| Ever since the1970s, the remediation of environmental pollution has attracted wordwide attention becase of the neccessay of sustainable development of human society. In recent years, photocatalysis has emerged as one of the most effective solution in the remediation of water and gas pollution, however, the application of photocatalysts suffers from their low efficency of solar energy utilization. In view of the efficient utilization of solar enery, the development of visible-light-driven photocatalysts has thus become indispensable. In the beginning, most work is focused on the search for visible light sensitive photocatalyst by modifying TiO2, whose development was far from the increasing demand of environmental remediation. Therefore, the exploration of novel excellent photocatalyst has become more and more attractive.The traditional photocatalytic reaction can be described as follows:upon light illumination with suitable enegy (matches or exceeds the band gap), charge separation take place to generate electron-hole pairs. Then, photogenerated electron and holes migrate to the surface to react with absorbed O2, H2O, and OH-, resulting in large amount of active oxygen radicals (e.g.·O2-, H2O2, and·OH), which can oxide the pollutant in water and gas directly. It is therefore therefore thought that the increase of active oxygen radicals is benefical for improving the photocatalytic activity. Generally speaking, the generation of active oxygen radicals is closely related to the band structure, the more negative conduction band and positive valence band are considered to be favorable for their generation. In general, both the photogenerated holes and electron can participate in the processes of dyes degradation, however, they should play different roles in the photocatalytic reaction. In a electron-dominated photacatalytic reaction, the more negative potential of the conduction band is considered to be better for photocatalytic activity enhancement.Hence, our work focused on exploring novel promising visible-light-driven photocatalysts by modifying semiconductor with more negative conduction band than the mostly studied TiO2at low temperature. This disssertation first introduced the environmental pollution, generation of photocatalysis, photocatalytic fundamental concepts and technologies, TiO2based visible-light-driven photocatalysts, and then reviewed the development of Indium and Niobium based ptotocatalysts. The synthetic strategies of carbon-modified niobium oxide (Nb2O5) nanostructures, C, N-codoped InOOH microspheres, hollow In(OH)xSy nanocubes, and flower-like In2S3nanospheres were developed. The crystal structure, composition, morphology, photocatalytic activity and mechanism of these resulting materials were characterized by XRD, XPS, SEM, TEM, DRS, and photocatalytic activity test. The detailed works were shown as following:1. Carbon-modified niobium oxide (Nb2O5) nanostructures, that firstly exhibited good visible lightphotocatalytic activity of Nb2O5species, were synthesized by utilizing a low temperature, one-pot nonaqueous sol-gel approach. The resulting products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, Infrared spectroscopy, and nitrogen adsorption. Unlike the commercial or other reported Nb2Os products that only respond to the UV-light irradiation, the present carbon-modified Nb2Os nanostructures obtained at200℃in our experiment exhibited much better photocatalytic activity on degradation of RhB under visible light, which was about39times of that of commercial NO2O5,18times of that of Degussa P25, and5times of that of carbon modified mesoporous TiO2. Moreover, these carbon-modified Nb2Os nanostructures were also able to efficiently split water under visible light. The growth mechanism and the origin of visible light photocatalyticactivity of the resulting Nb2Os nanostructures were proposed. These carbon-modified Nb2Os productsare expected to be more suitable candidates than that of the most studied TiO2as visible light photocatalysts.2. We demonstrate that C, N-codoped InOOH microspheres could be prepared by using a facile citric acid assisted hydrothermal method at220℃. The citric acid could not only perform as a complexing agent to control the morphology and the size, but also serve as a carbon source and a reducing agent for C and N codoping, which could be successfully tuned by adjusting the amount of citric acid. The XPS results revealed that interstitial N and surface carbonaceous species were found in InOOH. The resulted C, N-codoped InOOH exhibited much higher activity than undoped InOOH, P25, and C, N codoped TiO2on the photocatalytic degradation of RhB under visible light irradiation. This work not only deepens understanding of the morphology evolution and C, N codoping processes of InOOH microspheres, but also provides new insight on the doping effects of C and N for visible light photocatalysis.3. In this work, we report that hollow In(OH)xSy nanocubes were fabricated for the first time by taking advantage of a facile solution-phase approach using thioacetamide as the sulfur source at a temperature as low as80℃. On the basis of the XRD, SEM, TEM, and HRTEM ananlysis, we proposed that the cooperative combination of oriented attachment and Ostwald ripening as well as chemical-etching process governed the crystal growth, resulting in the formation of the hollow In(OH)xSy nanocubes in this study. More importantly, RhB and NO could be effectively removed under visible light with the as prepared hollow In(OH)xSy nanocubes. The photocatalytic experiments revealed that these low temperature synthesized hollow In(OH)xSy nanocubes were more efficient than P25and In(OH)xSy counterpart hydrothermally synthesized at180℃(In(OH)xSy-180). The porous structures, larger surface area, and new valence band of low temperature synthesized hollow In(OH)xSy nanocubes were thought to account for their superior photocatalytic activity. Among all the In(OH)xSy samples, the one with original S/In ratio of0.500in synthetic solution exhibited the highest photocatalytic removal efficiencies of RhB, while the other with original S/In ratio of1.000removed NO most efficiently. We systematically studied the photocatalytic process of RhB on In(OH)xSy and analyzed their different photocatalytic performances on removing RhB and NO. This study reveals that these hollow In(OH)xSy nanocubes are promising for environmental remediation.4. A general one-pot solvothermal process was employed to prepare flower-like In2S3nanospheres by employing water as the solvent at a temperature as low as80℃. The photocatalytic activities were evaluated by degrading Methyl orange (MO), Orange G (OG), Rhodamine B (RhB), and Methylene blue (MB) under daylight lamp. It was found that the as-prepared flower-like In2S3nanospheres exhibited better photocatalytic activity than the In2S3counterpart prepared at160℃. Moreover, we studied the photocatalytic mechanism and found that the photogenerated holes were mainly responsible for the degradation of anionic dyes MO and OG, while photogenerated electrons were more important in removal of cationic dyes RhB and MB. To the best of our knowledge, this is the first report on reaction mechanism of photocatalytic degradation of anionic and cationic dyes by flower-like In2S3nanospheres. More importantaly, the photocatalytic activity were tested under weak daylight, which make it promising in practical application in the future.
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