In order to increase the solar light utility and improve the photocatalytic activity in visible light, it is significant to synthesize TiO2 photocatalyst with good performance in visible light photoactivity. As an effective method to modify the band structure of semiconductors, doping is also widely adopted for the band structure modification of TiO2. In this thesis, a novel method of B and N co-doping for the photoactivity enhancement of TiO2 in visible light region was developed. The doping states of the dopants, the visible light absorption, the photocatalytic activity under visible light irradiation and the relationships among them in this B, N-co-doped TiO2 system were also explored.
B, N-co-doped nanocrystalline TiO2 powders were synthesized through two-step hydrothermal process and nitridation treatment, and were characterized by TG-DSC, XRD, HRTEM, XPS, FTIR, Raman spectroscopy, UV-Vis absorption spectroscopy, and their photoactivity was evaluated under visible light irradiation. The results obtained are as follows:
(1) The doping state of boron is essential for visible light adsorption and for the synergistic effects of B, N-co-doping. The chemical states of B atoms changed as the increase of B concentration and the nitridation treatment, from the formation of B2O3/BN without bonding with TiO2 to the formation of B2O3/BN and surface B-Ti-O, N-B-Ti-O states, and to the enrichment of B2O3/BN;
(2) The B-Ti-O and N-B-Ti-O bonds on the TiO2 surface can change the band structure of TiO2, which causes the enhancement of visible light absorption;
(3) The theoretical models of B-Ti-O and N-B-Ti-O structures on TiO2 surface were developed and calculated by first principle method, which shows that these structures can stably exist on the surface of TiO2. The DOS of the doped TiO2 reveals that the localized states around Fermi level is the physical basis for visible light absorption performance of the doped TiO2. Meanwhile, some of the localized states of the N-B-Ti-O structure may extend the lifetime of excitons, effectively enhancingthe visible light photocatalytic activity of the doped TiO2.
In general, we developed a novel method to obtain B, N binary doped TiO2 for the enhancement of both visible light absorption and visible light photoactivity. The results obtained enrich the understanding of non-metal doped TiO2 and are helpful for the further development and the applications of non-metal doped TiO2.
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