Preparation Of Manganese Dioxide Nanocomposite And Its Application In Environment And Energy Storage

With the continuous advancement of modernization,energy and environmental issues have become major issues facing human society.Supercapacitor has become a research hotspot in the energy field due to their high energy density and fast charge-discharge rate.In addition,air pollution is one of the key concerns in environmental issues;Among them,volatile organic compouds（VOC）have great harm to human health and effective dection and removal of VOC gas is an important project in the current field.Metal oxides have extremely high application prospects in the above fields due to their unique physical and chemical properties.Especially,manganese dioxide（Mn O₂）has attracted extensive attention from researchers due to its high theoretical specific capacity,high formaldehyde removal efficiency and low cost.However,its poor conductivity,poor formaldehyde removal efficiency relative to noble metals and easy aggregation of particles greatly limit its wide application.Focusing on these issues,this research mainly improves its performance by preparing manganese dioxide-based nanocomposites and discusses its application in supercapacitor and formaldehyde removal.In order to solve the problem of poor electrochemical performance caused by poor Mn O₂conductivity,manganese dioxide/three-dimensional graphene nanocomposite（Mn O₂/3D-RGO）with a three-dimensional porous network structure was prepared by self-assembly using the electrostatic interaction between graphene oxide and manganese dioxide nanoparticles.The microstructure and electrochemical performance of nanocomposite were adjusted by adjusting the amount of Mn O₂ added.Mn O₂/3D-RGO exhibits good mechanical properties and can be directly made into supercapacitor electrode without the addition of conductive and adhesives agents.When the mass ratio of graphene oxide and manganese dioxide comes to 1:2,Mn O₂/3D-RGO show the best electrochemical performance.The specific capacity of the electrode reached269 F/g at a current density of 1 A/g and when the current density increased to 3 A/g,the specific capacity was 165 F/g.Due to the porous network structure and good conductivity of graphene,the electrochemical performance of Mn O₂ has been improved.Aiming at the problem of insufficient formaldehyde removal efficiency and easy aggregation of particles,the cerium oxide-copper oxide-manganese dioxide ternary metal oxide nanocomposite was grown on activated carbon by redox co-precipitation（Ce Cu Mn O_x/AC）.The cerium copper manganese oxide nanoparticles have a particle size of 50-80 nm and are evenly dispersed on the surface of activated carbon.When the metal oxide loading is 20%and the mass ratio of cerium oxide,copper oxide and manganese dioxide is 0.4:4:6,the Ce Cu Mn O_x/AC catalyst exhibits extremely high formaldehyde removal efficiency.The Ce Cu Mn O_x/AC catalyst’s removal efficiency of formaldehyde gas of 2 mg/m³ and 8 mg/m³reaches 98.8%and 95.5%within 2 hours,which is much higher than Mn O2 nanoparticles（～70%,2 mg/m³）and has good stability.Due to the synergistic effect of activated carbon and manganese dioxide and the doping of cerium copper oxide,the formaldehyde removal efficiency of Mn O₂ is improved,which is beneficial to the practical application of manganese dioxide-based catalysts.Furthermore,tricobalt tetraoxide（Co₃O₄）was selected as the principal part of gas sensing material due to its good gas sensing performance.The zeolite imidazolate framework material containing zinc and cobalt（ZIF-8/ZIF-67）was prepared by chemical co-precipitation method as a precursor,and zinc oxide-tin oxide-cobalt tetraoxide（Zn O-Sn O₂-Co₃O₄）hollow nanocube with rich porous structure was prepared by high temperature calcination and galvanic replacement reaction.Due to its unique nanostructure,the Zn O-Sn O₂-Co₃O₄ composite exhibits good gas-sensitivity.When the amount of Zn O added is 5%and the operating temperature is226℃,the sensitivity of Zn O-Sn O₂-Co₃O₄ to acetone and ethanol gas（100 ppm）reaches 6.339and 6.494,respectively,and the sensitivity has a good logarithmic relationship with the concentration of acetone and ethanol gas,which is beneficial to the real-time detection of acetone and ethonal gas.