Sonochemical degradation of ofloxacin in aqueous solutions.

The use of low frequency (20 kHz), high energy ultrasound for the degradation of the antibiotic ofloxacin in water was investigated. Experiments were performed with a horn-type ultrasound generator at varying applied power densities (130-640 W/L), drug concentrations (5-20 mg/L), hydrogen peroxide concentrations (0-100 mM) and sparging gases (air, oxygen, nitrogen and argon). In general, conversion (which was assessed following sample absorbance at 288 nm) increased with increasing ultrasound energy and peroxide concentration and decreasing initial drug concentration. Moreover, reactions under an argon atmosphere were faster than with diatomic gases, possibly due to argon's physical properties (e.g. solubility, thermal conductivity and specific heat ratio) favoring sonochemical activity. Overall, low to moderate levels of ofloxacin degradation were achieved (i.e. it never exceeded 50%), thus indicating that radical reactions in the liquid bulk rather than thermal reactions in the vicinity of the cavitation bubble are responsible for ofloxacin degradation.

Synthesis and photocatalytic activity of boron-doped TiO(2) in aqueous suspensions under UV-A irradiation.

Boron-doped TiO(2) photocatalysts were synthesized employing a sol-gel method. Boric acid was used as the boron source and titanium tetra-isopropoxide as the TiO(2) precursor, both dissolved in isopropanol. Nominal boron to titanium atomic ratios were in the range 0 to 4%. After the hydrolysis step, two different procedures for the recovery of TiO(2) were followed, based on either centrifugation of the resulting reaction mixture or evaporation of the solvent under reduced pressure, both followed by a subsequent calcination step performed at 400 or 500 degrees C. The photocatalytic efficiency of the synthesized photocatalysts was assessed by measuring the photocatalytic mineralization of dichloroacetic acid in aqueous suspensions under UV-A irradiation and it was compared to the corresponding efficiency of the commercial Degussa P 25 TiO(2). Photocatalytic efficiency of the synthesized catalysts was higher for the boron-doped TiO(2) synthesized at 2% boron to titanium nominal atomic ratio, centrifuged after the hydrolysis step followed by calcinations at 400 degrees C. However, all photocatalysts synthesized in this work showed lower photocatalytic activity than Degussa P 25 TiO(2), thus highlighting the need of further improvements of the proposed method.

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

The conversion of the antibiotic ofloxacin and the beta-blocker atenolol by means of TiO(2) photocatalysis was investigated. Irradiation was provided by a UVA lamp at 3.37x10(-6)einstein/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 H(2)O(2) (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 TiO(2) was found to be more active than other TiO(2) 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 H(2)O(2), 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 H(2)O(2) 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.