Photocatalytic treatment of phenol with visible light irradiation

The problem of pollution reduction in aqueous streams containing refractory compounds is of great importance for many industries. Phenol and phenolic substances have attracted more attention because of their toxicity and frequency of use in industrial processes. In the past decade, considerable attention has focused on photocatalytic degradation of phenol. Titanium dioxide (TiO ₂) has proven to be an effective photocatalyst for the oxidative decomposition under UV irradiation. However, the relatively wide gap of TiO ₂ limits further application of the material in the visible light region (λ>400 nm). The aim of the present research is to investigate the feasibility of removing phenol by the N-doped TiO₂ catalysts and S-doped TiO₂ catalysts adsorbed with ferric iron which are responsive to visible light irradiation. With these intentions, degradation of aqueous phenol solution with photocatalyst powders was investigated under both UV and visible light irradiation. 12-19% TOC removal efficiencies were achieved in 6 hr reaction time for N-doped catalysts under visible light irradiation at pH 3.0 and the degradation rates for the mineralization were found to vary between 0.022 and 0.048 mol l^-1 hr^-1. S-doped catalysts proved to be more efficient as compared to the N-doped catalysts. The degradation rates for the mineralization under visible light were calculated as 0.083 and 0.120 mol l^-1 hr^-1 for S-doped TiO₂ catalysts adsorbed with different percentages of ferric iron (5wt% and 10wt%) at pH 3.0, respectively. S-doped catalysts were also effective under UV light source with removal efficiencies up to 70%.