Studies On The Photocatalytic Reduction Of CO₂ Over TiO₂ Modified With Hap

The photocatalytic reduction of the greenhouse gas CO₂ to high value-added hydrocarbon fuel isone of the most promising methods to solve the energy crisis and environmental pollution.Among the many semiconductors,TiO₂ has become the focus because of its low cost,easy to obtain,good stability,non-toxicity and potential high activity.However,the defects of TiO₂ itself,like the low separation efficiency of photogenerated electron hole pair,the low reaction kinetics,and the selectivity for the product,make the reduction performance of CO₂ still have some limitations.The surface adsorption chemistry of CO₂ on the oxides show that the surface atom of the oxides can interact with CO₂ to form adsorbed CO₂?ad?.The structure of the adsorbed CO₂?ad?can reduce the barrier of CO₂ reduction.Therefore,regulating the adsorption of CO₂ on semiconductor surface will provide an effective strategy for improving the photocatalytic activity of CO₂ reduction.In this paper,the surface modification of hydroxyapatite was used to improve the photocatalytic activity of TiO₂ for CO₂ reduction.The main contents are as following:1.The photocatalytic reduction of CO₂ with multifunctional hydroxyapatite modified TiO₂:The HAP/TiO₂ composites were successfully prepared by hydrothermal method using Ca?OH?₂??NH₄?₂HPO₄?TiO₂ as raw materials,and their structures and performances were tested by a series of characterization methods.Scanning electron microscopy?SEM??X-ray powder diffraction?XRD??Transmission electron microscopy?TEM?showed that HAP was uniformly dispersed on the surface of TiO₂.The photocatalytic performance test showed that in the presence of H₂O,the activity of HAP/TiO₂ was significantly enhanced compared with that of TiO₂.The yield of CH₄ was 40 times that of TiO₂,and the selectivity of CH₄ is significantly improved.Photoelectrochemical measurements showed that HAP/TiO₂ exhibited higher charge separation and faster charge transfer efficiency;in situ infrared spectroscopy?IR?method was used to determine the adsorption species and intermediate products of the CO₂ reduction reaction,while the confocal laser scanning microscope was used.?CLSM?characterizes reactive oxygen species?ROS?produced during H₂O oxidation.The study shows that:HAP modification of TiO₂ improves the photocatalytic activity of TiO₂.2.Study on Photocatalytic Activity of Sr-doped hydroxyapatite-modified TiO₂:Sr-HAP/TiO₂composite catalyst with Sr/Ca=1:3,1:5,1:10,1:15,1:20 prepared by in-situ growth and in-situ hydrothermal method.XRD?EDS?SEM?UV-Vis?IR?XPS were used to characterize the structure and morphology of Sr-HAP/TiO₂.UV-Vis spectrophotometer was used to analyze the blue degradation performance of methylene blue with different doping content of Sr-HAP/TiO₂.The results show that when Sr:Ca=1:15,it is compared with the single TiO₂ and HAP/TiO₂-2.photocatalytic reduction of CO₂ by cerium-doped hydroxyapatite-modified TiO₂,the performance also increased significantly,the yield of CH₄was 67 times that of TiO₂,which was 1.68 times higher than that of HAP/TiO₂,and showed high selectivity to CH₄,It is further indicated that Sr-doped HAP modified TiO₂ can improve the photocatalytic reduction of CO₂ by HAP/TiO₂.3.Photocatalytic performance of Ba doped HAP modified TiO₂:Ba-HAP/TiO₂ composite catalysts were prepared by hydrothermal method and the effects of Ca content and Ba content on photocatalytic activity of CO₂ reduction were investigated.The physicochemical properties of the composite catalysts were characterized by XRD?SEM?EDS?UV-Vis?IR?XPS.And through the photocatalytic reduction of CO₂ performance tests showed that when the Ba doping amount was 7%,the composite catalyst exhibited450 times higher activity than TiO₂,and showed higher CH₄ selectivity.The results of the dissertation show that the modification of TiO₂ on the basis of HAP can improve the photocatalytic activity of TiO₂ in reduction of CO₂,and provide important theoretical and experimental references for the construction of highly efficient and stable surface materials modified semiconductor systems.