Unexpected Enhancement of Electrocatalytic Nature of Ti/(RuO2)x–(Sb2O5)y Anodes Prepared by the Ionic Liquid-Thermal Decomposition Method

Research trends in the development of anodes for electrochemical oxidation of wastewater

The review focuses on the recent development in anode materials and their synthesis approach, focusing on their compatibility for treating actual industrial wastewater, improving selectivity, electrocatalytic activity, stability at higher concentration, and thereby reducing the mineralization cost for organic pollutant degradation. The advancement in sol–gel technique, including the Pechini method, is discussed in the first section. A separate discussion related to the selection of the electrodeposition method and its deciding parameters is also included. Furthermore, the effect of using advanced heating approaches, including microwave and laser deposition synthesis, is also discussed. Next, a separate discussion is provided on using different types of anode materials and their effect on active •OH radical generation, activity, and electrode stability in direct and indirect oxidation and future aspects. The effect of using different synthesis approaches, additives, and doping is discussed separately for each anode. Graphene, carbon nanotubes (CNTs), and metal doping enhance the number of active sites, electrochemical activity, and mineralization current efficiency (MCE) of the anode. While, microwave or laser heating approaches were proved to be an effective, cheaper, and fast alternative to conventional heating. The electrodeposition and nonaqueous solvent synthesis were convenient and environment-friendly techniques for conductive metallic and polymeric film deposition.

On the behaviour of Atrazine removal from water using fabrics as anodes and cathodes

This study examines the degradation of atrazine (ATZ) with Pt-modified textile electrodes using an electrochemical method that is comparatively studied in two electrochemical cell configurations: cells with separated anodic and cathodic compartments (divided configuration); and without any separation (undivided configuration). The influence of the presence of chloride ions was studied. The best results were obtained when an undivided cell was used. The morphology and composition of the dispersed Pt coatings were analyzed using field emission scanning electron microscopy (FESEM) and Energy Dispersive X-Ray Analysis. The FESEM analyses confirmed that the textile surface was effectively modified by the electrocatalytic material. High performance liquid chromatography, gas chromatography mass spectrometry, and spectroscopic methods were used to follow the evolution of major oxidation products. Total organic carbon, chemical oxygen demand, and total nitrogen were used to evaluate the degradation efficiency of treated aqueous solutions. The experimental results obtained indicate that the efficiency of the electrochemical treatment was high with a low energy consumption when using electrodes based on textile materials, such as anodes or as cathodes (in particular, in electrolysis without compartment separation). All these can be produced at very competitive prices.

Electrochemical and/or microbiological treatment of pyrolysis wastewater

Electrochemical oxidation may be used as treatment to decompose partially or completely organic pollutants (wastewater) from industrial processes such as pyrolysis. Pyrolysis is a thermochemical process used to obtain bio-oil from biomasses, generating a liquid waste rich in organic compounds including aldehydes and phenols, which can be submitted to biological and electrochemical treatments in order to minimize its environmental impact. Thus, electrochemical systems employing dimensionally stable anodes (DSAs) have been proposed to enable biodegradation processes in subsurface environments. In order to investigate the organic compound degradation from residual coconut pyrolysis wastewater, ternary DSAs containing ruthenium, iridium and cerium synthetized by the 'ionic liquid method' at different calcination temperatures (500, 550, 600 and 700 °C) for the pretreatment of these compounds, were developed in order to allow posterior degradation by Pseudomonas sp., Bacillus sp. or Acinetobacter sp. bacteria. The electrode synthesized applying 500 °C displayed the highest voltammetric charge and was used in the pretreatment of pyrolysis effluent prior to microbial treatment. Regarding biological treatment, the Pseudomonas sp. exhibited high furfural degradation in wastewater samples electrochemically pretreated at 2.0 V. On the other hand, the use of Acinetobacter efficiently degraded phenolic compounds such as phenol, 4-methylphenol, 2,5-methylphenol, 4-ethylphenol and 3,5-methylphenol in both wastewater samples, with and without electrochemical pretreatment. Overall, the results indicate that the combination of both processes used in this study is relevant for the treatment of pyrolysis wastewater.

Treatment of actual effluents produced in the manufacturing of atrazine by a photo-electrolytic process

The photo-assisted electrochemical degradation of a real effluent of the atrazine manufacturing process containing atrazine, simazine, hydroxy-triazine and propazine was carried out galvanostatically using a pilot-scale tubular flow reactor prototype containing DSA^® and Ti as cathode. The effluent was mainly characterized by a high amount of NaCl, required in the synthesis route used, and it was used as taken in the factory. The variables for process optimization were the current density (3.0, 6.0, and 9.0 mA cm^-2) and flow rate (300 and 3,000 L h^-1). These later values produces laminar and turbulent flow regimes, with Reynolds numbers of 1,100 and 11,000, respectively. None of the four organics contained in the waste is refractory to the photo-electrochemical treatment and they are depleted with the photo-electrolytic technology using large current densities and appropriate electric charge passed. Both direct electrochemical process and mediated anodic oxidation occur during the treatment. First process occurs at turbulent flow condition and low current densities, while the chemical oxidation process happens at laminar flow condition and high current densities. Atrazine and propazine are efficiently removed at laminar flow conditions, with an almost total depletion for the largest current densities. On the contrary, simazine is efficiently removed in turbulent flow conditions and intermediate current density, with removals higher than 90% for 20 kWh m^-3. These results have great significance because they demonstrate the applicability of the electrochemical technology in the treatment of real industrial wastes with a cell specially designed to attain high efficiency in the removal of pollutants.