Research On The Designing Preparation And Photoreduction CO₂ Performance Of Gallium-based Composite Photocatalytic Materials

Photocatalytic reduction of CO2 to carbon-based fuel as a non-polluting and sustainable new energy pathway is of great significance for improving the greenhouse effect and buffering energy shortages.The development of high performance and high stability photocatalyst has always been the core of CO2 photocatalytic conversion technology.However,most of the existing common single-component and structural catalytic materials have problems such as low light utilization efficiency,low quantum efficiency,and short catalytic life.Therefore,constructing multi-component composite materials by utilizing the functional synergy between the constituent elements and the energy band coupling is the main development direction for the future development of high-efficiency CO2 photocatalytic materials.In this thesis,we select several gallium-based composites as research objects,the electronic structures were regulated by constructing heterostructures and forming solid solutions etc.At the same time,their photoreduction CO2 catalytic properties and possible activity enhancement mechanisms were systematically studied.The main results are as follows:1.CO1-xZnxGa2(1-x)Fe2xO4(0?x?0.6)solid solution photocatalysts were prepared by molten salt method using sodium chloride and potassium chloride as molten salt medium.The morphology,composition and structure of CO1-xZnxGa2(1-x)Fe2xO4(0? x?0.6)solid solution samples were studied by SEM,TEM,XPS,DRS and other characterization methods.It is proved that the cubic phase ZnFe2O4 has been successfully introduced into the crystal structure of CoGa2O4.The main products of solid solution photocatalysts are CO and CH4 under simulated sunlight irradiation.Photocatalytic CO2 reduction experiments show that when x=0.35,the photocata lytic efficiency of the catalyst is almost twice as high as that of pure CoGa2O4 under the same conditions.Combined with catalyst characterization and first-principles calculations,it is found that by forming solid solution phase,not only the band gap is effectively reduced,but also the dispersion of the CoGa2O4 band is enhanced,and the effective mass of the carrier of the solid solution is effectively reduced,thereby improving the activity of photocatalytic CO2 reduction.2.Nano-heterojunction semiconductor materials with one-dimensional CoGa2O4/p-Ga2O3 core-shell structure were prepared by two-step impregnation-annealing method with GaOOH nanorods as precursor.The test results show that the main product of photocatalytic reduction of CO2 is CO under simulated solar irradiation.The photocatalytic activity of the heterojunction is much better than that of the pure phase CoGa2O4 and ?-Ga2O3.Through the exploration of photocatalytic mechanism,it is found that the introduction of CoGa2O4 not only effectively improves the light absorption capacity of ?-Ga2O3,but also increases the heterogeneous interface area,improves the separation efficiency of photogenerated carriers,and inhibits charge recombination,thereby increasing photocatalytic activity.3.A series of ?-In2O3/ct-Ga2O3 composites were prepared using ion exchange-annealing two-step method by changing the content of gallium with In(OH)3 nanosheets as precursors.The composition,morphology and structure of ?-In2O3/a-Ga2O3 were studied by SEM,TEM,XPS and ICP etc.The photocatalytic CO2 activity of different samples of the system were studied under sunlight irradiation.The photocatalytic activity of the composite was found to be much higher than that of pure phase?-In2O3 and ?-Ga2O3.The factors affecting photocatalytic activity were discussed by DRS,PL,EIS etc.and the photocatalytic mechanism of the system was further explored.In the ?-In2O3/?-Ga2O3 composites,the photogenerated electrons in the conduction band of ?-Ga2O3 migrated to the conduction band of ?-In2O3 after irradiation,which increased the probability of photogenerated electrons participating in the CO2 reduction reaction.Meanwhile the holes in the valence band of ?-Ga2O3 inhibit the recombination of photogenerated electron-hole pairs due to the hysteresis reaction.4.Using sodium titanate nanobelts as precursorss combined with ion exchange-calcination two-step method,induced Zn2Ti3O8 in situ transformation to ZnTiO3 and Zn2TiO4 phase,and successfully obtained Zn2Ti3Os/ZnTiO3 and Zn2TiO4/R-TiO2 with heterostructures,at the same time.The catalytic performance of the catalytic conversion of CO2 and H2O to carbon-based fuels was investigated.The results show that the photocatalytic properties of Zn2Ti3O8/ZnTiO3 and Zn2TiO4/R-TiO2 composite photocatalysts were better than those of single-phase titanium catalysts under 254 nm(16 W)UV irradiation.The photocatalytic activity of Zn2Ti3O8/ZnTiO3 remained unchanged during the 12 h cycle.Combined with catalyst composition,structural characterization and theoretical calculations,it is found that the existence of "junction" can not only effectively improve the spectral response range of photocatalyst,but also be a key factor to improve the separation efficiency of electron-hole pair.