Preparation, Modification, And Hydrogen Sensing Of TiO₂ Nanotubes Arrays

As a widely used clean energy source,H₂ has the characteristics of flammability and explosiveness and prone to fire and explosion accidents during production,transportation and storage,so it is especially necessary to effectively detect and monitor H₂.Semiconductor metal oxide gas sensors have been widely studied by scholars because of their low cost,stable physical and chemical properties,and wide source of materials,it is of great significance and research value to detect the initial leakage of H₂ by gas sensor.TiO₂ as a widely used semiconductor metal oxide material,is one of the most studied materials in the gas sensitive domain.In this paper,the anodization process was systematically studied,and the effects of water content in the reaction voltage,reaction time,and electrolyte concentration on the morphology of TiO₂ nanotubes were investigated,and the process for the synthesis of TiO₂ nanotubes was optimized.On the basis,anodized processes were used to prepare highly ordered TiO₂ nanotubes with a length of 3-4 μm and a diameter of 100 nm.By preliminary detection of six target gases,we found that TiO₂ nanotubes had the best selectivity for H₂,and systematically tested the gas-sensitive properties of H₂ in the air.In the temperature range of 200-350 ℃,the minimum detection temperature for hydrogen is 200 ℃,where the response to 1000 ppm H₂ is 21 and the lower limit of detection is 20 ppm.The optimum temperature of TiO₂ nanotubes for H₂ is 325 ℃,the response value to 1000 ppm H₂ reaches 459 and the response time is 2 s.However,the recovery time of TiO₂ nanotubes needs several hundred second.SnO₂@TiO₂ nanotubes samples were prepared by impregnation method,and 20-1000 ppm of H₂ was tested for gas sensitivity at 200-350 ℃.It was found that a small amount of SnO₂ load has significant gas sensitivity to H₂.As a result,with the compound amount continues to increase,the gas-sensing performance significantly decreases,and the immersed 5 mM TiO₂ nanotubes sample exhibits the best performance.For a 5 mM sample,the response to 300 ppm H₂ reached 953 at 275 ℃and the response time was only 5 s,compared with the performance of 0 mM sample,which exhibited a 15-fold larger response and 2-fold shorter response/recovery time than the pristine TiO₂ nanotubes at 275 ℃,and the optimal operating temperature was reduced by 75 ℃.The linear relationship between the response value and the response time in both logarithmic coordinates and H₂ concentration showed different power-law exponents before and after the～120 ppm concentration point,indicating that the gas-sensing mechanism changed before and after this.The superior gas sensing properties of SnO₂@TiO₂ nanotubes for H₂ are mainly attributed to the unique morphology and n-n heterojunction between TiO₂ and SnO₂.Finally,a summary of the thesis and prospects and recommendation for future research are presented.