Visible light photocatalytic degradation of pollutants in surface water, Limpopo, South Africa

Abstract: A novel silver and vanadium co-doped titanium dioxide (Ag, V-TiO2) photocatalyst was achieved by a simple sol-gel hydrothermal method. The co-doped Ag, V-TiO2 photocatalyst exhibited high photocatalytic activity as compared to synthesised titanium dioxide (TiO2), silver doped titanium dioxide (Ag-TiO2) and Vanadium dope titanium dioxide (V-TiO2). The co-doped Ag, V-TiO2 illustrated a shift in the absorption edge, enhancing the visible light absorption capacity. The optical absorption of co-doped Ag, V-TiO2 achieved a reduced band gap energy (Eg) of 2.2eV as compared to Ag-TiO2 (2.8eV) and V-TiO2 (2.3eV), while TiO2 obtained a band gap energy of 2.9eV. The codoped photocatalyst inherited morphological and structural compositions that depicted the lattice fringes for both anatase and rutile in its crystalline phase. This analysis was in good agreement with results obtained by X-ray diffraction (XRD) characterisation techniques. Co-doped Ag, V-TiO2 showed excellent photocatalytic abilities under visible light irradiation. The degradation of Methylene blue (MB) was achieved within the first 15min. The kinetic study for the degradation of (MB) followed the pseudo-first order reaction. More interestingly, it was found that the photocatalytic degradation performance had a direct relation with the intensity plane ratio corresponding to [101] / [110]. The effects of co-doping showed a shift in spectrum to the visible light region. This was evident in the study of binding energies presented by X-ray photoelectron spectroscopy (XPS). Thus, the effects of co-doping TiO2 showed achieving well desirable reduction in the band gap energy and enhancements in the photocatalytic activity, reporting excellent removal rates of 99.33%. The evaluation of photocatalytic degradation of pollutants in water from River water in Limpopo (Mathibeng) and Mpumalanga Witbank (Ezinabeni) gave a clear indication that the synthesized Ag, V co-doped TiO2 photocatalyst was effective in removing nitrate, nitrites, humic substance, aromatics, Trihalomethanes (THM) and organic concentration. Furthermore, the GC-MS analysis of the water samples proved the organic pollutants removal with a removal efficiency of 77.84%. These finding open up a solution for the treatment of surface and river water where the concentration of pollutants are low.M.Ing. (Mechanical Engineering