Research On Performance Improvement And Mechanism Of Layered Double Hydroxide Photocatalytic Degradation Of NO_x

Enviromental pollution is increasing serious due to rapid development of modern industry,in which air contamination is particularly prominent,contributing to a serious threat to human health and ecological environment.As important pollution factors in atomosphere,NO_xis strictly controlled by the state.Thus,various techenology,such as adsorption separation,low temperature catalytic combustion,etc,is applied to remove NO_x,in which photocatalytic oxidation techenology,as an environment friendly,sustainable and economic technology,has attracte much attention due to the ablility enable NO_xto non toxic and harmless products.Besides,semiconductor photocatalyst is key.Therefore,it is of significant to explore semiconductor materials with low cost,high efficiency and stable performance for development of photocatalysis.Therefore,considering that the earth has abundant reserves of Mg and Al elements,this paper uses Mg Al-LDH as a model photocatalyst for photocatalytic purification of NO_x.However,Mg Al-LDH itself has a wide forbidden band width,cannot be excited by visible light,and the absorption area in the ultraviolet light region is also very weak.Among various semiconductor control methods,ion doping is one of the simplest and easy to analyze.At the same time,Ni element has intrinsic light absorption.Therefore,a series of Mg Al-LDH photocatalysts with Ni partially substituted for Mg were synthesized by hydrothermal method to improve the activity and explore its mechanism of action.The results showed that the photocatalytic performance of Mg Al-LDH nanosheets（Ni/LDH）in which part of Mg²⁺was replaced by Ni²⁺was significantly improved.When the substitution rate of Mg²⁺is 25%,under ultraviolet light irradiation,Ni/LDH has the highest removal rate of NO,42.10%（87.2%of which is converted into nitrate）,and the production of NO₂,a toxic by-product that is much more toxic than NO,is extremely low at 6 ppb.In addition,we have proved through experiments that the OH^-carried by Ni/LDH can be converted into·OH by capturing light-excited holes,which has great significance for the practical application of LDH in the removal of atmospheric pollutants in the future.Among them,Ni²⁺optimizes the energy band structure of LDH（regulated from 5.11 e V to 4.36 e V）and brings more electronic defects,which leads to easier activation of surface OH^-,which in turn leads to increased production of reactive oxide species（ROS）,and then promote the improvement of photocatalytic performance.In view of the abundant OH^-on the surface of LDH,it can be used as the precursor of·OH,which can improve the problem of limited photocatalyst efficiency due to low atmospheric humidity and low surface moisture concentration（water is the precursor of·OH in general photocatalytic systems）.We guess that combining LDH with other photocatalysts can provide OH^-for general photocatalysts and improve photocatalytic activity.Here,（Bi O）₂CO₃（BOC）,which has a certain visible light absorption and a high positive valence band,is selected as the model catalyst and is physically mixed with Ni Fe-LDH to obtain BOC/Ni Fe-X（denoted as Ni Fe-X,X=1,2,3,4,X represents Ni/Fe ratio）.The experimental results show that the photocatalytic activity of Ni Fe-LDH under visible light is significantly improved,with the highest activity reaching 54.45%,stable performance and high conversion efficiency.In addition,we have proved through experiments that the increased activity is mainly due to the OH^-which is easily activated on the surface of LDH consumes a large number of photo-generated holes,reduces the possibility of electron recombination,promotes the charge separation and transfer of BOC/Ni Fe-X,thereby increasing the ROS produced and improving the visible light catalytic activity of BOC.At the same time,combined with experimental and theoretical methods,it reveals the OH^-the most easily activated Ni and Fe coordination sharing coordination situation and the mechanism of photocatalytic oxidation of NO.The OH^-activation scheme proposed in this paper can also be extended to other surface-enriched OH^-semiconductor photocatalysts,providing new ideas for the further development of photocatalysis.