Modified Graphite Felt Cathode Research Articles

TCE degradation of modified graphite felt cathode in a flow-through electro-Fenton system and its H2O2 production ability in a real contaminated field

A modified graphite felt (MGF) was prepared with carbon black (CB) and polytetrafluoron (PTFE) for cathodic electrochemical H2O2 production, which was used in a flow-through cathodic electro-Fenton reactor to degrade chlorinated hydrocarbons. Cathode electrode was floating on aqueous surface and 369.1 mg/L H2O2 could be produced after 1 h 150 mA power applied without O2 aeration. The main O2 source for H2O2 production was confirmed from air with this floating position. In a 2.0 L flow-through cathodic electro-Fenton system, 95.97 % degradation efficiency for 5.0 mg/L trichloroethylene (TCE) was achieved in 90 min with 13.4 mL/min influent rate. Reducing the reactor volume to 0.14 L, 5.0 mg/L TCE could be degraded completely in 10 min with continuous 4 L influent. The mixed chlorinated hydrocarbons (TCE, cis-1,1-dichloroethylene, 1,2-dichloroethane, and dichloromethane) were also rapidly degraded in 20 min. The flow-through cathodic electro-Fenton reactor presented excellent degradation ability for chlorinated hydrocarbons with a smaller volume. In the simulated sand tank system, after continuously operated 27 days, H2O2 concentration in electrode well was still remained at 80 mg/L. In the contaminated field in Tianjin, China, H2O2 yield of MGF in groundwater could keep at about 60 mg/L after 220 min operating.

Promoted electrochemical degradation of triclosan with persulfate on Fe-Ni oxide modified graphite felt cathode

Advanced oxidation processes (AOPs) based on persulfate (PS) have shown great potential in wastewater treatment. In this work, FeNiO-modified Graphite felts (GF) cathodes (FeNiO/GF) were prepared to construct an activation system for electrochemical activation of persulfate (EA-PS). The effect of condition parameters (current density, PS concentration and pH) on the degradation of triclosan (TCS) in the EA-FeNiO/GF-PS system was investigated. The results showed that FeNiO loaded on the GF enhanced the cathodic activation of PS. The EA-FeNiO/GF-PS system showed excellent degradation of various pollutants at PS concentration of 1.0 mM and current density of 10 mA/cm2. Electron paramagnetic resonance and free radical quenching experiments showed that •OH, SO4•–, O2•– and 1O2 all contributed to the degradation of triclosan (TCS), with SO4•– and •OH being the major free radicals. The electrochemical performance tests and the XPS characterization of the FeNiO electrode results demonstrated that the valence cycling of Fe and Ni was accelerated under the action of an electric field. In addition, FeNiO/GF had excellent reusability and was unaffected by the actual water matrices. This study provided an effective strategy for the degradation of organic pollutants in water treatment.

In-situ fabrication from MOFs derived MnxCo3-x@C modified graphite felt cathode for efficient electro-Fenton degradation of ciprofloxacin

Since high degradation efficiency and environmental friendliness, the Electro-Fenton technology has been widely applied to remove antibiotics in wastewater. In-situ loading of electrochemically active metals on graphite felt (GF) is considered as a promising strategy for improving its electrocatalytic activity and reusability. Here, a series of Mn/Co MOFs derivatives modified graphite felt cathodes (MnxCo3-x@C-GF) were fabricated without any binder, which was used for the treatment of ciprofloxacin (CIP). The morphology, pore structure and electrochemical activity of MnxCo3-x@C-GF changed by adjusting the ratio of Mn/Co in the MOF-74 precursor. Owning to the optimized Mn/Co ratio, Mn2Co1@C-GF exhibited the most excellent catalytic ability with hierarchical porous structure and faster electron transfer. The results showed that the CIP degradation efficiency could reach 99.8% in 60 min. Mn2+/3+/4+ and Co3+/2+ enhanced the generation of active radicals (·OH) by Fenton-like reaction and further improved degradation performance. In addition, the cathode had maintained good stability during four cycles. This work provides an alternative strategy for fabricating efficient self-supporting cathode materials in the future.

