The Study of Semiconductor Heterostructures for Photocatalysis and Photoelectrochemical Water Splitting.

摘要

Activated carbon, graphene, carbon nanotubes and fullerene were incorporated into TiO2 to produce carbon-based TiO2 hybrid nanostructures by a solvothermal approach and thermal annealing. The superiority in photocatalytic activities of this carbon-based TiO2 samples on the RhB molecules orignated from the excellent adsorption property, favourable chemical bond formation (Ti-O-C), narrower bandgap, smaller particle size and effective charge carriers separation of the nanocomposites. In a related work, ultra-small Ag nanocrystallites-decorated TiO2 hollow sphere heterostructures were prepared which showed excellent photodegradation performance for RhB. In this metal-semiconductor heterostructures, the Ag nanocrystallites with high crystallinity reduced the recombination rate of charge carriers and favoured the charge transfer across the interfaces. The increased adsorbed surface oxygen, upward shift of Fermi level and increased electron density due to coupling of Ag had contributed to the charge transfer and improvement of quantum efficiency. Furthermore to the study of photocatalytic composites, porous graphitic carbon nitride was synthesized by the controllable thermal polymerization of urea in air. The textural, electrical and optical properties of the samples were tuned by varying the heating rate. In a related work, MoS2 nanosheets were coupled into the carbon nitride to form MoS 2/C3N4 heterostructures samples whose kinetic rate was 3.6 times faster than that of bare carbon nitride. As analyzed by SEM, TEM, UV-Vis absorption, PL and photoelectrochemical measurements, the intimate contact interface, extended light response range, enhanced separation speed of charge carriers and the high photocurrent density upon MoS2 coupling were the major factors to the photocatalytic promotion while using MoS2/C3N4 heterostructures. This thesis also reported the fabrication of Ni(OH)2/Ti-Fe2O 3 photoanode by a two-step hydrothermal method for the use in water splitting. It was found that Ti doping had promoted the photovoltage of hematite by surface modification rather than increasing the donor density, while the loading of Ni(OH)2 had further improved the photoelectrochemical performance of Ti-Fe2O3 by reducing both the over-potential of oxygen evolution reaction and the recombination rate of the charge carriers. Another than the Ni(OH)2 loading, the water splitting performance of hematite could also be improved via surface engineering by using CTAB. It was found that the CTAB-Fe2O3 had promoted the photocurrent of pristine hematite by two times at 1.23 V vs. RHE. The increase in carrier&