Research On Preparation And Properties Of Toluene And Xylene Gas-sensing Materials Based On Ag-LaFeO₃

With the development of economy,air pollution is increasingly serious.Among these pollutant gases,toluene and xylene gases are carcinogenic,therefore,detection of these toxic and harmful gases at the low concentration has drawn considerable attention in the scientific community and attached great significance for environmental safety and human health.Low response,poor selectivity and high working temperature are main limitations for practical application of toluene and xylene gas sensors.Therefore,not only are gas-sensing materials with good selectivity,high response,low energy consumption and low cost necessary,but also exhibiting vital application prospect.In this paper,Ag-LaFeO3 nanoparticles(ALFO NPs)were prepared by microwave-assisted synthesis combined with molecular imprinting techniques to obtain toluene gas sensing materials and devices with high sensitivity,high selectivity,low operating temperature and excellent stability.First,toluene was chosen as a template molecule,the ALFO gas sensing material which was previously reported by our group,was used as a cross-linker to prepare a highly selective gas-sensing material with specific recognition function for toluene.Meanwhile,the effects of different types and amounts of functional monomers on the structure and properties of ALFO-based xylene gas sensing materials were investigated.The micro/nanostructured molecular imprinted ALFO NPs were prepared by the lotus leaf template method.The composition,structure.and morphology were characterized by various characterization methods.The gas-sensing properties were tested through gas-sensing tester.The main research contents are listed as below:(1)Porous Ag-LaFeO3 nanostructures synthesized in microwave-assisted route have small particle size and no by-products.The best performance of ALFO NPs shows response of 36.2 to 5 ppm xylene at an optimum working temperature of 99?.In addition,there are no significant responses to other interfering gases such as ethanol,acetone,formaldehyde,benzene and xylene.The microwave-assisted synthesis process can provide a higher synthesis rate.(2)ALFO NPs synthesized by sol-gel method were modified by molecular imprinting technique to fabricate a xylene sensor.Methacrylic acid(MAA)and hydroxyethyl methacrylate(HEMA)were selected as functional monomers,respectively.The response of the fabricated sensor to 5 ppm xylene(36.2)is about 30 times higher than that of the modified ALFO at 99°C.The response time and recovery time were 114 s and 55 s,respectively.Molecular imprinting provides a new method to modify ALFO-based gas sensing materials.(3)The porous micro/nanostructured ALFO NPs were successfully synthesized using lotus leaf as a bio-template.Co:mbined with molecular imprinting technology,the selectivity of gas sensor is improved by unique recognition site of xylene and larger specific surface area.ALFO NPs exhibit relatively high response(Rg/Ra = 16.76 to 10 ppm),fast gas response and recovery(68 s and 36 s)towards xylene at a working temperature of 125?.The sample also shows excellent humidity stability and long-term stability.This result provides a convenient and environmentally friendly new method for the detection of xylene gas.