Controllable Preparation And Gas Sensing Properties Of Biomass-based Carbon-metal (Co, Mn) Oxide Composites

Nowadays,the rapid development of the chemical industry has brought serious air pollution problems.NO₂gas is already an important pollution component,which not only leads to the formation of photochemical smog and acid rain,but also causes serious respiratory and nervous system diseases,which has a huge hazard on human health.Therefore,research and development of highly sensitive gas sensors to effectively detect NO₂concentration has become one of the important research issues in the field of monitoring pollutant gases,and it also has important practical application value and commercial development prospects.In recent years,biomass has become a high-quality alternative to carbon materials due to its rich yield,wide sources,and renewable advantages.The prepared carbon material has the advantages of low price,large specific surface area,and controllable biological structure,and can be used as adsorbents,catalysts,soil amendments and other fields.Therefore,this work selects hemp stalk,a biological waste,to replace porous carbon material by simply heat-treating it to derive BC material,and the bio-morphology MnO₂/BC and Co₃O₄/BC composite materials with biomass carbon as the template were synthesized by simple vacuum impregnation and CVD heat treatment.And through the use of SEM,TEM,XRD,BET and other characterization testing methods,the structure,morphology and composition of the prepared composite materials were analyzed and discussed,and the growth mechanism was also discussed.And assembled a gas sensor(piece),detected the gas sensitivity of the composite material at room temperature(RT),and carried out the following research work:First,different reagents were used to activate BC,Ni(NO₃)₂·6H₂O and KMnO₄were used as raw materials,and a simple hydrothermal and calcination method can be controlled to prepare a mesoporous biomass morphology of Ni-doped MnO₂composite.Material(MnNi-BC).The Ni-MnBC composite material with a hierarchical porous structure provides NO₂gas with adsorption-desorption and diffusion channels,and the doping of Ni makes the surface of MnO₂have more active sites and increases the degree of graphitization of BC,which enhances The rapid electron transfer ability;in addition,the activated BC promotes the growth of MnO₂along the(211)crystal plane orientation,which is beneficial to the generation of oxygen vacancies,provides more active sites,and enhances the gap between MnO₂and activated BC The synergistic effect of the impact on its sensing performance.Compared with MnBC and Ni2-MnBC,the optimized Ni5-MnBC sensor has the best gas sensitivity at room temperature:for100ppm NO₂,its gas sensitivity response value is 67.00,the response and recovery time are 8 and 27 s,and the detection limit It is 10 ppb.And it has good repeatability,continuous stability for 70 days,excellent selectivity and humidity resistance.Therefore,Ni5-MnBC can be considered as an excellent sensing material at room temperature.Secondly,on this basis,consider further solving the problem of slow response recovery time of the sensor at room temperature.Using Co(NO₃)₂·6H₂O and dimethylimidazole as raw materials,a biologically porous Co₃O₄/biochar composite material(CoBC)was designed and synthesized by simple vacuum impregnation and then high-temperature calcination.On the one hand,the uniform growth and dispersion of the porous Co₃O₄on the BC surface is beneficial to the adsorption-desorption and diffusion of the gas to be measured;on the other hand,the surface of the porous hollow concave Co₃O₄dodecahedron(PHCD Co₃O₄)provides a large number of active sites,and The graphitization degree of BC is effectively improved,and the ability of electron transfer is enhanced;in addition,the heterojunction and interface defects formed by PHCD Co₃O₄and BC also further improve the gas sensing performance.The optimized CoBC-700 sample has the best NO₂gas sensitivity at room temperature:the response to100 ppm NO₂reaches 34.1,the response time is 1.33 s,and the detection limit is as low as 10 ppb.And the CoBC-700 sensor also has 35 days of stability,good repeatability and excellent selectivity.Therefore,CoBC-700 is a good sensitive material for NO₂ sensors at room temperature.