Gas Sensing Properties Of Zeolites/P-type Oxide Semiconductors Composites Materials

P-type metal oxides have great research value in the field of gas sensing,but they have room for improvement in selectivity and response value.How to improve their gas sensing performance has become the focus of research.Zeolite has attracted more and more attention in the field of gas sensors in recent years because of its porous channel framework,large specific surface area structure,molecular sieve,catalysis,adsorption and other characteristics.In this paper,ZSM-5,HY,NaA zeolite were compounded with CuO and NiO by coating,mixing and excessive impregnation.NiO was doped with Fe and then compounded with zeolite.The effects of zeolite types,compounding methods,Si/Al ratio and metal oxide types on improving gas sensing properties of P-type metal oxides were studied.The main work is as follows:The CuO gas sensor was modified by ZSM-5,HY and NaA zeolites in three compound ways.The composites were characterized by XRD and SEM,and tested the gas sensitivity of methanol,ethanol,formaldehyde,acetone,toluene,benzene and ammonia.The results show that CuO has a high response to ethanol and acetone.Compared with CuO,only the response of NaA/CuO composite elements to toluene was slightly inhibited,and the response to the best gas-ethanol was increased up to 2.5 times;the response of ZSM-5/CuO composite elements to toluene was significantly increased,and the response to toluene was increased up to 11 times.Among them,the response of 2:1(mass ratio C:Z)component to acetone and toluene were increased and to other gas decreased which improved the gas selectivity;the response of HY/CuO composite components to toluene and acetone increased significantly,and the response to acetone was increased up to 3.2 times.NiO gas sensors were modified by ZSM-5,HY and NaA zeolites in three compound ways.Gas sensing results show that NiO has a highest response to methanol.Compared with NiO,the optimum gas for all zeolite/NiO composite elements is methanol,and the response to methanol was increased up to 1.7-2 times.In NaA/NiO and HY/NiO composites,impregnation is the best compound method;in ZSM-5/NiO composites,the response value of silicon-aluminium ratio 470 to gas is higher than that of silicon-aluminium ratio 70.NiO was doped with 3% Fe(NiO-Fe).NiO-Fe gas sensors were modified by four kinds of zeolites in three compound ways.Gas sensing results show that the optimum gas for Fe-doped NiO element is ethanol,no inhibiting gas there,and the response is 3 times of NiO.Compared with NiO-Fe,the optimum gas for NaA/NiO-Fe,HY/NiO-Fe composite elements is ethanol,no inhibiting gas there,and the response to ethanol was increased up to 1.3-1.4 times.In ZSM-5/NiO-Fe composite elements,only the response of impregnated composite elements to toluene was increased.The response of mixed and coated composite elements to methanol and acetone increases remarkably,no inhibiting gas there.The response value of acetone was increased up to 5.2 times and the response value of methanol was increased up to 2 times.All the results were combined with XRD,SEM,EDS,BET and other characterization methods.The gas sensing properties of zeolite/P-type metal oxide composites were explained in terms of gas sensing model,doping mechanism,zeolite adsorption,catalysis and so on.