Application of Ti/RuO2–Ta2O5 electrodes in the electrooxidation of ethanol and derivants: Reactivity versus electrocatalytic efficiency

Electrochemical Fenton-based treatment of tetracaine in synthetic and urban wastewater using active and non-active anodes

The electrochemical degradation of tetracaine hydrochloride has been studied in urban wastewater. Treatments in simulated matrix with similar ionic composition as well as in 0.050 M Na₂SO₄ were comparatively performed. The cell contained an air-diffusion cathode for H₂O₂ electrogeneration and an anode selected among active Pt, IrO₂-based and RuO₂-based materials and non-active boron-doped diamond (BDD). Electrochemical oxidation with electrogenerated H₂O₂ (EO-H₂O₂), electro-Fenton (EF) and photoelectro-Fenton (PEF) were comparatively assessed at pH 3.0 and constant current density. The pharmaceutical and its byproducts were oxidized by OH formed from water oxidation at the anode surface and in the bulk from Fenton's reaction, which occurred upon addition of 0.50 mM Fe²⁺ in all media, along with active chlorine originated from the anodic oxidation of Cl^- contained in the simulated matrix and urban wastewater. The PEF process was the most powerful treatment regardless of the electrolyte composition, owing to the additional photolysis of intermediates by UVA radiation. The use of BDD led to greater mineralization compared to other anodes, being feasible the total removal of all organics from urban wastewater by PEF at long electrolysis time. Chlorinated products were largely recalcitrant when Pt, IrO₂-based or RuO₂-based anodes were used, whereas they were effectively destroyed by BDD(OH). Tetracaine decay always obeyed a pseudo-first-order kinetics, being slightly faster with the RuO₂-based anode in Cl^- media because of the higher amounts of active chlorine produced. Total nitrogen and concentrations of NH₄⁺, NO₃^-, ClO₃^-, ClO₄^- and active chlorine were determined to clarify the behavior of the different electrodes in PEF. Eight intermediates were identified by GC-MS and fumaric and oxalic acids were quantified as final carboxylic acids by ion-exclusion HPLC, allowing the proposal of a plausible reaction sequence for tetracaine mineralization by PEF in Cl^--containing medium.

Electrochemical decolorization of methyl red by RuO2-IrO2-TiO2 electrode and biodegradation with Pseudomonas stutzeri MN1 and Acinetobacter baumannii MN3: An integrated approach

Textile effluent consists of enormous quantities of toxic dyes, which are being discharged into natural aqueous system and thus contaminate the water quality. Hence it is important to develop an eco-friendly and cost effective technology to treat the dyes contaminated wastewater. In this research, an integrated approach of electrochemical oxidation (EO) and biodegradation process (BP) was studied of methyl red (MR) dye. In EO, RuO₂-IrO₂-TiO₂ is used as anode and titanium mesh electrode as cathode. This was followed by BP of the treated EO effluent. Various parameters viz., pH (5-10), sodium chloride concentrations (NaCl) (1-5 g L^-1) and current density (10-30 mA cm²) were optimized. The results of the EO showed 99.96% of MR decolorization within 10 min at pH of 5, NaCl of 2 g L^-1 and current density of 30 mA cm². The EO treated MR was further treated by BP Pseudomonas stutzeri MN1, Acinetobacter baumannii MN3 and mixed consortia of MN1 and MN3. The out of three treatments, the results of mixed consortium BP showed 90% removal of COD at the end of 24 h. The phytotoxic evaluation using Vigna radiata seeds confirmed the toxicity of untreated MR solution, whereas, 100% germination was observed in treated (biodegraded) MR solution. Overall these results evidenced that MR dye was completely decolorized and mineralized by EO and BP within 10 min and 24 h respectively. Hence, this integrated approach can be used as an effective degradation method to treat dyes in the textile industry.

Potentiometric RuO2-Ta2O5 pH sensors fabricated using thick film and LTCC technologies

The paper reports on the preparation, properties and application of potentiometric pH sensors with thick film RuO2-Ta2O5 sensing electrode and Ag/AgCl/KCl reference electrode screen printed on an alumina substrate. Furthermore, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temperature cofired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental composition, and microstructure of the films were investigated by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2-12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li(+), Na(+) and K(+) as interfering ions. The applicability of the sensors for pH measurement of river, tap and distilled water, and some drinks was also tested.

Sequential electrochemical treatment of dairy wastewater using aluminum and DSA-type anodes

Dairy wastewater is characterized by a high content of hardly biodegradable dissolved, colloidal, and suspended organic matter. This work firstly investigates the performance of two individual electrochemical treatments, namely electrocoagulation (EC) and electro-oxidation (EO), in order to finally assess the mineralization ability of a sequential EC/EO process. EC with an Al anode was employed as a primary pretreatment for the conditioning of 800 mL of wastewater. A complete reduction of turbidity, as well as 90 and 81% of chemical oxygen demand (COD) and total organic carbon (TOC) removal, respectively, were achieved after 120 min of EC at 9.09 mA cm(-2). For EO, two kinds of dimensionally stable anodes (DSA) electrodes (Ti/IrO₂-Ta₂O₅ and Ti/IrO₂-SnO₂-Sb₂O₅) were prepared by the Pechini method, obtaining homogeneous coatings with uniform composition and high roughness. The (·)OH formed at the DSA surface from H₂O oxidation were not detected by electron spin resonance. However, their indirect determination by means of H₂O₂ measurements revealed that Ti/IrO₂-SnO₂-Sb₂O₅ is able to produce partially physisorbed radicals. Since the characterization of the wastewater revealed the presence of indole derivatives, preliminary bulk electrolyses were done in ultrapure water containing 1 mM indole in sulfate and/or chloride media. The performance of EO with the Ti/IrO₂-Ta₂O₅ anode was evaluated from the TOC removal and the UV/Vis absorbance decay. The mineralization was very poor in 0.05 M Na₂SO₄, whereas it increased considerably at a greater Cl(-) content, meaning that the oxidation mediated by electrogenerated species such as Cl₂, HClO, and/or ClO(-) competes and even predominates over the (·)OH-mediated oxidation. The EO treatment of EC-pretreated dairy wastewater allowed obtaining a global 98 % TOC removal, decreasing from 1,062 to <30 mg L(-1).