| 摘要: |
| 氮氧化物（NOx）是形成臭氧和二次气溶胶的重要前体物之一，开发高效的NOx控制技术对我国大气污染防治具有重要意义。光催化技术作为一种新型的高级氧化技术，对环境浓度水平的空气污染物具有良好的去除效果，是当前研究的热点。本文总结了近年来光催化材料对污染物NOx催化降解的研究进展，包括：（1）讨论了NOx光催化氧化去除机理；（2）详细综述了提高光催化材料性能的三大主要措施：增强催化剂的光吸收效率，提升载流子分离和迁移效率以及构筑表面活性位；（3）阐述了半导体光催化技术在净化空气方面的应用，并指出光催化技术在去除NOx方面的发展前景。 |
| 关键词: NOx NO光催化氧化去除机理 光催化剂 |
| DOI：10.7515/JEE201706002 |
| CSTR：32259.14.JEE201706002 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41401567，41573138） |
| 英文基金项目:National Natural Science Foundation of China (41401567, 41573138) |
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| Research and development on nitrogen oxides removal by semiconductor photocatalysis |
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YAO Jie, ZHANG Yufei, WANG Yawen, CHEN Meijuan, HUANG Yu, CAO Junji
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1. College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2. Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
3. School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
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| Abstract: |
| Background, aim, and scope In recent years, the haze phenomenon is more serious in China, especially in some typical cities. This phenomenon has a serious impact on climate, air quality and human health. Nitrogen oxides (NOx) is one of the main components of haze. And NOx (NO, NO2) generated from the combustion of fossil fuels have attracted lots of attentions, which can lead to a wide variety of atmospheric environmental problems, like acid rain, haze, photochemical smog and so on. The exhaust emissions of motor vehicle and combustion of fossil fuels are the culprit, which causing air pollution in urban environment. Therefore, taking effective measure and technical of control NOx levels in the atmosphere, which has an important practical significance to improve air quality of our country. Using solar energy to solve environment problem has attracted increasing attention. Photocatalysis technology can direct use solar energy to remove contaminants at room temperature. Therefore, photocatalysis is considered to potential technology for air purification. Materials and methods This paper reviews studies about the developments on NOx removal by semiconductor photocatalysis, focusing on photocatalytic mechanism, modifications of photocatalyst, practical application and the development prospects in removal of NOx. Results When the semiconductor material is activated with light of wavelength equal to or greater than the band gap energy. The electrons of semiconductor valence band are stimulated transition to its conduction band, at the same time, the same number of holes left in valence band, thus creating electronic-hole pairs. Discussion According to the recognized photocatalytic model, the charge carrier diffuse to the surface of catalysis. On the one hand, the holes with oxidizing ability can directly react with NOx. On the other hand, the holes also react with water molecules adsorbed onto the semiconductor surface to form OH·. The electrons can react with oxygen molecules to generate ·O2−. The OH· and ·O2− have strong oxidizing, which can oxidize nitric oxides. According to our investigation, in the case of sufficient oxygen, the purpose of photocatalysis is to transform NO into NO3− vis the formation of intermediate (NO2, HNO2). In the current study, The NO photocatalytic oxidation main mechanism for photocatalysts went through three states (NO → HNO2 → NO2 → HNO3). The development of high efficient photocatalytic is incomparably important to the practical application of photocatalysis technology. There are three methods to improve photocatalyst performance. (1) Enhancing the light absorption efficiency of photocatalyst. i. By narrow band gap semiconductor sensitization broad band gap semiconductor, can broaden the optical response of photocatalytic materials to improve the photocatalytic efficiency. ii. And that, Metal or nonmetal doped-semiconductor can form impurity level, which can reduce the band gap of photocatalytic materials to improve the absorption of light. (2) Promoting the separation and migration efficiency of charge carrier. i. Manufacture heterojunction, and the built-in electric field can promote the separator and migration of photo-production electron-hole pair. ii. The electron of catalyst spontaneously migrate to metal, which enhance the migration and separation of carrier. (3) Increasing the surface active sites. i. Synthesizing catalysis of special morphology, which can increase specific surface area and reaction sites to improve the photocatalytic performance. ii. Synthesizing catalysis with high active exposure crystal faces or surface defects. Above modification strategies can effectively regulate the band structure, interface properties, specific surface area and active site of the material, which can improve the light absorption ability, electronic-hole separation efficiency and surface reaction rate of semiconductor photocatalyst. Conclusions Semiconductor photocatalysis is a promising technology for low concentration air purification, with strong oxidation ability, no energy consumption, no secondary pollution etc. Therefore, it drew great attention from researchers and developed rapidly. However, the current photocatalytic technology is not yet mature. So there are still some problems on the theory research and practical application. Recommendations and perspectives The depth exploration of photocatalysis mechanism and the development of high efficient photocatalyst will be the focus of the future development direction. |
| Key words: NOx NO photocatalytic oxidation mechanism photocatalyst |