Electrogeneration of H2O2 utilizing anodic O2 on a polytetrafluoroethylene-modified cathode in a flow-through reactor

Efficient electrogeneration of hydrogen peroxide (H2O2) is critical for treatment of refractory pollutants by the electro-Fenton process. An effective strategy is developed by combining a flow-through reactor with a polytetrafluoroethylene (PTFE)-modified graphite felt cathode. In this design, anodic oxygen is directly used for efficient H2O2 generation at the modified cathode. Experimental results show that the modified cathode with the optimum PTFE content can produce 29.6 mg/L of H2O2, which is 16 times higher than the unmodified graphite felt cathode for a flow rate of 3 mL/min. Maximum H2O2 production, up to 30.7 mg/L, was obtained under the following conditions: 120 mA, 3 mL/min, initial pH 13, no external aeration.

A novel core-shell Fe@Co nanoparticles uniformly modified graphite felt cathode (Fe@Co/GF) for efficient bio-electro-Fenton degradation of phenolic compounds

In this study, a core-shell Fe@Co nanoparticles uniformly modified graphite felt (Fe@Co/GF) was fabricated as the cathode by one-pot self-assembly strategy for the degradation of vanillic acid (VA), syringic acid (SA), and 4-hydroxybenzoic acid (HBA) in the Bio-Electro-Fenton (BEF) system. The Fe@Co/GF cathode showed dual advantages with excellent electrochemical performance and catalytic reactivity not only due to the high electron transfer efficiency but also the synergistic redox cycles between Fe and Co species, both of which significantly enhanced the in situ generation of H2O2 and hydroxyl radicals (OH) to 152.40 μmol/L and 138.48 μmol/L, respectively. In this case, the degradation rates of VA, SA, and HBA reached 100, 94.32, and 100%, respectively, within 22 h. Representatively, VA was degraded and ultimately mineralized via demethylation, decarboxylation and ring-opening reactions. This work provided a promising approach for eliminating typical recalcitrant organic pollutants generated by the pre-treatment of lignocellulose resources.

Modification of graphite felt doped with nitrogen and boron for enhanced removal of dimethyl phthalate in peroxi-coagulation system and mechanisms.

To enhance the generation of hydrogen peroxide (H2O2), a modified graphite felt cathode doped with nitrogen and boron was developed and used in peroxi-coagulation system to degrade dimethyl phthalate (DMP). After a simple modification method, the yield of H2O2 on cathode increased from 9.39 to 152.8mg/L, with current efficiency increased from 1.61 to 70.3%. Complete degradation of DMP and 80% removal of TOC were achieved within 2h at the optimal condition with pH of 5, cathodic potential of - 0.69V (vs. SCE), oxygen aeration, and electrode gap of 1cm. Possible mechanism with synergistic effect of electro-Fenton and electrocoagulation process in the peroxi-coagulation system was revealed via quenching experiments. The prospect of this system in the effluent of landfill leachate and domestic sewage was studied, achieving 50% and 61% of DMP removal in 2h. This efficient system with simple modified cathode had promising prospects in practical applications.

Electro-Fenton and photoelectro-Fenton degradation of sulfamethazine using an active gas diffusion electrode without aeration

A novel superhydrophobic gas diffusion electrode based on carbon black (CB)- polytetrafluoroethylene (PTFE) modified graphite felt cathode was prepared to increase oxygen mass transfer efficiency and produce hydrogen peroxide at the gas-liquid-solid three-phase interface without aeration. The gas diffusion electrode system was further tested for the degradation of sulfamethazine (SMT) by electro-Fenton (EF) and photoelectro-Fenton (PEF). In the EF process, SMT was removed effectively, but the mineralization degree was not high due to the generation of organic acids which were difficult to be further degraded. While in the PEF process, organic contaminant can be destroyed by the combined action of Fe2+/H2O2, UV/H2O2 and UV radiation, and more efficient mineralization (>83.5%) at low current (50 mA) was attained, which might be attributed to the high H2O2 utilization (70–90%), rapid regeneration of Fe2+ and photolysis of intermediates. In addition, it was verified that the PEF system had a good adaptability to pH and pollutant concentration. Compared with aeration system, the use of this active gas diffusion cathode in electrochemical advanced oxidation processes significantly reduced energy consumption.

