Modification And Properties Of Methanol Gas-sensing Materials Based On Ag-LaFeO₃

Methanol（CH₃OH）is a flammable,colorless,highly volatile liquid that is harmful to human health.It is one of the commonly used raw materials in the chemical industry.Real-time monitoring of the concentration of methanol gas in the environment is necessary to ensure safety and human health.Among them,the methanol gas sensor is an economical,convenient methanol monitoring device that can be widely applied and has great development prospects.Compared with the detection of ethanol,acetone,formaldehyde,toluene,xylene,etc.,there are relatively few research reports on methanol gas sensors.Therefore,it is urgent to develop of a fast,reliable,and stable methanol sensor.Gas-sensitive materials are the core of gas-sensitive sensors.In this thesis,Ag-LaFeO₃ molecularly imprinted polymers（SLMs）are used as the matrix materials to adjust the morphology,construct p-n heterojunctions,use carbon quantum dots and single-atom modification methods for multiple modifications to obtain SLMs-based methanol gas-sensitive materials with high sensitivity,high selectivity and low operating temperature.At the same time,the corresponding gas-sensing mechanism is analyzed and researched to provide experimental and theoretical base for the practical application and development of methanol gas-sensing sensor.The main research contents and results are as follows:（1）The morphology of SLMs was adjusted by the template method and hydrothermal method,and SLMs semi-hollow spheres（SLMs SHSs）,SLMs core-shell spheres（SLMs CSMs）and SLMs fibers（SLMs fibers）were obtained,these materials with special morphologies are composed of nanoparticles（10-350 nm）,which has a higher porosity and specific surface area.Compared with pure SLMs,it is found that the adjustment of the morphology improves sensitivity of the material to methanol.Among them,the response value of SLMs CSMs to methanol is the best.At a working temperature of 215℃,the response to 5 ppm methanol reaches 33.7,and t_res and t_recare42 s/57 s.When the methanol concentration is as low as 1 ppm,the response value can also reach 15.2.By adjusting the morphology of SLMs,the crystal grain size of the material is reduced,the specific surface area and porosity of the material are increased,the gas sensor’s adsorption of oxygen and methanol gas is promoted,the sensitivity of the material to methanol gas is improved,and the working temperature of the sensor is reduced.（2）Based on SLMs CSMs gas-sensitive materials,the p-n heterojunctions of SnO₂,ZnO and SLMs CSMs（SnO₂/SLMs CSMs and ZnO/SLMs CSMs）were constructed by hydrothermal method,which accelerate the transmission of electrons in the gas-sensitive materials and shortens its response recovery time to methanol gas,while also improves the response value and reduces the working temperature.Compared with SLMs CSMs,the gas sensitivity of ZnO/SLMs CSMs to methanol is nearly doubled,the working temperature drops from 215℃to 99℃,and t_resand t_rec from 42 s/57 s to 7.5s/5.9 s.The construction of the heterojunction improves the transmission of electrons in the material,thereby improving the conductivity of the gas-sensitive material,and increasing the material’s response recovery time to methanol gas.（3）ZnO/SLMs CSMs are modified by B,N and B,N co-doped carbon quantum dots（BCQDs,NCQDs and BNCQDs）and Pt single atom to construct a double heterojunction.And because the surface of BCQDs,NCQDs and BNCQDs is rich in oxygen-containing groups and defects,as well as the spillover effect of Pt single atoms and high catalytic activity,the surface of the synthesized gas-sensitive material has abundant active sites and strong adsorption capacity for oxygen,which reduces the adsorption energy and activation energy barrier of material for oxygen and test gas.Its gas-sensing performance is as follows:the gas-sensitive material obtained by modifying ZnO/SLMs CSMs with BNCQDs and Pt,the response value to 5 ppm methanol increased to 640.63,while the operating temperature was reduced to 86℃,and the response value to 100 ppb methanol also reached about 40.The experimental results show that the introduction of BNCQDs and Pt effectively improves the response value of the material to methanol and reduces its detection limit and working temperature for methanol.The modification of ZnO/SLMs CSMs by CQDs co-doped with B,N and B,N leads to the formation of multiple heterojunctions such as p-n,p-p or n-n between the materials,which accelerates the carrier transport in the materials,thereby promoting the adsorption,diffusion and reaction of methanol gas on the surface of the material.When Pt single atom acts as a catalyst,it will reduce the adsorption activation energy of O₂molecules on the surface of the sample,and promote the reaction of methanol gas with negative oxygen ions,thus improving the sensitivity of the material to methanol gas.