Indirect Oxidation Process Research Articles

Differences in anodizing of two copper-containing coordination compounds by different degradation factors: Experiments and DFT calculations

Copper phthalocyanine (CuPc) and copper formazan (CuFz) are typical coordination compounds widely utilized due to their physicochemical properties and biochemical behavior. The production and application of CuPc and CuFz have produced large amounts of copper-containing wastewater and aromatic organics, posing great risks to human health and the environment. This research introduced a feasible and efficient treatment method based on BDD anodic oxidation for CuPc and CuFz wastewater and provided a novel perspective on the degradation differences of the two pollutants through DFT calculation. Firstly, the color removal efficiency and chemical oxygen demand (COD) during the anodic oxidation of the two molecules were compared. Secondly, the effect of pH, inorganic anions type, and current density on the oxidative degradation of CuPc and CuFz was discussed. Thirdly, cyclic voltammetry (CV) was carried out to evaluate the direct anodic oxidation speed of CuPc and CuFz. Then, the principal reactive oxygen species (ROS) of CuPc and CuFz in the indirect oxidation process were investigated through free radical quenching and Electron paramagnetic resonance (EPR) spectroscopy. The functional group changes in degradation, the degradation products, and the shed copper ions were also analyzed. Finally, the global, local, and condensed properties and CuPc and CuFz reaction sites to be attacked by ROS were theoretically analyzed using density functional theory (DFT) calculation. Altogether, this study can help broaden the discussion and further the understanding of the links between the electrochemical oxidation pathway and decolorization of coordination compounds.

Electromediated Alcohol-Based Passerini-Type Reaction

AbstractAn electrochemical variant of the alcohol-based oxidative Passerini reaction is reported here. It relies on an indirect anodic oxidation process followed by a three-component coupling, in which TEMPO serves as a key redox mediator. This electrochemical approach permits to operate without the need for a metal catalyst nor oxygen atmosphere and allows the use of nonactivated alcohols as reaction partners. It could be applied to the preparation of good variety of α-acyloxy-carboxamides in yields ranging from 24% to 80%.

Boosting electrochemical oxidation of As(III) on Fe-doped RuO2/PEDOT/SnO2 nanocomposite anode: Fabrication, performance and mechanism

Design of electrode materials for stable and efficient electrocatalytic oxidation of As(Ⅲ) in arsenic-contaminated groundwater poses a great challenge due to the rapid deactivation of catalysts resulting from the high oxygen evolution potential (OEP) and considerable barrier to generating reactive oxygen species (ROS). Herein, an innovative TNAs/SnO2/PEDOT/Fe(III)-RuO2 multilayer electrode was synthesized by utilizing a PEDOT-coated SnO2 interlayer as a supportive framework to combine Fe-doped amorphous RuO2 catalytic layer with TiO2 nanotube array substrate. Such electrode exhibited high activity and stability for the oxidation of As(III) to As(V) due to the large surface area provided by the TiO2 nanotube arrays and the SnO2/PEDOT interlayer for facilitating the growth of the catalytic layer. The electrochemically active surface area of the electrode reached as high as 31.7 mF/cm2. Impressively, the doping of Fe into RuO2 layer led to a remarkable increase in the OEP value to 3.12 V, which boosted the indirect oxidation process mediated by ROS at a lower potential to achieve the As(III) oxidation ratio of 98.5%. DFT calculations revealed that the Fe-doped amorphous RuO2 weakened the adsorption strength of ·OH and ·SO4− intermediates and lowered the energy barrier for generating ROS. Combined with ESR results, the formation of ·OH and ·SO4− with strong oxidizing properties was fully verified, providing further evidence for the involvement of ROS as the main mediator of the oxidation mechanism of As(III). This work may provide valuable perspectives into the design of catalytic layer structures and heteroatom doping modifications for composite-coated electrodes.

