| The acceleration of national industrialization process has met the people’s requirements for social development,but also has destroyed the original ecological environment.As an important support for economy and transportation,a large number of pollutants produced by the burning of fossil fuels have caused serious air pollution,which directly affects the normal life of human beings and increases the risk of human diseases.As a typical atmospheric pollutant,NOx is one of the precursors of acid rain,haze,ozone layer destruction and other severe environmental problems.Therefore,it is urgent to develop sustainable NOx pollution control technology.Although selective catalytic reduction is a widely used NOx removal technology in industry,it does not have economic advantages and wide applicability in the treatment of low concentration NOx in the atmosphere.Photocatalytic technology is a new technology,which can utilize solar energy to remove pollutants under mild conditions,and has a broad application space for the purification of low concentration of NOx in the atmosphere.Photocatalytic NOx removal technology has also attracted more and more attention.At present,most studies on the photocatalytic removal of NOx focus on the development and performance optimization of new catalysts,and few studies on the mechanism of photocatalytic oxidation of NOx are available.Clarifying the NOx photocatalytic oxidation transformation pathway can guide the development of photocatalysts with better performance and provide theoretical support for the design of practical photocatalytic purification devices.Based on semiconductor engineering defects and plasma resonance theory,we synthesized cerium oxide with rich oxygen vacancies or gold loading,found that oxygen vacancy or gold loading can enhance the photocatalytic oxidation of NO by cerium oxide,and explored the mechanism of photocatalytic oxidation of NO,aims to further understand the interface mechanism of photocatalytic oxidation of NOx,provide new insight for atmospheric NOx pollution purification,and provide theoretical support for the development of efficient photocatalytic devices.1.Oxygen vacancy is one of the most common surface defects of metal oxides.We synthesized cerium oxide with oxygen vacancies by hydrothermal method,and explored the influence of oxygen vacancy on the photocatalytic oxidation of NO by effectively regulating the oxygen vacancy concentration.The photocatalytic oxidation of NO experiment showed that the NO removal efficiency of cerium oxide was 50%,and the amount of the by-product NO2 was only 10 ppb,and the selectivity of nitric acid products exceeded 95%.Combining with theoretical calculation and mechanism exploration experiment,we found that oxygen vacancy was the key to the efficient photocatalytic removal of NO by cerium oxide.Oxygen vacancy,as the adsorption site and reduction site of O2,can activate O2 to produce ·O2-,and ·O2-can completely oxidize NO to generate NO3-,effectively inhibiting the formation of toxic by-products NO2.Meanwhile,as a defect level,oxygen vacancy can effectively inhibit the combination of photogenerated electrons and holes,further enhancing the performance of catalyst oxidation to remove NO.2.The plasmon resonance effect induced by noble metal nanoparticles is an effective strategy for the efficient utilization of solar energy and the noble metal itself is usually the active site for the adsorption and subsequent catalysis of reactant molecules in catalytic reactions.Therefore,we tried to load gold nanoparticles on the surface of the defected cerium oxide to construct a new reaction site for the removal of NO.The photocatalytic oxidation of NO experiment showed that the NO removal efficiency of gold-loaded cerium oxide reached 65%,which was 15%higher than that of unloaded cerium oxide,and the selectivity of nitric acid products was over 97%.The theoretical calculation results showed that the introduction of gold nanoparticles broke through the original single active center of the defective cerium oxide and realized NO oxidation with double active centers.TPD experiment showed that oxygen vacancy was the adsorption site of O2,while gold was the adsorption site of NO,which provided a spatial location for effective activation of small molecules.The monochromatic photocatalytic experiment and infrared experiment further proved the role of the gold nanoparticles in photocatalytic oxidation of NO,NO adsorbed on the gold particles was activated into NO by mild hot holes,O2 adsorbed on the oxygen vacancy was activated into·O2-,these two kinds of activated molecules reacted at the interface between cerium oxide and gold,and then realized NO oxidation with double active centers.Gold particles enhanced the visible light response of cerium oxide through the plasma resonance effect,so that more electrons participated in the activation of molecular oxygen and further improved the removal efficiency of NO. |
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