Free-standing open-ended TiO2 nanotube membranes and their promising through-hole applications

Abstract

Free-standing open-ended TiO2 nanotube membranes were fabricated by raising voltage for a short time at the end of anodization process. Benefiting from its semiconducting nature and distinctive through-hole structure, the applications of open-ended TiO2 nanotube membranes on flow-through photocatalysis and nanoreactor were demonstrated. As for flow-through photocatalysis, the photocatalytic property of TiO2 is beneficial to reduce the concentration of RhB solution during RhB molecules diffuse through open-ended TiO2 nanotube membrane. As for nanoreactor application, CdS@TiO2 core–shell nanocables were successfully fabricated by a simple paired-cell reaction. A possible formation mechanism for the growth of core–shell structure was discussed on the basis of a series of electron microscopy characterization results. In addition, we evaluated the photocatalytic activity of CdS@TiO2 samples synthesized at different reaction time through the degradation of rhodamine B under simulated sunlight irradiation. It was found that the CdS@TiO2 samples synthesized at 24h exhibited about 100% enhanced photocatalytic activity as compared to bare TiO2 nanotubes, while the CdS@TiO2 samples synthesized at 48h (core–shell nanocables) had the equivalent photocatalytic activity to the bare TiO2 nanotubes. Such behavior that the photocalytic activity changes with CdS loading amount results from a compromise between a larger amount of light absorption and a lower efficiency of charge separation, as well as limited diffusion by channel blocking higher degree of CdS loading.