Acid modified graphite felt cathode electrode for low temperature H2/Br2 redox flow battery

Acid modified graphite felt cathode electrode for low temperature H2/Br2 redox flow battery

Kinetics and mechanisms of oxytetracycline degradation in an electro-Fenton system with a modified graphite felt cathode

The removal of trace antibiotics from the aquatic environment has received great interest. In this investigation, NaOH activated graphite felt (NaOH-GF) was characterized by multiple-methods, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle, linear sweep voltammetry (LSV) and electron paramagnetic resonance (EPR). The NaOH-GF was then used as the cathode in the electro-Fenton process for oxytetracycline (OTC) degradation, the experiment was carried out in an undivided and light-proof beaker with a Pt anode and a NaOH-GF cathode at pH 3. The results showed that the modification with NaOH enhanced the antibiotics degradation efficiency of graphite felt by increasing the oxygen reduction capacity and hydroxyl radicals yielding rate. Complete OTC removal was achieved at 5.17 mA cm−2 after 40, 60 and 90 s with initial OTC concentration of 22, 44, and 66 μM, respectively. With an initial OTC concentration of 44 μM, after 30 min the removal rates of chemical oxygen demand (COD) by Raw-GF and NaOH-GF were 59.18% and 83.75%, respectively. The proposed degradation mechanism of OTC was an EF process, which consisted of hydroxylation, secondary alcohol oxidation, demethylation, decarbonylation, dehydration and deamination. This study demonstrates that NaOH activated GF cathode possesses high degradation capacity and good stability. It provides insight into the removal of non-biodegradable antibiotics and may shed light on future to its practical application.

Self-powered electrochemical system by combining Fenton reaction and active chlorine generation for organic contaminant treatment

Environmental deterioration, especially water pollution, is widely dispersed and could affect the quality of people’s life at large. Though the sewage treatment plants are constructed to meet the demands of cities, distributed treatment units are still in request for the supplementary of centralized purification beyond the range of plants. Electrochemical degradation can reduce organic pollution to some degree, but it has to be powered. Triboelectric nanogenerator (TENG) is a newly-invented technology for low-frequency mechanical energy harvesting. Here, by integrating a rotary TENG (R-TENG) as electric power source with an electrochemical cell containing a modified graphite felt cathode for hydrogen peroxide (H2O2) along with hydroxyl radical (•OH) generation by Fenton reaction and a platinum sheet anode for active chlorine generation, a self-powered electrochemical system (SPECS) was constructed. Under the driven of mechanical energy or wind flow, such SPECS can efficiently degrade dyes after power management in neutral condition without any O2 aeration. This work not only provides a guideline for optimizing self-powered electrochemical reaction, but also displays a strategy based on the conversion from distributed mechanical energy to chemical energy for environmental remediation.

Novel electrodes for cathode electro-Fenton oxidation coupled with anodic oxidation system for advanced treatment of livestock wastewater

With the rapid development of livestock industry, a large amount of livestock wastewater generates in China in recent years. The conventional treatment process for livestock wastewater, including anaerobic digestion and anoxic-oxic treatment, is very common in China for the low operational cost. However, the very low BOD5/CODCr ratio (<0.1) in the associated effluent renders the further treatment process very difficult. In this study, a PbO2 anode coupled with a 2-ethylanthraquinone (EAQ)-modified graphite felt cathode was used to treat the livestock wastewater (BOD5/CODCr < 0.1) discharged from the conventional two-stage anoxic/oxic (A/O) process. The results of scan electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transforminfrared spectroscopy (FTIR) show that the prepared PbO2 electrode has a smaller crystal size, higher oxygen evolution reaction (OER) potential and an excellent electro-catalytic performance compared to a purchased PbO2 electrode, and the EAQ-modified graphite felt cathode has a higher content of oxygen-containing functional groups and higher oxygen reduction reaction (ORR) electro-catalytic performance than pristine graphite felt. The results of the electrolysis experiment showed that the BOD5/CODCr ratio was increased from 0.084 to 0.42 with 71.5% CODCr removal after 80 min of electrolysis, when the Fe2+ concentration was 0.3 mM. The .OH produced in the electrolysis system was captured successfully by electron paramagnetic resonance (EPR).

