Drugs degrading photocatalytically: Kinetics and mechanisms of ofloxacin and atenolol removal on titania suspensions

Abstract

The conversion of the antibiotic ofloxacin and the ß-blocker atenolol by means of TiO2 photocatalysis was investigated. Irradiation was provided by a UVA lamp at 3.37×10-6einstein/s photon flux, while emphasis was given on the effect of catalyst type and loading (50–1500mg/L), initial substrate concentration (5–20mg/L), initial pH (3–10) and the effect of H2O2 (0.07–1.4mM) as an additional oxidant on substrate conversion and mineralization in various matrices (i.e. pure water, groundwater and treated municipal effluent). Conversion was assessed measuring sample absorbance at 288 and 224nm for ofloxacin and atenolol, respectively, while mineralization measuring the dissolved organic carbon. Degussa P25 TiO2 was found to be more active than other TiO2 samples for either substrate degradation, with ofloxacin being more reactive than atenolol. Conversion generally increased with increasing catalyst loading, decreasing initial substrate concentration and adding H2O2, while the effect of solution pH was substrate-specific. Reaction rates, following a Langmuir–Hinshelwood kinetic expression, were maximized at a catalyst to substrate concentration ratio (w/w) of 50 and 15 for ofloxacin and atenolol, respectively, while higher ratios led to reduced efficiency. Likewise, high concentrations of H2O2 had an adverse effect on reaction, presumably due to excessive oxidant scavenging radicals and other reactive species. The ecotoxicity of ofloxacin and atenolol to freshwater species Daphnia magna was found to increase with increasing substrate concentration (1–10mg/L) and exposure time (24–48h), with atenolol being more toxic than ofloxacin. Photocatalytic treatment eliminated nearly completely toxicity and this was more pronounced for atenolol.