Activated Carbon Fiber Cathode Research Articles

Sustainable Electrochemical Activation of Self-Generated Persulfate for the Degradation of Endocrine Disruptors: Kinetics, Performances, and Mechanisms.

This study presents an electrolysis system utilizing a novel self-circulation process of sulfate (SO42-) and persulfate (S2O82-) ions based on a boron-doped diamond (BDD) anode and an activated carbon fiber (ACF) cathode, which is designed to enable electrochemical remediation of environmental contaminants with reduced use of chemical reagents and minimized residues. The production of S2O82- and hydrogen peroxide (H2O2) on the BDD anode and ACF cathode, respectively, is identified as the source of active radicals for the contaminant degradation. The initiator, sulfate, is identified by comparing the degradation efficiency in NaSO4 and NaNO3 electrolytes. Quenching experiments and electron paramagnetic resonance (EPR) spectroscopy confirmed that the SO4-· and ·OH generated on the ACF cathode are the main reactive radicals. A comparison of the degradation efficiency and the generated S2O82-/H2O2 of the divided/undivided electrolysis system is used to demonstrate the superiority of the synergistic effect between the BDD anode and ACF cathode. This work provides evidence of the effectiveness of the philosophy of "catalysis in lieu of supplementary chemical agents" and sheds light on the mechanism of the generation and transmission of reactive species in the BDD and ACF electrolysis system, thereby offering new perspectives for the design and optimization of electrolysis systems.

Electrochemical activation of peracetic acid with activated carbon fiber cathode for sulfamethoxazole elimination: Long-lasting catalytic performance and mechanism

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) could generate various radicals with low by-product generation, making them a vital technology in the remediation of organic pollution. Maintaining the activity and continuous operation of catalytic systems in water treatment processes was a highly challenging research topic. Herein, the electrochemical process with an activated carbon fiber (E-ACF) cathode was devised to boost the activation of PAA (E-ACF-PAA) for persistent elimination of organics. Compared to other commonly used electrodes, the ACF cathode displayed superior PAA activation ability and higher sulfamethoxazole (SMX) removal. The applied cathodic electric field could protect ACF from PAA oxidation, maintaining its long-term catalytic ability over 50 cycles. Based on radical quenching studies, the EPR test, and the estimation of radical contribution, the E-ACF-PAA process was identified as a radical dominant system. Importantly, isolated chamber experiments proved that PAA was mainly decomposed on the cathode to produce hydroxyl radicals (OH) for SMX degradation, while the anode played a negligible role. According to toxicity prediction and algae growth tests, the degradation products were harmless to the aquatic ecology. Remarkably, continuous flow experiments over a 24 h and different water matrix tests have also proven applicability in practical scenarios. This work provided novel insights into the electrochemical activation of PAA and further expanded the potential applications of PAA-based AOPs in the remediation of organic pollution.

Enhanced photoelectrocatalytic decomplexation of Ni-EDTA and simultaneous recovery of metallic nickel via TiO2/Ni-Sb-SnO2 bifunctional photoanode and activated carbon fiber cathode

In order to enhance Ni-EDTA decomplexation and Ni recovery via photoelectrocatalytic (PEC) process, TiO2/Ni-Sb-SnO2 bifunctional electrode was fabricated as the photoanode and activated carbon fiber (ACF) was introduced as the cathode. At a cell voltage of 3.5 V and initial solution pH of 6.3, the TiO2/Ni-Sb-SnO2 bifunctional photoanode exhibited a synergetic effect on the decomplexation of Ni-EDTA with the pseudo-first-order rate constant of 0.01068 min−1 with 180 min by using stainless steel (SS) cathode, which was 1.5 and 2.4 times higher than that of TiO2 photoanode and Ni-Sb-SnO2 anode, respectively. Moreover, both the efficiencies of Ni-EDTA decomplexation and Ni recovery were improved to 98% from 86% and 73% from 41% after replacing SS cathode with ACF cathode, respectively. Influencing factors on Ni-EDTA decomplexation and Ni recovery were investigated and the efficiencies were favored at acidic condition, higher cell voltage and lower initial Ni-EDTA concentration. Ni-EDTA was mainly decomposed via ·OH radicals which generated via the interaction of O3, H2O2, and UV irradiation in the contrasted PEC system. Then, the liberated Ni2+ ions which liberated from Ni-EDTA decomplexation were eventually reduced to metallic Ni on the ACF cathode surface. Finally, the stability of the constructed PEC system on Ni-EDTA decomplexation and Ni recovery was exhibited.

