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We present results of our theoretical study on the mechanism and thermodynamics of the incineration of oxalic acid H 2 C 2 O 4 on a boron-doped diamond electrode. The reaction is assumed to occur in aqueous solution in several steps, of which the first, the most important, is the generation of the OH radical according to an outer sphere mechanism. The energy balance and barrier for this step as well as for all subsequent steps (OH reaction with oxalic acid leading to creation of HC 2 O 4 radical, its C C bond dissociation and OH reaction with the COOH radical) were evaluated by performing quantum calculations with the MP2 and three DFT methods and the aug-cc-pVTZ basis set. The results indicate that the first step is characterized by a rather low activation energy of 0.25 eV and by a relatively high transfer coefficient of ~ 0.7. The next process - detachment of H atom from oxalic acid by OH radical – meets an energy barrier of 0.55 eV; for all subsequent steps the activation energies are much smaller. The overall incineration reaction is found to be highly exothermic by ca. 7 eV. Our results are also applicable to similar inert electrodes. [ABSTRACT FROM AUTHOR]

A 4 cm 2 BDD/TiO 2 electrode has been synthesized by a novel method in which nano-particulated TiO 2 (P25, Degussa) was electrophoretically deposited onto a boron-doped diamond (BDD) substrate, followed by sintering at 450 °C. Its surface characteristics were analyzed by SEM-EDX. The electrocatalytic behavior of the BDD/TiO 2 electrode was clarified from the cyclic voltammetry of a 0.50 M K 4 [Fe(CN)₆] solution. The much higher electroactive area of the nano-structured TiO 2 deposit over the hybrid electrode gave much higher currents of the Fe(CN) 6 3– /Fe(CN) 6 4– pair than using the raw BDD electrode. When BDD/TiO 2 was used in the anodic oxidation of 50 mg L − 1 Acid Blue 80 solution at pH 3.0 and 5.0 at 22.5 mA cm − 2 in the dark, it decolorized much more rapidly the dye solution compared to anodic oxidation with BDD. This was related to the production of greater amounts of hydroxyl radical at the high electroactive area of the nano-structured TiO 2 . Quicker color removal was obtained by photoelectrocatalysis by irradiating the BDD/TiO 2 anode with a 75 mW cm − 2 UVA light (λ max = 365 nm). The dye concentration decay was always much faster than decolorization due to the formation of more recalcitrant colored products from the attack of oxidizing species. In 60 min, photoelectrocatalysis removed 96% of Acid Blue 80. The use of nano-structured TiO 2 deposited onto BDD as anode in photoelectrocatalysis then exceeds the efficiency of anodic oxidation with the best anode known of BDD. [ABSTRACT FROM AUTHOR]

Catechol, one of the most abundant compounds in olive mills wastewaters, which is generated in the Fenton degradation of various aromatic compounds, is a toxic, possible carcinogen, persistent pollutant and it is not readily biodegradable. Hence, its degradation requires the utilization of advanced oxidation processes (AOPs). Here, the electrochemical treatment of aqueous solutions of catechol was investigated. The utilization of various electrochemical processes, such as electro-Fenton (EF), direct anodic oxidation (AO), indirect oxidation by electro-generated active chlorine and coupled processes was investigated. Furthermore, the effect of various operating conditions (including the nature of anode for AO, the initial pH and the current density) was widely studied in order to optimize the selected electrochemical processes. For EF process, the effect of the nature of the catalyst (homogeneous FeSO 4 and heterogeneous pyrite and chalcopyrite) was also analysed. It was shown that both EF and AO, under proper operating conditions, allow a very high removal of the TOC, while the indirect oxidation by electro-generated active chlorine is poorly effective. The utilization of a coupled EF-AO process allowed enhancing the abatement of both catechol ad TOC with respect to single processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stability of Pt-BDD for dissolved H 2 could be maintained with only electrochemical pretreatment. • The ability of Pt-BDD to detect dissolved H 2 was comparable with GC technique. • Pt-BDD shows a good response for dissolved H 2 even in the tap water with a low solution conductivity. • Pt-BDD could be promoted as a dissolved H 2 sensor in an aqueous media. The detection of molecular hydrogen in water using platinum modified boron doped diamond (Pt-BDD) was presented. A clear peak of hydrogen desorption was observed around −0.1 V in 0.1 M KCl solution. With a simple electrochemical pretreatment, the signal at Pt-BDD electrode was found to be higher and more stable compared to those using bare Pt electrode. The performance of the sensor was compared with gas chromatography method. The result shows a similar trend with either same or different concentration of H 2. Lastly, the measurement was successfully conducted in the tap water even without addition of electrolyte. These result shows that Pt-BDD could be promoted as a good electrode candidate for sensing dissolved H 2 in the water-based solution. [ABSTRACT FROM AUTHOR]

