Adsorption and visible-light-derived photocatalytic kinetics of organic dye on Co-doped titania nanotubes prepared by hydrothermal synthesis

A hydrothermal treatment combined with metal doping was employed to prepare highly porous Co-doped TiO2 nanotubes (TNTs) for enhancement of adsorption and visible-light-driven photocatalysis capabilities of basic violet 10 (BV10) from liquid phase. The specific surface area of prepared TNTs can reach the maximal value of ∼379 m2/g. These tubes are hollow scrolls with a typical outer diameter of about 10–15 nm, inner diameter 5–10 nm and length of several micrometers. The anatase-type of TNTs has an average Co-dopant concentration of 5 × 1020 ions/cm3, determined by an electron dispersive X-ray spectrometer. The adsorptive surface coverage on TNTs was found to be ca. 7.61–7.63%, showing a low affinity between BV10 molecules and TNTs. A pseudo-second-order reaction model was used to fit with the experimental data of adsorption and photocatalystic kinetic curves. The adsorption rate constant has one order higher than the photocatalytic rate constant, reflecting that the photocatalysis of the basic dye is the rate-determining step during the adsorption/photocatalysis process. These novel Co-doped TNTs are believed to be a promising candidate in a variety of photocatalysis applications because of the combination effect of a high porosity with a photocatalysis under visible illumination.