全太阳光谱光热催化降解VOCs的研究进展

Research Progress on Photothermocatalytic Degradation of VOCs under Full Solar Light

光热协同催化技术是将光催化低温反应的优势和热催化治理高浓度有机污染物且稳定性好的优势有机结合,是一种能够高效、稳定降解净化挥发性有机物(VOCs)的新途径,很好地解决了光催化治理VOCs存在的易失活、效率低、光能利用率低等问题。总结了近年来全太阳光谱驱动光热催化降解VOCs的研究进展。归纳了光热催化剂的构筑,既可以通过TiO_(2),ZnO,CeO_(2),Co_(3)O_(4),锰氧化物(MnO_(x))等单一半导体氧化物实现,也可以通过光催化剂与热催化剂复合、金属离子掺杂修饰热催化剂、贵金属负载半导体氧化物进一步提升光热催化氧化VOCs的催化活性。梳理了光热催化降解VOCs的机制,从光热协同催化氧化反应到全光谱光致热催化氧化,再通过全光谱光活化效应增强光致热催化活性。对光热催化氧化VOCs的研究进行了总结和展望。

With the development of economy and society,air pollution control has been received great attention from all over the world.Volatile organic compounds(VOCs),as the main source of air pollution,are widely derived from the emission of corporate exhaust gas,the combustion of outdoor fuels,the use of solvents,and the volatilization of interior building decoration materials.VOCs seriously threaten human health.Therefore,it is an urgent need to develop new materials,new mechanisms and new technologies,which can efficiently and stably degrade and purify VOCs.Photothermocatalytic synergetic effect technology is an organic combination of the advantages of photocatalytic reaction at low-temperature and thermocatalytic degradation for high-concentration organic pollutants with well stability.It is a new approach to the efficient and stable degradation of VOCs.It can well solve the problems in the photocatalytic degradation of VOCs,such as easy deactivation,low efficiency,and poor utilization of light energy etc.This paper systematically summarized the recent research progress of full solar light driven photothermocatalytic degradation of VOCs.The construction of the normal photothermocatalysts was introduced in this paper.Catalysts with photothermocatalytic synergetic effects should satisfy the requirements of both photocatalysts and thermocatalysts.On the one hand,as a photocatalyst,it should have strong light absorption properties at least in a certain wavelength range.On the other hand,as a thermocatalyst,it should be able to degrade high-concentration VOCs at higher temperatures.Firstly,single semiconductor oxides,especially photocatalysts,had already been achieved many researches,but there were still problems such as poor photocatalytic performance and stability,low efficiency,and far from practical applications etc.The typical photocatalysts,such as TiO_(2)and ZnO could carry out thermocatalytic reaction,but the reaction temperature of thermocatalysis was relatively high(usually higher than 240℃to start thermocatalysis),and the energy consumption was too large.The typical thermocatalysts,such as CeO_(2),Co_(3)O_(4),MnO_(x),etc.,could occur thermocatalytic oxidation at lower temperature,but the photocatalytic process was difficult to happen.Therefore,the usage of a single semiconductor oxide as a photothermocatalyst still had many limitations.Secondly,the photocatalysts were combined with thermocatalysts to prepare composite catalysts.The photothermal synergetic catalysis could be realized by the migration of active species between the constructed interfaces,which could not only reduce the thermal reaction temperature of the photocatalyst,but also solve the photocatalysis problem of the thermocatalyst.Thirdly,metal ion doping thermocatalysts presented well photothermocatalytic activity for VOCs under full solar light.The thermocatalytic oxidation of manganese oxides had high degradation rate and excellent stability for the treatment of VOCs.So manganese oxides were considered as potential substitutes for noble metal catalysts.A lot of work had been carried out to use metal ions doping manganese oxides to reduce the thermocatalytic temperature for VOCs treatment.Fourthly,the noble metals,such as Pt,Au and Ag,supported on semiconductor oxides could improve the separation efficiency of photogenerated charges,increase the photocatalytic activity,and enhance the absorption of light through the surface plasmon effect.The interaction between noble metal nanoparticles and semiconducting oxides could enhance the thermocatalytic activity.Therefore,supporting noble metals on semiconducting oxides had also become a popular choice for photothermal degradation of VOCs.Then,the mechanism on the photothermocatalytic degradation of VOCs was combed to photothermocatalytic synergetic oxidation,full solar light driven thermocatalytic oxidation,and the enhanced light driven thermocatalytic activity through full solar light photoactivation effect.The mechanisms of the photothermocatalysis under full solar light for VOCs degradation were detailed as follows:(1)The photothermocatalytic synergetic effect.TiO_(2),ZnO,CeO_(2)and other photocatalysts could trigger not only the photocatalytic reaction,but also the thermocatalytic reaction.The active species generated by the photocatalytic reaction could accelerate the thermocatalytic reaction,to achieve photothermocatalytic synergetic effect.(2)The full solar light driven thermocatalytic oxidation.The catalysts must have strong absorption in the full spectral region and can efficiently convert the absorbed light energy into heat energy,resulting in a surface equilibrium temperature higher than the light-off temperature of thermocatalysis.At the same time,the catalysts necessarily needed a lower light-off temperature and the excellent thermocatalytic activity.(3)The full solar light photoactivation effect.Surface plasmonic photocatalysts exhibited thermionic-induced photoactivation effect under full spectrum illumination.Hot electrons could initiate coupling energy transfer with surface adsorbed molecules and activate adsorbed molecules.When the local heating temperature caused by electron-phonon scattering was higher than the light-off temperature of the catalyst,the thermal catalytic reaction would be promoted.The full solar light photoactivation effect was a unique and interesting effect,involving the excited electrons of the photothermocatalyst and the adsorption and reaction of the surface reactants,which can further improve the activity of the full solar light photothermocatalysis.Therefore,the in-depth exploration of the mechanism of photoactivation effect and the oxidation reaction of excited state photothermocatalysts were the research trends and hot issues of photothermocatalytic oxidation of VOCs in the future.Finally,the prospects of photothermal synergetic catalysis were presented,and the development for the governance of the high concentration and diverse composition VOCs was highlighted.