Surface Construction Of Ultrathin Bismuth Vanadate Nanosheets And Performance Of Photocatalytic Imine Synthesis

In the face of current challenges such as climate change and energy crisis,carbon neutrality and emission peak have become the requirements and goals of development.Developing a low-carbon economy and clean energy is an actively explored approach in the field of science and technology.Photocatalytic technology using clean and green solar energy has gradually become a popular new technology,showing broad application prospects.Photocatalytic organic conversion is the conversion of organic compounds into target products through chemical reactions involving catalysts.The conversion process is mild and environmentally friendly,making it one of the key research directions in the field of photocatalysis.The key scientific issue of photocatalytic organic conversion is"precision",which means achieving precise selection of target products through specific reaction processes,thereby improving the selectivity of the overall reaction.The solution lies in clarifying the product selective conversion pathway,clarifying the catalytic conversion mechanism of organic molecules,revealing the structure-activity relationship between the structure and reaction performance of the catalyst,and focusing on exploring the functional role of catalytic sites.Based on the rich surface sites and adjustable energy band structure of ultra-thin two-dimensional（2D）bismuth vanadate nanosheets,a multifunctional catalyst with visible light absorption was constructed through surface design.Its catalytic performance in the selective oxidative coupling of benzylamine to benzyl alcohol and the synthesis of imines by benzylamine coupling reaction was investigated.The chemical states,surface electronic structures,and interfacial catalytic processes of the surface atoms of the catalyst were systematically investigated using a series of spectroscopic and electron microscopic characterizations such as XRD,XPS,DRS,and in situ FTIR.The specific adsorption and activation of substrate molecules on the surface of the catalyst were explored,revealing that the selective conversion path of substrate molecules is closely related to the surface state of the catalyst,and based on this,a synergistic catalytic mechanism for surface functional sites was proposed.The specific research content is as follows:（1）Ultrathin bismuth vanadate nanosheets（BVO-NS）were synthesized by one-step solvothermal method as multi-functional photocatalysts.Pd（0.5 wt%）nanoclusters were deposited by photolithography to construct Pd_0.5/BVO-NS composite catalysts with oxygen enriched vacancies.Under visible light and ambient pressure air conditions,N-benzylidene benzylamine was accurately synthesized by oxidative coupling of benzylamine with benzyl alcohol.The conversion of benzylamine was 95.7%,and the yield of imine was 98.9%.XPS and EPR results show that the introduction of Pd causes changes in the electron density on the surface of BVO-NS,resulting in the formation of partial oxygen vacancies.These vacancies induce the enrichment of O₂ molecules from the air onto the BVO-NS surface.In situ FTIR showed that the surface metal sites,as Lewis acid sites,selectively adsorb benzyl alcohol molecules through Bi··OH C-to form a double coordination bond at the interface,inducing polarization and activation of the C O bond.With the promotion of the Pd site,the surface adsorbed O2 molecules are converted and activated into active oxygen species.Based on this,we propose a possible synergistic mechanism between surface oxygen vacancies,low coordination metal sites,and surface Pd sites.（2）A Z-type CdS/BVO-NS heterojunction was successfully constructed using CdS nanoparticles loaded with ultra-thin bismuth vanadate nanosheets（BVO-NS）.The composite catalyst showed good catalytic performance in photocatalytic benzylamine coupling,achieving a benzylamine conversion of 96.5%and imine selectivity of>98%under room temperature and atmospheric pressure air conditions.The morphology and electronic structure of CdS/BVO-NS were characterized by SEM,TEM,XRD,DRS,and XPS to reveal the effect of heterojunction on the chemical state of metal sites on the surface of BVO-NS.In situ infrared spectroscopy and EPR further elucidate the chemisorption behavior of reactant molecules on the catalyst surface and intermediate active species.Explore the functional components and mechanism of the heterojunction catalyst,and propose a feasible catalytic reaction mechanism.This work provides an effective model for exploring the synergistic relationship between surface species and surface defect removal,and provides theoretical guidance for the construction of efficient multifunctional catalysts.