Preparation Of Manganese-based Layered Double Hydroxide With High Catalitic Ozone Decomposition Preformance

Ozone is widely used in industrial processes,such as water and soil cleaning,disinfection of animal and plant product,bleaching textiles,disinfection of medical supplies,etc.Long-term exposure to ozone will cause great harm to human health,ecosystems and urban constructions.With its strong oxidizability,ozone can react with unsaturated organic compounds rapidly,destroying the structure and declineing the performance of corresponding materials.MnO2 seems to be the most promisingozone decomposition catalyst,but low specific surface area and sharp decline in activity limits the catalytic efficiency.Therefore,it is necessary to develop new kind of ozone decomposition catalysts.The structure composed of layered double hydroxides(LDHs)is interchangeable,and the laminates have metal elements of different valence states.It is of great theoretical significance and practical value to study the catalytic ozone decomposition performance of LDHs by converting the types and quantities of the laminate elements.Herein,the effect of the content of LDHs and particle size on the catalytic decomposition performance of ozone were studied.The results show that the best particle size is 40-60 mesh and the best mass ratio is 1:9 when mixed with silicon carbide.On this basis,a series of MgMnAl-LDHs with different oxidation state of manganese were synthesized through regulating the preparation temperature.The valence state of manganese in LDHs was studied by XPS,and the results show that the valence state of manganese in MgMnAl-LDHs is a mixed valence state rather than a single valence state,and the proportion of Mn2+decreases with increasing temperature also increased from 2.8 to 3.2.Through the study on the catalytic ozone decomposition performance of LDHs samples containing different manganese valence states,it was found that as the average valence state of manganese in the sample increased,the ozone decomposition efficiency decreased from 63.8%to 15.2%.Reducing the mixed valence state of manganese is beneficial to improving the catalytic decomposition performance of manganese-based layered double hydroxides.With the controllability of the composition of LDHs laminate,a series of MgMnAl-LDHs with different Mg/Mn/Al molar ratios were prepared.XRD,SEM,ICP,O2-TPD and XPS were used to characterize the MgMnAl-LDHs.It is found that with the increase of manganese content in LDHs,the specific surface area and oxygen vacancy of LDHs decreased,and the chemical bond between LDHs and surface oxygen was stronger,and the catalytic decomposition capacity of ozone decreased.At the same time,through the comparative study of the valence state of manganese on the surface of MgMnAl-LDHs and the content of manganese,it was found that the valence state of manganese can be modulated by adjusting the proportion of metal elements on the laminate of LDHs.The valence state of manganese in Mg1.4Mn0.6Al-LDH prepared by adjusting the ratio of Mg/Mn/Al is only 2.3,and its catalytic decomposition efficiency of ozone is 2.5 times than that of α-MnO2 while manganese content is only one-quarter of α-MnO2.It also show good stability and recycling performance.Besides,the influence of Mn at different valence state on catalytic ozone decomposition was investigated by density functional theory(DFT)calculation,it is found that the Mn2+facilitates the desorption of generated oxygen on the surface of LDHs,while Mn3+and Mn4+contribute to the dissociation of adsorbed ozone.This result indicates that the low mixing valence state of manganese-based layered double hydroxide can effectively improve desorption of generated oxygen and the ozone catalytic decomposition performance.