Hydrogen Sulfide Gas Sensing Performance Based On Li_0.5La_0.5TiO₃

According to the"Three-Year Action Plan to Win the Blue Sky Defense War"promulgated by the State Council,air pollution,especially the monitoring and treatment of toxic and harmful gases is one of the key tasks.From time to time,relevant parties have reported that toxic and harmful gases cause explosions or leakage caused by casualties in daily life and operations.It is necessary to monitor the air quality at all times and to alert and prevent toxic and harmful gas leaks in time.Hydrogen sulfide?H₂S?gas is a colorless,highly toxic and harmful gas that exists in many fields closely related to humans.At present,metal oxide semiconductor H₂S gas sensing materials with tungsten oxide,titanium dioxide,zinc oxide,tin oxide and iron oxide as the core have been extensively studied.Although these materials have better sensitivity to H₂S gas and the preparation process is relatively mature,the response/recovery time to H₂S gas is generally longer.Due to the serious harm of H₂S,research and development of gas-sensitive materials that can quickly respond to H2S are particularly important.In recent years,perovskite structural materials?strontium titanate,barium titanate,copper calcium titanate,etc.?have also been gradually applied in the field of gas sensing.Li_0.5La_0.5TiO₃?LLTO?material is often used as an inorganic solid electrolyte in solid-state lithium ion batteries.Due to its specific cubic perovskite structure and the instability of the A site,there is a large surface vacancy concentration here.This can provide more active sites for gas adsorption.In this paper,the LLTO with a specific cubic perovskite structure was prepared by the solvothermal method for the first time in the field of hydrogen sulfide sensing.The microstructure design of the material was changed by changing the preparation conditions of pure LLTO.The heterogeneous structure is built to study the gas sensing performance of the sensor.The details are as follows:?1?Li_0.5La_0.5TiO₃?LLTO?with specific structure was prepared by solvothermal method,and then the different preparation methods and reaction parameters were compared to obtain the best LLTO preparation scheme.At the same time,the paper also studied the The effect of preparation conditions on its H₂S gas sensing performance.The study found that the lithium lanthanum titanate prepared by the solvothermal method has a porous spherical shape and high purity,and shows good response performance to H₂S gas.Through the comparison of the results,it was found that the reaction was carried out for 6 h at a solvothermal temperature of 150?,and then sintered at a temperature of 700? for 5 h at a rate of 5?/min to obtain hollow microspheres with a hollow surface and porous surface.The structure provides sufficient diffusion channels to H₂S gas adsorption.At the optimal working temperature of 340?,the response/recovery rate to 30 ppm hydrogen sulfide gas is0.9 s/0.9 s,the highest response value is 4.25,and it also shows a higher selectivity to hydrogen sulfide gas.?2?In order to improve the response sensitivity and response temperature,the energy band structure is controlled by Fe doping.The study found that Fe-doped modified LLTO hollow porous nanomicrosphere sensors showed an n-type response to hydrogen sulfide in a wide temperature range?160?400??.Under optimal conditions,the response of 5 wt%Fe-doped LLTO sensor at 300? to 30 ppm hydrogen sulfide reaches 19.8,and the response and recovery time at this time is 0.5s/0.7 s.In addition,the detection limit of 5 wt%Fe-doped LLTO sensor is as low as100 ppb,and it has good repeatability and long-term stability.The main reason for the enhanced gas sensing performance of Fe-doped LLTO nanomicrospheres:the specific surface area of the sample after doping increases,providing more reaction sites for the gas and the reaction medium;after doping,more oxygen vacancies are generated and enhanced The chemical absorption of O₂and the generation of adsorbed oxygen(O^-and O^2-);doping leads to a reduction in the band gap of LLTO,which promotes the transfer of its conduction band charge to the adsorbed gas molecules,forming with oxygen in the air More adsorbed oxygen ions increase the bending degree of the electron depletion layer on the surface of the material,which helps to increase the resistance of the material,thereby increasing the response performance of the sensor.?3?Pure LLTO hollow porous micro-nano structure materials were prepared by solvothermal method,and?-Fe₂O₃/LLTO heterojunction materials with different mass ratios were prepared by compounding?-Fe₂O₃,comparing the LLTO and?-Fe₂O₃/LLTO sensors Hydrogen sulfide sensitive characteristics.The experimental results show that the optimal working temperature?180??of?-Fe₂O₃/LLTO gas sensor is lower than that of LLTO?340??.And the operating temperature range of?-Fe₂O₃/LLTO gas sensor is between 50?340?,close to room temperature response,compared with pure LLTO?260?400??,it has more excellent low temperature response performance.Under optimal conditions,at the optimal response temperature of 180?,the response value of?-Fe₂O₃/LLTO to 30 ppm hydrogen sulfide is 27.9,which is 6.5 times that of pure LLTO.The?-Fe₂O₃/LLTO gas sensor has a wider operating temperature range,a lower operating temperature and a response temperature close to room temperature,a higher response and a lower detection limit.The excellent performance of?-Fe₂O₃/LLTO is attributed to the synergistic effect of?-Fe₂O₃and LLTO and the interface effect of n-n homo-junction.The combined effect of the two can effectively improve the gas-sensitive characteristics of the material.