Synthesis And Modification Of Anatase TiO₂ Mesocrystals And Their Applications In Visible Light Driven Photocatalysis

Mesocrystals are of great interest for a wide range of applications owing to their unique structural features and properties.The realization of well�defined metal oxide mesocrystals through a facile and green synthetic approach still remains a great challenge.Here,a novel synthesis strategy is reported for the production of spindle�shaped anatase TiO₂ mesocrystals with a single�crystal�like structure,which was simply achieved through the one�step hydrolysis reaction of TiCl3 in the green and environment friendly media polyethylene glycol?PEG�400?without any additives.Such anatase mesocrystals were constructed from small nanocrystal subunits??1.5�4.5 nm in diameter?and formed through oriented aggregation of the nanocrystals pre�formed in the reaction system.Owing to their novel structural characteristics,the as�synthesized anatase mesocrystals could be easily fused in situ into porous single crystals by annealing in air.More significantly,after being annealed in vacuum,Ti³⁺ sites could be easily induced in the anatase crystal lattice,resulting in the formation of Ti³⁺ self�doped anatase mesocrystals.The main research contents and results are as follows:1.The spindle�shaped anatase TiO₂ mesocrystals with a single crystal-like structure were simply achieved through a one-step hydrolysis reaction of TiCl3 in polyethylene glycol?PEG�400?,a green and environment friendly media.We had studied their growth process and proposed the mechanism for the formation of anatase TiO₂ mesocrystals.The modifing by Ti³⁺ could greatly enhance visible light photocatalysis of TiO₂ mesocrystal owing to its narrower bandgap.We also systematically studied its morphology,mesocrystal structure,light absorption activity,doping and electrochemical performance.The thus�transformed mesocrystals exhibited enhanced visible light activity towards the photocatalytic oxidation of nitric oxide?NO?to NO3-?55.0%?and photocatalytic reduction of Cr???to Cr????99.2%?,which could be largely attributed to their intrinsic Ti³⁺ self�doped nature,as well as high crystallinity and high porosity of the mesocrystalline architecture.2.The synthesis of heterojunction nanocomposites of g�C₃N₄/TiO₂ was simplyachieved by in�situ growth anatase TiO₂ mesocrystals on g�C₃N₄ in a solvothermal reaction system,after being annealed in Ar atmosphere,Ti³⁺sites could be easily induced into the anatase crystal lattice.It was worth noting that the adding of g�C₃N₄ didn't change the morphology,mesocrystal structure of spindle-shaped anatase TiO₂ mesocrystals,confirming the robust of TiO₂ mesocrystals synthesis system.The morphology,mesocrystal structure,light absorption activity,doping of the nanocomposite were systematically studied.We also had studied the photocatalytic property of catalysts toward oxydation of Methyl orange?MO?and reduction of Cr???,and found out the active species that dominate the photocatalytic activities by trapping experiments and proposed the photocatalytic mechanism.