Study On Synthesis And Photocatalytic Mechanism Of Nano-TiO₂ With Coordination Carboxyl Group And Oxygen Vacancy

Nano-titanium dioxide?Nano-TiO₂?has been widely concerned in the field of environmental photocatalysis due to its unique physical and chemical properties,such as high specific surface area,strong photogenerated hole oxidation capacity,large abundance,non-toxic and good stability and so on.However,there are still some problems that limit the further development and application of TiO₂ photocatalytic technology.For example,nano-TiO₂ has a large band gap?3.2 e V?,making it difficult to utilize visible light.Nano-TiO₂ has high photocarrier recombination rate and low quantum efficiency.In addition,when nano-TiO₂ enters the suspended water environment for photocatalytic reaction,we also lack sufficient understanding of the changes in surface chemical state and the resulting changes in photocatalytic performance.In order to deal with the above problems,this study started from the preparation of nano-TiO₂ and carried out the following two research works:?1?A series of nano-TiO₂ photocatalysts co-existed with surface acetate ligands?SALs?and surface oxygen vacancy defects?SOVDs?were synthesized by sol-hydrothermal method at different hydrothermal temperatures.The SOVDs of nano-TiO₂ were covered by SALs,which coordinated with nano-TiO₂ in two modes:bidentate chelating and bidentate bridging modes.The synergistic effect of SOVDs and SALs reduces the actual band gap of TiO₂ and the main VB edge moves forward.At the same time,appropriate SOVDs can effectively promote the separation of photogenic carriers.The synergistic effect of the above factors significantly enhanced the photocatalytic degradation ability of phenol by nano-TiO₂.It was found that nano-TiO₂prepared at 150?hydrothermal temperature had the highest visible light catalytic activity for phenol,which was mainly degraded through the direct photogenerated hole oxidation process.?2?Nano-TiO₂ prepared based on this experiment showed good visible light catalytic activity in the cycle degradation process,and the effect of the actual photocatalytic suspension reaction system on the surface chemical state of nano-TiO₂ and its photocatalytic performance was preliminarily explored.It was found that the dissociation adsorption of water molecules and the adsorption of polytetrafluoroethylene impurities from the stirred rotor were the main factors to change the surface chemical state of nano-TiO₂ photocatalyst?especially SALs?.The dissociation adsorption of water molecules reduced the number of carboxyl ligands on the catalyst surface and changed the coordination configuration of carboxyl ligands on the catalyst surface,thus affecting the cyclic degradation efficiency of the catalyst for phenol.In addition,during the long-term stirring,the rotor surface material polytetrafluoroethylene was detached and adsorbed on the catalyst surface,which increased the carrier compound rate and further reduced the photocatalytic cycling degradation efficiency.