| Metal oxide semiconductor（MOS）materials have the characteristics of fast response,low cost and high reliability,and are emerging candidates for monitoring toxic and harmful gases.ZnO is an n-type semiconductor with a band gap of 3.37 e V,which is widely used in the detection of chemical gases such as C6H7N,CH3COCH3,NO2,HCHO,CH4,CO and H2S because of its abundant source,low price,green and non-toxic,high conductivity and good stability.In2O3,another typical n-type semiconductor,has a wide direct bandgap of 3.6 e V and variable conductivity sensitive to oxygen vacancies.Therefore,wurtzite ZnO crystals and In2O3 rutile structure crystals perform well in gas sensitivity.However,its own limitations hinder its further development and application in the field of sensing.In particular,the construction of heterostructures is an effective way to improve its sensing performance.There are two main methods for constructing heterostructures:one is to prepare heterojunctions by contacting two metal oxides;the other is the synthesis of heteroatom-doped materials.In this paper,a series of ZnO and In2O3 nanomaterials with different morphologies were obtained by solvothermal method,and their growth mechanism and sensing performance were studied.The main research contents include the following aspects:（1）Metal oxide sensors face the challenge of high response and fast recovery at low operating temperatures for the detection of toxic and flammable hydrogen sulfide（H2S）gases.Herein,novel In-doped ZnO with sunflower-like structure and tunable surface properties were rationally synthesized.The substitutional In atom in ZnO crystal can dramatically enhance their concentration of oxygen vacancies（Ov）,and the In-ZnO sites are responsible for fast recovery,and the formation of sub-stable sulfide intermediates give rise to the high response towards H2S.As a result,the response of the optimized 4In-ZnO sensor is 3538.36 to 50 ppm H2S at low operating temperature of 110°C,which is 106 times higher than that of pristine ZnO.Moreover,the response time and recovery time to 50 ppm H2S are 100 s and 27 s,respectively,with high selectivity and stability.First-principles calculations revealed that 4In-ZnO with rich Ov exhibited higher adsorption energy for H2S molecule than pristine ZnO,resulting in effortless H2S detection.Our work lays the foundation for the rational design of highly sensitive gas sensors through the precise doping of atoms in oxygen-rich vacancies in semiconductor materials.（2）Hetero-atom doping is an effective way to improve the sensing performance of metal oxide semiconductor gas sensors.However,the synergistic effects generated from hetero-atom substitution in In2O3 lattice and the relationship between the fine surface structure and sensing performance is still ambiguous.Here,Ni substitution in shuttle-like In2O3 nanoparticles have been successfully synthesized,and the materials are fabricated as gas sensor to detect ammonia,which is a toxic molecule that is harmful for human healthy.We find the 2 wt%Ni-doped In2O3 NPs exhibit high sensitivity（Ra/Rg=2569.42 towards 50 ppm NH3 at 140°C）,achieving 34 folds improvement compared with pristine In2O3 NPs.The sensor also shows good long-term stability,high selectivity and fast response/recovery（23/10 s）.Detail structural analysis illustrate the substitution of Ni in rh-In2O3 phase and surface O-（ad）species neighboring the substitution sites are recognized as the active sites,and the reactive oxygen species and surface Br?nsted acidity can be dramatically enhanced after Ni modification,which contribute to the improvement of sensing performance.Our work illustrate the synergistic effects of hetero-atom doping on the sensing performance and pave the way for design of high performance sensing materials.（3）The rational construction of metal oxides heterojunctions is an effective method to enhance their gas-sensing performance of metal oxide semiconductors.However,La2O3-In2O3 heterojunctions can be hardly obtained by conventional impregnation and thermal treatment because the harsh conditions are required for the ex-solution of La3+in In2O3lattice.Herein,MOF-derived synthesis method is applied to synthesize the La2O3-In2O3 heterojunctions,and the uniform hollow La2O3-In2O3nanotube can be obtained after annealing at 450°C.Additionally,the La2O3-In2O3heterojunctions are further fabricated as gas sensors to monitor the accurate concentration of TEA molecules.Compared with the pristine In2O3 and La doped In2O3（La-In2O3-RW）samples,La2O3-In2O3 heterojunctions exhibit the best sensing performance for 50 ppm TEA at low working temperature of 120°C（Ra/Rg=458.13）,which is 4.8 times and 1.9 times higher than pristine In2O3and La-In2O3-RW.Moreover,the sensors also exhibit good long-term stability and high selectivity at low working temperature.The excellent sensing performance can be attributed to the synergistic effect between La2O3 and In2O3species including the modified electronic structure,the formation of electron depletion layer,the wide distribution of acid sites and O-2（ad）and O-（ad）species. |