Electrochemical oxidation of phenol in a PtRu/NbC membrane-based catalytic nanoreactor

Electrochemical oxidation has attracted growing attention to treat organic in wastewater. However, achieving a high reactor efficiency and harmless treatment of the toxic organics is still a significant challenge. In this work, the bimetal Pt and Ru were firstly co-electrodeposited on the surface of nanoporous niobium carbide (NbC) membranes (∼8.3 nm pore size) applying for anode in flow-through reactor for phenol electrochemical oxidation. In a continuous flow-through reactor, the single-pass removals of phenol and chemical oxygen demand (COD) were 99.7 % and 74.2 %, respectively, with a short hydraulic retention time of 342 s, demonstrating rapid phenol degradation that is an order of magnitude shorter than those reported in other studies. This excellent reactor efficiency was ascribed to a large interfacial reaction area providing by the pollutant phase-catalytic membrane-green product phase. We compared the mass transfer of flow-through and flow-by reactor testifying the high efficiency of flow-through reactor. The excellent stability of PtRu/NbC anode enable this reactor to operate 50 h stably. Moreover, the presence of low or non-toxic (catechol and acetic acid) as the residues of phenol degradation resulting from the contribution of synergistic reaction between direct and indirect oxidation process.

Synthesis of defective Ni-Mn layered double hydroxides nanosheets via alkali-assisted Mo doping for urea electro-oxidation

Urea oxidation reaction (UOR) with favorable thermodynamic potential provides a good application prospect in renewable energy infrastructure. However, the sluggish kinetics caused by 6e- transfer greatly hinders the usage of urea as fuel, efficient catalysts are urgently needed in consequence. In response, alkali-assisted Mo doped into Ni-Mn layered double hydroxides (Mo-NiMnLDH-OH) with laminate structure is synthesized via one-pot hydrothermal method. The alkali-assisted Mo doping contributes the modified morphology and microstructure, the tuned chemical states of Ni and Mn species, simultaneously generates defects and more active sites. The existence of alkali plays a vital role in promoting the Mo doping. Without alkali, the Mo doping should damage the laminate structure, and the chemical states of active sites cannot be efficiently tuned. When used as catalyst for UOR, the current density of 45.3 mA cm−2 and a specific current activity of 1132.8 mA cm−2 mg−1 for Mo-NiMnLDH-OH can be achieved at the potential of 1.623 V (vs. RHE), which is 4-fold higher than that for Ni-Mn layered double hydroxides without doping. Both indirect electrochemical and direct urea oxidation processes occur when using Mo-NiMnLDH-OH as catalyst, and the existence of Mo species will facilitate the occurrence of direct urea oxidation process. This work paves an effective way to synergistically engineer of Mo doping and defects into Ni-based layered double hydroxides for UOR.

Sodium-alginate-laden MXene and MOF systems and their composite hydrogel beads for batch and fixed-bed adsorption of naproxen with electrochemical regeneration

Sodium alginate (SA)-laden two-dimensional (2D) Ti3C2Tx MXene (MX) and MIL-101(Fe) (a type of metal–organic framework (MOF)) composites were prepared and used for the removal of naproxen (NPX), following the adsorption and electrochemical regeneration processes. The fixed-bed adsorption column studies were also conducted to study the process of removal of NPX by hydrogels. The number of interactions via which the MX-embedded SA (MX@SA) could adsorb NPX was higher than the number of pathways associated with NPX adsorption on the MIL-101(Fe)-embedded SA (MIL-101(Fe)@SA), and the MX and MIL-101(Fe) composite embedded SA (MX/MIL-101(Fe)@SA). The optimum parameters for the electrochemical regeneration process were determined: charge passed and current density values were 169.3 C g−1 and 10 mA cm−2, respectively, for MX@SA, and the charge passed and current density values were 16.7 C g−1 and 5 mA cm−2, respectively, for both MIL-101(Fe)@SA and MX/MIL-101(Fe)@SA. These parameters enabled excellent regeneration, consistent over multiple adsorption and electrochemical regeneration cycles. The mechanism for the regeneration of the materials was proposed that the regeneration of MX@SA and MIL-101(Fe)@SA involved the indirect electrooxidation process in the presence of OH radicals, and the regeneration of MX/MIL-101(Fe)@SA involved the indirect oxidation process in the presence of active chlorine species.

