Synthesis And Photocatalytic Properties Of Calcium Titanate Matrix Composites

The use of artificial photosynthesis to split water into hydrogen and convert carbon dioxide into clean fuels and chemicals is of great significance for alleviating environmental problems caused by the greenhouse effect and reducing dependence on fossil energy.As a representative of titanium-based perovskite oxides,calcium titanate（CaTiO₃）has stable properties,strong chemical corrosion resistance,suitable conduction band and valence band positions,and the alkaline earth metal calcium is relatively active in the adsorption of CO₂,so it is expected to become a high-efficiency photocatalytic materials for the preparation of hydrocarbon fuels.At the same time,although the research of single perovskite materials for photocatalytic water splitting for hydrogen production and CO₂ reduction has made some progress in recent years,how to improve the rate of charge transfer on the surface of catalyst and the consumption of photogenerated carriers is still an urgent problem to be solved in the process of photochemical reduction.Considering that the excellent electrical conductivity of metals is conducive to electron transport,and different band gap semiconductors can control the separation efficiency of photogenerated carriers,the construction of composite materials is expected to break through the bottleneck of single material performance.Based on the above background,in this thesis,the synthesized calcium titanate was used as the carrier material to compound with non-noble metals Cu,Cu₂O and SnS₂/SnS,respectively.And the composition,structure and photohydrolysis of water for hydrogen production and catalytic reduction of CO₂ were investigated.The main content is as follows:（1）The CaTiO₃/Cu composites were synthesized by ethylene glycol-mediated solvothermal method.The composition,structure and optical properties of the composites were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）,and ultraviolet-visible diffuse reflectance spectroscopy（DRS）.The results show that copper nanoparticles are deposited on the surface of prismatic calcium titanate.The photocatalytic performance of the composites was evaluated by the activity of photo-splitting water for hydrogen production.It is shown that the CaTiO₃/Cu-0.05 sample exhibits the highest rate of 251μmol h^-1g^-1 and it can still maintain a good hydrogen production effect after five cycling.Through photoluminescence spectroscopy（PL）,photocurrent response（PC）and electrochemical impedance（EIS）experiments,it was demonstrated that the introduction of metallic copper can construct a Schottky heterojunction with calcium titanate,which accelerates the separation rate of photogenerated charges and migration efficiency,and then promote calcium titanate splitting water to produce hydrogen.（2）The CaTiO₃/Cu₂O composite was prepared by hydrazine hydrate reduction at room temperature,and their composition,structure and optical properties were characterized by XRD,XPS,SEM and DRS.It was found that the Cu₂O particles had good contact with the prismatic calcium titanate.The results showed that the main product of photocatalytic reduction of CO₂is CO.Among them,the composite CaTiO₃/Cu₂O-0.72 sample has the highest CO generation efficiency of 2.01μmol h^-1g^-1.Based on the,photoluminescence（PL）,photocurrent response（PC）and electrochemical impedance（EIS）test results,the CaTiO₃/Cu₂O composite material has higher photogenerated charge separation and migration efficiency.In addition,combined with XPS analysis and coumarin fluorescent probe experiments,the pathway of charge separation was explored,indicating that CaTiO₃/Cu₂O composites promoted photogenerated charge separation by forming Z-scheme heterojunctions.（3）The CaTiO₃/SnS₂/SnS composites were synthesized by hydrothermal method,and their composition and structure were characterized by XRD,SEM,XPS and DRS.It was found that two-dimensional SnS₂/SnS was grown on the surface of CaTiO₃.The CO₂ photoreduction results show that the products of photoreduction of CO₂ by the composite material are CH₄ and CO.Among those photocatalysts,CaTiO₃/SnS₂/SnS-0.4 had the best results,the production of CH₄ is 4.92μmol h^-1g^-1 and that of CO is 1.67μmol h^-1g^-1.Furthermore,photoluminescence（PL）,photocurrent response（PC）and electrochemical impedance（EIS）test results show that the CaTiO₃/SnS₂/SnS composite has higher charge separation efficiency than single CaTiO₃,which is the main reason for its enhanced photocatalytic CO₂ reduction efficiency.