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Bismuth complex oxides, in particular, bismuth tungstate, have recently attracted attention as promising photocatalytic materials for water treatment processes. In the present work, photocatalytic bismuth tungstate films were prepared by pulsed direct current (DC) reactive magnetron sputtering of Bi and W targets in an Ar/O 2 atmosphere onto spherically-shaped glass beads. The uniform coverage of the substrate was enabled by the use of oscillating bowl placed underneath the magnetrons. The atomic ratio of Bi/W was varied through the variation of the power applied to the magnetrons. The deposited coatings were analyzed by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy and atomic force microscopy. The photocatalytic properties of the films were studied via the methylene blue (MB) degradation process under artificial (fluorescent light) and natural (sunlight) irradiation, and compared to the photocatalytic performance of titanium dioxide coatings deposited onto identical substrates. The results showed that the photocatalytic performance of bismuth tungstate and bismuth oxide-coated beads was superior to that exhibited by TiO 2 -coated beads. Overall, reactive magnetron co-sputtering has been shown to be a promising technique for deposition of narrow band gap bismuth-based semiconducting oxides onto irregularly-shaped substrates for potential use in water treatment applications.

Several studies have reported the adverse effects of recalcitrant compounds and emerging contaminants present in industrial effluents, which are not degradable by ordinary biological treatment. Many of these compounds are likely to accumulate in living organisms through the lipid layer. At concentrations above the limits of biological tolerance, these compounds can be harmful to the ecosystem and may even reach humans through food chain biomagnification. In this regard, advanced oxidation processes (AOPs) represent an effective alternative for the removal of the pollutants. This study focused on the AOP involving the use of ultraviolet radiation in homogeneous and heterogeneous systems. Based on the literature review, comparisons between natural and artificial light were established, approaching photoreactors constructive and operational characteristics. We concluded that the high availability of solar power in Brazil would make the implementation of the AOP using natural solar radiation for the decontamination of effluents feasible, thereby contributing to clean production and biodiversity conservation. This will serve as an important tool for the enforcement of environmental responsibility among public and private institutions.

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In this study, photo-Fenton systems using visible light sources with iron and ferrioxalate were tested for the DOC degradation and decolorization of textile wastewater. Textile wastewaters originated after the dyeing stage of dark-colored tissue in the textile industry, and the optimization of treatment processes was studied to produce water suitable for reuse. Dissolved organic carbon, absorbance, turbidity, anionic concentrations, carboxylic acids, and preliminary cost analysis were performed for the proposed treatments. Conventional photo-Fenton process achieved near 99 % DOC degradation rates and complete absorbance removal, and no carboxylic acids were found as products of degradation. Ferrioxalate photo-Fenton system achieved 82 % of DOC degradation and showed complete absorbance removal, and oxalic acid has been detected through HPLC analysis in the treated sample. In contrast, photo-peroxidation with UV light was proved effective only for absorbance removal, with DOC degradation efficiency near 50 %. Treated wastewater was compared with reclaimed water and had a similar quality, indicating that these processes can be effectively applied for textile wastewater reuse. The results of the preliminary cost analysis indicated costs of 0.91 to 1.07 US$ m for the conventional and ferrioxalate photo-Fenton systems, respectively. Graphical Abstract ᅟ.