A Novel Chemical-Electrochemical Hydrogen Production from Coal Slurry by a Two-Step Process: Oxidation of Coal by Ferric Ions and Electroreduction of Hydrogen Ions.

Hydrogen production from the electrolysis of coal slurry is a promising approach under the condition of low voltage (0.8–1.2 V) and medium temperature. However, the rate of hydrogen production is slugged by poor anode kinetics, under an electrochemical condition that results from the collision of the coal particles with the anode surface. This paper reports a novel process that consists of two steps: the oxidation of the coal slurry by ferric ions(III) in a hydrothermal reactor at a temperature of 120–160 °C and the electro-oxidation of ferric ions(II) in the electrochemical cell to produce hydrogen. This technique circumvents the technical issues experienced in the conventional coal slurry electrolysis process by adopting a two-step process consisting of solid–liquid reactions instead of solid–solid reactions. This indirect oxidation process produced a current density of 120 mA/cm2 at room temperature and a voltage of 1 V, which is higher than the values reported in the conventional processes. An investigation of the oxidation mechanism was carried out via scanning electron microscopy, Fourier-transform infrared spectroscopy and elemental analysis. The results obtained showed that the oxidation of coal by ferric ions occurs from the surface to the inner parts of the coal particles in a stepwise manner. It was also revealed that the ferric ions in the media increased the active interfaces both of the coal particles and of the anode electrode. This explains the high hydrogen production rate obtained from this process. This novel discovery can pave the way for the commercialization of coal slurry electrolysis.

Insight into the rapid elimination of low-concentration antibiotics from natural waters using tandem multilevel reactive electrochemical membranes: Role of direct electron transfer and hydroxyl radical oxidation

Herein, we reported a tandem multilevel reactive electrochemical membrane (REM) system was promising for the rapid and complete removal of trace antibiotics from natural waters. Results indicate that a four-stage REM module-in-series system achieved steady over 98% removal of model antibiotic norfloxacin (NOR, 100 μg·L−1) from wastewater treatment plant final effluent and surface water with a residence time of 5.4 s, and the electric energy consumption was only around 0.007–0.011 kWh·m−3. As for the oxidation mechanism, direct electron transfer (DET) oxidation process played an important role in NOR rapid oxidation, enabling the REM system to tolerate various •OH scavenges in natural waters, including natural organic matters, Cl- and HCO3-, even at very high concentration levels. Meanwhile, •OH-mediated indirect oxidation process promotes the oxidation and mineralization of NOR. Although the DET-dominated oxidation mechanism makes the REM system cannot achieve the complete mineralization of NOR with residence times of few seconds, the antibacterial activity from NOR was completely eliminated. This REM system featured effective removal performance of trace contaminants with low energy cost and was tolerant to complex waster matrix, suggesting that it could be a powerful supplementary step for wastewater/water treatment.

Optimization of photo-electro/Persulfate/nZVI process on 2-4 Dichlorophenoxyacetic acid degradation via central composite design: a novel combination of advanced oxidation process.

2-4 Dichlorophenoxy acetic acid is most publicly applied from chlorinated phenoxy acids herbicides. In this research, central composite design for optimization of photo-Elecro/persulfate/nZVI process to degradation and mineralization of this herbicide in aqueous solution to environment protection was applied. The initial pH (2-4), persulfate anion concentration (0.25-0.5mg/L), direct electrical (0.5-1 A), herbicide concentration (50-100mg/l), nZVI dose (0.05-1mg/L), and reaction time (50-100mg/l) are independent variables optimized. Also, the synergist effect, COD and TOC removal, the effect of radical scavengers, and by-products were investigated. The fitting of the model, suggested a quadratic model (R2 = 0.9926). F-value and P value of ANOVA were 719.81 and 0.0001 respectivelty. After optimizing the PEP/nZVI process, the proposed optimal conditions was pH = 3.4, persulfate concentration equal to 0.49mg/l, in 1 A direct current, nZVI dose equal to 0.1mg/l, in 50.05mg/l herbicide concentration as an initial concentration, in 80min reaction time. The theoretical and actual removal was evaluated 91.99% and 92%, respectively. In the optimum condition, 45.4% synergist effect indicated. 78.3% and 66.5% of initial COD and TOC were decreased. 39.02% of Cl ion was released form 2,4-D structure. The presence of radical scavengers have an adverse impact on the performance of process. The highest amount of radical scavenging was in methanol, tert-butyl alcohol and bicarbonate ions at concentrations at 50mM/l. The kinetic data was fitted via pseudo-first-order reaction (R2 = 0.99).The direct and indirect oxidation process lead to formation of several organic by-products which were confirmed by GC-MS analysis.

