Improved visible photocatalytic activity of TiO₂ nanoparticles to use in submerged membrane photoreactor for organic pollutant degradation

In this study, photocatalytic activity of TiO₂ nanoparticles under visible light was improved and the modified photocatalysts were used in a pilot-scale continuous submerged photocatalytic membrane reactor (SPMR) for decolorization of Reactive Orange 29 (RO29) under visible light irradiation. The Taguchi method was used to optimize the activation of TiO₂ nanoparticles. Effect of the activation precursors (urea, thiourea, ammonium thiocyanate and sulfanilic acid), TiO₂: precursors w/w ratio (1:1–1:6), activation time (1–7 h) and activation temperature (350–500 °C) on the visible photocatalytic efficiency of the nanoparticles was investigated to achieve maximum decolorization efficiency. X-ray diffraction, scanning electron microscopy, Fourier transform infrared and diffuse reflection spectroscopy analysis were used to characterize the photocatalysts. The results presented that the doping source and the doping source:TiO₂ ratio had the most and the lowest effect on the TiO₂ activation process, respectively. When urea was applied as an activation precursor with mass ratio of 6:1 to TiO₂ at 450 °C for 5 h, the decolorization efficiency of 84.2% was obtained in a continuous SPMR system. The RO29 degradation intermediates were analyzed by gas chromatography coupled with mass spectroscopy technique.