Nanostructured N-doped TiO2 coated on glass spheres for the photocatalytic removal of organic dyes under UV or visible light irradiation

For the applications of photocatalytic processes aimed to the removal of pollutants from wastewater, slurry reactors that employ aqueous suspension of titanium dioxide nanoparticles are not suitable due to the inconvenient and expensive separation of photocatalyst from treated wastewater. To overcome this drawback, the nanosized titanium dioxide needs to be immobilized on a transparent support. In the present paper, recyclable visible-light active N-doped TiO2 photocatalyst was immobilized on glass spheres using a simple sob gel method. The decrease of N-doped TiO2 crystallites size was obtained with the addition of Triton X-100 as surface-active agent. The effect of sol gel synthesis temperature was investigated on the crystallization and crystallites size of N-doped TiO2 obtaining that the best temperature for the immobilization through dip-coating process was found at 20 degrees C. The removal of methylene blue (MB) and eriochrome black-T (EBT) in aqueous solutions was tested to evaluate the photocatalytic activity of the immobilized photocatalyst. The optimization of N-doped TiO2 amount on glass spheres was evaluated using MB as model pollutant. In particular, it was found that until four dip-coating steps, the photocatalytic activity increased. Moreover, the N-doped TiO2 immobilized on glass spheres (NDc) can be easily separated from the reaction mixture, and maintained excellent photocatalytic activity and durability after four cycles. Finally, NDc showed a high photocatalytic activity in the decolorization and mineralization of MB and EBT both under UV and visible light irradiation. (C) 2015 Elsevier B.V. All rights reserved.