Adsorption and Degradation Kinetics of Methylene Blue on As-prepared and Calcined Titanate Nanotubes

Abstract

Titanate nanotubes were prepared by hydrothermal synthesis, followed by Titanate nanotubes were prepared by hydrothermal synthesis, followed by proton exchange, and calcined at 250°C for 2h. The properties of prepared nanotubes were investigated with field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), adsorption-desorption N2 isotherms and UV-Vis diffuse reflectance spectroscopy (DRS). As-prepared sample displayed strongly aggregated nanotubes with crystal structure of H2Ti2O5×H2O. Calcination yielded with loss of interlayer water and partial transformation of nanotubes to anatase phase. Adsorption and photocatalytic decomposition of methylene blue, used as a model pollutant, on as–prepared and calcined titanate nanotubes have been studied. It was established that calcination at 250°C for 2h improves the adsorption and photocatalytic properties of titanate nanotubes. It was shown that pseudo–second–order model was the most appropriate to describe adsorption of methylene blue on titanate nanotubes. Affinity toward methylene blue of 48.45mg g-1 and 95.24mg g-1 has been established for as-prepared and calcined titanate nanotubes, while equilibrium adsorption was attained in 120min. Adsorption process is controlled by intraparticle diffusion and surface sorption in both samples, but the contribution of surface sorption is greater for the calcined sample. The pseudo-first-order kinetic is an acceptable model for photocatalytic dye degradation process on titanate nanotubes. It was shown that the calcination slightly increased the photocatalytic activity of titanate nanotubes.