Composite Modification Based On Lithium Lanthanum Titanate Nanomaterials With Ultra-fast And High Response To H₂S Gas

With the progress of industrialization and the economic development,more and more toxic gases appear in our daily life.Gas sensor can detect the concentration of toxic gas in real time and can play a great role in monitoring the gas environment.As a kind of flammable and explosive toxic gas,H₂S gas widely exists in our daily life.H₂S can not only pollute the environment and corrosion equipment causing irreparable economic losses,but also have great harm to people’s body.The 20-30 ppm concentration of H₂S can cause systemic symptoms,then cause slight conjunctivitis.When the concentration of H₂S exceeds 250 ppm,it will cause irreversible damage to human body.Therefore,it is very important to monitor H₂S gas in real time for human health and environmental protection.For the detection of H₂S gas,researchers have prepared a special perovskite material La_0.5Li _0.5TiO₃（LLTO）gas sensing material.But LLTO still has some shortcomings such as low response value and high working temperature.In view of the shortcomings of LLTO,this work uses LLTO as the base material,then makes the H₂S gas sensor with high sensitivity and low working temperature performance by combining semiconductor metal oxide.Because of the high sensitivity and low operating temperature but the long response time in H₂S detection.SnO₂was compounded with other gas-sensitive materials,frequently to improve the sensing characteristics of the material for H₂S.（1）LLTO-SnO₂ nano-composites with different composite ratios were prepared by solvothermal method.Not only a series of characterization methods were used to characterize the structure and phase composition of the composites,but also the gas sensing properties of the composites were tested by the gas sensor tester.And the gas sensing mechanism was studied through the characterization results.It was found that the content ratio of LLTO to SnO₂ is 1:1,that is to say,LLTO（0.50）-SnO₂（0.50）nanocomposite has a good response on 30 ppm H₂S.The minimum response temperature of the composite to H₂S is 160℃,and the optimal working temperature of the composite to H₂S is 260℃.At the optimal working temperature the sensitivity to 30 ppm H₂S reaches 19,and the response time can be reduced to 1 s.In addition,the response still has a high response at a lower concentration of H₂S gas（5 ppm）,and has good selectivity and cycle stability.LLTO-SnO₂ nano-composite can produce good gas sensing properties to H₂S,which is mainly due to the synergistic effect of surface oxygen defects and the n-n heterojuction structure.（2）At first,LLTO nano-materials were prepared by solvothermal method,and then LLTO-SnO₂ tubular nano-materials were prepared by electrospinning.The sensing performance of the composite nano-materials for H₂S gas was tested.The H₂S sensing mechanism of LLTO-Sn O2 composites was investigated by combining the characterization of the structure,morphology,elemental composition and energy band theory of the nanomaterials.The optimum working temperature of the composite is reduced to 160°C compared to the optimum working temperature of pure LLTO（340°C）.The maximum response values and response times for the four composite samples of LLTO-SnO₂（1:6）,LLTO-SnO₂（1:2）,LLTO-SnO₂（1:1）and LLTO-SnO₂（2:1）to 30 ppm H₂S gas at the optimum working temperature are 520/8.85 s,192/3.20 s,107/1.96 s,56/1.08 s.The response values of LLTO-SnO₂ composites to H₂S increased gradually with the increase in the proportion of SnO₂,while the response time became longer.The composites were found to have good selectivity and cyclic stability for H₂S.There are several reasons that LLTO-SnO₂ tubular structure nanomaterials have excellent sensing performance to H₂S gas:（1）LLTO-SnO₂ tubular structure nano-materials have high specific surface area.（2）LLTO-SnO₂ tubular structure nanomaterials have large initial potential of oxygen reduction,which makes it easier for oxygen molecules to combine with the electrons in the conduction band.（3）The n-n heterojunction structure is formed in LLTO-SnO₂ tubular nanomaterials,which can produce greater resistance differences.