Electrocatalytic degradation of sulfamethazine on IrO2-RuO2 composite electrodes: influencing factors, kinetics and modeling

In this study, IrO2-RuO2 composite electrodes were prepared and well characterized. The electrode exhibited a compact structure, with the IrO2-RuO2 binary oxide coatings appearing as finely dispersed crystals. The IrO2-RuO2 composite electrodes were used as the anode to degrade sulfamethazine (SMT) via the indirect oxidation process of hydroxyl radicals. The optimum degradation conditions of SMT were as follows: initial concentration: 50 mg/L; current density: 40 mA/cm2 and initial pH: 6.0 at a supporting electrolyte (Na2SO4)concentration of 0.2 mol/L. The IrO2-RuO2 composite electrodes effectively removes chemical oxygen demand (COD) from actual wastewater: the removal rate was 49.17%. The after-treatment COD value was 107.83 mg/L lower than China's urban sewage COD discharge standard (120 mg/L). These results indicate that the electrocatalytic degradation of SMT with electrodes is feasible. Besides, the effects of the experimental conditions on the sensitivity of the experiment were studied by using an established mathematical model and an artificial neural network (ANN) model representing the first time, which can be used to effectively predict and guide the removal of COD from SMT-containing wastewater using IrO2-RuO2 composite electrodes. The modeling results show that reaction time was the most significant factor affecting SMT removal efficiency, whereas pH value was the most important factor affecting COD removal efficiency.

Comparing the electrochemical degradation of the fluoroquinolone antibiotics norfloxacin and ciprofloxacin using distinct electrolytes and a BDD anode: evolution of main oxidation byproducts and toxicity

The effects of the supporting electrolytes (SEs) Na2SO4, NaCl, Na2CO3, NaNO3, and Na3PO4 on the anodic oxidation of norfloxacin (NOR) and ciprofloxacin (CIPRO), assessed by the respective degradation kinetics and byproducts and electrolyzed solution antimicrobial activity, are compared. Galvanostatic anodic oxidations were performed in a filter-press flow cell fitted with a boron-doped diamond anode. Removal rates higher than the theoretical one for a process purely controlled by mass transfer were found for all SEs, indicative of contribution by indirect oxidation processes. However, the removal rates for NaCl were about tenfold higher, with the lowest energy consumption per order (ECO) of targeted pollutant removal rate (ca. 0.7 kW h m–3 order–1), a very competitive performance. The TOC removal rates were also affected by the SE, but not as markedly. The antimicrobial activity of the electrolyzed solutions against Escherichia coli showed distinct temporal profiles, depending on the fluoroquinolone and SE. For instance, when Na3PO4 was used, the antimicrobial activity was completely removed for NOR, but none for CIPRO; conversely, when NaCl was used, complete removal was attained only for CIPRO. From LC-MS/MS analyses of Na3PO4 electrolyzed solutions, rupture of the fluoroquinolone ring leading to byproducts with no toxicity against E. coli occurred only for NOR, whereas exactly the opposite occurred for the NaCl solutions. Clearly, the nature of both the SE and the fluoroquinolone influence the oxidation steps of the respective molecule; this was also evidenced by the distinct short-chain carboxylic acids identified in the degradation of NOR and CIPRO.

