 4Au NPs.It can be seen that in situ reduction of (NH 4)2PdCl 6leads to Pd NPs with the size of 3nm and a narrow size distribution (Fig.4a ,b).The repre-sentative TEM image of Pd 4Au NPs is shown in Fig.4c .It is clear that the average size of Pd 4Au NPs is 4.5nm.Simi-larly,Fig.4d indicates that the Pd 4Au NPs also possess a narrow size distribution.The size of Pd 4Au NPs is a little larger than that of Pd NPs,which may be ascribed to thefactFig.4The HRTEM images of Pd (a )and Pd 4Au NPs (c ).The particle size distribution of Pd (b )and Pd 4Au NPs (d )based on 100randomly selectedparticlesFig.5The TEM images of Pd 4Au NPs (a )and Pd 4Au/CNTs (b )Colloid Polym Scithat Au was grown on the surface of Pd NPs to form Pd 4Au NPs.The TEM results are in accordance with the explana-tion of the UV-vis spectra and XRD patterns.The representative TEM images of Pd 4Au NPs and Pd 4Au/CNTs are shown in Fig.5.It can be seen that the as-prepared Pd 4Au NPs are uniform and monodisperse (Fig.5a ).The CNTs suspension and Pd 4Au NPs suspension were vigorously stirred to prepare a Pd 4Au/CNTs electro-catalyst for comparison.The CNTs were functioned as physical supports for metal NPs,not as anchor for single particle.Therefore,the Pd 4Au NPs are not supported uni-formly on the CNTs as shown in Fig.5b .The EDS analysis spectra of Pd and Pd 4Au NPs are shown in Fig.6.A large amount of Pd NPs was successfully prepared by in situ reduction and confirmed by EDS analy-sis (Fig.6a ).It can be seen from Fig.6b that the Pd 4Au NPs are grown as original ratio of chemicals.Consequently,the Pd 4Au NPs can be prepared with small size and a narrow size distribution by in situ reduction and replacement reac-tions in H 2O/TX-100/[BMIM]PF 6microemulsion.In a word,the H 2O/TX-100/[BMIM]PF 6microemulsion was considered as a benign medium for preparing ultrafine bimetallic nanoparticles.The special microstructure of IL microemulsion can offer superior location for fabrication of bimetallic materials.Furthermore,the synthetic procedure is green without additional reducing agent or higher temperature.Electrooxidation of ethanol on the Pd 4Au/CNTs electrocatalystFigure 7shows the cyclic voltammetry (CV)curves of Pd/CNTs-and Pd 4Au/CNTs-modified GC electrodes in 1.0M KOH containing 1.0M ethanol at the scan rate of 50mV s −1.As it is known,the ratio of the forward anodic peak currentdensity (I f )to the backward one (I b )can comparatively quan-tify the catalyst tolerance to carbonaceous species accumula-tion [38].The values of I f on the Pd/CNTs and Pd 4Au/CNTs are 9.65and 28.56mA cm −2,respectively;the corresponding values of I b are 9.89and 26.61mA cm −2.The Pd 4Au/CNTs electrode exhibits about threefold higher catalytic activity,and the I f /I b value of Pd 4Au/CNTs (1.07)is larger than that of Pd/CNTs (0.97).All the results may be caused by the special microstructure of Pd 4Au NPs and the synergic effect between Pd and Au during the catalytic process [39].Chronoamperometry tests were also performed to inves-tigate the long-term performance of these electrocatalysts during oxidation.It can be seen from Fig.8that the polar-ization current for the ethanol electrooxidation showsaFig.7CVs of Pd/CNTs-modified (black line )and Pd 4Au/CNTs-mod-ified (red line )GC electrodes in 1.0M KOH containing 1.0M ethanol at the scan rate of 50mV s −1.The metal loading for each sample is 4μgColloid Polym Scirapid decay during the initial period because of the poison-ing of the intermediate species [40].However,the Pd 4Au/CNTs-modified electrode exhibits a higher initial current and much slower current decay as compared with the 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Ⅲ-PNVA-co-PSt纳米微球的合成及其性能研究1 Eu()孙雨薇1，倪忠斌1，傅成武1，黄晓华1, 2，陈明清1*1江南大学化学与材料工程学院，江苏无锡 (214122)2南京师范大学化学与环境科学学院，南京 (210097)E-mail：mqchen@摘要：合成了具有核壳结构的以聚苯乙烯为核，聚N-乙烯基乙酰胺为壳的单分散纳米级共聚微球PNVA-co-PSt及其与Eu3+的配合物，并用透射电子显微镜、Zeta-电位、红外光谱、Ⅲ-PNVA-co-PSt 紫外光谱以及荧光光谱分别对其进行了表征。

红外、紫外光谱表明，在Eu()配合物微球中Eu3+离子可能与PNVA侧链酰胺基团的氧原子和氮原子发生配位作用；荧光Ⅲ-PNVA-co-PSt配合物微球受到260nm波长的紫外光激发后，在584和光谱显示，Eu()612nm处产生增强的Eu3+的特征发射峰，说明在Eu3+离子和PNVA-co-PSt微球之间能够发生有效的Förster能量传递。

关键词：核壳纳米微球；Eu3+；紫外光谱；荧光光谱中图分类号：O614.3; O6411.引言稀土有机高分子除了具有高分子材料优良的加工性能和力学性能外，由于稀土元素独特的电子结构，还兼具有特有的光、电、磁等特性[1-4]。

近年来，稀土高分子化合物因其独特的荧光特性受到各国科学工作者的广为关注[5，6]。

N-乙烯基乙酰胺（NVA）是一种无毒、生理相容性好的酰胺类单体，其均聚物聚N-乙烯基乙酰胺（PNVA）可溶于水和醇类极性有机溶剂，且经过水解后可生成水溶性阳离子型聚乙烯胺（PVAm），既可以作为功能性高分子广泛应用，也可作为制备其它功能聚合物的基本原料[7]。

本文拟在改进无皂种子乳液聚合配方的基础上，制备单分散的以聚苯乙烯(PSt)为核、聚N-乙烯基乙酰胺(PNVA)为壳的（PNVA-co-PSt）核壳结构纳米微球，并加入稀土离子Eu3+，使其与壳层中PNVA上的基团配位，形成稀土Eu(Ⅲ)-PNVA-co-PSt微球配合物。