Instantaneous Current Efficiency Research Articles

Excellent treatment effect of actual wastewater from a pesticide plant using electro-Fenton process catalyzed by natural pyrite

The experiment used natural pyrite as catalyst for electro-Fenton process to treat actual wastewater containing high concentrations of chlorine salts from a pesticide factory in Guangdong province, China. It revealed that under the optimized conditions of initial pH of 3, electrode spacing of 4 cm, and current density of 40 mA/cm2, excellent treatment effect was achieved using 3 g/L pyrite as catalyst with graphite cathode and Ti/RuO2-IrO2-SnO2 anode after a duration of 3 h. Specifically, the removal efficiencies of chemical oxygen demand (COD), absorbance at 478 nm (I478), ammonia nitrogen (AN) and total nitrogen (TN) reached 99.1 %, 99.8 %, 98.9 % and 46.0 % respectively, and instantaneous current efficiency (ICE) at 3 h and energy consumption (EC) were 48.16 % and 97 kWh/kgCOD. Pyrite exhibited good reusability, mainly due to its proper dissolution capacity to renew surface active sites. It was speculated that the nitrogen removal of pesticide wastewater might mainly owe to the oxidation of NH4+ by chlorine/hypochlorite which were based on anode discharge reaction of contained Cl−. The electro-Fenton process catalyzed by natural pyrite showed good potential for efficiently treating the actual pesticide processing plant wastewater with high contents of chlorine salts.

Hybrid treatment of olive mill wastewater by iron-catalyzed percarbonate and peroxymonosulfate oxidation followed by electrooxidation

In this study, hybrid advanced oxidation processes were applied to effectively treat olive mill wastewater (OMW). In the first stage of the hybrid process, Fe2+-activated peroxymonosulfate (PMS) and percarbonate (PC) oxidation processes were applied. Optimum conditions for maximum chemical oxygen demand (COD), ultraviolet absorbance at 254 nm (UV254), and color removal were determined. Since the difference between the removal efficiencies of the two processes was negligible, the Fe2+-activated PC process was selected. Under optimum conditions (pH: 4, PC dose: 10 g/L, Fe2+ dose: 5 g/L, reaction time: 60 min) with the Fe2+-PC process, 43.3 % COD, 69.4 % UV254, and 88.6 % color removal were obtained. In the second stage, the electrooxidation (EO) process was applied to the effluent of the Fe2+-PC process. Different anode materials were evaluated in EO based on their pollutant removal efficiency, specific energy consumption, anode efficiency, and instantaneous current efficiency, and IrO2-coated Ti (Ti/IrO2) was selected. In the EO process using Ti/IrO2 anode, 1.75 A, pH 3.5, and 120 min, 59.6 % COD, 94.5 % UV254, and 100 % color removal efficiency were achieved. A total of 77.1 % COD, 98.3 % UV254, and 100 % color removal efficiencies were obtained with hybrid processes, and it was seen that hybrid advanced oxidation is an effective application in removing pollutants from OMW.

Electrochemical Oxidation of Organic Pollutants in Aqueous Solution Using a Ti4O7 Particle Anode.

Anodes based on substoichiometric titanium oxide (Ti4O7) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). Recent work has shown that REMs with large pore sizes (0.5-2 mm) are highly efficient (comparable or superior to boron-doped diamond (BDD) anodes) and can be used to oxidize a wide range of contaminants. In this work, for the first time, a Ti4O7 particle anode (with a granule size of 1-3 mm and forming pores of 0.2-1 mm) was used for the oxidation of benzoic, maleic and oxalic acids and hydroquinone in aqueous solutions with an initial COD of 600 mg/L. The results demonstrated that a high instantaneous current efficiency (ICE) of about 40% and a high removal degree of more than 99% can be achieved. The Ti4O7 anode showed good stability after 108 operating hours at 36 mA/cm2.

