作为软模板和甲基橙聚吡咯的制备

Preparation and characterization of PPy with methyl orange as soft templateMei Li •Wenguang Li •Jun Liu •Jinshui YaoReceived:8July 2012/Accepted:19July 2012/Published online:27July 2012ÓSpringer Science+Business Media,LLC 2012Abstract PPy nanotubes were succesfully synthsized in neutral MO aqueous solutions by in situ polymerization using FeCl 3or APS as oxidant respectively.These nano-tubes were characterized with SEM,TEM,FTIR XRD and EDS and results showed MO molecules entered into the PPy chain as dopant.The good conducting characteristic may be related to the higher doping level of the MO and conductivity of the PPy nanotubes was up to 29.07S Ácm -1.The shape of the obtained PPy would be changed slightly and its solubility was greatly improved because of the addition of HCl in neutral MO aqueous solutions.1IntroductionConducting polymer micro/nanotubes,being excellent candi-dates for use as molecular wire materials due to their one-dimensional structure and metal-like conductivity [1,2],have also been extensively explored [3,4].Basically,micro/na-notubules of conducting polymers have been obtained by twotypical methods:template-directed synthesis and template-free growth.The former method uses track-etched polymeric membranes or porous alumina as ‘‘hard templates’’to prepare tubular structures in the pores [5].Recently,the template-directed method has been proven to be an effective and versatile technique to synthesize conducting polymer tubes with uniform dimensions.However,the used hard-template materials usually have to be removed using strong acids/bases or an organic medium or with elevated temperature after the synthesis [6].From the viewpoints of safety and environmental hazards,such a process greatly increases the cost and risk for large-scale manufacture.Furthermore,the extremely harsh post-treatment conditions may drastically alter or even destroy themicro/nanostructures of the resulting materials.On the other hand,a template free method has been invented and developed recently to synthesize conducting polymer micro/nanotubules by employing ‘‘soft templates’’such as organic acids,surfactant micelles,liquid crystalline,and reverse micro-emulsions [7].It is proposed that the soft templates promote the conducting polymer to grow in a tubular form and need not be removed after the polymerization.In such cases,however,the soft templates are often not quite stable,the versatility for different systems is poor and the multi-formity of final products is obvious [8].Until now,it remains a desirable target to develop a convenient synthetic method to obtain exclusive hollow micro/nanotubular structures using a template (hard or soft)that is highly stable under the reaction conditions and can be facilely removed in the post-treatment process.Among the family of conducting polymers,polypyrrole (PPy)has been most extensively studied because these products exhibit good environmental stability and the elec-trical properties can be modified by changing the oxidation and protonation states [9].To fabricate PPy nanotubules,we have recently developed a fibrillar self-degraded template composed of anionic azo dye methyl orange (MO)and FeCl 3M.Li (&)ÁW.Li ÁJ.Liu ÁJ.YaoSchool of Materials Science and Engineering,Shandong Polytechnic University,Daxue Road,Western University Science Park,Jinan 250353,People’s Republic of Chinae-mail:limei@;plum3lm@M.Li ÁJ.YaoShandong Provincial Key Laboratory of Processing and Testing Technology of Glass and Functional Ceramics,Jinan 250353,People’s Republic of ChinaM.Li ÁJ.YaoKey Laboratory of Amorphous and Polycrystalline Materials,Shandong Polytechnic University,Jinan 250353,People’s Republic of ChinaJ Mater Sci:Mater Electron (2013)24:906–910DOI 10.1007/s10854-012-0847-x[10].In this paper,anionic azo dye methyl orange dissolved in water and MOfibril was formed as a soft template for the fabrication of conducting PPy microtubules.PPy nanotubes with different diameter were obtained after the polymeriza-tion of monomers onfibril surface when the oxidant(APS or FeCl3)was added slowly.Thisfinding provides us a facile and inexpensive way to fabricate conducting polymer nanotubes.Moreover,it may open a new route to design orchestrate particular shape and morphology of micro/ nanostructures.2Experimental2.1Preparation of samplesThe experimental conditions were listed in Table1in detail. In a typical procedure as S-2,1.95g(7.22mmol)of FeCl3 was dissolved in150mL of0.30mM MO(sodium4-[4‘-(dimethylamino)phenyldiazo]phenylsulfonate)((CH3)2NC6 H4-N=NC6H4SO3Na)deionized water solution.Afloc-culent precipitate appeared immediately.Then0.5mL (7.22mmol)of pyrrole monomer was added into it and the mixture was stirred at room temperature for24h.The formed PPy precipitate was washed with deionized water/ ethanol several times untilfiltrate was colorless and neutral, andfinally dried under a vacuum atmosphere at40°C for 24h.Replacing the oxidant FeCl3with ammonium peroxy-sulfate(APS)and repeating the above process,black PPy precipitate was obtained.2.2CharacterizationThe