Surface Interface Regulation Of Bismuth-based Photocatalytic Materials And Their Photocatalytic Performance For β-O-4 Ketone Lignin Model

As a renewable biomass resource with the largest content of aromatic monomers in the world,lignin has a great potential to be converted into high value-added aromatic compounds.However,lignin is difficult to be depolymerized duo to its complex structures.Traditional depolymerization methods are harsh and complicated,which is not conductive to the practical application of lignin conversion.In recent years,semiconductor photocatalytic depolymerized of lignin has attracted extensive attention due to its mild,reaction condition and high selectivity.Bismuth-based semiconductors have been becoming a hot research topic due to their stable structure,low cost and good response to visible light.The smooth separation and migration of photogenerated carriers at the surface/-interface is an important prerequisite for constructing efficient photocatalysts,and the surface structure and properties of materials are key factors affecting the photogenerated charge transfer behavior.Reasonable and effective regulation of the surface structure for catalysts can greatly promote the separation and migration of photogenerated charges,which is conducive to further improving the performance of the photocatalysts.In order to further promote the application of photocatalysis technology in lignin depolymerization,this dissertation aims at easy recombination of photo-generated carriers in semiconductor photocatalysts.Through regulation and optimization of surface and interface microstructure,a model material system is constructed using bismuth-based materials,which greatly improves the photocatalytic performance of the semiconductors,and oxidation reaction system ofβ-O-4 ketone lignin model was constructed based on bismuth semiconductor modification.The main contents include:（1）A cocatalyst CuO supported BiVO₄ nanorod photocatalyst was developed via in-situ growth method and applied for depolymerization ofβ-O-4 lignin model compounds 2-phenoxy-1-acetophenone.It was found that the photogenerated holes generated by excitation of BiVO₄ can be quickly transferred to the surface of CuO and participate in the lignin oxidation reaction after being injected into the cocatalyst under the action of an interfacial electric field.In the presence of the CuO/BiVO₄,the conversion rate of the lignin model substance was 88.1%,and the selectivity of Cα-Cβbond cleavage was 86.5%under simulated sunlight irradiation for 10 h.The depolymerization products are mainly benzoic acid,phenyl formate,phenol,formic acid,and benzaldehyde.The accumulation of total products of aromatic compounds was 888.56μmol g^-1 h^-1.（2）The ultrathin sheet Bi₃O₄Cl was modified by combining S doping and oxygen vacancies to prepare S doped Bi₃O₄Cl composite photocatalyst.The catalytic depolymerization performance of a lignin model compound,2-（2-methoxyphenyloxy）-1-acetophenone,was investigated.Experimental results and theoretical calculations show that doping with S can generate impurity levels and defects between the layers of Bi₃O₄Cl,that can promote the separation and migration of photogenerated carriers;On the other hand,the surface sites introduced by impurities can increase the adsorption of O₂ on the catalyst surface.These synergistic effects promote the formation rate of photoactive species and thus demonstrate better visible light catalytic activity.Under visible light irradiation for 10 hours and acetonitrile as the reaction solvent,the conversion rate of the lignin model substance can reach 99.4%,and the C-O bond selectivity was93.3%,respectively.The main products are 2-hydroxyacetophenone,guaiacol,acetophenone,benzoic acid,benzaldehyde,and 2-methoxyphenyl formate.（3）The formation of heterojunction via combining semiconductors is an effective way to improve the separation and migration of photogenerated charges.A highly active Ag I/Bi₂Sn₂O₇ Z type composite photocatalyst was prepared with a simple in-situ precipitation method.Due to the unique charge transfer path of Z-type heterojunction,Ag I/Bi₂Sn₂O₇ composite materials have more effective photogenerated carrier separation efficiency and stronger redox ability compared to Ag I or Bi₂Sn₂O₇.Ag I/Bi₂Sn₂O₇ demonstrateds better catalytic performance under simulated sunlight irradiation at room temperature.With 3-hydroxy-2-（2-methoxyphenyloxy）-1-（4-methoxyphenyl）propyl 1-ketone as the lignin model containingγ-OH substrate,the conversion rate of lignin model could reach 98.3%,and the selectivity of C-O bond cleavage was 99.99%,respectively.The accumulation of products reached1668.38μmol g^-1 h^-1,after the reaction was in acetonitrile under the atmosphere of O₂ for 10h.It was.（4）Based on the above results,CuO/BiVO₄,S-Bi₃O₄Cl and Ag I/Bi₂Sn₂O₇were applied to explore the depolymerization of real lignin of alkali wood.The results indicate that the modified bismuth-based material can depolymerize the real lignin under the simulated sunlight irradiation at room temperature.