Enhanced activation of hydrogen peroxide using nitrogen doped graphene for effective removal of herbicide 2,4-D from water by iron-free electrochemical advanced oxidation

Degradation of the herbicide 2,4-dichlorophenoxiacetic acid (2,4-D) in aqueous solutions has been studied by electrochemical oxidation process using N-doped graphene modified graphite felt cathode with ammonium nitrate as nitrogen source. The graphene was obtained via electrochemically exfoliated method (EEGr). Different ratios of EEGr/ammonium nitrate (1:0, 1:1, 1:3, 1:7) modified cathodes (N0-EEGr-GF, N1-EEGr-GF, N3-EEGr-GF, N7-EEGr-GF) were explored with electrochemical characterizations, and it was verified that N1-EEGr had the most significant catalytic performance for accelerating the activation of in-situ generated H2O2 into hydroxyl radicals. The effects of operating parameters such as applied potential, solution pH and initial concentration of 2,4-D on the degradation efficiency with N1-EEGr-GF were investigated. A fairly high mineralization rate (88%) was attained at pH 7 after 480 min electrolysis of 20 mg L−12,4-D solution. The N-doped graphene as catalyst was found to be more efficient in degradation performance compared with the unmodified graphite felt cathode. The electrochemical advanced oxidation process using this modified cathode allows extension of the working pH range compared to electro-Fenton process which is optimal at pH 3. Finally, a plausible pathway for 2,4-D mineralization was proposed according to the identified intermediated products.

Persulfate enhanced photoelectrocatalytic degradation of cyanide using a CuFe2O4 modified graphite felt cathode

In order to remove cyanide (CN−) from wastewater, a photoelectrocatalytic (PEC) system was constructed using TiO2 nanorods (NRs) anode and CuFe2O4 modified graphite felt (CuFe2O4/GF) cathode. With the addition of persulfate (PS), the performance of PEC for the removal of CN− with an initial concentration of 0.9 mM was increased from 31.10% to 98.21% in 120 min and the pseudo-first-order rate constant was calculated to be 0.0314 min−1. The removal rate of CN− was accelerated with the decrease of initial CN− concentration and the increase of PS dose. The optimal bias potential for the removal of CN− and the recovery of Cu was 1.00 V. Results of radical quenching experiments and electron spin resonance analysis suggested that OH and SO4− were generated by a Fenton-like process in the PEC/PS system. As proved by the XPS analysis, Cu(II) in CuFe2O4 cathode was dissolved by CN− into solution and then partially transformed to Cu(I). When CN− was removed, dissolved Cu ions were deposited onto the surface of CuFe2O4 cathode forming Cu2O. In addition, the dissolved Cu ions can also be deposited on TiO2 photoanode forming CuO. Cu(I) ions reacted with PS through a Fenton-like reaction, generating SO4−, which enhanced the oxidation ability of the PEC/PS system. The results provided a promising way to treat the industrial cyanide effluents efficiently.

Highly energy-efficient removal of acrylonitrile by peroxi-coagulation with modified graphite felt cathode: Influence factors, possible mechanism

A highly energy-efficient peroxi-coagulation (PC) process was developed based on modified graphite felt, and the acrylonitrile removal efficiency was also comparatively studied by electro-Fenton (EF) and electrocoagulation (EC). The results showed that acrylonitrile was slowly and ineffectively removed by EC and EF, whereas by PC it was not only more rapid, but also effective at wide pH ranges of 3.0–9.0, which overcame the pH limitations for EC and EF. In addition, the electric energy consumption (EEC) of EF, EC and PC was 36.01, 14.43 and 3.08 kWh/kg respectively, suggesting PC was more economical. The influence of important operating factors such as pH, applied current and initial concentration were investigated for these three processes. The production of OH and transformation of iron ions were analyzed to explore the mechanisms of PC process. Compared to conventional treatment methods, PC was more cost-effective due to the combined action of OH as well as the coagulation with the formed Fe(OH)3 precipitate. Primary intermediates were identified by GC–MS analysis, and a possible pathway was proposed by the action of OH in EF and the hydrogenation in EC. This work demonstrated that PC is cost-effective and has potential for the degradation of acrylonitrile.

