Freeze-Drying Preparation Of 2D TiO₂ Nanocomposites For Photocatalytic Applications

In recent years,the development of semiconductor photocatalysts is in the ascendant.The basic research and technological development of two-dimensional materials have also made great progress.The two-dimensional semiconductor materials have shown unique properties in a wide range of applications.Photocatalytic degradation is also one of the ways to solve the current environmental problems.The two-dimensional titanium dioxide nanomaterial(TiO2)is recognized as the most promising environmental protection photocatalyst material with potential for development and application.In order to improve the visible-light response and quantum utilization of nano-TiO2 materials,researchers have been looking for ways of improving the visible light photocatalytic efficiency of nano-TiO2 materials.To solve the current problem of the photocatalytical efficiency of two-dimensional TiO2 nanomaterials,this article not only broadens the spectral response range of TiO2 but also effectively reduces the recombination probability of photogenerated carriers by means of semiconductor compounding and metal oxide doping,which enhances the visible-light catalytic activity of TiO2 and applies it into photocatalytic degradation of organic pollutants.The main research results are as follows:1.Preparation of 2D TiO2 nanosheets by freeze-drying method(FD)and formation mechanism of nanosheet structure:In this paper,water-soluble titanium complex(peroxotitanate)was used as a titanium source and prepared by freeze-drying assisted sol-gel method.It has a unique two-dimensional ultra-thin(2.0-3.Onm)and porous TiO2 nanosheet.The formation mechanism of this nanosheet structure is that the water-soluble titanium complexes are connected to each other due to the existence of a large number of hydroxyl groups(-OH)on the surface,and the particles of these compounds gradually pile up to form a nanosheet structure.The freeze-drying method is to form a hierarchical structure characterized by "fence" near the position where the original ice is located,and the ice is sublimated during the freeze-drying process to leave the system,and the original thin porous structure is preserved.2.Preparation of N-doped TiO2 composites co-composited with C-dots and g-C3N4(FD-C-dots/g-C3N4/N-TiO2):In this paper,melamine(MA)was used as the precursor of C-dots/g-C3N4,amino group and melamine were used as N source.The ultra-thin porous C-dots/g-C3N4/N-TiO2 composite nanosheet structure was obtained by the same freeze-drying method.The visible-light photocatalytic activity of the compound has obviously improved by degradation of methylene blue(MB).Through radical quenching experiments,the main active substances in the photocatalytic process were determined.Finally,a possible mechanism of photocatalytic degradation of MB was elucidated.3.Preparation of metal-N co-doped TiO2 composites(FD-M/N-TiO2):Metal nitrates(MNO3)are used as precursors of metal oxides and amino groups in water-soluble titanium complexes are used as N source.The same ultra-thin porous M/N-TiO2 composite nanosheet structure was obtained by the same freeze-drying method.The visible-light photocatalytic activity of the compound has obviously improved by degradation of methylene blue(MB)and selective reduction of 4-nitrophenol(4-NP).Finally,a possible photocatalytic degradation of MB has been elucidated.