In-situ Synthesis Of Ti-based Heterojunctions And Their Visible-light Photocatalytic Activities

Pure TiO2 has many disadvantages as a photocatalyst including low efficiency in use of solar energy and low quantum efficiency. Combining semiconductors with narrow band gap to form heterostructured composites can lead to the enhancement in isolation of photoinduced electron-hole pairs and the improvement of the utilization for sunlight. In this paper, a series of TiO2-based heterojunction nano-photocatalysts have been synthesized so as to improve its photocatalytic ability. Then the as-prepared samples have been characterized by X-ray diffraction(XRD), Transmission electron microscopy(TEM), Scanning electron microscopy(SEM), UV-Vis diffuse reflectance(DRS), X-ray spectroscopy(XPS). The relationships among photocatalytic activity and heterojunction structure, morphology, pore structure, and surface area of the samples were discussed. The results show that the TiO2-based heterojunctions exhibit good photocatalytic abilities under visible light irradiation.The detailed research contents of this thesis are presented as follows:1. An in-situ microwave-assisted synthesis approach has been employed to prepare N-Ti O2/g-C3N4 composites using H2TiO3 as the reactant and NH3·H2O as the N-doping source. In this way, the N-TiO2/g-C3N4 composite catalysts have a porous structure and large surface areas. Degradation of rhodamine B(Rh B) and methylene blue(MB) were carried out to evaluate the photocatalytic activity of samples under visible-light irradiation. N-Ti O2/g-C3N4 composite with 40wt% N-Ti O2 exhibits the highest photocatalytic activity and the optimal temperature is 400 oC. The increased photocatalytic activity of N-TiO2/ g-C3N4 composites could be attributed to the formation of the heterojunction between N-Ti O2 and g-C3N4, which suppresses the recombination of photoinduced electron-hole pairs.2. Using a hydrothermal route, TiO2/g-C3N4 composites with a porous structure and large surface areas has been obtained for photocatalytic water splitting. Due to the H2O2 as solvent during sythesis, the crystallization of TiO2 was increased and the optimal calcinations temperature was decreased. As it turned out, the producing hydrogen efficiency of TiO2/g-C3N4 composites was much higher than pristine g-C3N4 under visible-light irradiation.3. Facets coupled BiOBr with amorphous TiO2 composite photocatalysts are synthesized via an in situ direct growth approach under microwave irradiation. In addition, characterizations indicate the heterointerface between BiOBr and amorphous TiO2 occurs mainly on the {001} facets of BiOBr. Degradation of methyl orange(MO) and phenol was implemented to appraise the photocatalytic activity of the crystalline composite heterojunction. The results show that the {001} facets coupled BiOBr with amorphous TiO2 composite photocatalysts lead to efficient separation of photo-generated electron–hole pairs between BiOBr and amorphous TiO2, enancing the quantum efficiency of BiOBr.