Study On Preparation And Properties Of Lithium Lanthanum Titanate/Oxide Semiconductor Composite H₂S Gas Sensing Materials

In recent years,more and more attention to people’s health and environmental protection.The toxic and harmful gases produced by industrial pollution have brought serious air pollution,which is a silent threat to human health and life safety.As a high-risk gas in daily production and life,hydrogen sulfide（H₂S）gas is flammable,colorless,and smelly.When exposed to a certain concentration of H₂S,it will damage human health.Therefore,the real-time,fast,efficient and accurate detection of H₂S is the key to ensuring the safety of production and human life.So far,metal oxide semiconductors（such as Sn O₂,WO₃,ZnO,Ce O₂and In₂O₃,etc.）gas sensing materials have been widely studied.As a new type of cubic perovskite structure gas sensing material,La_0.5Li_0.5Ti O₃（LLTO）has a fast response to H₂S,however,it has the problems of high working temperature and low sensitivity.In terms of this issue,LLTO-metal oxide semiconductor heterojunction sensing materials were conducted,to improve their H₂S sensitivity performance and obtain hydrogen sulfide gas sensor with excellent comprehensive gas sensing performance.Also,the gas sensing mechanism was discussed.The specific research contents are as follows:（1）ZnO and LLTO nano-spherical composite materials（SZTO）with different molar ratios were prepared by a simple solvothermal synthesis method.SZTO’s composition,morphology and structure were analyzed by XRD,SEM,XPS,BET,UV-vis,ORR and other testing and characterization methods.The results show that the surface morphology and size of the composite materials are similar to LLTO,but the energy band gap is narrowed and the oxygen reduction capacity is enhanced,which are beneficial to improve the gas sensing performance.The pure LLTO and SZTO composite materials were applied to the hydrogen sulfide gas sensor.And comparing the gas sensing properties of the two sensors to H₂S.The results showed that the sensitivity of the SZTO composite sensor is increased from 4.09 to 7.99compared with the LLTO sensor,and the optimal working temperature is reduced by100°C,while showing good repeatability,stability and selectivity.（2）The nano-spherical LLTO precursor was prepared by solvothermal synthesis method firstly,and then composited with nano-ZnO by the impregnation method,to prepare a gas sensitive material（JZTO）with n-n homo-heterojunction structure of ZnO and LLTO,and then tested the H₂S gas sensing performance.The results show that after composite ZnO,the optimal working temperature of the JZTO composite sensor was reduced from 340°C to 240°C compared with the LLTO sensor,and the sensitivity reaches 10.63,which is 2.6 times the highest sensitivity of pure LLTO.The significantly improved sensing performance of JZTO composite materials can be mainly attributed to the synergistic effect of n-n homo-heterojunction,increased surface oxygen vacancy concentration,improved specific surface area,enhanced oxygen reduction performance and reduced forbidden band width.（3）LLTO-In₂O₃nanorod composite materials were prepared by the combination of solvothermal synthesis and electrospinning technology with substance ratios of 2:1,1:1 and 1:2,respectively.The series of composite materials were systematically tested for hydrogen sulfide sensitivity in the working temperature range of 50～400°C.The results show that the initial response temperature of the LLTO-In₂O₃composite sensor is 50°C.Compared with pure LLTO sensor,the initial response temperature is reduced by 150°C,which greatly broadens the working temperature range and basically realizing the accurate detection of hydrogen sulfide at low temperature.The optimal working temperature of LLTO-In₂O₃（1:1）is reduced from 340°C to 160°C.And the safety and stability of the sensor are enhanced.Meanwhile,under the optimal conditions,the maximum response value of the LLTO-In₂O₃composite sensor to 50ppm H₂S reaches 116.61,which is 28.51 times that of the pure LLTO sensor.At the same time,the comprehensive sensing performance is significantly improved.This research provides a new direction for the further development of sensors with high safety factor and overall excellent performance,which will show great potential in subsequent practical applications.