Preparation Of Conducting Polymers/Inorganic Nanocomposites And The Study Of Their Catalytic Properties

From a material researcher viewpoint, the advancement of science and technologyprovides the materials smaller and smaller dimensions with enhanced performance. With thenaissance and rapid development of nanotechnology, nanomaterials exhibited superiorproperties and have been applied in various areas including electronic industry, chemicalindustry, mechanical engineering, medication and warindustry. Intrinsically conductingpolymers have been studied extensively due to their intriguing electronic and redox propertiesand numerous potential applications in many fields since their discovery in1970s. In the pastdecade, conducting polymers （especially polyaniline and polypyrrole） with variousnanostructures have been successfully synthesized via many different methods and showedenhanced properties, such as chemical, electronic and sensing properties. However, besidesthe pursuit of high performance in a certain aspect, materials must also have versatility for thedemond of practical application. To improve and extend their functions, the fabrication ofmulti-functionalized conducting polymer nanocomposites has attracted a great deal ofattention. There are various synthetic strategies to fabricate conducting polymernanocomposites. Different methods result in different interfacial adhesion between conductingpolymers and the secondary component as well as different manner of their combination,leading to the corresponding distinct properties of the as-prepared conducting polymer composites. Besides, the size of the inorganic component plays an important role on theproperties of its nanocomposites. Generally, the smaller are the inorganic particles, the higherperformance they exhibit. Therefore, how to prepare well dispersed inorganic nanostructureswith small size through controlling the experimental methods and conditions is an importantresearch topic in the field of conducting polymer/inorganic nanocomposite.Based on the above two considerations, we have successfully synthesized five kinds ofconducting polymer/inorganic nanocomposites with high performance in two different ways.Firstly, in order to achieve the synergistic effect of each component, we improved thedispersion and compatibility of each component as well as the interfacial adhesion betweenthe composite components by changing the preparation methods. Secondly, we prepared welldispersed inorganic nanostructures with small size via controlling the growth rate andenvironment of inorganic component, to produce conducting polymer/inorganicnanocomposites with high performance. We have prepared Pt/PPy hybrid microspheres,PPy/TiO₂/Pd composite nanofibers, PANI/Cu₉S₅composite nanofibers, PANI/PB compositenanofibers and GO/PANI/PB composite nanosheets through various synthetic strategies. Themorphologies of these binary or ternary conducting polymer composites were characterizedby scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Theirchemical composition and crystalline forms were studied via FTIR, XRD, XPS measurements,etc. Moreover, we have studied their catalytic activities in detail, including chemical catalysis,electrocatalysis and peroxidase-like catalysis. The conclusions of this thesis are as follows:1. We have successfully prepared the core-shell structured Fe₃O₄/PPy compositemicrospheres through surfactant-directed chemical oxidation polymerization. Then, usingFe₃O₄/PPy composite microspheres as supporter, ultra-high-density Pt nanoparticles with themean diameters of around4.1nm were well deposited on the PPy shell by reducing H2PtCl6with HCOOH. Meanwhile, the Fe₃O₄core was dissolved by the H+produced by the reactionprocess, leading to the hollow PPy microspheres. It is found that GCE modifed by theobtained Pt/PPy hybrid hollow microspheres exhibits superior electrocatalytic activitytowards the reduction of H₂O₂. The modified electrode displays a fast response time （<2s） and a relatively low detection limit of1.2μM （S/N=3）, compared with a certain HRP-basedbiosensors.2. We have successfully encapsulated conducting