Catalytic performances and leaching behavior of typical natural iron minerals as electro-Fenton catalysts for mineralization of imidacloprid

Catalytic performances and leaching behavior of 9 natural iron minerals as heterogeneous electro-Fenton catalysts for the treatment of imidacloprid wastewater were studied. The results showed that magnesioferrite exhibited the best catalytic ability among these minerals with UV absorbance at 270 nm (UV270) removal of 83.59% and COD removal of 49.11% within 4 h using graphite cathode and Ti/(RuO2)0.88-(IrO2)0.12 anode at initial pH 3 with a catalyst dose of 5 g/L, a current density of 40 mA/cm2 and an electrode spacing of 2 cm. The instantaneous current efficiency (ICE) at 4 h and energy consumption (EC) reached 2.30% and 2.20 kWh/gCOD respectively. It was found that the components contained in natural iron minerals, such as Al, alkali metal (K) and alkaline earth metals (Mg, Ca, Ba), would dissolve into the electrolyte solution, raising the final pH to 6.5–8.5 and ultimately reducing the reaction efficiency. Except magnetite and magnesioferrite, other minerals, such as ilmenite and V-Ti magnetite, were likely to cause secondary pollution. The subsequent adjustment to alkaline state for chemical precipitation of leached Mn was needed. Pyrite showed relatively high leachability in hazardous elements (especially Pb), which should be carefully evaluated before its actual application in electro-Fenton process.

Minimization of refractory COD in the waste water stream

This paper shows the present scenario of the electrochemical oxidation cum electrocoagulation for the treatment of the refractory Chemical Oxygen Demand (COD) in the industrial waste water stream. The present work discussed about the design engineering canvas representing the electrochemical oxidation process for the treatment of the industrial waste water stream. The effects of flow rates and residence time (s) were investigated on degradation of chemical oxygen demand(COD), color, electrochemical degradation index (EDI), total dissolved solid (TDS), turbidity, salinity, and instantaneous current efficiency (ICE). In this work, we have also designed a prototype of electrochemical cell in which different parameters are studied, namely, current intensity, agitation speed, amount of coagulant, and time of process. It is found that after the proper completion of the process the impurity gets settled at the bottom in the form of sludge and some of the light particles float on the surface. The impurities were removed with thehelp of membrane. The present work also compares the advantages of the electrochemical oxidation cum electrocoagulation process with other process used for the treatment of the refractory COD.

Electrochemical treatment for leachate membrane retentate: Performance comparison of electrochemical oxidation and electro-coagulation technology.

With the widespread use of membrane in advanced treatment of leachate, China produces a large amount of leachate membrane retentate (LMR) (≈23.4 million tons) annually, which is usually treated by incineration or recirculation in engineering, but these technologies have many drawbacks. LMR is suitable for electrochemical treatment due to its high electrical conductivity. This study compared the performances of electrochemical oxidation (EO) and electro-coagulation (EC) technology on LMR treatment under different experimental conditions, including anode material, current density, initial pH and reaction time. We found that EO optimal conditions achieved 70.1%, 83.1%, 78.7%, 98.7%, and 69.7% removal of total organic carbon (TOC), UV absorption (at 254nm), chromaticity, ammonia nitrogen (NH3-N), and total nitrogen (TN), respectively. Compared with EO, EC exhibited a similar removal ability for orgainics and better removals of chroma, but much less performance for removing nitrogen pollutants in the same reaction time, that is, removals of NH3-N and TN were only 31.5% and 36.2%, respectively. Meanwhile, EC showed much higher instantaneous current efficiency of COD than EO under its optimal reaction time (120min). In addition, the UV-Vis spectra and 3D fluorescence spectra indicated that EO exhibited relatively outstanding performance in decomposing dissolved organic matter (DOM) with rather complicated structures than EC. Also, the flow field-flow fractionation technique demonstrated that EO preferentially destroy humic-like, large molecular weight DOM, and converting them to smaller molecules, which resulted in more volatile organic compounds in EO samples than EC samples. While EC had little selectivity in the removal of organics, except humic-like DOM with relative small molecular. These findings can provide a theoretical basis for the electrochemical treatment of LMR.