Highlights: [•] Anodic oxidation and electro-Fenton were used in electrooxidation of 2-chlorobenzoic acid (2-CBA). [•] Anodic oxidation with BDD was more powerful in mineralization of 2-CBA than electro-Fenton with Pt. [•] Electro-Fenton with BDD anode exhibited better oxidation and mineralization performances. [•] Complete mineralization of 2-CBA was achieved at 3h by electro-Fenton with BDD anode. [•] Decay kinetics of 2-chlorobenzoic acid by OH followed pseudo-first-order reaction. [ABSTRACT FROM AUTHOR]

Abstract: European Water Framework Directive and the Predicted Non Effect Concentrations for water organisms require determination of lead at very low concentrations: 1.2μg/L. These low concentrations, generally in complex sample matrixes, have influence on the sensitivity and accuracy of the analytical method. Hence, prior to a determination, a clean-up and/or enrichment step is highly necessary. In this work, for the first time, the determination of Pb was performed using Differential Pulse Anodic Stripping Voltammetry (DPASV) on a Boron-Doped Diamond microcell directly in the room temperature ionic liquid (RTIL) extracting phase: Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide which contained the complexing agent Trioctylphosphine oxide (TOPO). The calibration curves with and without TOPO are linear in the concentration range 0–4μg/L of Pb, with a detection limit (DL) of 0.3μg/L. The optimum conditions for higher concentration factor were determined: the aqueous phase should be a 0.1M citrate buffer with pH 2. The obtained concentration factor was 5.0±0.2 for lead in RTIL without chelating agent TOPO, and 9.0±0.10 in IL with chelating agent TOPO. [Copyright &y& Elsevier]

Abstract: Electrochemical degradation of toxic and persistent organic pollutant 2-Nitrophenol (2-NP) in acidic medium of pH 3 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation using BDD anode (AO-BDD), electro-Fenton (EF-Pt) and anodic oxidation coupled to electro-Fenton (EF-BDD) processes under galvanostatic electrolysis conditions. The effect of current density and 2-NP initial concentration on the degradation rate and solution TOC removal efficiency was studied. The oxidation power of these processes has been comparatively studied in a one compartment cell with platinum (Pt) or boron doped diamond (BDD) anode. Results obtained show that acidic solutions of 2-NP can be efficiently mineralized by all EAOPs under examination, with increasing oxidation/mineralization power in order AO-Pt

Abstract: The electrochemical oxidation of oxalic acid (OA) was performed in a micro flow cell equipped with a boron doped diamond (BDD) anode. This preliminary study demonstrates that a flow cell with a micrometric distance between the cathode and the anode can be used to perform the electrochemical treatment of waters contaminated by organic pollutants in the absence of added supporting electrolytes with high abatements. The effect of the distance between the cathode and the anode, the flow rate and the current density on the abatement of oxalic acid and on the current efficiency was in particular studied. [Copyright &y& Elsevier]

