Preparation And Photocatalytic Properties Of TiO₂-based Catalysts Isolated From Cocatalysts

Converting solar energy into clean fuels can effectively solve energy and environmental crises.For example,the chemical storage of solar energy can be achieved by converting carbon dioxide(CO₂)into valuable fuels through the photocatalytic reduction process.Low-cost titanium dioxide(TiO₂)has a suitable energy band structure and high light corrosion resistance.It has proved very promising for the photoreduction of CO₂ using water as a source of electrons and protons.However,the narrow spectral response range(only the ultraviolet region)and the rapid recombination of light-induced electron-hole pairs in the original TiO₂ result in low solar energy utilization and limited photocatalytic efficiency.Therefore,from a practical point of view,it is of great significance to improve the visible light absorption and electron-hole separation efficiency of TiO₂.This thesis takes the hollow structure TiO₂ as the research object.It can be modified by supporting catalysts and forming heterojunctions with other semiconductor materials,which can improve visible light absorption,promote charge transfer and inhibit the recombination of charge carriers.The performance of photocatalytic reduction of carbon dioxide.The main research contents of this paper are as follows:(1)The design and preparation of H-TiO_2-x NT/NC-CoNi nanotubes and their performance test for photocatalytic reduction of CO₂.With carbon nanofibers(CNFs)as the substrate,TiO₂ nano-layers are coated on the surface of CNFs by a kinetic coating method to obtain CNFs@TiO₂ nanowires,and then CNFs@TiO₂ are calcined in a muffle furnace at high temperature to obtain TiO₂ nanotubes.The inside and outside of the tube are coated with a layer of MOF-CoNi to obtain TiO₂@MOF-CoNi nanotubes.Finally,TiO₂@MOF-CoNi nanotubes are heat-treated in nitrogen and H₂/Ar mixed gas streams to obtain H-TiO_2-x NT/NC-CoNi nanotubes.tube.H-TiO_2-x NT/NC-CoNi has high photocatalytic CO₂ reduction activity.The enhanced photocatalytic activity is attributed to the photogenerated electrons generated by H-TiO_2-x being captured by the CoNi alloy on the surface,realizing efficient spatial separation of electrons and holes and inhibiting the recombination of charges.This work provides an effective method for synthesizing a TiO₂-based photocatalyst with high-efficiency photocatalytic reduction of CO₂.(2)The design and preparation of MnO₂/TiO₂ NT/Au catalyst and its performance test for photocatalytic reduction of CO₂.Firstly,MnO₂ nanowires were synthesized by hydrothermal method,and TiO₂ nano-layers were coated on MnO₂ nanowires by kinetic coating method to obtain MnO₂@TiO₂ core-shell nanowires,which were deposited on the surface of the prepared MnO₂@TiO₂ core-shell nanowires by light deposition.The noble metal Au particles are loaded on it,and finally part of the MnO₂ is removed in the ethylenediamine solution while the amine group is inserted into the surface of the TiO₂.A spatially separated MnO₂/TiO₂ NT/Au photocatalyst with a double co-catalyst was obtained.The MnO₂/TiO₂ NT/Au hierarchical structure photocatalyst has a high CO₂conversion rate.The reduction co-catalyst Au and the oxidation co-catalyst capture the photogenerated electrons and holes generated by TiO₂ NT,respectively,to achieve efficient spatial separation of electrons and holes and inhibit the recombination of charges.It shows that the dual co-catalyst has a synergistic effect in separating photogenerated carriers.It also provides more catalytic active sites for photocatalytic reactions.This research provides a reasonable photocatalyst design scheme for improving the CO₂ conversion rate.(3)The design and preparation of CoO_x/Zn Fe₂O₄@H-TiO_2-x/Au-Cu hollow core/shell nanosphere catalyst and its photocatalytic performance test for CO₂ reduction.Using carbon spheres as a template,a combination of impregnation,solvothermal,calcination and kinetic coating methods were used to prepare surface oxygen-rich vacancies Zn Fe₂O₄@TiO₂ double-shell hollow heterostructure nanospheres(Zn Fe₂O₄@H-TiO_2-x),and combined with spatially separated CoO_x and Au-Cu bimetallic co-catalysts.The dual co-catalyst of Zn Fe₂O₄@TiO₂ heterojunction and spatial separation can significantly promote the separation of photo-induced carriers.Combining the unique hollow double-shell heterostructure characteristics and improved surface state properties,the hybrid nanospheres can effectively adsorb and activate CO₂molecules.These advantages make the gas-phase photocatalytic CO₂ reduction activity of the optimized catalyst significantly higher than the control CoO_x/Zn Fe₂O₄/Au-Cu and Zn Fe₂O₄@H-TiO_2-x double-shell hollow nanospheres.At the same time,the gold-copper bimetal effect improves the CO₂ conversion rate and CH₄ selectivity.This work provides a reasonable photocatalyst design and improves the CO₂ conversion rate and CH₄ selectivity.