Electro-peroxone enables efficient Cr removal and recovery from Cr(III) complexes and inhibits intermediate Cr(VI) generation in wastewater: Performance and mechanism

Available oxidation processes for removing Cr(III) complexes from water/wastewater usually encounter the formation of highly toxic Cr(VI) and the generation of Cr enriched waste sludge, posing challenges on the subsequent disposal. Herein, we achieve efficient removal of Cr(III)-organic complexes and simultaneous recovery of Cr from wastewater with enhanced curtailment of intermediate Cr(VI), by using an electrochemically driven peroxone (i.e., electro-peroxone) process with activated carbon fiber (ACF) electrodes. For Cr(III)-EDTA, electro-peroxone could remove ∼90% total Cr from 11.50 mg/L to 1.20 mg/L and ∼80% total organic carbon, with a strong curtailment of Cr(VI) to less than 0.2 mg/L. Additionally, the process could obtain a complete recovery of the removable Cr, of which 78.3% are enriched at ACF cathode as amorphous Cr(OH)3 deposits and the remaining 21.7% are adsorbed at the anode, thus avoiding the generation of Cr laden sludge. Mechanism studies show the electro-generated H2O2 reacts with O3 to generate abundant HO· for decomplexation, which sequentially oxidizes Cr(III) to Cr(VI), and degrades the released EDTA via stepwise decarboxylated process, as confirmed by HPLC analysis. Multiple pathways including electro-reduction, H2O2 reduction and electro-adsorption synergistically curtail and immobilize the formed intermediate Cr(VI). ACF characterizations and continuous 5-cycle experiments substantiate the excellent reusability of the ACF electrodes. Moreover, this process exhibits satisfactory effectiveness to Cr(III) complexed with other ligands (e.g., citrate and oxalate), and complexed Cr(III) in the real electroplating wastewater. We believe this study would provide an efficient and eco-friendly alternative for Cr(III) complexes removal from wastewater.

Electro-Fenton oxidation of a β-lactam antibiotic cefoperazone: Mineralization, biodegradability and degradation mechanism

Oxidation of a commonly-used β-lactam pharmaceutical, cefoperazone (CFPZ), was systematically investigated by anodic oxidation (AO), AO in presence of H2O2 electro-generation (AO-H2O2) and electro-Fenton (EF) processes with an activated carbon fiber cathode from the biodegradability viewpoint. The degradation and mineralization rates increased in a sequence of AO < AO-H2O2 < EF. Even CPFZ could be efficiently degraded in EF process, achieving complete CFPZ mineralization was rather difficult. Thereby, the biodegradability of the effluent after electrochemical pretreatment was examined to test the feasibility of the combination of electrochemical and biological processes. The results suggested that compared with AO and AO-H2O2, EF process could effectively transform the non-biodegradable CFPZ into biocompatible materials with a high BOD5/COD value (0.33 after 720 min), allowing the possible biotreatment for further remediation. This behavior was relatively accorded with the average oxidation state (AOS) results, evidencing the potential of EF process in enhancing the biodegradability of CFPZ. The determination of inorganic ions revealed that N in CFPZ molecular was oxidized into NH4+ and NO3− ions in EF process. Oxalic, succinic, oxamic, fumaric and formic acids were also formed. Besides, six aromatic by-products were qualified and a possible pathway involving hydrolysis, hydroxylation and decarboxylation during CFPZ mineralization was proposed.