Energy efficiency improvement on in situ generating H2O2 in a double-compartment ceramic membrane flow reactor using cerium oxide modified graphite felt cathode

Electrochemical technology offers the possibility of in situ hydrogen peroxide generation whose productivity greatly depends on the cathode properties and the reactor configuration. Herein, cerium oxide modified graphite felt is prepared and used as cathode. Ceramic membrane is integrated dividing the cell to two compartments and preventing decomposition of cathode-generated H2O2 at the anode. H2O2 is found almost impermeable through the membrane as concentration difference <0.5M. The double-cell reactor performs higher energy efficiency than the conventional electrolytic cell. And H2O2 accumulation rate has been enhanced in the double-cell in comparison with the undivided one, no matter using either bared or modified cathode. Operation parameters including flow rate of O2 (FO2), flow rate of electrolyte solution (Fsolution), applied current (I) and pH were optimized. Accumulated concentration of H2O2 on the modified cathode reached 260.7mg/L with the current efficiency up to 75.7% (working conditions CNa2SO4=0.05M, pH=2, I=50mA, FO2=0.2L/min and Fsolution=800μL/min). The yield was 3.8 times higher than using the unmodified cathode. Energy consumption was reduced to 4.8kWh/kg in the double-cell system (22.1kWh/kg in the single-cell). In a conclusion, the double-compartment flow reactor is an improved configuration for energy effectiveness and increased productivity of H2O2 for E-Fenton process.

Graphite felt electrochemically modified in H2SO4 solution used as a cathode to produce H2O2 for pre-oxidation of drinking water

Abstract The efficiency of graphite felt (GF) as a cathode to electro-generate H2O2 in neutral water was improved after the GF was electrochemically oxidized in H2SO4 solution. Raman spectra, SEM and XPS showed that certain oxygen-containing functional groups were introduced onto the surface of the GF after modification. The electrochemical behavior of the electrodes showed that the 2-electron-reduction of oxygen gas on the modified GF cathode was enhanced which is beneficial for the electrochemical generation of H2O2 in neutral water. The electrolysis tests in static and flowing cells showed that the efficiency of electro-generation of H2O2 for the treated GF increased by 6 times as compared with the original one.

Electrogeneration of hydrogen peroxide for electro-Fenton system by oxygen reduction using chemically modified graphite felt cathode

A simple chemical method using hydrazine hydrate as the main reagent was firstly used to modify graphite felt as cathode for efficient electro-Fenton process. The influences of the different concentration of hydrazine hydrate were comparatively studied on the yield and current efficiency of H2O2 production, confirming that the modified cathode had much higher electrocatalytic activity. The optimum concentration of the hydrazine hydrate was 10%, and the yield of H2O2 was as 2.6 times as that without modification under the same conditions. The cyclic voltammetry analysis indicated that the modified cathodes exhibited stronger current responses and more negative hydrogen evolution potentials than the unmodified one. The operational parameters such as cathodic potential, pH and O2 flow rate were optimized for the efficient H2O2 electrogeneration. The maximum accumulation of H2O2, up to 247.2mg/L, was obtained at −0.75V (vs. SCE) and O2 flow rate of 0.4L/min. The influence of pH on the yield of H2O2 was slight, but it was obvious on current efficiency. The modified cathode was confirmed to be more efficient in degradation of p-nitrophenol by electro-Fenton process at both acidic and neutral pH, indicating the positive effect of chemical modification onto the performance.

Conversion of Carbon Dioxide to Metabolites by &amp;lt;i&amp;gt;Clostridium acetobutylicum&amp;lt;/i&amp;gt; KCTC1037 Cultivated with Electrochemical Reducing Power