Electrochemical removal of synthetic methyl orange dyeing wastewater by reverse electrodialysis reactor: Experiment and mineralizing model

In this paper, the synthetic methyl orange (MO) dyeing wastewater treated by a reverse electrodialysis reactor (REDR) with 40 member pairs was investigated first. The boron-doped diamond (BDD) and carbon felt were adopted as an anode and a cathode in the REDR. The influences of operation parameters on the chemical oxygen demand (COD) removal efficiency were detected and explored. Then, a mathematical model of organic mineralizing was developed for the REDR to predict the variation of COD removal efficiency with treating time under the different operation conditions. Finally, the energy consumption of the wastewater treated by the REDR was analyzed. The results showed that raising the working fluid flowing velocity and electrode rinse solution flowrate improved the COD removal efficiency and instantaneous current efficiency (ICE), and reduced the total energy consumption (TEC) of the REDR. Raising the initial MO concentration could significantly reduce the TEC despite the COD removal efficiency being near. Since the main energy consumed by the REDR was salinity gradient energy (SGE) from waste heat conversion or the natural environment, the energy cost of REDR treating wastewater has been reduced significantly.

Aqueous phase of thermo-catalytic reforming of sewage sludge – quantity, quality, and its electrooxidative treatment by a boron-doped diamond electrode

Pyrolysis is a promising conversion technology to produce biofuels from residues such as sewage sludge. In this study, the chemical composition and the amount of the resulting aqueous phase from the thermo-catalytic reforming process of sewage sludge at different process parameters are compared to those of non-catalytic fast pyrolysis processes from literature. Furthermore, electrooxidation using a boron-doped diamond (BDD) electrode was investigated as purification technology for the resulting aqueous phase. The results of this study show that the quantity of the aqueous phase strongly depends on the temperature of the thermo-catalytic reforming process and is presumably governed by the influence of secondary gas-carbonisate reactions like the water gas shift reaction. Higher reaction temperatures result in a reduced amount of the aqueous phase. The chemical composition of the aqueous phase of fast pyrolysis processes was comparable to that obtained at the thermo-catalytic reforming process. To reduce the chemical oxygen demand (COD) and the number of refractory substances to a level at which the aqueous phase can be discharged into a conventional wastewater treatment plant, electrooxidation experiments with the aqueous phase of the thermo-catalytic process were carried out using a BDD electrode. The treatment efficiency was investigated in galvanostatic operation varying the applied current density and the flow rate of the aqueous phase. A COD removal of 94.6% was achieved after 0.54kWh at an instantaneous current efficiency of 0.47 at a current density of 50 mA/cm2 and a flow rate of 3.7 L/min. This indicates that electrooxidation by a BDD electrode can be a promising purification technology for the aqueous phase from pyrolysis of sewage sludge. However, the high energy consumption of the process will need to be addressed in future studies to make the process economically feasible.

Removal of Bentazone Pesticide from Aqueous Solutions by Electro-oxidation Method

