In-situ Synthesis Of Ag/Bi₁₂SiO₂₀/BiOBr Thin Film And Its Photocatalytic CO₂ Reduction Performance

Excessive consumption of fossil fuels and large amounts of CO₂ emissions have led to an urgent energy and environmental crisis.With the innovation of chemistry as well as chemical industry and the progress of science and technology,CO₂,as a kind of rich"carbon source"resource utilization,is used as a resource to"turn waste into treasure",which can realize the development of a green and low-carbon circular economy,and promote"carbon neutrality"and"carbon peak"in our country,and become a forward-looking and strategic topic in the chemical industry.Since Nature first converted CO₂ into formic acid,formaldehyde and methanol through the GaP photoelectrode system in 1978,reducing and oxidizing CO₂ and H₂O into hydrocarbon fuel storage via green and clean solar energy not only achieves CO₂emission reduction,but also realizes renewable energy,which is quite favored by research scholars.However,the core of achieving high-efficiency photocatalytic reduction of CO₂ is the construction of an efficient photocatalyst system.BiOBr has become one of the research hotspots due to its unique layered structure,suitable band gap width and excellent photocatalytic performance.However,the single powder catalyst has problems such as high photo-generated electron-hole pair recombination rate,easy agglomeration,difficult recovery,and secondary pollution,which severely restrict its engineering process.In response to the above problems,a high-efficiency BiOBr-based thin film photocatalyst system was prepared in situ on the Bi substrate,and modified via constructing a heterojunction and noble metal deposition modification strategy,which can not only effectively promote the photo-generated charge separation as well as transfer efficiency and enhance the CO₂ reduction performance,but also solve the problem of powder catalyst immobilization.The specific research content is as follows:(1)Synthesis of Bi₁₂SiO₂₀/BiOBr composite thin film and its photocatalytic CO₂reduction performance.Using Bi plate and Ti sheet as anode and cathode,respectively,a novel Bi₁₂SiO₂₀/BiOBr composite thin film was successfully prepared from Bi plate via in-situ electrochemical ion exchange.The influence of electrolyte acidity and alkalinity,reactant concentration and reaction time on the composition is studied,and a reasonable formation mechanism is proposed based on the characterization results such as SEM.The Bi₁₂SiO₂₀/BiOBr composite thin film exhibits excellent photocatalytic activity and stability of CO₂ reduction to CO under the irradiation of Xe lamp(20.68?mol·m^-2·h^-1),which are 1.5and 2.4 times that of single BiOBr and Bi₁₂SiO₂₀ thin film,respectively.The high activity of the composite film can be attributed to two aspects.The one is that the special nanosheet honeycomb morphology causes multiple reflection of incident light to increase light absorption.The other is that the band gaps of Bi₁₂SiO₂₀ and BiOBr is well matched to form a p-n heterojunction,which effectively promotes the separation of photogenerated e^-and h⁺,and improves the photocatalytic efficiency.(2)Synthesis of Ag/Bi₁₂SiO₂₀/BiOBr composite thin film and its photocatalytic CO₂reduction performance.To further improve the photocatalytic performance,the Bi₁₂SiO₂₀/BiOBr composite thin film was modified with Ag nanoparticles(NPs)by the in-situ photo-deposition method,and the amount of Ag deposition was explored.As the amount of Ag deposition increases,the photocatalytic performance of the composite film first increases and then decreases,and the 1.5 wt.%-Ag/Bi₁₂SiO₂₀/BiOBr composite thin film exhibits the highest CO rate(33.47?mol·m^-2·h·^-1)and cycle stability,1.62 times of that before Ag modification.The characterization results of UV-vis-DRS,photocurrent,EIS,etc.illustrate that the SPR effect of Ag NPs makes the light absorption band edge red-shift and improve the absorption of visible light.Besides,according to the different energy band bending between noble metal and semiconductors(p and n-type),Ag NPs act as the intermediate bridge between Bi₁₂SiO₂₀(n)and BiOBr(p)to form a special Z-scheme charges transport path,additionally,the Schottky barrier function between Ag and semiconductors hinders the reverse migration of charges,realizing the efficient separation of photogenerated charges,improving the photocatalytic efficiency.In short,electrochemical ion exchange technology is an effective method to design and manufacture thin film catalysts with excellent photocatalytic performance,and the construction of heterostructures and precious metal deposition modification strategies can effectively improve the photocatalytic CO₂ reduction performance.Our research provides excellent insights and ideas for the precise design of in-situ immobilization technology and modification strategies for solar photocatalytic reduction of CO₂ photocatalyst systems.