纳米SiC基光催化剂研究进展

Advances in Nanostructured Silicon Carbide Photocatalysts

工业化无疑促进了经济的发展,提高了生活水平,但也导致了一些问题,包括能源危机、环境污染、全球变暖等,其中这些所产生问题主要是由燃烧煤炭、石油和天然气等化石燃料引起的。光催化技术具有利用太阳能将二氧化碳转化为碳氢化合物燃料、从水中制氢、降解污染物等优点,从而在解决能源危机的同时避免环境污染,因此被认为是解决这些问题的最有潜力的技术之一。在各种光催化剂中,碳化硅(SiC)由于其优良的电学性能和光电化学性质,在光催化、光电催化、电催化等领域具有广阔的应用前景。本文首先系统地阐述了各种SiC的合成方法,具体包括模板生长法、溶胶凝胶法、有机前驱物热解法、溶剂热合成法、电弧放电法,碳热还原法和静电纺丝等方法。然后详细地总结了提升SiC光催化活性的各种改性策略,如元素掺杂、构建Z型(S型)体系、负载助催化剂、可见光敏化、构建半导体异质结、负载炭材料、构建纳米结构等。最后重点论述了半导体的光催化机理以及SiC复合物在光催化产氢、污染物降解和CO_(2)还原等领域的应用研究进展,并提出了前景展望。

Industrialization undoubtedly boosts economic development and improves the standard of living;however,it also leads to some serious problems,including the energy crisis,environmental pollution,and global warming.These problems are associated with or caused by the high carbon dioxide(CO_(2))and sulfur dioxide(SO_(2))emissions from the burning of fossil fuels such as coal,oil,and gas.Photocatalysis is considered one of the most promising technologies for eliminating these problems because of the possibility of converting CO_(2)into hydrocarbon fuels and other valuable chemicals using solar energy,hydrogen(H_(2))production from water(H_(2)O)electrolysis,and degradation of pollutants.Among the various photocatalysts,silicon carbide(SiC)has great potential in the fields of photocatalysis,photoelectrocatalysis,and electrocatalysis because of its good electrical properties and photoelectrochemistry.This review is divided into six sections:introduction,fundamentals of nanostructured SiC,synthesis methods for obtaining nanostructured SiC photocatalysts,strategies for improving the activity of nanostructured SiC photocatalysts,applications of nanostructured SiC photocatalysts,and conclusions and prospects.The fundamentals of nanostructured SiC include its physicochemical characteristics.It possesses a range of unique physical properties,such as extreme hardness,high mechanical stability at high temperatures,a low thermal expansion coefficient,wide bandgap,and superior thermal conductivity.It also possesses exceptional chemical characteristics,such as high oxidation and corrosion resistance.The synthesis methods for obtaining nanostructured SiC have been systematically summarized as follows:Template growth,sol-gel,organic precursor pyrolysis,solvothermal synthesis,arc discharge,carbon thermal reduction,and electrospinning.These synthesis methods require high temperatures,and the reaction mechanism involves SiC formation via the reaction between carbon and silicon oxide.In the section of the review involving the strategies for improving the activity of nanostructured SiC photocatalysts,seven strategies are discussed,viz.,element doping,construction of Z-scheme(or S-scheme)systems,supported co-catalysts,visible photosensitization,construction of semiconductor heterojunctions,supported carbon materials,and construction of nanostructures.All of these strategies,except element doping and visible photosensitization,concentrate on enhancing the separation of holes and electrons,while suppressing their recombination,thus improving the photocatalytic performance of the nanostructured SiC photocatalysts.Regarding the element doping and visible photosensitization strategies,element doping can narrow the bandgap of SiC,which generates more holes and electrons to improve photocatalytic activity.On the other hand,the principle of visible photosensitization is that photo-induced electrons move from photosensitizers to the conduction band of SiC to participate in the reaction,thus enhancing the photocatalytic performance.In the section on the applications of nanostructured SiC,photocatalytic H_(2)production,pollutant degradation,CO_(2)reduction,photoelectrocatalytic,and electrocatalytic applications will be discussed.The mechanism of a photocatalytic reaction requires the SiC photocatalyst to produce photo-induced electrons and holes during irradiation,which participate in the photocatalytic reaction.For example,photo-induced electrons can transform protons into H_(2),as well as CO_(2)into methane,methanol,or formic acid.Furthermore,photo-induced holes can convert organic waste into H_(2)O and CO_(2).For photoelectrocatalytic and electrocatalytic applications,SiC is used as a catalyst under high temperatures and highly acidic or basic environments because of its remarkable physicochemical characteristics,including low thermal expansion,superior thermal conductivity,and high oxidation and corrosion resistance.The last section of the review will reveal the major obstacles impeding the industrial application of nanostructured SiC photocatalysts,such as insufficient visible absorption,slow reaction kinetics,and hard fabrication,as well as provide some ideas on how to overcome these obstacles.