Fixed-bed reactor packed with pumice-supported TiO2 for the treatment of polluted water by solar-driven photocatalytic oxidation.

A bench-scale tubular photo-reactor was built to evaluate the solar-driven TiO2-based photocatalytic degradation of synthetic polluted water samples. The reactor was designed as a compound-parabolic-collector and operated in batch mode using TiO2 P25 immobilized on a bed of pumice. The immobilization of TiO2 on pumice was carried out using a facile dip impregnation method followed by heat treatment. The obtained material was characterized by SEM, EDS, XRD, and nitrogen adsorption. It was possible to impregnate up to 68.5 mg of TiO2 per gram of pumice stones of 8-14 mm. Conversions of up to 35-40 and 62-69%, after 4 h of treatment and UV doses of 20.8 ± 3.5 kJ L-1, were achieved when the catalyst was used immobilized on pumice stone and in the form of a suspension, respectively. The stability and reusability of the catalyst-coated support was tested through a series of consecutive photocatalytic experiments. After four consecutive runs, the immobilized catalyst showed a decrease in its photoactivity leading to removal levels of 23%.

Decoration of alumina hollow fibers with zinc oxide: improvement of the photocatalytic system for methylene blue degradation.

The photocatalytic degradation of methylene blue (MB) in aqueous solutions and under visible light was investigated with dispersed and supported zinc oxide (ZnO) as catalysts. The ZnO catalyst was successfully impregnated in asymmetric alumina hollow fibers by the simple vacuum-assisted dip-coating method. According to energy-dispersive analyses, the photocatalyst was homogenously distributed in the substrate. A strong correlation was observed between the initial dye concentration and the efficiency of the supported photocatalyst. For the initial MB concentration of 5 mg L-1 and catalyst dosage of 1 g L-1, the photocatalytic system with both dispersed and supported catalysts reached almost 100% of MB degradation. The photocatalytic process followed the pseudo-first-order kinetic model, and, for the initial MB concentration of 5 mg L-1, the apparent constants were 0.05415 and 0.00642 min-1 for suspended and supported catalysts, respectively. The treated MB solutions presented low phytotoxicity to the germination Lactuca sativa seeds with germination indexes greater than 80% after irrigation with the treated MB solutions. The produced supported ZnO catalyst showed suitable photocatalytic stability even after several reuse cycles.