Towards a large scale aqueous sol-gel synthesis of doped TiO2: Study of various metallic dopings for the photocatalytic degradation of p-nitrophenol

In this paper, an easy aqueous sol-gel synthesis developed previously by Mahy et al. [1] is adapted to produce highly active TiO2 catalysts doped with Fe3+, Ag+, Cu2+, Zn2+, Cr3+, Mn2+, and Co2+ ions and Pt metallic nanoparticles. Samples are characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), Mossbauer spectroscopy, transmission electron microscopy (TEM), nitrogen adsorption-desorption measurements and diffuse reflectance spectroscopy measurements. Results show that the samples are composed of anatase-brookite TiO2 nanoparticles with a spherical shape and mean diameter of around 5-8 nm and a surface area of between about 150-250 m(2) g(-1). In each doped sample, the dopant is present in the form added during the synthesis, given that the sample has not undergone any particular treatment. Photoactivity tests show improvement in catalyst activity for Fe3+, Ag+, Cu2+, Zn2+, and Al3+ ion and Pt metallic nanoparticle dopants, while a decrease of activity is obtained for Cr3+, Mn2+ and Co2+ ion dopants. For some dopants, the activity of TiO2 doped with metallic ions and synthesized from the aqueous sol-gel process is equal or superior to the activity of the commercial photocatalyst Degussa P25. Some mechanisms are proposed to explain these modifications of activity with doping. Furthermore, cost comparison at laboratory scale showed that Zn and Cu nitrate salt dopings are clearly less expensive for a halogen light (UV/visible) or low energy light enhanced catalyst and may be considered for industrial applications. Using this method, a large scale Zn-doped TiO2 photocatalyst is synthesized with properties homologous to the lab-scale product. Results show that the aqueous sol-gel synthesis developed previously can be easily adapted for doping in order to produce an up-scalable synthesis. (C) 2016 Elsevier B.V. All rights reserved.