Degradation of polar and non-polar pharmaceutical pollutants in water by solar assisted photocatalysis using hydrothermal TiO2-SnS2

Photocatalytic performance of a hydrothermally obtained TiO2-SnS2-HT composite was evaluated for the degradation of polar and non-polar pharmaceuticals in water, diclofenac (DCF) and memantine (MEM) respectively, under simulated solar irradiation. Favourable action of SnS2 for band gap narrowing and consequent higher effectiveness of TiO2-SnS2-HT in comparison to TiO2-P25 benchmark, came forth in the case of DCF, which is prone to adsorption and subsequent h(+) attack under illumination. Subpar degradation of MEM was attributed to its' non-reactive structure and the lack of surface interactions in accordance with the density functional theory calculations, which indicated lower interaction energies for SnS2 and MEM than SnS2 and DCF. In comparison, the initial removal of DCF at pH 4 was 59.8% with 50% SnS2 wt.%, whereas the removal of MEM was <5.3%. After 60 min of treatment, TiO2-SnS2 with 50% SnS2 wt.% achieved DCF conversion of 76.21%, outperforming the benchmark TiO2-P25, however in the case of MEM the conversion was miniscule. Solar/TiO2-SnS2 treatment of DCF yielded a decrease of toxicity towards Vibrio fischeri whilst biodegradability remained low. The observed decrease in effectiveness of solar/TiO2-SnS2 treatment in the presence of water matrix constituents is mainly contributed to sulfates and phosphates, acting as h(+) scavengers.