A flow-through electro-Fenton process using modified activated carbon fiber cathode for orange II removal

This study investigated the removal of Orange II by an electro-Fenton process using a novel recirculation flow-through reactor. The hydrogen peroxide was generated in-situ on the activated carbon fiber (ACF) modified with carbon black and polytetrafluoroethylene (PTFE). The modified ACF cathode was characterized by scanning electron microscopy (SEM) and nitrogen adsorption-desorption study. In light of the production of H2O2 and removal of Orange II, the optimum weight percentage of PTFE in the mixture of carbon black and PTFE was 75%. The effects of some important operating parameters such as current and flow rate were investigated. The best Orange II removal reached 96.7% with mineralization efficiency of 55.4% at 120 min under the current of 100 mA, initial pH 3, Fe2+ 0.3 mM and the flow rate of 7 mL min−1. The cathode exhibited good regeneration ability and stability. OH was proved to be the main oxidizing species in this flow-through electro-Fenton system. This work demonstrated that such electro-Fenton process using modified ACF cathode was promising for the degradation of organic pollutants.

Recovery of Phosphorus from Hypophosphite-Laden Wastewater: A Single-Compartment Photoelectrocatalytic Cell System Integrating Oxidation and Precipitation.

Recovery of phosphorus through precipitation from hypophosphite-laden wastewater is more difficult than from orthophosphate-laden wastewater because of the higher solubility of hypophosphite (H2PO2-). Herein, a single-compartment photoelectrocatalytic (PEC) cell system consisting of a TiO2/Ni-Sb-SnO2 bifunctional photoanode and an activated carbon fiber (ACF) cathode with dosing Fe2+ ions was developed for recovery of phosphorus in the form of FePO4 from hypophosphite-laden wastewater. In the PEC process, H2PO2- with an initial concentration of 1.0 mM was completely oxidized and recovered within 30 min at 3.0 V, and the pseudo-first-order rate constant of H2PO2- oxidation was ∼4 times than that in the electrocatalytic process and even ∼89 times than that in the photocatalytic process. The bifunctional photoanode can simultaneously generate •OH radicals and O3; the ACF cathode can electrogenerate H2O2; H2O2, O3, and the added Fe2+ can interact with each other to produce •OH radicals and Fe3+ ions. •OH radicals mainly from the Fenton process were responsible for oxidation of H2PO2- to PO43-, which immediately combined with Fe3+ to form FePO4 at the optimized conditions to realize recovery of phosphorus. The long-term stability of this system was demonstrated. The efficiency for actual electroless nickel plating effluents was exhibited.

Removal of sulfamethoxazole in water by electro-enhanced Co2+/peroxydisulfate system with activated carbon fiber-cathode.

The ACF-cathode/Co2+/PDS system was validated to effectively remove sulfamethoxazole (SMX), a typical carcinogenic and refractory antibiotic from the aqueous environment. The experimental conditions such as initial pH, PDS, Co2+ concentrations, and current density were optimized. Moreover, the system exhibited excellent ability for SMX degradation in surface water and tap water. It was proved that ACF-cathode/Co2+/PDS consumes much less electrical energy per order (EEO) values than Pt-cathode/Co2+/PDS processes. More importantly, due to the cathodic protection, the removal rate of SMX within 30min was satisfactory even after ACF used for 10 cycles continuously. In addition, the cobalt residue in the ACF-cathode/Co2+/PDS process was much lower than that of Pt-cathode/Co2+/PDS system due to the deposition of cobalt on ACF surface. The catalytic system not only had high catalytic performance, but also had less cobalt residue in the solution and lower power consumption. Therefore, the study provided a novel technology for the removal of refractory pollutants in water.

Electrochemical/Fe3+/peroxymonosulfate system for the degradation of Acid Orange 7 adsorbed on activated carbon fiber cathode.

