Preparation, Characterization And Catalytic Performance Of TiO₂Nanotubes-Based Catalysts

TiO2nanotubes have attracted considerable attention because they possess excellent physical and chemical properties, such as low cost, nontoxicity, high photoactivity, high chemical stability, nanotubular morphologies and higher surface areas, and been widely used in many applications such as photolectric materials, photocatalytic materials and catalyst support. However, many defects, such as low efficiency of solar energy utilization, wide bandgap, quick recombination of photogenerated electron-hole pairs, restricted TiO2nanotubes for use. Moreover, TiO2nanotubes prepared by hydrothermal process had bad thermal stability as catalysts. It needs considerable work for researchers to improve TiO2structure and catalytic performancs by reducing the bandgap, inhibiting the recombination of photogenerated electron-hole pairs and increasing TiO2nanotubes thermal stability. To overcome the drawbacks of TiO2mentioned above, TiO2nanotubes supported noble metal and metallic oxide were prepared and improved the photocatalytic activities for degradation of organics, oxidation of ethanol to acetaldehyde and CO2photoreduction. TiO2nanotubes supported amorphous Co-B catalysts were prepared via WI-CRP and used for cyclohexene hydroformylation. Due to high surface area, optical structure and special electronic, and high thermal stability, g-C3N4supported Cu2O was used to investigate the catalytic performance of CO oxidation. The primary work was as follows:Highly photo-stable palladium-loaded TiO2nanotubes (Pd/TNTs) were prepared by a simple photo-decomposition method and characterized with ICP, XRD, UV-Vis, DRS, TEM, XPS, PL, N2adsorption-desorption and photocurrent measurement. TEM images showed that the samples had a tubular structure. XPS results revealed that most of the palladium was present as Pd0. The photocatalytic performance was evaluated by monitoring the catalytic activity for the degradation of methyl orange solution under both UV and simulated sunlight irradiation. Pd/TNTs with0.3wt%Pd displayed higher activity than P25. The active species in the photocatalytic process were investigated by using different types of active species scavengers. h+was the major reactive species in the photodegradation over the Pd/TNTs.Ag2O-loaded TiO2nanotubes (Ag2O/TNTs) were prepared via deposition-precipitation and characterized with SEM, TEM, XPS and UV-vis. The photocatalytic performance was evaluated by monitoring the catalytic activity for the degradation of methyl orange solution under both UV and simulated sunlight irradiation. The influence of Ag2O content on catalytic performance of Ag2O/TNTs was also discussed. Ag2O/TNTs with10.7wt%displayed the highest photoactivity. Ag2O nanoparticles as electron capture agent were loaded on TNTs, which can inhibit the recombination of photogenerated electron-hole pairs. However, Ag2O could be reduced by the photogenerated electrons from TiO2nanotubes under UV irradiation, indicating that Ag2O had bad photostability. Photocatalytic selective oxidation of ethanol to acetaldehyde was investigated under UV. The influences of Ag2O content and reaction time on catalytic performance of Ag2O/TNTs were discussed. The optimal reaction condition is t=10h, Ag2O content=10.7wt%, the highest acetaldehyde yield is63.9mmol. TiO2nanotubes were used to investigate the photocatalytic activities for CO2photoreduction. It can be found that there would be formed an amount of reducing Ti3+on the surface of TNTs, when the reaction system was added in glucose under Ar or CO2atmosphere.g-C3N4was prepared by a simple pyrolysis of urea and characterized with XRD and FT-IR. The influence of calcination temperature on catalytic performance of g-C3N4was discussed. The results indicated that the optimal calcination temperature is540℃. Two procedures were utilized for preparing g-C3N4/TNTs and evaluated by monitoring the catalytic activity for the degradation of methyl orange. Cu2O/g-C3N4were prepared via liquid phase deposition-precipitation and characterized with XRD, TEM, SEM and N2adsorption-desorption. According to the XRD and TEM,(111) crystal plane is in a dominant position in Cu2O and Cu2O/g-C3N4. The catalytic performances for the degradation of phenol, the absorpotion of methyl orange and CO oxidation were preliminary discussed. The ratio of Cu2O and g-C3N4is4:10exhibiting the best catalytic activity. TiO2nanotubes supported amorphous Co-B catalysts (Co-B/TNTs) were prepared via WI-CRP. The catalysts were characterized with TEM, XPS, TPD, nitrogen adsorption and so on. The catalytic performances and stabilities of Co-B/TNTs for hydroformylation of cyclohexene as well as the influence factors, such as reaction media, Co loading, etc. were investigated. The Co-B/TNTs not only exhibited better catalytic performances in ether than in acetone and alcohol, but also showed higher activities and stabilities than TiO2powder supported amorphous Co-B under the same reaction conditions. The reuse of Co-B/TNTs was also tested, and the results showed that the used catalysts maintained high catalytic activity.