Enhanced Photocatalytic CO₂ Reduction Performance Of Bi₂WO₆ With Metallic Bi Induced By Oxygen Vacancy

With the rapid development of the social economy,the constant consumption of fossil energy has caused the increasing concentration of CO2 in the atmosphere,which leads to a series of global problems.How to effectively reduce the atmospheric CO2 content has become the focus of researchers.Photocatalytic CO2 reduction technology uses solar energy to reduce CO2 into valuable hydrocarbon fuels,which can truly achieve a benign carbon cycle.Owing to the mild and clean reaction condition,this technology has a bright prospect in solving energy and environmental problems.As the core of solar photocatalytic reduction of CO2,the design and development of low-cost,efficient and stable catalytic materials has become the focus of research.Bi2WO6（BWO）has become one of the preferred materials for photocatalytic reduction of CO2 owing to its unique layered structure,favourable visible light photocatalytic activity,high thermal stability and photostability,environmental friendliness and so on.However,pristine Bi2WO6 has a low efficiency of photocatalytic reduction of CO2 on account of its wide band gap,high recombination rate of photogenerated electrons and holes,and few exposed active sites reduce.In thesis,the strategy of oxygen vacancy construction and in-situ Bi unit loading was adopted to improve the catalytic properties of Bi,and then improve the catalytic reduction efficiency.In thesis,the strategies of constructing oxygen vacancy and loading in-situ Bi nano-particles were adopted to improve the catalytic performance of BWO.The specific research contents are as follows:（1）The initial BWO samples were prepared by using a simple hydrothermal method,and the samples containg oxygen vacancies were prepared by further using annealing process.The introduction of oxygen vacancy promoted the photocatalytic reaction comprehensively,and the CO formation rate of the sample with defects was twice as much as that without defects.The internal link between oxygen vacancy and CO2 reduction performance improvement was explored by combining experimental characterization and density functional theory（DFT）analysis.Specifically,the oxygen vacancy is prefered to the[Bi2O2]²⁺layers on BWO（010）surface.The defect introduction would produces a new impurity level,and thus broadens the light absorption range.At the same time,the adsorption configurations of the species would be affected owing to chemical state variations after introducing vacancy,and thus the rate-limiting barrier would be lower.（2）In order to further improve the photocatalytic performance and ensure the activity of the oxygen vacancy,the catalyst samples containing Bi nanoparticle and oxygen vacancy were prepared by using the mild thermite reduction method at different temperatures to annealing prefect BWO.The successful preparation of the material was confirmed by using morphology and structure characterization.On the other hand,the unique surface plasmon resonance effect of Bi elemental,which improves the light absorption capacity of samples and the charge separation and transfer efficiency,was confirmed by combining a series of spectral analysis with DFT theory.Meanwhile,it was confirmed that Bi could be used as the surface active sites to activate adsorption molecules,further reduce the rate-limiting potential barrier,and improve the oxygen vacancy activity owing to prevent the oxygen-containing groups from being adsorbed at the oxygen defect site.In addition,the photocatalytic CO2 reduction performace of different samples under visible light irradiation was measured,and the optimal CO production rate reached 5.94μmol·g^-1·h^-1.