Preparation Of Porous Alumina-based Photocatalyst And Its Performance For CO₂ Reduction

Nowadays,with the rapid depletion of fossil fuels（coal,natural gas,and oil）,and the problems of greenhouse gas emissions caused by its utilization,finding a long-term sustainable supply of renewable energy and transforming the main greenhouse gas CO₂has become a hot topic.The use of solar photocatalytic reduction of CO₂ to convert CO₂into fuel or chemical raw materials is an excellent way to solve the above problems.Al₂O₃is widely used as a support or co-catalyst in the field of photocatalysis due to its good adsorption performance,thermal stability,low cost and easy availability.Our research team in the early stage found that amorphous Al₂O₃ has a certain photocatalytic activity,but there are still some disadvantages.In order to improve the performance of photocatalytic reduction of CO₂ by amorphous Al₂O₃ photocatalyst,it was modified by changing the calcination temperature,modifying it with basic elements,and constructing a hierarchical structure of hollow microspheres.The main contents are as follows:1)A boehmite（AlO（OH））precursor with a hierarchical spindle-like structure was prepared by a simple hydrothermal method,and then calcined at different temperatures to obtain a series of Al₂O₃ photocatalysts with different crystallinity.SEM and TEM results show that the catalyst still has a hierarchical spindle-like structure and contains an irregular porous structure that results in a large specific surface area.The activity of the catalyst was examined by experiments of reducing CO₂ under simulated sunlight.The results show that the amorphous Al₂O₃ photocatalyst exhibits the best photocatalytic activity when the calcination temperature is 400℃.The PL and ESR tests show that the amorphous Al₂O₃ photocatalyst has abundant defect sites on the surface when calcined at400℃.The existence of defect sites improves the separation efficiency of photogenerated electron-hole pairs,thereby improving the photocatalytic activity of the catalyst.2)Modification of hierarchical spindle-like amorphous Al₂O₃ photocatalysts using alkaline metal Ca.The ESR results show that Ca is not doped into Al₂O₃,it may exist on the surface of Al₂O₃ in the form of CaO.The results of photocatalytic reduction of CO₂show that when the molar amount of Ca element accounts for 4%of Al element,the catalyst has the best photocatalytic activity.The presence of CaO improves the basicity of the amorphous Al₂O₃ catalyst,thereby increasing its ability to adsorb CO₂ and further improving its photocatalytic activity.3)Flower-like hollow microspheres and urchin-like hollow microspheres amorphous Al₂O₃ photocatalysts with hierarchical structures were synthesized by hydrothermal method using CTAB and TX-100 as templates,respectively.The prepared catalyst has a macroporous hollow structure and an irregular porous structure.The photocatalytic reduction of CO₂ activity of Al₂O₃ photocatalysts with hollow structures is greater than that of hierarchical spindle-like Al₂O₃ photocatalysts,and urchin-like hollow microsphere Al₂O₃ photocatalysts have the highest photocatalytic activity.The hollow microsphere structure causes the catalyst to have a higher specific surface area and more surface defects,which improves the catalyst’s ability to adsorb CO₂ and the separation efficiency of photo-generated carriers,thereby improving the photocatalytic activity of the catalyst.