Silylation and sulfonation of structured supported catalysts active in the decoloration of azo-dyes under visible light

Abstract

Structured silica woven fabrics have been derivatized with functional groups able to anchor by exchange of Fe3+-ions and TiO2 showing a stable performance during the visible light induced decoloration of the Orange II azo-dye. The kinetics and efficiency of the decoloration mediated by the catalytic loaded silica fabrics with Fe3+-ions were seen to be much higher than found with homogeneous Fenton reagents (Fe3+/H2O2) with the equivalent Fe3+ content. The same was observed for derivatized membranes where TiO2 has been anchored as the active catalyst surface species. In the case of the silica Fe3+-ions loaded fabrics, the decoloration was studied as a function of the amount of H2O2 oxidant added in solution, the intensity of the applied visible light and the concentration of the initial Orange II. In the case of the silica-TiO2 fabrics the decoloration kinetics was observed to be a function of the O2 present in solution. In the case of the derivatized Fe3+ and TiO2 loaded silica fabrics, the decoloration process presented three common features: (a) the decoloration process was observed only in the presence of light pointing to a photo-induced process in both cases, (b) the decoloration was also observed to be truly catalytical following repetitive cycles for Orange II, and finally (c) the decoloration processes were limited by the mass transfer kinetics taking place at the surface of both derivatized fabric catalyst and proceeded with about the same kinetics in both cases. The numerical values for the diffusion distance of the radicals species OH and HO2 as well as the decrease in the concentration of radicals away from the silica fabric during the photodegradation of Orange II is estimated by the Smoluchowski diffusion equation.