Solar photocatalytic degradation of propyl paraben in Al-doped TiO2 suspensions

Abstract

The photocatalytic degradation of propyl paraben (PP) over Al-doped TiO2 suspensions under simulated solar radiation was investigated. The catalysts were prepared by a co-precipitation method with the dopant content varying from 0.04 to 2wt%. The catalyst with 0.04wt% dopant was more effective than the rest, presumably due to a more efficient separation of the photogenerated charges associated with a greater crystallite size. Subsequent experiments with this catalyst showed that the rate of PP degradation (i) generally increased with increasing catalyst concentration in the range 125–1000mg/L, and decreasing PP concentration (in the range 210–1687μg/L), and (ii) was impeded at alkaline conditions (pH range 3–9). Moreover, degradation in pure water was always faster than in actual (i.e. bottled water, treated wastewater, surface water) or synthetic (i.e. pure water spiked with humic acid, t-butanol, chloride and bicarbonate ions) water matrices, pinpointing the competitive behavior of non-target water constituents. Conversely, the addition of persulfate had a beneficial effect on the rate of degradation since it acted both as electron acceptor and a source of extra sulfate radicals.