The kinetics of the electro-oxidation degradation of prepared aqueous solutions containing bentazone as a model compound of the thiadiazine group of pesticides was studied in the lab. The oxidation process was conducted under galvanostatic polarization in natural model media using boron-doped diamond (BDD) cathode and anode. Chemical oxygen demand (COD) estimation along the electro-oxidation treatment processing allowed the assessment of kinetic of organic compounds decay as well as the instantaneous current efficiency. The obtained data reflected that the degradation of bentazone pesticide is significantly dependent on initial amount of bentazone pesticide, current density and electrolytes concentration. COD removal follows a pseudo first-order kinetic and the electro-oxidation process was under the control of mass transport within the range studied, regardless the conditions of experimental. The COD removal rate increases with applied current density until 20 mA/cm2 and decreases for higher values. Two different concentrations supporting electrolyte (5mM, 10mM) were used. The rate of degradation increased significantly with increasing electrolyte concentration. The best obtained conditions for COD removal efficiency on the BDD electrode to degrade bentazone solutions (COD= 91.18 %) include operating at 20 mA/cm2 and 10 mM Na2SO4 as supporting electrolyte. This arrangement and condition allow to approximately complete degradation of bentazone in just 80 min. A decrease in the relative toxicity index value along the electro-oxidation indicate toxic compounds disappearance. The initial toxicity EC50 (5 min) and (15min) were decrease by 81% and 94% The kinetics of the electrooxidation degradation of prepared aqueous solutions containing bentazone as a model compound of the thiadiazine group of pesticides were studied in the lab. The oxidation process was conducted under galvanostatic polarization in natural model media using boron-doped diamond (BDD) cathodes and anode. Chemical oxygen demand (COD) estimation along the electro-oxidation treatment processing allowed the assessment of kinetic of organic compounds decay as well as the instantaneous current efficiency. The obtained data reflected that the degradation of bentazone pesticide is significantly dependent on initial amount of bentazone pesticide, current density and electrolytes concentration. COD removal follows a pseudo first-order kinetic and the electrooxidation process was under the control of mass transport within the range studied, regardless the conditions of experimental. The COD removal rate increases with applied current density until 20 mA/cm2 and decreases for higher values. Two different concentration (5mM, 10mM) were used. The rate of degradation increased significantly with increasing electrolyte concentration. The best obtained conditions for COD removal efficiency on the BDD electrode to degrade bentazone solutions (COD= 91.18 %) include operating at 20 mA/cm2 and 10 mM. This arrangement and condition allow to approximately complete degradation of bentazone in just 80 min. A decrease in the value of  relative toxicity index along the electrolysis indicate the disappearance of toxic compounds. The initial toxicity EC50 (5min) and (15min) were reduced by 81% and94% respectively after 80 minutes.

Chelate-modified Electro-Fenton process for mixed industrial wastewater treatment

ABSTRACT Mixed industrial wastewater (combined wastewater from small-scale industries) treatment is challenging due to the change in characteristics of the wastewater ( time and quantity). The Electro-Fenton (EF) process is one of the effective techniques for the degradation of organic pollutants from the wastewater, but it works under low pH condition, which is one of the major disadvantages of the EF process. To overcome this disadvantage, the chelate-modified EF process was used in this study. In the chelate-modified EF process, EDTA was used as the chelating agent to form complex with Fe ions and to enhance Fenton reaction at near neutral pH. Ti electrode coated with RuO2 was used as anode and graphite as cathode. The batch reactor was operated by varying initial pH, Fenton reagent dosage and chelating agent dosage. The results demonstrate that the chelate-modified EF process gives effective COD removal (67%) at near neutral pH, as comparable to that of the EF process (66%) at acidic pH. Highlights The Chelate-modified EF process for the removal of COD at near neutral pH Treatment of the mixed industrial wastewater with very low BOD/COD ratio Influence of Fenton catalyst and chelating agent dosage on COD removal. Comparable COD removal of 67% with Chelate-modified EF at near neutral pH and 66% with EF at acidic pH. Mineralization current efficiency and instantaneous current efficiency for COD removal.

A novel electrodeposited sandwich electrode with an efficient performance in complex water treatment

The use of an electrocatalytic surface coating is important in environmental remediation using electrochemistry. In this work, a novel Ti/calcined graphene (CG)/PbO2 sandwich electrode was successfully fabricated by a simple electrodeposition strategy for the efficient electrocatalytic oxidation of dye wastewater. The Ti/CG/PbO2 electrode coating was uniform and the structure was compact. As the electrocatalyst was rich in graphene, the novel electrode possessed higher oxygen evolution potential, lower charge transfer resistance, stronger stability, longer service life and higher instantaneous current efficiency (ICE) compared with traditional Ti/PbO2 electrode, thus exhibited better electrocatalytic oxidation activity and mineralization capacity. At a current density of 50 mA/cm2, up to 30 mg/L of methylene blue (MB) was almost completely oxidized in 1 h, while the MB removal efficiency at the Ti/PbO2 electrode only reached 78.2 ± 0.01%. Various influencing factors were designed to simulate the changes of the wastewater system, importantly and interestingly, the electrode still owned the advantages of high-efficiency electrocatalytic oxidation in the complex changes of a wastewater system like pH range of 3–11 and various electrolyte concentrations. The as-prepared electrode could still maintain good degradation efficiency after 30 cycles. It was worth mentioning that the COD value was reduced to about 0 when using this electrode to deal with the actual printing and dyeing wastewater. The results showed that the Ti/CG/PbO2 electrode was promising in the degradation of pollutants.

