| Solar energy driven water splitting catalyzed by semiconductors is the most effective way to solve the environmental pollution and the energy crisis.However,the key to restrict the practical application of this technology is the lack of highly efficient and stable photocatalysts.Although researchers have gained a deep comprehension about basic principles of semiconductor-based photocatalysis,there are still many difficulties and challenges to resolve.For instance,the Schottky junction between metal co-catalysts and semiconductor photocatalysts is known to be in favor of the separation of photogenerated charge carriers,but the interfacial effects with respect to crystal faces are often ignored;Regardless of the improvement of charge carrier generation and separation efficiency via doping,the oxidation/redox catalytic property of photogenerated carriers at the surfaces has been not fully understood in the doped photocatalysts to date.Once these problems are settled,we can get a more comprehensive and profound understanding about photocatalysis,which help us to design photocatalysts with better performances.In this thesis,we attempted to investigate the influence of the Schottky barrier on the separation process of photogenerated carriers by the method of loading Au nanoparticles onto different crystal faces.In addition,the effect of metal doping on the interfacial catalytic reaction of photogenerated carriers was studied by taking nickel doped TiO2 for example.The main contents are summarized as following:(1)Anatase TiO2 nanocrystals with predominant {101} crystal faces(i.e.,TiO2(101))or {001} crystal faces(i.e.,TiO2(001))were specially prepared to investigate the relationship between their surface structure and the corresponding electronic structure as well as energy band structure.Our results show that the electronic structure of TiO2(101)is entirely different from that of TiO2(001).We find that that single-electronic O· is only detected in TiO2(101),while TiO2(001)is more easily reduced.In addition,the UV-Vis absorption spectra and MOott-Schottky analysis further reveal that the flat band potential of TiO2(001)is 0.24 V lower than that of TiO2(1 01),despite that the two TiO2 nanocrystals possess the same band gap.This result well explains why a spatial separation phenomenon spontaneously occur in TiO2 nanocrystals with exposed {101} and {001} facets.On this basis,we investigated the influence of TiO2/Au Schottky junctions formed on different TiO2 facets on the separation efficiency of the hot electrons produced by the surface plasmonic resonance of Au.We find that the number of hot electrons transferred from Au to TiO2(001)is more than that to TiO2(101)due to the lower flat potential of TiO2(001).As such,the recombination of hot electrons and holes is significantly suppressed in the case of TiO2(001)/Au,which leads to the better hydrogen evolution performance of TiO2(001)/Au under visible light than TiO2(l01)/Au.(2)Spindle-like Ni2+ doped anatase TiO2 nanocrystals were successfully prepared via a hydrothermal route with potassium titanate nanowires as precursors.The UV-Vis absorption spectra reveal that Ni2+-doped TiO2 nanocrystals can absorb the light in the regions of 400?500 nm and 600?800 nm,in addition to ultraviolet light below 400 nm.Moreover,the hydrogen production rate of the TiO2 nanocrystals under the full spectrum light is significantly enhanced through a proper amount of Ni doping.According to the hydrogen production experimental results under visible light and fluorescence decay analysis,we find that this improved photocatalytic performance of Ni2+-doped TiO2 nanocrystals is not attributed to the enhancement of the light absorption efficiency and the separation efficiency of photogenerated charge carriers.We propose that the doping of Ni2+ may promote the reaction rate of photogenerated carriers on the surface of TiO2 nanocrystals. |
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