Highly Efficient Photocatalytic Oxidation Of NO_x With Polyoxometalates And The Related Mechanisms

With the thirteenth five-year plan in full swing,the domestic industrialization process has reached a new unprecedented height.While industrial civilization has improved people’s quality of life,environmental pollution comes along and is getting worse day by day.Lots of air contaminants produced by the combustion of fossil fuel have caused severe air pollution,which leads to significant harm to people’s living.As a typical atmospheric pollutant,NOx is a primary contributor for acid rain,haze,ozone layer destruction and other severe environmental problems.It is urgent to develop efficient and economical technologies to eliminate NO contamination,which accounts for 95%of NOx.A variety of NOx removal methods have been carried out in the industry.Selective catalytic reduction is a widely used NOx removal technology,but it is expensive and less efficient in the treatment of low concentration NOx in urban environments.Photocatalytic technology has recently been regarded as an attractive alternative technology for NO removal because it is efficient and eco-friendly.The core of photocatalysis is photocatalyst.Most of the research on NO removal photocatalysts focused on metal oxide,C3N4 and bismuth catalysts,but few on other catalysts.The development of other NO removal photocatalysts will bring new possibilities for NO removal.Polyoxometalates have rich structures and applications due to its long history and mature research,and some POMs have been industrialized.As a photocatalyst,POMs can be excited by UV or near-visible light,and had numerous studies on water oxidation,CO2 reduction,and pollutant degradation.POMs maybe have the potential for photocatalytic NO oxidation.Initiation of NO removal POMs photocatalysts will greatly broaden the selection range of NO photocatalysts and provide new ideas and theories for the treatment of air pollution basis.In this paper,a tungstosilicic acid catalyst with high photocatalytic NO oxidation activity was prepared,and its reaction mechanism was investigated.This is the first study on the photocatalytic NO oxidation by POMs.Based on this,an butyl functional group doped phosphotungstic acid catalyst was prepared.The doping of the organic functional group can improve the hydrophobicity of the catalyst,and then increase the photocatalytic activity of NO in the catalyst.These studies provide novel research ideas for the purification of atmospheric NOx pollution,and provide theoretical support for the development of high-efficiency photocatalytic devices.In this paper,a tungstosilicic acid catalyst with high photocatalytic NO oxidation activity was prepared.Under simulated sunlight,the catalyst exhibits a good NO removal ration(54%)and most of NO was directly oxidized to nitrate with selectivity exceeding 95%.Through trapping experiments and EPR characterization,we found that in the polyoxometalate photocatalytic NO oxidation process,the active species are electrons and superoxide radicals.Through Fourier transform in situ infrared spectroscopy and temperature-programmed desorption experiments,we found that the protons present in the form of H3O+ are the adsorption and activation centers of NO.This chapter is the first discovery of photocatalytic NO oxidation by POMs,laying a foundation for the study of POMs photocatalytic NO oxidation.Based on the research conclusions of silicotungstic acid catalysts,phosphotungstic acid catalysts modified with butyl functional groups were designed.After modifying,the activity of this catalyst was 2.2 times higher than that of phosphotungstic acid under simulated sunlight,and the selectivity to nitrate products remains 90%.Through various characterization,it was found that the modifying of functional groups mainly changes the hydrophobicity of the catalyst,which can inhibit the competitive adsorption of water and NO in the reaction and enhance the adsorption of NO.This result can improve the practicality of POMs catalysts because most areas are high air humidity in China.It can serve as a guide in using photocatalysts for NO removal in high humidity environment,and help us design highly efficient NOx removal systems.