• BNT2 was mineralized using a filter-press electrochemical reactor. • The process involved electrochemical generation of H 2 O 2. • Complete BNT2 mineralization (100% TOC removal) occurred after 120 min. • The process was found to have an average current efficiency of 70% and an energy consumption of 10.8 kWh (g TOC)−1. This project assessed the mineralization of Black NT2 (BNT2), a diazo dye frequently used in tanneries, using electrochemical technologies based on boron-doped diamond electrodes (BDD). The experimental trials included adding an Fe2+-catalyzed process known as the electro-Fenton (EF) reaction. The process was carried out in a recirculating pre-pilot plant that used a filter-press electrochemical reactor connected to a reservoir. The pre-pilot reactor was equipped with a BDD plate anode coupled with a BDD cathode to electrogenerate hydrogen peroxide (H 2 O 2) in situ. The effects of experimental variables such as current density (j) and initial BNT2 concentration were tested. The best conditions to mineralize an initial BNT2 concentration equivalent to 250 mg L−1 of total organic carbon (TOC) in a 50 mM Na 2 SO 4 solution using the EF process were 0.3 mM Fe2+, pH 3.0, j = 30 mA cm2, and Q = 12 L min−1. After 90 min of treatment, 100% TOC abatement was achieved. In all cases, TOC decreased following a pseudo-first-order kinetics. For the highest initial dye concentration, 100% TOC was achieved after 120 min, with 70% average current efficiency and 0.01088 KWh (g TOC)−1 energy consumption at the end of the process. For experiments without complete mineralization, the evolution of some nontoxic, short-chain carboxylic acids—such as oxalic, maleic, succinic, acetic, and formic—were quantified using high performance liquid chromatography (HPLC) analysis. These findings suggest that the EF reaction is an interesting, feasible alternative for enhanced dye degradation in tannery water treatment processes. [ABSTRACT FROM AUTHOR]

This work studies the effect of the anode and cathode materials on the degradation of the herbicide clopyralid. Different electrochemical advanced oxidation processes (EAOPs), including electrochemical oxidation with electrogenerated hydrogen peroxide (EO-H 2 O 2), electro-Fenton (EF), and photoelectro-Fenton (PEF) were carried out. The first experiments were focused on the effect of the cathode, where the use of the hydrophobic carbon felt modified by the deposition of carbon black & PTFE mixture (MCF) improves the H 2 O 2 production in comparison to a conventional carbon felt (CF), regardless of the anode material employed. On the other hand, a laser-made Ti/Ru 0.3 Ti 0.7 O 2 mixed metal oxide (MMO) and a commercial boron-doped diamond (BDD) were compared as anodes. Results obtained point out that the MMO anode promotes the accumulation of this oxidant (H 2 O 2) in bulk. Once characterized by the production of hydrogen peroxide, the second part of this study focused on the degradation of clopyralid with the MCF cathode with different EAOPs. Results demonstrate that clopyralid fastly degrades in the sequence EO-H 2 O 2 < EF < PEF, and almost complete mineralization occurs for EF and PEF employing MMO or BDD as the anode. Synergy effect study shows that irradiation of 9 W UVC produces a positive synergistic effect of 81.7% and 41.55% (for the PEF-MMO and PEF-BDD, respectively), ascribed to the additional removal of aromatic intermediates by the UVC and the activation of H 2 O 2. At the end of the treatment, mineralization of the herbicide was attained at 1.22 kW h (g−1 TOC). Finally, considering the lower cost of the prepared MMO, these findings demonstrate the potentiality of using modified carbon felt combined with the laser-made Ti/Ru 0.3 Ti 0.7 O 2 anode for the treatment of polluted waters. Unlabelled Image • The modified carbon felt allowed achieving higher values of H 2 O 2. • Perchlorates detected using BDD vary in the sequence OE < EF < PEF. • No perchlorate was detected when working with the Ti/Ru 0.3 Ti 0.7 O 2. • Mineralization is achieved only when Fe2+ ions are added in EF and PEF treatments. • Although clopyralid was mineralized with both anodes, MMO is more cost-efficient. [ABSTRACT FROM AUTHOR]

