The Synthesis And Photocatalytic CO₂ Reduction Of Ultrathin Bismuth Oxybromide Based Materials

With the accelerate progress of the industrialization,the excessive consumption of fossil energy leads to energy shortage for the world.At the same time,the emission of waste gas has caused serious greenhouse effect.Therefore,it is urgent to optimize the energy structure and develop the clean energy.Photocatalytic technology can effectively transform CO₂ to carbon-based chemicals by renewable sunlight,which is an effective way to reduce atmospheric CO₂ content and alleviate energy crisis.So photocatalytic technology has important research value.The core of photocatalytic CO₂ reduction lies in the design of effient photocatalyst.However,semiconductor photocatalysts such as halogen bismuth oxide bismuth（Bi OX,X=Cl,Br,I）,metal oxides,nitrides and so on,all have good catalytic activities and stabilities.However,there are still reveals some problems in the catalysts,such as:high carriers recombination rates,unsatisfactory adsorption-activation of CO₂ molecules and poor light absorption performance,which cannot meet the requirements of practical application.In this paper,series targeted optimizations in the composition and structure of bismuth oxybromide materials have been carried out to significantly improve its photocatalytic CO₂ reduction performance.Specific research contents are as follows:（1）The uniform Bi OBr atomic layers were induced by solvothermal method with polyvinylpyrrolidone（PVP）structure guide agent.Then,a series of oxygen vacancies structures with different concentrations were further constructed on the surface of catalyst by UV irradiation.Electron paramagnetic resonance（EPR）,X-ray photoelectron spectroscopy（XPS）and transmission electron microscopy（TEM）show that the thickness of OV-Bi OBr atomic layers（OV-Bi OBr-2）is 2-3 layers.The above results prove that the CO yield of OV-Bi OBr-2(10.15μmol g^-1)is 1.99 times than that of Bi OBr atomic layers(5.09μmol g^-1)under visible light irradiation（λ>400nm）.According to transient photocurrent response test,UV-vis diffuse reflectance spectra（DRS）and CO₂ adsorption curve,the introduction of OVs on the surface of catalyst can enhance the visible light absorption performance,promote the efficient migration and separation of charge carriers and effectively improve the CO₂adsorption performance.Therefore,the prepared materials with rich OVs show significantly enhanced performance of photocatalytic CO₂ reduction.The possible photocatalytic mechanism of CO₂ reduction has been investigated through in situ Fourier infrared spectroscopy（In situ FT-IR）.（2）The ultrathin Bi OBr was prepared using CTAB as precursor.Ultrathin Bi OBr was prepared by solvothermal and calcination two-step method,and the Au/Bi OBr nanocomposite was prepared by visible light（λ>400 nm）deposition technology.The results of TEM and XPS show that Au/Bi OBr material has been prepared successfully.The CO yield of Au/Bi OBr(135.3μmol g^-1)was 1.52 times than that of ultrathin Bi OBr(89.0μmol g^-1)under the irradiation of 300 W Xenon lamp.The CO yield of Au/Bi OBr(16.43μmol g^-1)was 2.54 times as much as ultrathin Bi OBr(6.46μmol g^-1)under visible light irradiation（λ>400 nm）.Transient photocurrent response tests and DRS results show that the unique plasma resonance effect of Au can effectively enhance the visible light absorption performance.At this point,Au acts as electron trap and hot electron donor to promote the efficient transport and separation of carriers.Thus,the photocatalytic CO₂ reduction performance of the catalyst was significantly enhanced.In the end,the possible mechanism of photocatalytic CO₂ reduction is revealed by in situ FT-IR spectroscopy.（3）In order to verify universality that the special plasma resonance effect of precious metals to enhance the photoelectric properties of Bi OBr materials,the Ag/Bi OBr composites with different Ag contents were prepared under UV irradiation.XPS results show that the prepared Ag/Bi OBr materials are congsisted of Bi,O,Br and Ag,in which Ag exists in the form of zero valence.The results of TEM show that the Ag particles on the Ag/Bi OBr surface form a tight interface structure with the ultrathin Bi OBr nanosheets.The CO yield(133.75μmol g^-1)of Ag/Bi OBr with the best activities（Ag/Bi OBr-2）is 1.51 times as much as UV-treated Bi OBr(88.83μmol g^-1)under 300 W xenon lamp irradiation.The CO yield of Ag/Bi OBr-2(6.83μmol g^-1)under visible light irradiation is 2.81 times than that of UV-treated Bi OBr(2.43μmol g^-1).Transient photocurrent response tests and DRS results show that the unique plasma resonance effect of Ag nanoparticles can effectively improve the response ability to visible light of the materials,and achieve rapid electron-hole pair separation.Therefore,the prepared Ag/Bi OBr-X（X=1,2,3）materials have significantly enhanced photocatalytic CO₂reduction performance.The possible photocatalytic mechanism of CO₂ reduction has been investigated through in situ FT-IR spectroscopy.