| With the rapid development of economy,science and technology,the level of social industrialization has been constantly improving.Human beings benefit from industrial civilization but at the same time they have been plagued by environmental issues and energy shortages.Especially in recent years,the constantly appearance of winter foggy weather in China has caused irreversible damage to human health.PM2.5 is the key factor leading to the atmospheric visibility decrease and haze generation,and the secondary organic aerosol(SOA)contributes significantly to the formation of high concentration particulate matter(PM2.5).Nitrogen oxides NOx,mainly refers to NO and NO2,is one of the important precursors of the secondary organic aerosol.Therefore,taking effective management and technical measures to control of NOx is an important way to improve China's air quality.Conventional methods such as physical or chemical adsorption and thermocatalytic reduction have been widely used to purify polluted air;however,the above strategies are not economically viable when dealing with air pollutants at low ppb concentration levels.And there are fatal disadvantages of using a large amount of precious metal,requiring a high reaction temperature,difficult product handling,and so on.Under the dual pressures of environmental pollution and energy shortage,it is more and more urgent to use photocatalytic technology to achieve high-efficiency removal of NOx under mild conditions.In recent years,photocatalytic oxidation have made great progress in NOx removal,and has developed a number of potentially useful high-performance catalysts.TiO2-based catalysts have achieved in indoor and outdoor applications in some fixed locations.It further proves that the photocatalytic oxidation of NOx are feasible and its value of in-depth study.However,there are still many problems that make it impossible to achieve large-scale and high-efficiency applications,including the low catalytic efficiency,the generation of toxic intermediates,the catalyst deactivation and its inherent mechanism remain unclear.The core of solving these problems is to clarify the surface reaction mechanism of pollutants on the catalyst surface in the process of photocatalytic oxidation of NOx.Therefore,it is of great guiding significance to study the reaction process of NO on the catalyst surface during the photocatalytic oxidation of NOx by effectively designing experiments.1.In the process of photocatalytic oxidation of NOx,NO mainly interacts with reactive oxygen species on the surface of the catalyst.It is of great significance to study the role of active species in the photocatalytic oxidation process and its transformation mechanism.In order to investigate the effect of different reactive oxygen species on the mechanism of photocatalytic oxidation of NOx,this chapter studies the difference of active species and intermediate products in the process of photocatalytic oxidation of NOx on different crystal planes by means of facet regulation strategy.In-depth analysis of the interaction and the conversion mechanism of NO with different activation degree of molecular oxygen and the photocatalytic NOx oxidation pathway.BiOCl nanosheets with(001)and(010)facet exposed were designed and synthesized,and the oxygen activation and the thermodynamic stability of different crystal planes and their NOx photooxidation reactivity were deduced.Through the experimental investigation and density functional theory calculations,it is found that the BiOCl(001)surface shows higher NOx oxidation efficiency than the(010)surface,while the former is more prone to pass ·O2-oxidation of NO and the(010)surface tends to pass O22-.In addition,the results of the simulation of geometric atomic arrangement and the detection of in-situ infrared intermediate species show that the oxidation of NO on the BOC-001 tends to form a monodentate nitrate intermediate adsorption configuration,whereas the BOC-010 is more prone to bidentate nitrate as the main intermediate.In this study,the mechanism of NO photocatalytic oxidation at different facet of BiOCl single crystal nanosheets was revealed at the atomic level,and the effect of molecular oxygen with different activation degrees on the photocatalytic oxidation of NO was systematically revealed.It is of great value for the rational design of high-efficiency photocatalysts.2.Compared with the traditional NO emission reduction strategy,photocatalytic oxidation to remove NOx without more toxic NO2 emission is a big challenge.The formation of NO2 in NO by photocatalytic oxidation is generally attributed to the existence of mono-oxygen species,such as the hole(O-)and hydroxyl radicals(·OH),the partial NO oxidation(NO(g)+ O-/· OH ? NO2(g)).In view of this,it is of great significance to adjust the existence of molecular oxygen reactive species to control the oxidation degree of NO,especially the superoxide radical(O2 + e?·O2-;NO(g)+·O2-?NO3-).BiOCl is a typical UV-responsive semiconductor that is receiving increasing attention due to its intervening oxygen vacancies(OVs)mediated photocatalysis.Well-designed oxygen vacancies with high catalytic activity on its prototype(001)surface extend the photo-responsive region of BiOCl to visible light and also enable the highly selective and efficient activation of O2 to · O2-.And by the revelation of the previous work,the amount of NO2 significantly reduced after the addition of K2C2O4 captured h+,indicating that the formation of NO2 is likely to be derived from the oxidation of h+.In this study,selective oxidation of NO to nitrates with a selectivity of over 99%was achieved by side-bridging the formation of superoxide radicals by well-designed oxygen vacancies on the BiOCl(001)surface as model photocatalysts.This study provides an in-depth analysis of the intermediate course of photocatalytic oxidation of NO and the acquired knowledge as a basis for the development of a complex NO removal system. |
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