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Defective TiO2-x nanocrystals based photocatalysts with enhanced photocatalytic activity
Muhammad Wajid Shah
学位类型博士
导师王传义
2016-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料物理与化学
关键词Nanocrystals Tio2 Bivo4 Defective Tio2-x Heterojunction
摘要

Defects are critically important for metal oxides in chemical and physical applications Defective TiO2-x plays vital role to enhance harvesting of solar light irradiation for renewable energy and environmental remediation. A facile hydrothermal approach has been developed to prepare defective TiO2-x nanocrystals using Ti (III)-salt as a precursor and L-ascorbic acid as reductant and structure direction agent. The prepared TiO2-x nanocrystals are composed of a highly crystallized TiO2 core and a disordered TiO2-x outer layer, possessing high surface area, controlled Vo concentration and tunable band gap via simply adjusting the amount of added L-ascorbic acid. Further different morphology of BiVO4 is prepared via hydrothermal method by using TiCl3 as structure directing agent with different pH. The as–prepared BiVO4 is couple with defective TiO2-x to form heterojunction. The BiVO4 and defective heterojunction are prepared via two step hydrothermal method with unique shuriken shape morphology. The unique morphology of BiVO4/TiO2-x heterojunction greatly enhances the surface area and suppresses the electron/hole recombination. Defective TiO2-x completely cover the BiVO4 and thus provide more surface area to adsorb the pollutant molecule. The incorporation of TiO2-x improves separation of photogenerated charge carrier and visible light absorption of BiVO4.In order to study the effect of defective TiO2-x on the crystalline morphology of BiVO4 is also studied. The BiVO4/TiO2-x is prepared via facile one step hydrothermal method and flower like morphology are obtained. The flower like crystalline structure is greatly affected by increasing the mole ratio of defective TiO2-x. These as-prepared defective TiO2-x, BiVO4, and BiVO4/TiO2-x heterojunctions plays a very important role in photocatalytic activities.The defective TiO2-x shows high photocatalytic efficiency in methylene blue and phenol degradation as well as in hydrogen evolution under visible light, underlining the significance of the present strategy for structural and band gap manipulation in TiO2-based photocatalysis. Consequently, the heterojunction composite exhibits enhanced photocatalytic efficiency for the degradation of phenol under visible light irradiation and are three times higher than bare BiVO4 with kinetic rate of 1.22 x10-2. The obtained BiVO4/TiO2-x achieves two folds higher photocurrent density at the potential of 0.6 V with standard calomel electrode (SCE) compared to bare BiVO4. The increase photocatalytic activity is attributed to large surface area and rectifying electron transfer across the heterojunction. It is suggested that the photo-exited electrons are effectively transferred from the valence band of defective TiO2-x to BiVO4, resulting effective electron-hole separation, which is responsible for high photocurrent densities and lower photoluminescence intensity. CO2 photoreduction with water vapor has been studied via BiVO4/TiO2-x heterojunction system with hierarchal flower like morphology. The production of CO and CH4 from CO2 are remarkably enhanced over BiVO4/ TiO2-x (1:2) that is 8 times more as compare to pure BiVO4 and defective TiO2-x. The increasing enhances photocatalytic activity of as-prepared defective TiO2-x, BiVO4/TiO2-x heterojunction and BiVO4/TiO2-x is referred to the defects (oxygen vacancies), small crystalline size, unique crystal morphology and large surface area. X-Ray photoelectron spectroscopy (XPS), are used to confirm the defects/ oxygen vacancies as well as interaction between BiVO4 and TiO2-x heterojunction. The structure morphologies are confirmed with SEM and HRTEM. UV-visible diffuse reflectance spectroscopy (DRS) shows the induce band gap to enhance visible light absorption, while the charge and hole recombination are studied by the Photocurrent densities and Photoluminance (PL) spectroscopy.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4556
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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Muhammad Wajid Shah. Defective TiO2-x nanocrystals based photocatalysts with enhanced photocatalytic activity[D]. 北京. 中国科学院大学,2016.
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