Study On Preparation And Gas Sensitivity Of Titania Nanotubes

Titania is a very important functional material with wide applications. Titania nanotubes own stronger adsorption ability because of its small size and bigger specific surface area. In addition, it can make impurities of sensor surface and prolong the service life of sensor if applied in sensors. Therefore, there is a good application prospect and research value of titania nanotubes in gas sensor field. In this paper, the preparation process and gas sensitivity of titania nanotubes were studied.In our experiment, anatase was used as start material, and the nanotubes were synthesized by hydrothermal treatment. By comparison tests, the effect of different factors such as reaction time, reaction tempreture, alkali concentration on formation of nanotubes were studied, the best fabrication process was selected. with the reaction time prolong, the length of nanotubes increase gradually, but the length become short and break if the reaction time up to 48h; with the reaction tempreture increase, more and more nanotubes appear, only when the temperature up to 210℃, all powder transformed into nanotubes; alkal concentration is a sensitive factor to nanotube formation, nanotubes can be obtained only in suitable alkal concentration, 10M is suitable; high quality nanotubes can be made when powder quantity and alkal proportion is 0.008. The optimal processing parameters got as follows: m_TiO2/v₍NaOH0(g/ml)≈0.008, reaction temperature is 210℃, the reaction time is 24h, the alkali concentration is 10M.The effect of hydrochloric acid concentrations on morphology and composition of prepared products was studied. Results shows that: the acid stability of nanotubes made in the best process is not very good, with the acid concentration increases, its length become shorter, continuity become bad and fragment appears as well; furthermore, the nanotubes may be disaapeared if the acid concentration is too high. The composition of nanotubes washed by HCl is the H₂Ti₃O₇.The formation mechanism was explored as well through the study of the influence of each affect factors on nanotubes'morphology. The formation mechanism of nanotubes can be concluded as follows: during hydrothermal treatment, the anatase powder reaction with NaOH firstly, then disintegrated into layer under high temperature, high pressure, then the layer curled into tube, finally the tube become longer through dissolving-absorption mechanism.The thermal stability of nanotubes was studied. we found that: the thermal stability of products is good at lower temperature,when the temperature is lower than 400℃, there is no change of its morphology and composition; the nanotubes become cluster and shorter when heat treatment tempreture is higher than 400℃, though its composition has no change compared with no heat treated product.Resistance gas sensors were made by water washing products, and gas sensitivities to toluene were measured. The gas sensitivities of no doped gas sensor to 5ppm and 10ppm toluene are 30% and 35% respectively, the response time are 2250s and 2150s, the recovery time are 1500s and 1250s; the gas sensitivities of doped gas sensor to 10ppm toluene are 25%, the response time and recovery time are 23s and 20s respectively.