The great versatility of semiconductor materials and the possibility of generation of electrons, holes, hydroxyl radicals, and/or superoxide radicals have increased the applicability of photoelectrocatalysis dramatically in the contemporary world. Photoelectrocatalysis takes advantage of the heterogeneous photocatalytic process by applying a biased potential on a photoelectrode in which the catalyst is supported. This configuration allows more effectiveness of the separation of photogenerated charges due to light irradiation with energy being higher compared to that of the band gap energy of the semiconductor, which thereby leads to an increase in the lifetime of the electron-hole pairs. This work presents a compiled and critical review of photoelectrocatalysis, trends and future prospects of the technique applied in environmental protection studies, hydrogen generation, and water disinfection. Special attention will be focused on the applications of TiO 2 and the production of nanometric morphologies with a great improvement in the photocatalyst properties useful for the degradation of organic pollutants, the reduction of inorganic contaminants, the conversion of CO 2 , microorganism inactivation, and water splitting for hydrogen generation.

Treatment of real effluents from industries using AOPs stands to be an imperative task of crucial importance yet quite huge a challenge largely given the nature of complexity of these wastewaters. The present work sought to develop a versatile system aimed at the treatment of real wastewater using a bubbling annular reactor, which enables us to test the efficiency of photolysis; photocatalysis, photoelectrocatalysis and direct ozonation using oxygen or ozone as gas flow. A TiO2 nanotubes electrode was used as photocatalyst in photocatalytic and photoelectrocatalytic measurements with and without coupling with ozonation under pH 3.0 and pH 8.0 leading to 50% of color removal after 60 min reaction. However, the results indicated 90% of color removal upon the bubbling of ozone after 15 min of treatment. A synergistic effect was observed in all experiments using the AOPs in the presence of ozone under both pH values. Interestingly though, 85% of decolorization was obtained through direct ozonation without any change in the effluent following 10 min of treatment. The results were discussed in terms of electric energy per order and were compared to those reported previously. For real textile wastewater, ozonation appears to be a promising candidate for full-scale effluent decolorization.

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A B S T R A C TSurface water contamination by dyes released from a variety of industries is an environmental problem of great concern. However, electrochemical oxidation is a promising alternative for water treatment. In this paper, we studied the electrochemical oxidation of Rhodamine B (RhB) dye on the Ti/RuO 2 -IrO 2 (DSA ® ) and SnO 2 anodes comparing their efficiencies. The effect of some parameters, such as current density, initial pH (pH 0 ), nature, concentration of electrolyte and temperature at the electrochemical oxidation was investigated evaluating the decolorization and the chemical oxygen demand (COD) removal at optimal conditions. Complete decolorization of RhB was achieved in the presence of chloride ions at different times using both electrodes. An optimum efficiency was obtained at pH 6.5, T = 25°C. Also, the current density of 40 mA cm −2 using the DSA electrode in NaCl 0.05 mol L −1 + Na 2 SO 4 0.1 mol L −1 mixture solution as a supporting electrolyte, 100% color removal and 61.7% chemical oxygen demand removal after 90 min of electrolysis were achieved. DSA showed better performance than SnO 2 in wide operating conditions and was proved to be more cost-effective and more efficient. The effectiveness of the degradation is explained by indirect electrochemical oxidation, where in the presence of chlorides electrolyte leads to the electro-generation of strong oxidant species, such as Cl 2 and ClO − ions, improving the efficiency of treatment at both electrodes.The DSA has been classified as 'active' or 'non-active' depending on

Photoelectrocatalytic oxidation (PEC) is known to be a powerful technique employed with the aim of promoting organic degradation. Its efficiency is nonetheless found to be dramatically decreased when applied in highly concentrated effluent treatment owing to the reduced transparency which minimizes the photons reaching the semiconductor surface. In light of that, the present work seeks to describe a novel combination of photoelectrocatalysis and ozonation (O 3 + PEC) techniques, aiming at achieving a faster decolorization of a highly concentrated solution and a higher rate of mineralization. The Acid Yellow 1 dye (AY1), widely used in cosmetics was chosen as a colorful solution model. TiO 2 nanotubes electrode was used as photoanode in an annular bubble reactor operating at 2.0 V with UV-B irradiation in the presence of 1.25 × 10 −4 mol min −1 of O 3. The main factors interfering in the O 3 + PEC process were optimized through UV/vis spectrophotometry, total organic carbon (TOC) and mass spectrometry measurements. After 20 min of treatment using the combined system, 100% of decolorization was observed while a total mineralization was seen following 60 min of treatment even in effluents containing 100 ppm AY1. Concomitantly, the combined system (O 3 + PEC) showed higher decolorization rate constant and lower energy consumption compared to the other techniques, showing that O 3 + PEC is a successful, efficient and cost-effective alternative for water treatment.

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