Controlled Preparation Of Supported Polyaniline/Metal Matrix Composities And Their Electrochemical And Catalytic Properties

Owing to their different inner and outer surface chemical properties,wide distribution,low cost and easy availability,halloysite nanotubes(HA)are widely used as supports for various catalysts.On the other hand,polyaniline(ANI)has attracted wide attention in the field of supercapacitors due to its excellent physical and chemical properties,such as high room temperature conductivity,good electrical properties and excellent environmental stability.And metal nanoparticles are also widely used in various fields such as catalysis and energy materials attributed to their high catalytic activity,large specific surface area and unique quantum size effect.In order to overcome the shortcomings of polyaniline and metal nanoparticles in practical applications,such as poor dispersion,poor selectivity to target reaction products and the use of stabilizers in the preparation of nanocatalysts,one-step liquid synthesis of etched halloysite nanotubes@polyaniline(eHA@PANI)and halloysite nanotubes@silver nanoparticles(HA@Ag)with etched halloysite nanotube and halloysite nanotube as supports are proposed in the dissertation.In addition,their electrochemical capacitance and cyclohexene catalytic oxidation properties were also studied detailedly.The main conclusions are as follows:1.Etched halloysite nanotubes@polyaniline composite(eHA@PANI)is prepared by low temperature liquid phase method.The halloysite nanotubes etched with concentrated HCl are used as carriers to induce the polymerization of aniline on the etched halloysite nanotubes to obtain etched halloysite nanotubes@polyaniline composites.The doping degree and redox states of polyaniline in etched halloysite nanotubes@polyaniline composite can be controlled by changing doping acid species(HC1,H2SO4,HNO3,H3PO4)and polymerization temperature.The results of FT-IR,UV-vis and XPS show that etched halloysite nanotubes@polyaniline composite prepared at 0 C and with HCl as dopant acid tuning the acid at 1 M(eHA/18h-PANI-HC1-0?)indicates the higher doping degree,and PANI is mainly present in the form of emeraldine salt(EM)in the composite.The electrochemical capacitance of the above synthesized etched halloysite nanotubes@polyaniline composites was studied.The electrochemical performance of eHA@PANI is assessed by cyclic voltammetry(CV)and galvanostatic charge/discharge(GCD).It indicates that doped acid and reaction temperature can not only affect the doping degree and redox state of PANI on eHA nanotubes,but also affect its electrochemical capacitance.eHA/18h-PANI-HC1-0°C with high doping degree also shows high specific capacitance(the specific capacitance is 703.2 F·g-1 at the current density of 1 A·g-i)and good cycle stability(the retention rate of capacitance after 300 cycles of charge and discharge is 77.6%).Compared with the bulk PANI(PANI-HC1-0°C)prepared under the same conditions,eHA/18h-PANI-HC1-0°C shows higher cyclic stability and specific capacitance,demonstrating it a potential electrode material for high-performing supercapacitors.2.Halloysite nanotubes@silver nanoparticles(HA?Ag)is synthesized by one-step liquid phase method at room temperature.In the solution of AgNO3 and n-butylamine in ethanol,silver ion(Ag+)is adsorbed on the surface of HA owing to its active negatively center of outer surface firstly;then the adsorbed Ag+ is reduced to nano-Ag by n-butylamine.Ag nanoparticles with different sizes and amounts can be obtained on HA by controlling the molar ratio of AgNO3 to n-butylamine during the preparation.TEM shows the amounts and sizes of Ag in HA@Ag increase with the decrease of AgNO3/n-butylamine molar ratio.And silver nanoparticles are well dispersed on the surface of the HA.The catalytic oxidation performance of cyclohexene by the above fabricated HA@Ag is studied.The cyclohexene catalytic oxidation performance is evaluated by gas chromatography-mass spectrometry(GC-MS)and gas chromatography(GC).It shows that the main product of cyclohexene oxidation by HA@Ag with OZ as oxidant in the absence of solvent is 2-cyclohexen-l-of.In addition,its catalysis performance is related to the molar ratio of AgNO3 to n-butylamine during the synthesis.HA/Ag-1:0.5(HA@Ag prepared with a molar ratio of AgN03 and n-butylamine at 1:0.5)exhibits the highest catalytic activity(61.20%conversion and 66.02%selectivity to 2-cyclohexen-l-ol).The optimum reaction conditions are as follows:reaction temperature(65 0C),reaction time(24 h),catalyst dosage(5 mg),purged O2 time(20 min).In addition,the catalyst(HA/Ag-1:0.5)recycling performance shows that the cyclohexene conversion decreased slightly after four cycles,indicating its good cycling stability.