Synthesis And Biomass Conversion Performance Of Polvaniline Based Nanocomposites

The depletion of fossil fuels has aroused public attention on the synthesis of high value-added chemicals by biomass conversion.Green and energy-efficient catalytic biomass conversion has become the focus of attention.Aiming at the drawbacks often involved in the catalytic hydrolysis of lignocellulose and catalytic oxidation of 5-hydroxymethylfurfural(HMF),such as high reaction temperature and pressure,toxic/expensive organic solvent and soluble alkali,a series of polyaniline based nanocomposites were prepared in combination of the unique doping/dedoping,solid alkali properties of polyaniline(PANI)and the characteristics of Buchwald-Hartwig(B-H)coupling reaction and were used as the catalysts for the corn cob lignocellulose hydrolysis to sugar and HMF oxidation to HMFCA in this dissertation.The main conclusions are as follows:1.A series of anilines(tris(4-aminophenyl)amine,1,4-phenylenediamine and 4,4’-diaminodiphenylamine)with different structures and N contents were employed to synthesize polyaniline(b PANI)by B-H coupling reaction with tris(4-bromophenyl)amine,respectively.The N atom content in polyaniline could be adjusted by the variety of aniline monomer.And the doping degree of polyaniline could be tuned by the variety/concentration of dopant acids in the doping process.FT-IR and XPS results showed that the proton content of b PANI doped by4 M HCl was in the order of b PANI2-4 M HCl>b PANI3-4 M HCl>b PANI1-4 M HCl.b PANI2was doped by various concentrations of HCl and it exhibited the doped b PANI2 showed the highest doping degree when the concentration of HCl was 4 M.2.The saccharification performance of corn cob lignocellulose hydrolysis was studied with doped b PANI as catalyst.It showed that the saccharification performance of corn cob lignocellulose hydrolysis mainly depended on the variety of anilines monomer and the variety/concentration of dopant acids in the synthesis of doped b PANI.The optimum aniline monomer,dopant acid and concentration are phenylenediamine,HCl and 4 M.Among them,b PANI2 doped by 4 M HCl(b PANI2-4 M HCl)under the optimal reaction conditions(20 mg b PANI2-4 M HCl,40 mg corn cob powder,1 m L H2O,90~oC,16 h)showed the highest corn cob lignocellulosic hydrolysis performance(61.75%corn cob lignocellulose conversion,50.15%total reducing sugar(TRS)yield).The results of recyclability experiments showed that the corn cob lignocellulose conversion and TRS yield decreased to 95.13%and 93.58%of the initial figures after 4 cycles,respectively,which demonstrated that b PANI2-4 M HCl enjoys a relatively good recyclability.According to the positive correlation between hydrolysis performance and proton content,the possible mechanism of the corn cob lignocellulose hydrolysis by B-H coupling synthesized polyaniline was proposed:the proton on the doped polyaniline in b PANI contributed to the major catalytic role,which could effectively attack theβ-1,4-glycosidic bond in cellulose and hemicellulose to produce O~+ions and reducing sugars;O~+ions subsequently reacted with H2O to form reducing sugars and release H~+.3.Halloysite nanotubes/PANI nanocomposites(HA/PANI)were prepared by in-situ polymerization of ANI on HA.TEM results showed that polyaniline has been successfully supported on the outer surface of halloysite nanotubes.Meanwhile,doping degrees and redox states(Q/B)of PANI on HA/PANI were adjusted by the variety of dopant acids.FT-IR and XPS results showed that the doping degree of HA/PANI prepared under 1 M acidity followed the order:HA/PANI-HCl(34.3%)>HA/PANI-H2SO4(27.5%)>HA/PANI-HNO3(25.4%)>HA/PANI-H3PO4(23.6%),whereas Q/B followed the reverse order:HA/PANI-HCl(1.00)<HA/PANI-H2SO4(1.16)<HA/PANI-HNO3(1.20)<HA/PANI-H3PO4(1.24).4.The HMF catalytic oxidation performance of the above prepared HA/PANI nanocomposites was studied.It showed that HA/PANI nanocomposite prepared with HCl as dopant acid demonstrated the highest catalytic activity(both HMF conversion and HMFCA selectivity were 100%)under the optimum reaction conditions(10 mg HA/PANI-HCl,0.50mmol HMF,2 m L H2O,1 bar O2,90~oC,26 h).Meanwhile,the recyclability experiments showed that the initial value(100%)of HMF conversion and HMFCA selectivity were still maintained after 4 cycles.According to the dedoping experiment and the effect of equal protic acid on HMF catalytic oxidation performance,the possible mechanism of catalytic oxidation of HMF to HMFCA by HA/PANI-HCl was also proposed:Firstly,O2 reacted with electrons and H2O to generate OH~-ions.The electrons were afforded by the lone pairs of electrons in nitrogen of supported PANI.Then,the OH~-ions added nucleophilically to the-CHO group of HMF to result in the formation of geminal diols.Finally,the OH~-ions would abstract hydrogen from geminal diols to form HMFCA and released electron.