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.

Electrochemical degradation of dye on TiO2 nanotube array constructed anode

A high oxygen evolution potential (2.6V) and conductivity of Ti/TiO2 NTs/Ta2O5-PbO2 anode was fabricated by mixed metal oxide. A well-aligned TiO2 nanotubes was successfully prepared by using 1-butyl-3-methylimidazolium tetrafluoroborate as the electrolyte. The surface structure of anodes were characterized by scanning electron microscope, X-ray diffraction and energy dispersive X-ray spectroscopy. During the electrochemical degradation experiments, the effects of different anodes, current density, initial pH value and concentration were discussed. The results showed that co-doped Ta2O5 coating is an effective method to improve the surface morphology and the electrochemical characterization of Ti/TiO2 NTs/PbO2. At the initial pH value of 3 and current density of 12 mA cm−2, the removal rates of Acid Orange 7 and total organic carbon with Ti/TiO2 NTs/Ta2O5-PbO2 anode were almost 100% and 98.3%. Comparing with Ti/PbO2 anode at the same charge consumption (3 A h L−1), the instantaneous current efficiency of the Ti/TiO2 NTs/Ta2O5-PbO2 anode and Ti/TiO2 NTs/PbO2 anode increased by 40.0% and 27.1%, respectively. The highest rate of k.OH on Ti/TiO2 NTs/Ta2O5-PbO2 anode was 12.4 μmol (L min)−1. The organic dyes are oxidized into CO2 and H2O by .OH radical. The reaction process and mechanism during the electrochemical degradation were discussed.

Electrochemical degradation of methylisothiazolinone by using Ti/SnO2-Sb2O3/α, β-PbO2 electrode: Kinetics, energy efficiency, oxidation mechanism and degradation pathway

Methylisothiazolinone (2-methyl-4-isothiazolin-3-one) (MIT) is a commonly used biocide in wastewater treatment processes. Residual MIT in wastewater leads to high environmental risks and toxicity. The degradation of MIT via electrochemical oxidation, including kinetics, energy efficiency, oxidation mechanism and degradation pathway, was investigated in this study. Findings from energy and cost evaluation by using electrochemical technology were compared with those of other technologies. Experimental results indicate that electrolyte, current density and initial concentration can significantly affect MIT degradation. The lowest electrical energy per order was less than 3.85 kWh m−3 when NaCl was used as the electrolyte. Electrochemical degradation is advantageous because it can be easily applied without adding chemicals into wastewater and has relative low costs. The oxygen evolution, production of recalcitrant byproducts, and the mass transfer limitation resulted in the decrease of instantaneous current efficiency and mineralization current efficiency. Electron efficiency analysis demonstrated that 68.8% of the electrons used for MIT oxidation were effectively utilized to mineralize MIT into CO2. The proportion of direct and indirect oxidation of MIT during electrochemical degradation was quantitatively determined as 37.7% and 62.3%, respectively. HO was the most effective species for MIT degradation. MIT degradation pathway was proposed, in which the CC bond in MIT was broken down. C3H7NOS and C3H7NO4 were detected, indicating the occurrence of ring opening reaction. Sulfur was oxidized into SO42− and cleaved from C3H7NOS.

Electrochemical destruction of RB5 on Ti/PtOx–RuO2–SnO2–Sb2O5 electrodes: a comparison of two methods for electrode preparation