In this research, metabolic fixation of CO2 by growing cells of C. acetobutylicum cultivated with electrochemical reducing power was tested on the basis of the metabolites production and genes expression. In cyclic voltammetry, electrochemical oxidation and reduction reaction of neutral red (NR) immobilized in intact cells of C. acetobutylicum was stationarily repeated like the soluble one in the condition without CO2 but the electrochemical reduction reaction was selectively increased by addition of CO2. In electrochemical bioreactor, the modified graphite felt cathode with NR (NR-cathode) induced C. acetobutylicum to generate acetate, propionate, and butyrate from CO2 in defined medium. When H2 and CO2 were used as an electron donor and an electron acceptor, respectively, C. acetobutylicum also produced the same metabolites in a defined medium. C. acetobutylicum was not grown in the defined medium without substituted electron donors (H2 or electrochemical reducing power). C. acetobutylicum cultivated with electrochemical reducing power produced more butyrate than acetate in complex medium but produced more acetate than butyrate in defined medium. The genes of encoding the enzymes catalyzing acetyl-CoA in C. acetobutylicum electrochemically cultivated in defined medium than conventionally cultivated in complex medium. These results are a clue that C. acetobutylicum may metabolically convert CO2 to metabolites and produce free energy from the electrochemical reducing power.

Bioelectrochemical Mn(II) Leaching from Manganese Ore by Lactococcus lactis SK071115

L. lactis sk071115 has been shown to grow more actively and generate lower levels of lactate in glucose-defined medium with nitrate than in medium with Mn(IV). By adding Mn(IV) to a L. lactis culture, lactate production was relatively reduced in combination with Mn(II) production, but cell mass production levels did not increase. Both cell-free extract and intact L. lactis cells reacted electrochemically with Mn(IV) but did not react with Mn(II) upon cyclic voltammetry using neutral red (NR) as an electron mediator. A modified graphite felt cathode with NR (NR-cathode) was employed to induce electrochemical reducing equivalence for bacterial metabolism. Cell-free L. lactis extract catalyzed the reduction of Mn(IV) to Mn(II) under both control and electrochemical reduction conditions; however, the levels of Mn(II) generated under electrochemical reduction conditions were approximately 4 times those generated under control conditions. The levels of Mn(II) generated by the catalysis of L. lactis immobilized in the NR-cathode (L-NR-cathode) under electrochemical reduction conditions were more than 4 times that generated under control conditions. Mn(II) production levels were increased by approximately 2.5 and 4.5 times by the addition of citrate to the reactant under control and electrochemical reduction conditions, respectively. The cumulative Mn(II) produced from manganese ore by catalysis of the L-NR-cathode for 30 days reached levels of approximately 3,800 and 16,000 mg/l under control and electrochemical reduction conditions, respectively. In conclusion, the electrochemical reduction reaction generated by the NR-cathode activated the biochemical reduction of Mn(IV) to Mn(II) by L. lactis.

Improvement of Ethanol Production by Electrochemical Redox Coupling of Zymomonas mobilis and Saccharomyces cerevisiae

Zymomonas mobilis was immobilized in a modified graphite felt cathode with neutral red (NR-graphite cathode) and Saccharomyces cerevisiae was cultivated on a platinum plate anode to electrochemically activate ethanol fermentation. Electrochemical redox reaction was induced by 3 approximately 4 volt of electric potential charged to a cathode and an anode. Z. mobilis produced 1.3 approximately 1.5 M of ethanol in the cathode compartment and S. cerevisiae did 1.7 approximately 1.9 M in the anode compartment for 96 hr. The ethanol production by Z. mobilis immobilized in the NR-graphite cathode and S. cerevisiae cultivated on the platinum plate was 1.5 approximately 1.6 times higher than those cultivated in the conventional condition. The electrochemical oxidation potential greatly inhibited ethanol fermentation of Z. mobilis but did not S. cerevisiae. Total soluble protein pattern of Z. mobilis cultivated in the electrochemical oxidation condition was getting simplified in proportion to potential intensity based on SDS-PAGE pattern; however the SDS-PAGE pattern of protein extracted from S. cerevisiae cultivated in both oxidation and reduction condition was not changed. When Z. mobilis culture incubated in the cathode compartment for 24 hr was transferred to S. cerevisiae culture in the anode compartment, 0.8 approximately 0.9 M of ethanol was additionally produced by S. cerevisiae for another 24 hr. Conclusively, total 2.0 approximately 2.1 M of ethanol was produced by the electrochemical redox coupling of Z. mobilis and S. cerevisiae for 48 hr.