Preparation Of Semiconductor Metal Oxides Sensing Materials And Their Gas Sensing Performance

Semiconductor metal oxides gas sensors were widely used in the field of gas monitoring due to high sensitivity,low cost,excellent stability and other advantages.So far,SMOs gas sensors were facing the challenges such as high operating temperature,longer response/recovery time and response to be promoted,which can be in demand.Therefore,it is significant to prepare a series of gas sensitive materials which have the advantage of high response values,lower operating temperature,shorter response/recovery time,superb selectivity and excellent long-term stability.In this study,the microstructure of SMOs gas sensor materials derived from transition metal polyol compounds and layered hydroxides possessing the advantages of adjustable component and morphology as well as stable structure are controlled by means of heterostructure engineering,aliovalent ion doping,and morphological engineering,which not only reduce the grain size,improve the pore volume and special surface area,enrich the number and activity of active sites in the surface of SMOs materials,but also optimal the electric structure and potential barrier of SMOs to facilitate the reaction between oxygen and test gas.In this way,we will obtain the gas sensor with lower operating temperature,high sensitivity,quick response/recovery speed and excellent selectivity and stability.The main content and research results were as follows:First,The hierarchical structure Zn/In-gly precursors with different Zn/In molar ratio of 5%、10%、20%and 30%were prepared via solvothermal method and hierarchical ZnO-In2O3 n-n heterostructures were obtained after calcination at 350℃。The structural compounds and microstructure morphology of ZnO-In2O3 n-n heterostructures were analyzed by a series of characterization,suggesting ZnO inhibited the growth of In2O3 crystals,improved the special surface area(137.1 m2g-1)of In2O3 crystals.In addition,the formation of n-n heterostructure increased the chemically absorbed oxygen content and change the resistance as a donor.Gas-sensitive performance test results showed that 20%ZnO/In2O3 sample exhibited to 50 ppm of ethanol at the optimum working temperature highest response value,which reached 170,and shorter response/recovery time(35/46 s).Otherwise,20%ZnO/In2O3 sample shows a wide detection range,excellent selectivity and superb long-term stability.The exist of ZnO-In2O3 heterostructure leads to smaller grain size,larger special surface area,electronic effect and structural effect(oxygen vacancies).Secondly,the salicylic anion-intercalated Sn-doped cobalt layered hydroxide whiskers were synthesized by urea decomposing method,and were calcined at 500℃ to obtain mesoporous cobalt oxide whiskers,The microstructures and morphologies of the Sn-doped Co3O4 were characterized by XRD,SEM,HRTEM,BET and XPS.Furthermore,Gas-sensitivity performance tests showed that the response value of 3%Sn/Co3O4 to 50 ppm of toluene gas reached 53.8 at 240℃,which is approximate 7.6 times higher than that of the pure Co3O4.Surprisingly,it is worth noting that the response and recovery time of the 3%Sn/Co3O4 to 50 ppm of toluene gas were 65 s and 64 s at 240℃,respectively.In addition,3%Sn/Co3O4 exhibited low detection limit,brilliant selectivity and superb long-term stability.The superb gas-sensing performance of 3%Sn/Co3O4 whiskers can be attributed to larger specific surface area,smaller grain size and decrease in concentration of holes,which can significantly promote the formation of active oxygen species in surfaceFinally,the hierarchical structure salicylic anion-intercalated Ti-doped cobalt layered doubled hydroxides with doping amount of 0.5%,1%,3%and 5%were prepared by urea decomposing method.After calcination at 450℃ and 500℃ mesoporous hierarchical structure assembled from Ti-doped Co3O4 nanosheets were prepared.The pure Co304 and Ti-doped Co304 hierarchical structure were analyzed by XRD,SEM,HRTEM,BET and XPS This study found that the Ti-doped Co3O4 hierarchical structure obtained from different calcian temperature has the smaller grain size,larger specific surface area(compared to pure Co3O4)and abundant mesopore structure.More interestingly,the amount of chemical absorbed oxygen specials in the surface of Co3O4 prepared from 450℃ is remarkably increasing,while the sample obtained from 500℃has the higher quantity of defect oxygen specials.In addition,the gas sensing test shows that gas sensor based on 3%Ti/Co3O4-450℃ exhibits the highest response value to xylene gas.The response value of the 3%Ti/Co3O4-450℃ to 50 ppm of xylene gas reached 64.5 at the optimal working temperature of 210℃,which is approximately 10 times than that of encounter oxides.And 1%Ti/Co3O4-500 gas sensor shows superior response to 50 ppm of toluene gas at the optimal working temperature of 240℃,reaching the response value of 56.3,which was about 9.6 times than that of Co3O4-500℃.These two gas sensors perform excellent repeatability after five cycles and remarkable stability after one-month test.It indicated that the excellent performance of Ti-doped Co3O4 is attributed to the decrease in the charge-carrier concentration caused by aliovalent ion doping,larger specific surface area and higher quantities of chemical oxygen species.In the end,the tuning of selectivity and sensitivity methylbenzene can be achieved by the control over the reforming of different defect structure and catalytic activity of Ti-doped Co3O4 through regulatable Ti concentration and calcian temperature.