The studies were performed with 100 mg/L of Reactive Black 5 dye (RB5) in batch reactors on Ti/PtOx–RuO2–SnO2–Sb2O5 electrodes prepared indigenously. The electrodes were fabricated using titanium substrate (plate) and coated with mixed metals of a fixed composition by standard thermal decomposition (STD) and polymeric precursor thermal decomposition (PPTD) methods. The electrolysis up to 1 h was accomplished at a constant current density of 50 mA/cm2. For the process, an initial pH of 2 was maintained with the dosage of 4 g/L NaCl as supporting electrolyte. The effects of electrodes on colour, chemical oxygen demand, and total organic carbon removal were investigated for destruction of RB5. In this comparative study, while complete decolourizations of water containing RB5 were achieved on the electrodes prepared by STD and PPTD methods, but COD and TOC removal was found to be different for different electrodes at operating conditions. The 87% COD and 83% TOC removals were achieved on Ti/PtOx–RuO2–SnO2–Sb2O5 electrode prepared by PPTD method, in comparison to 83% COD and 80% TOC removals on the electrode prepared by STD method. The two types of electrodes were compared based on removal rate constant, mass transfer coefficient, instantaneous current efficiency, energy consumption, and accelerated life test. The energy demand for RB5 removal in this study was less than 250 kWh/kg COD, which is much lower than the reported values in similar studies. Further, the performance of electrodes was compared employing scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis for coating deposited on Ti substrate, and also by cyclic voltammetry.

What is the efficiency of electro-generation of chlorine with a solid polymer electrolyte assembly?

The use of a solid polymer electrolyte (SPE) in an anode/SPE/cathode sandwich has emerged as a promising electrochemical configuration to reduce the terminal voltage and thus energy consumption during electrolysis. This study for the first time investigates and compares the efficiency of the electrochemical chlorine production process as well as estimates and compares energy consumption with and without a SPE assembly in the electrolytic cell. Results indicate that at the same current density of 12.5 mA/cm2, Cl2 production rate and instantaneous current efficiency (ICE) were higher when no SPE was used than with a functional SPE, most likely because the SPE occupied one side of the electrode surface, thus limiting the contact of Cl− with its surface to generate Cl2. However, increasing the current density to 31.25 mA/cm2 with a functional SPE resulted in an almost equal Cl2 production rate to that at 12.5 mA/cm2 without a functional SPE, and still the energy consumption per mass of produced Cl2 was the same, although lower ICE was achieved. The study also further investigated the effect of flowrate, and the influence of initial Cl− concentration and the initial pH for the system with the functional SPE.

Towards the scale up of a pressurized-jet microfluidic flow-through reactor for cost-effective electro-generation of H2O2

The performance of a novel pressurized-jet microfluidic flow-through electrolyzer for the production of aqueous solution of H2O2 is assessed in this work. The reactor design is based on three aspects i) minimizing ohmic drops, by reducing the interelectrode gap to 150 μm and the use of a Duocel® aluminum foam as cathodic support; ii) maximizing mass transport, due to the use of three-dimensional electrodes fed in flow-through and iii) optimizing the aeration system coupling a pressurized circuit and a jet aerator. Results show that H2O2 can be produced with an instantaneous current efficiency of ≅ 100% up to 20 mA cm−3 and a corresponding production rate of 13.1 mg H2O2 h−1 cm−3 in a cathode of 16.5 cm3. Low ohmic resistances were measured even in low-conductive electrolytes, as for example 6 Ω in 0.0035 M Na2SO4 (0.7 mS cm−1). The electrical energy consumption of 3.65 kWh kg H2O2−1 at 10 mA cm−3 in 0.05 M Na2SO4 is the lowest reported so far in neutral-acid medium, confirming the cost-effectiveness of the system. A preliminary scale-up by increasing the cathode volume three times (up to 49.5 cm3) allowed the production rate to be multiplied by the same factor and confirms that the system is scalable. Theoretical calculations suggest that the cathode could be expanded up to 3600 cm3 (1 m thickness) under those aeration conditions (6 bar and 160 dm3 h−1 recirculation flow).