polypyrrole （PPy） into electrospunTiO₂nanofibers to form PPy/TiO₂nanocomposites using V2O5as an oxidant and sacrificialtemplate via a simple vapor phase polymerization approach. Furthermore, the as-preparedPPy/TiO₂composite nanofibers were used as nanoreactors for loading Pd nanoparticles. Thecharacterization results display that some very fine Pd nanoparticles with an average diameterof2.0nm are grown onto the PPy/TiO₂composite nanofibers uniformly. The PPy/TiO₂composite nanofiber supported Pd nanoparticles exhibited a high activity towards the catalytichydrogenation of p-nitrophenol with the kinetic rate constant （Kapp） of12.2×10^-3s^-1. Due tothe existence of TiO₂component, the Kappin the eighth cycle for the reduction ofp-nitrophenol could still reach7.13×10^-3s^-1, indicating that the catalyst exhibits a goodstability against poisoning by the product of the reaction.3. Firstly, we have prepared PANI nanofibers doped with thioglycolic acid （TA）. Thenusing the TA, which is bonding with PANI molecular chain through electrostatic interactions,as S resource, the PANI/copper sulphide composite nanofibers with good compatibility wereprepared via hydrothermal method. XRD results indicated that copper sulphides are in theform of Cu₉S₅, and TEM images showed that the diameters of Cu₉S₅nanoparticles were in therange of5-20nm. FTIR specta indicated that strong interaction between Cu₉S₅nanoparticlesand PANI existed. The peroxidase-like activity of the PANI/Cu₉S₅composite nanofibers wasevaluated by catalytic oxidation of peroxidase substrates3,3’,5,5’-tetramethylbenzidine（TMB） in the presence of hydrogen peroxide. The catalytic data revealed that PANI/Cu₉S₅composite nanofibers possessed intrinsic peroxidase-like activity. Furthermore, arising fromthe positive synergetic efects of Cu₉S₅nanoparticles and PANI, the PANI/Cu₉S₅compositecatalysts indeed possessed higher peroxidase-like activity than pristine Cu₉S₅nanostructuresor pristine PANI nanofibers.4. Using PANI nanofiber as a reducer and supporter, we have successfully prepared PB nanoparticles with small size through the reaction between the slowly released Fe2+from thereduction of Fe3+by PANI nanofibers and [Fe（CN）6]3-. TEM images showed that the meandiameters of PB nanoparticles were about20nm and they were well dispersed on the surfaceof the PANI nanofibers. The catalytic experiment results indicated that PANI/PB compositenanofibers possessed superior peroxidase-like activity. Similar to peroxidase, the catalyticactivity of PANI/PB composite nanofibers is dependent on pH and H₂O₂concentration. Theresults show that the optimal pH for the oxidation of TMB was evaluated to be4.0. On thebasis of the peroxidase-like property of PANI/PB composite nanofibers, a colorimetricmethod for H₂O₂detection was designed. UV-vis spectra indicated that it could detect as lowas1μM H₂O₂, and the absorbance at652nm was proportional to H₂O₂concentration in therange of1-16μM （R=0.998） with a detection limit of0.2μM （S/N=3）. Taken together,PANI/PB composite nanofibers are good peroxidase-like catalysts for colorimetric detectionof H₂O₂with low concentration.5. We have successfully prepared GO/PANI composite nanosheets via in situ chemicaloxidation polymerization approach. Then using the composite nanosheets as a reducer andsupporter, we obtained PB nanoparticles with small size. TEM images showed that thediameters of PB nanoparticles were in the range of20-30nm and they were well dispersed onthe surface of GO/PANI composite nanosheets. The as-synthesized GO/PANI/PB compositenanosheets were used as enzyme-less catalysts to modify electrode in order to study theirelectrocatalytic activities towards H₂O₂. Experiment data indicated that the electrode modifiedwith GO/PANI/PB composite nanosheets exhibited good electrocatalytic activities towardsthe reduction of H₂O₂with high sensitivity, which is up to305.7μA mM-1cm-2, wide linearrange of4-320μM （R2=0.999） and low detection limit of0.11μM （S/N=3）. Compared with acertain PB-based biosensors, the GO/PANI/PB composite nanosheets modified electrodeexhibits much higher sensitivity and lower detection limit.