Impact of sulfate ion addition on electrochemical oxidation of anaerobically treated landfill leachate using boron-doped diamond anode

Anaerobic biological process is commonly applied for treating leachate generated from solid waste landfill. However, it is often found less effective to degrade leachate contaminants with low biodegradability, high salinity, and rich nutrient constituents. High concentration of organic and nitrogen still remained in the effluent of landfill leachate treated by anaerobic processes. Therefore, further treatment is required to efficiently meet the effluent standard prior to release into water bodies. In this study, electrochemical oxidation process using boron-doped diamond anode was investigated as a post-treatment for the treatment of anaerobically treated leachate effluent. Boron-doped diamond anode is able to generate of active species, such as OH·, Cl·, Cl2·−, and SO4·− as well as other oxidative agents to promote more indirect oxidation processes of non-biodegradable organic contaminants. The effect of sulfate ion addition on the overall performance of the electrochemical oxidation was investigated in a lab-scale of three-compartment electrochemical reactor, consisting of anode, cathode, and central compartments. A 2-L of the pre-treated leachate was recirculated in a batch mode by applying constant current density of 25, 37.5, and 50 mA cm−2. The optimum removal of nitrogen and organic contaminants were obtained about 59% and 93%, respectively, at current density of 37.5 mA cm−2, molar ratio 1:1 of [SO42−]:[Cl−] sulfate ion addition based on specific energy estimation and removal efficiency. The implied removal of 2.28 g COD and 1.77 g total inorganic nitrogen with the total energy required was 5.7 Wh g−1 COD and 7.5 Wh g−1 N, respectively. The results also revealed that addition of sulfate ion enhances organic removal through indirect oxidation and leads to the formation of nitrate without affecting overall total nitrogen removal.

Treatment of dyeing wastewater by combined sulfate radical based electrochemical advanced oxidation and electrocoagulation processes

Electrochemical advanced oxidation process (EAOP) and electrocoagulation (EC) are two promising techniques that have been used for the abatement of wide variety of organic contaminants. However, a few researchers have reported the combined use of these techniques for real wastewater, which is important for field implementation of the techniques. This article presents the comparative performance of combined sulfate radical based EAOP + EC and EC + EAOP processes for the treatment of real field dyeing wastewater. Pt/Ti plate was used as anode and iron plate was used as cathode. It was found that sulfate radical was generated by both cathodic reduction of persulfate and activation of persulfate by ferrous ions. Anodic oxidation by Pt/Ti anode and indirect electrochemical oxidation processes are also contributed in pollutant removal. Instantaneous current efficiency was found to increase with increase in persulfate concentration and with reduction in COD. EAOP followed by EC was found to be better approach than EC followed by EAOP as the former combination yielded higher COD reduction of 93.5% with lesser specific energy consumption and lesser sludge generation. Sludge generated after the treatment process was characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD) techniques.

Direct and indirect electrochemical oxidation of ethanethiol on grey cast iron anode in alkaline solution

In this study, the electrochemical generation of ferrate (Fe(VI)) from grey cast iron anode in sodium hydroxide (NaOH) solution was utilized in situ to degrade the malodorous pollutant of ethanethiol (C2H5SH). During electrolysis, C2H5SH was oxidized by the combination of direct anodic oxidation and Fe(VI) oxidation (indirect oxidation). The direct anodic oxidation process, which played an important role in the decontamination process but was often disregarded in related studies, was investigated in detail. The electrochemical generation of Fe(VI) was investigated, and the maximum current efficiency of Fe(VI) generation was obtained in 14 M NaOH solution. The voltammetry studies of the grey cast iron anode in NaOH solutions containing and without C2H5SH revealed that the dissolution of anode was improved in the presence of C2H5SH. A decrease in NaOH concentration increased the contribution of direct anodic oxidation but decreased the electrochemical generation of Fe(VI). C2H5SH was degraded on the grey cast iron anode at a higher rate in less concentrated NaOH solution (k = 4.15 × 10−2 min−1 in 2 M NaOH solution), which could be ascribed to the enhancement in direct anodic oxidation as well as in the oxidizing power of Fe(VI). Higher current density promoted the degradation rate of C2H5SH in both direct and indirect oxidation processes, but it also decreased the current efficiency due to the improvement of the side reactions. Additionally, the in-situ and on-line applications of the electrochemical generated Fe(VI) in recent studies were presented and discussed. This study provides a comprehensive understanding of C2H5SH oxidation on grey cast iron anode, and offers a feasible electrochemical scrubbing approach using grey cast iron as the anode for C2H5SH odors control.