In this work, the removal of the non-readily biodegradable herbicide clopyralid by electrochemical (EC) and photoelectrochemical (PhEC) oxidation with different anode materials were conducted looking to improve not only its oxidation but also its biodegradability. First, in order to find out optimal conditions, it was carried out EC and PhEC degradations in chloride medium, at current densities ranging from 30 to 100 mA cm−2 during 1 h (0.8–2.7 A h L−1), using as anodes MMO-RuO 2 TiO 2 , MMO-RuO 2 IrO 2 , MMO-IrO 2 Ta 2 O 5 and boron-doped diamond (BDD). Results show better efficiencies on clopyralid removal for MMO-RuO 2 IrO 2 and BDD anodes at lower current densities. Then, the influence of all anodes on clopyralid transformation was evaluated, extending the electrolysis and photoelectrolysis for 8 h applying 30 mA cm−2 (6.4 A h cm−3). At these conditions, better outcomes are observed for PhEC degradation, where complete pollutant removal is attained for BDD anode and 88.7% for MMO-RuO 2 IrO 2 , while COD removal is 47.7% for MMO and 43.1% for BDD anode. Then, short-term biodegradability tests, conducted for EC and PhEC processes, pointed out that MMO-RuO 2 TiO 2 is the most promising anode material, being capable of improving biodegradability in 48.2% and 53% for EC and PhEC degradation, respectively. The toxicity of treated solutions using MMO-RuO 2 TiO 2 and BDD anodes in both EC and PhEC degradation were compared, employing the inhibitory effect in the bioluminescence of marine bacteria Vibrio Fisheri. Toxicity assessments show that toxicity significantly reduces by using the MMO-RuO 2 TiO 2 in NaCl and Na 2 SO 4 medium for both processes. Finally, this study demonstrates that photoelectrolysis with MMO anodes was the most effective strategy in order to increase biodegradability in chloride media, as well as to reduce the toxicity of the treated waste. Unlabelled Image • Clopyralid can be removed using electrolysis and photoelectrolysis. • Degradation is more efficient at low current densities using MMO-RuO 2 TiO 2 anode. • Readily biodegradability could be doubled by photoelectrolysis with MMO-RuO 2 TiO 2. • Treated solutions with MMO-RuO 2 TiO 2 reduced their toxicity. Not the case of using BDD. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of dibenzothiophene and two derivatives, namely 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, was investigated either separately or as a mixture, on a BDD anode in a miscible acetonitrile (87.5% v/v)–water (12.5% v/v, 0.01 M NaNO 3) solution. Linear sweep voltammetry, cyclic voltammetry, chronoamperometry and bulk electrolysis under potentiostatic conditions suggested the probable occurrence of two pathways: direct electrochemical oxidation and indirect reaction with hydroxyl radicals and other reactive oxygen species formed at the BDD anode surface during water discharge. The products extracted upon electrolysis at 1.5 and 2.0 V vs. SCE were analyzed by Fourier-transform infrared spectroscopy, gas chromatography–mass spectrometry and ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry (UHPLC-ESI-Q-TOF-MS). The main molecules identified were the corresponding sulfoxides or sulfones, depending on the applied anodic potential. Possible oxidation routes for the dibenzothiophene compounds are proposed. Unlabelled Image • Electrochemical oxidation of dibenzothiophenes in CH 3 CN/H 2 O using a BDD anode • Oxidation is direct or mediated by reactive oxygen species like OH. • Selective oxidation of single compounds or mixtures to sulfoxides or sulfones • The conversion depends on concentration, applied potential and water content. • The electrochemical reactivity on BDD decreases as: 4,6-DMDBT ≥ 4-MDBT > DBT. [ABSTRACT FROM AUTHOR]