Preparation and characterization of Fe-Ce co-doped Ti/TiO2 NTs/PbO2 nanocomposite electrodes for efficient electrocatalytic degradation of organic pollutants

To further improve the electrocatalytic activity and stability of PbO2 electrode in refractory organic pollutants treatment, Fe and Ce co-doped Ti/TiO2 nanotube (TNTs)/PbO2 electrode was successfully synthesized by pulse electrodeposition. The morphology, crystallinity and elemental composition Ti/TNTs/Fe-Ce-PbO2 electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impendence spectroscopy (EIS) were utilized to investigate the electrochemical performance of electrodes. Results showed that Ti/TNTs/Fe-Ce-PbO2 electrodes (P) possessed finer grain size and higher specific surface than other three PbO2-based electrodes. The electrochemical measurements showed that Ti/TNTs/Fe-Ce-PbO2 electrodes (P) exhibited higher oxidation peak current, oxygen evolution potential and strong capability of ·OH generation than those of other three kinds of electrodes. The experiments on degradation of methylene blue (MB) also indicated that Ti/TNTs/Fe-Ce-PbO2 electrodes (P) have higher chemical oxygen demand (COD) removal efficiency and instantaneous current efficiency (ICE) than the Ti/TNTs/Fe-Ce-PbO2 electrodes (D). Meanwhile, high reusability and safety were achieved by Ti/TNTs/Fe-Ce-PbO2 electrodes (P) when treating wastewater containing organic dyes.

Construction of a bifunctional electrode interface for efficient electrochemical mineralization of recalcitrant pollutants

To further improve the electrochemical performance of a boron-doped diamond (BDD) electrode, a two-dimensional, macroporous, Sb-doped SnO2 film is constructed on BDD to obtain a bifunctional electrode interface (denoted Mp-SnO2/BDD) with an ordered, monolayer, photonic-crystal template using a sol-gel method. SEM images confirm that the SnO2 film consisted of innumerable, uniform, nanosized SnO2 particles and numerous macropores with diameters of 200–300 nm, and some BDD polycrystallites are exposed in those macropores. The microstructure endows Mp-SnO2/BDD with a high oxygen evolution potential (2.23 V), good conductivity (175 O), and excellent electrocatalytic activity. To evaluate the degradation capability, the electrocatalytic oxidation of a high concentration of clofibric acid (CA) is studied in detail. The CA and chemical oxygen demand (COD) removals on Mp-SnO2/BDD are above 90% after 240 min. The degradation rate constant on Mp-SnO2/BDD is 1.6 times that on BDD. Compared with BDD and traditional SnO2/Ti, Mp-SnO2/BDD exhibites a higher instantaneous current efficiency and lower electrochemical energy consumption. In addition, we qualitatively and quantitatively analyze the intermediates in the degradation process and proposed three possible oxidative decomposition pathways for CA. Mp-SnO2/BDD is expected to be a promising anode for organic wastewater treatment.

Maximization of current efficiency for organic pollutants oxidation at BDD, Ti/SnO2-Sb/PbO2, and Ti/SnO2-Sb anodes

Whereas electrochemical oxidation is noted for its ability to degrade bio-refractory organics, it has also been incorrectly criticized for excessive energy consumption. The present paper rectifies this misunderstanding by demonstrating that the energy actually consumed in the degradation process is much less than that wasted in the side reaction of oxygen evolution. To minimize the side reaction, the possible highest instantaneous current efficiency (PHICE) for electrochemical oxidation of phenol at Boron-doped Diamond (BDD), Ti/SnO2-Sb/PbO2 (PbO2), and Ti/SnO2-Sb (SnO2) anodes has been investigated systematically, and found to reach almost 100% at the BDD anode compared with 23% at the PbO2 anode and 9% at the SnO2 anode. The significant discrepancy between PHICE values at the various anodes is interpreted in terms of different existing forms of hydroxyl radicals. For each anode system, the PHICEs are maintained experimentally using a computer-controlled exponential decay current mode throughout the electrolysis process. For applications, the minimized energy consumption is predicted by response surface methodology, and demonstrated for the BDD anode system. Consequently, almost 100% current efficiency is achieved (for a relatively meagre energy consumption of 17.2 kWh kgCOD−1) along with excellent COD degradation efficiency by optimizing the initial current density, flow rate, electrolysis time, and exponential decay constant. Compared with galvanostatic conditions, over 70% of the energy is saved in the present study, thus demonstrating the great potential of electrochemical oxidation for practical applications.