morphology of the product was directly observed with scanning electron microscopy(SEM)(FEIco-Holland,JSM-6700F)and transmission electron microscopy(TEM)(JEOL, JEM-1011).An X-ray diffraction(XRD)pattern was taken with a Shimadzu XRD6000instrument at a10°/min scanning speed from10°to80°.FTIR spectra of the samples were obtained with a Shimadzu FTIR-8400s spectrophotometer in the4,000–500cm-1range,the sample was impressed into KBr pellets.EDS results were tested by Vario EL elementar analysen syetem GmbH.Germany.Four-point probes resis-tivity measurement system was received from GuangZhou and the electrical conductivity of composites was measured using four-point probes technique at room temperature.3Results and discussion3.1Structures and morphologyIn the SEM images(Fig.1a,b),the tubular and granular morphology,which correspond to the case of different oxidant of APS and FeCl3,are observed.The surface of theTable1The conductivity and solubility of PPy prepared in different conditions Sample MO(g)HCl(ml)Oxidant(g)Molar ratio ofoxidant to monomerConductivity[SÁcm-1]Solubility inCH2Cl2(g/L) S-1––FeCl31.9510.00050.0010S-20.098–APS1.65129.070.0420S-30.098–FeCl31.951 2.1050.1241S-40.0980.4APS1.6510.3460.2587S-50.0980.5APS1.6510.50.2500S-60.0980.6APS1.6510.90910.1682S-70.0980.7APS1.6510.0250.3124 Fig.1The SEM images of PPy nanotubes with different oxidants a S-2b S-3nanotubes is rough and composed with many PPy granules.The tubular structure of PPy-MO is further confirmed by TEM micrograph where outer and inner diameters of the hollow nanotubes are about 300and 30nm,in Fig.2a and the corresponding values are about 200and 20nm in Fig.2b respectively.Figure 3shows the FT-IR spectra of different MO-oxidant templates.It can be seen that the peaks at 2,924and 2,854cm -1in curves a and b which are attributed to the stretching vibration mode of methylene groups in the long alkyl chains of MO molecules indicating the presence of more MO molecules.The characteristic PPy peaks are located at 1,535and 1,454cm -1due to the pyrrole ring stretching and the conjugated C–N stretching mode,respectively.The peaks at 1,294and 1,031cm -1are related to the in-plane vibrations of C–H,1,166cm -1is assigned to the C–N stretching mode [11–13],In addition,the peaks at 898,673cm -1correspondsto the stretching vibration of the SO 3¯group,which indicates the MO entering the PPy nanotubes as dopant [14].The XRD patterns of the PPy nanotubes prepared with different oxidants are shown in Fig.4.As shown in Fig.4,the broad reflection centered at 2h value of 10°and 27°wascharacteristic of the doped amorphous PPy.Another three diffraction peaks at 2h =17°,43°,54°in curves a and b are more obvious than curve c,especially in curve b.This change may suggest that the regular array of PPy molecules to some extent when APS is used as oxidant which is beneficial to the conductivity as shown in Table 2.The results of the EDS analysis are shown in Table 2.It can be seen that PPy was doped with –SO 32-which was supplied with MO.Correspondingly,the electric conduc-tivities of the nanotubes at room temperature were 2.105and 29.07S Ácm -1respectively.In comparison with some results reported previously [9,15–17],the conductivities here are rather higher mainly because of the higher doping level of the products,which has been implied from the high mass percent values of S elements shown in Table 2.3.2SolubilityIn order to improve the solubility of the obtained PPy,HCl was added into the MO solutions in the syntheticprocessFig.2The TEM images of PPy nanotubes with different oxidants a S-2bS-3Fig.3The FTIR spectra of PPy nanotubes a S-3b S-2cS-1Fig.4The XRD spectra of PPy nanotubes a S-3b S-2c S-1and the SEM images of S-4,S-5,S-6and S-7were shown in Fig.5.The tubular and granular morphology of PPy co-existed in different samples which implied that the addition of HCl influenced the aggregation of MO mole-cules.The MO tubes were destroyed to different degrees by HCl which leaded to more PPy particles occurred in the prepared samples.These samples show better solubility in CH2Cl2as shown in Table1and the best value is0.3124g/ L when the amount of HCl is0.7ml.At the same time,the conductivity of above samples decreased greatly which gave a hint that the increase of the solubility was at the expense of the decrease of conductivity.4ConclusionIn summary,we have demonstrated a simple and general strategy by using a soluble MO template in neutral aqueous solutions for the construction of conducting polymer nano-tubes.The MO template is readily dissolved in neutral water,so the microstructures of the resulting materials will not be destroyed during the template-removing process.PPy nano-tubes have been prepared using this MO template and exhibited good conducting characteristic.Further investigations are now focusing on enlarging the versatility of the template for con-structing nanotubular structural materials,and exploring more application by increasing its solubility and manufacturing. 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