| Ti O2 has excellent photocatalytic activity, however, its wide bandgap(Eg=3.2e V) led to the poor performance of using solar light. Coupling Ti O2 with other semiconductors of narrow bandgap can provide a beneficial solution for this drawback. This work attempts to combine Ti O2 and silicon which has narrow bandgap of Eg=1.12 e V to form the Ti O2/Si photocatalytic materials. From the application point of view, it can be more easily to prepare large area Ti O2 thin films on the So G Si by using liquid phase deposition(LPD). The results show that the visible light absorption and photocatalytic performance of the Ti O2/Si composite material is greatly improved, which makes this approach shows a good prospect in the field of solar photocatalytic degradation.In this paper, Ti O2 thin films have been prepared respectively on several substrates with different microstructures and their photocatalytic performances were studied systematically. The main studies are concluded as following:First, the preparation process of LPD-Ti O2 films was optimized, such as the concentration of(NH4)2Ti F6 and H3BO3, deposition temperature, deposition and annealing temperature. On the basis of this study, we determined the best film preparation process: 0.1mol/L(NH4)2Ti F6 and 0.4 mol/L H3BO3 were mixtured as precursor solution, then LPD process was reacted at a temperature of 55℃, finally as-grown Ti O2 films was annealed at a temperature of 700℃.Second, the reflectivity properties of Ti O2 film on the different substrates were investigated. Ti O2 films with different thickness were prepared on the micron-textured ptype mc-Si wafers(MT p-Si) by changing the deposition time to compare their reflectivity before and after coating. The average reflectivity of MT p-Si is 24.5%, which was largely reduced to 8.2% after coating a Ti O2 thin film with 90 nm thickness, and showing an excellent anti-reflection effect.Third, the light trapping properties of Ti O2 thin films grown on Quartz, MT p-Si, nano-textured p and PN type Si wafers(NT p-Si and NT pn-Si) before and after coating were studied. NT p-Si with nanostructure showed better light trapping property, i.e. the average reflectance ~17.5% of NT p-Si sample was reduced to ~5.3% with a 90 nm Ti O2 coating. In addition, the introduction of PN had no effect on the structure and reflectivity of thin film.Fourth, we measured and compared the photocatalytic performance of the four kinds of Ti O2 films under UV-visible light illumination. The results show that the Ti O2 thin film prepared on quartz had catalytic ability only in the ultraviolet spectrum, NT p-Si with nanostructure showed superior photocatalytic propertiy to quartz and MT p-Si, i.e. 79%@4h under UV--visible light illumination, especially ~49%@4h enhancement was achieved under only visible light illumination. Further, the degradation efficiency had ~5% increasement by introducing the PN junction.In summary, Ti O2 thin films were grown on So G mc-Si wafers with different multiscale structures by using a liquid phase deposition(LPD) method. It was found that due to the carrier injection from mc-Si wafers, the photocatalytic activity of the Ti O2 films could be expanded from the ultraviolet to the visible light region. In addition, further enhanced visible light photocatalytic properties could be achieved by introducing a nanotexture and PN junction into the mc-Si wafer, which was ascribed to the excellent light trapping and strong carrier separating properties. Our results suggest that density-graded nanostructures applied to the Ti O2 photocatalyst can enhance optical absorption, benefit carrier separation, and improve photocatalytic activity. |
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