Enhanced triallyl isocyanurate (TAIC) degradation through application of an O3/UV process: Performance optimization and degradation pathways

Triallyl isocyanurate (TAIC, C12H15N3O3) has featured in wastewater treatment as a refractory organic compound due to the significant production capability and negative environmental impact. TAIC degradation was enhanced when an ozone(O3)/ultraviolet(UV) process was applied compared with the application of an independent O3 process. Although 99% of TAIC could be degraded in 5 min during both processes, the O3/UV process had a 70%mineralization rate that was much higher than that of the independent O3 process (9%) in 30 min. Four possible degradation pathways were proposed based on the organic compounds of intermediate products identified during TAIC degradation through the application of independent O3 and O3/UV processes. pH impacted both the direct and indirect oxidation processes. Acidic and alkaline conditions preferred direct and indirect reactions respectively, with a pH of 9 achieving maximum Total Organic Carbon (TOC) removal. Both CO32– and HCO3– decreased TOC removal, however only CO32– negatively impacted TAIC degradation. Effects of Cl– as a radical scavenger became more marked only at high concentrations (over 500 mg/L Cl–). Particulate and suspended matter could hinder the transmission of ultraviolet light and reduce the production of HO$ accordingly.

Treatment of mixed industrial wastewater by electrocoagulation and indirect electrochemical oxidation

Treatment of mixed industrial wastewater is a challenging task due to its high complexity. This work scrutinizes the electrochemical treatment of mixed industrial wastewater, specifically electrocoagulation and indirect electrochemical oxidation processes through COD and color removal studies. Both processes are found to be more efficient at the wastewater pH. Monopolar connection was found more effective than bipolar connection for the removal of COD and color from wastewater. The monopolar connection removed COD up to 55% and color 56% whereas bipolar connection leads to the removal of 43% and 48% respectively at wastewater pH with an applied voltage 1.5 V in the course of 1 h of electrolysis.In the case of indirect electrochemical oxidation process using graphite electrodes, the COD and color abatement efficiencies of the indirect electrochemical oxidation process were found as 55% and 99.8%, respectively within 1 h of electrolysis conducted at pH 7.7, applied voltage 4 V, and NaCl concentration 1 g L−1. This work also highlights the importance of the presence of electrolytes in the indirect electrochemical oxidation process as the external addition of sodium chloride significantly enhanced both COD and color elimination efficiency.

Assessment of graphite electrode on the removal of anticancer drug cytarabine via indirect electrochemical oxidation process: Kinetics & pathway study

In this paper degradation of cytarabine drug has been studied through electrochemical oxidation process by using graphite electrode. The performance of graphite electrode on the degradation of cytarabine was evaluated by investigating the effects of key parameters: pH (3-9), current density (5-20mAcm-2) and initial pollutant concentration (5-50mgL-1) with 0.05M NaCl as supporting electrolyte. Highest removal efficiency (98%) for 20mgL-1 of initial cytarabine solution was attained within 60min electrolysis at 10mAcm-2. The increase in degradation rate of cytarabine was possibly because of the active chlorine species originated at anode during the electrolysis. Further, efficiency of the graphite electrodes was compared with a metal electrode (copper) and results showed that the cytarabine degradation was facilitated by the in-situ generated OH radicals. However, only 82% of cytarabine was removed after 60min of reaction time at 15mAcm-2. The scum of Cu2+ ions deposited on the anode surface inhibit the mass transfer among the cytarabine molecules and generated hydroxyl radicals. The kinetic study also suggests faster reaction rate at graphite (0.12 min-1) than copper (0.05 min-1) electrode. The increase in electrolyte concentration enhanced the degradation rate and decreased the energy consumption from 3.66 to 0.66kWh m-3. Cytosine was identified as the major transformation product from the UV-Vis spectral analysis and LC-MS analysis. Further, total organic carbon analysis depicts that only 60% of the parent molecule was mineralized. Hence, graphite was found to be an efficient anode material as compared to copper for cytarabine degradation.

The performance of MnO2/graphite electrode for TOC removal from wastewater by indirect electrochemical oxidation process

Electrochemical oxidation in the presence of sodium chloride used for removal of phenol and any other organic by products formed during the electrolysis by using MnO2/graphite electrode. The performance of the electrode was evaluated in terms fraction of phenol and the formed organic by products removed during the electrolysis process. The results showed that the electrochemical oxidation process was very effective in the removal of phenol and the other organics, where the removal percentage of phenol was 97.33%, and the final value of TOC was 6.985 ppm after 4 hours and by using a speed of rotation of the MnO2 electrode equal to 200 rpm.

A comprehensive study of electrochemical disinfection of water using direct and indirect oxidation processes

The electrochemical disinfection (ECD) has achieved much attention due to its environmental compatibility, simplicity and production of oxidizing species. In the present study, the ECD of total coliform (TC) and fecal coliform (FC) was investigated with a focus on direct and indirect oxidation using a series of anodes (stainless steel (SS)/lead (Pb) O2 (SS/PbO2), stainless steel, titanium (Ti), platinum (Pt), graphite (GP) and Pb/PbO2). The influence of electrode material, current density (CD), charge passed, initial pH values, different concentrations of NaCl, TDS, electrical conductivity (EC) and energy consumption on process performance was examined. The amount of in situ generated active chlorine during the process under the optimal conditions for each anode was found to be effective in removal of bacterial. The disinfection system was very efficient in bacterial elimination in presence of 0.01 M NaCl. An increase in CD from 0.16 to 0.5 mA/cm2 resulted in a decrease more than 60% in log 10 bacterial load for all electrodes except Pt. Among anodes investigated, SS/PbO2 demonstrated the highest efficiency (complete inactivation) in 5 min by applying 0.01 M NaCl in current density of 0.5 mA/cm2 when charge passed was >15 C. The efficiency of the anodes in inactivation of TC and FC was in the order of SS/PbO2 > SS > Ti > Pt > GP > Pb/PbO2. In spite of the high efficiency of the electrochemical method in removing TC and FC, indirect oxidation has a higher efficiency due to the production of strong oxidants such as radical hydroxyl and active chlorine.

In Search of the Active Chlorine Species on Ti/ZrO2-RuO2-Sb2O3 Anodes Using Dems and XPS

Evidence to what it is identified in the literature as “active chlorine” in indirect oxidation processes occurring on Ti/ZrO2-RuO2-Sb2O3 anodes is provided in this study. To discriminate such behavior, different catalysts are prepared using the Pechini method varying ZrO2 content, at different Zr/Ru molar ratios: 1, 0.5 and 0.3. The characterization of the materials using X-ray photoelectron spectroscopy (XPS) reveals that no solid solution (Ru-Zr) or any doping that affects the crystalline phase of Zr are obtained, while Sb2O3 was surface-segregated from the bulk to the anode surface affecting the outmost 3-5 nm surface layers. There are enormous impacts on the catalytic activity and adsorption properties of the structures as ZrO2 content is increased. The presence of ZrO2 and Sb2O3 shrink the number of favorable oxygen adsorption sites in Ti/ZrO2-RuO2-Sb2O3 catalysts, whence the adsorption energies for oxygen-metal interactions became lower than for Ti/RuO2. Differential electrochemical mass spectroscopy (DEMS) and electrochemical experiments qualitatively indicate that a lower amount of ZrO2 in the ternary electrode induce a better catalysis towards the oxygen evolution reaction (OER, O2 production), while the ionic currents for and species drop. This behavior suggests that chloride oxidation needs to encompass the mitigation of the OER as the percentage of ZrO2 is increased in the anode. Active chlorine could stem from species since it was produced in larger amounts than according to the pH of the electrolyte, and in adequate levels to generate the degradation of organic compounds.