Acid Orange 7 (AO7), as a most common and widely used synthetic dyes in the printing and dyeing industry, was hardly degradable by traditional wastewater treatment methods. Here, activated carbon fiber (ACF) as an in-situ regenerated cathodic adsorbent in the electrochemical/Fe3+/peroxymonosulfate process (EC/ACF/Fe3+/PMS) was firstly investigated for AO7 removal and compared with several different processes. The results indicated that the effective adsorption of AO7 on ACF can be enhanced under electrolytic conditions, while the adsorbed AO7 on ACF can be completely degraded and mineralized in EC/ACF/Fe3+/PMS process resulting in the in-situ regeneration of ACF. Besides, the electrical energy per order values were investigated, which showed an apparent reduction of electrical energy consumption from 0.42831 to 0.09779 kWh m-3 when ACF-cathode replaced Pt-cathode. Further study revealed that higher conversion rate of Fe2+ from Fe3+ was observed with ACF-cathode. It deserved to be mentioned that the removal efficiency of AO7 was satisfactory and stable even after reusing ACF cathode for 10 times. Furthermore, structure and elements of ACF surface were investigated, which indicated the structure of ACF was intact in EC/ACF/Fe3+/PMS due to inhibition of ACF corrosion by electron migration at cathode. In addition, the total iron content of the effluent in EC/ACF/Fe3+/PMS was lower than that of EC/Fe3+/PMS due to the deposition of iron on ACF-cathode surface. Therefore, advantages of EC/ACF/Fe3+/PMS for AO7 degradation were not only a much higher oxidation efficiency and in-situ regenerated cathodic adsorbent, but also a lower electrical energy consumption and lesser iron ions contents in the effluent.

Electrochemical activation of peroxymonosulfate with ACF cathode: Kinetics, influencing factors, mechanism, and application potential

The combination of peroxymonosulfate (PMS) and electrolysis with an activated carbon fiber (ACF) as cathode (E-ACF-PMS) was systematically investigated. A synergistic effect was observed in the E-ACF-PMS process. Compared with the E-ACF-PDS process, the E-ACF-PMS process spent one-third as much energy for elimination of carbamazepine (CBZ). Increased PMS concentration, current density, and pH value significantly enhanced CBZ elimination. It was also noted that the presence of phosphate (PO43−), bicarbonate (HCO3−), and humic acid (HA) inhibited CBZ removal, while the presence of chloride ion (Cl−) accelerated it. According to radical scavenging experiments and the estimation of relative contribution, reactive oxygen species oxidation (including OH, SO4•−, and 1O2) played an important role in CBZ degradation, accounting for 75.67%. We systematically explored the production mechanism for 1O2 and the results demonstrated that 1O2 was mainly generated on the cathode, rather than generated by O2•− or O2 reported by other researchers. Possible degradation pathways for CBZ in E-ACF-PMS process were also proposed. Finally, the potential for practical applications was explored and compared with E-ACF-PDS. The results of SEM images, BET, and nitrogen adsorption isotherm before and after ACF reuse for 50 times suggested that ACF could maintain its adsorption capacity and catalytic ability in the E-ACF-PMS process. Testing also suggested that the protection of ACF in electrochemical oxidation was based on its relatively high current intensity and removal efficiency. The removal efficiencies of other organic pollutants, including nitrobenzene (NB), sulfamethoxazole (SMX), diclofenac (DC), and tetracycline (TC) were also evaluated. In addition, experiments were conducted to study the effects of different water matrices and toxicology implications and results demonstrated that substituting PMS for PDS in an E-ACF system could create a more efficient, sustainable, and with less secondary toxicity process for wastewater treatment.

Effect of surface properties of activated carbon fiber cathode on mineralization of antibiotic cefalexin by electro-Fenton and photoelectro-Fenton treatments: Mineralization, kinetics and oxidation products

Solutions of 200 mg L−1 cefalexin (CLX), an antibiotic with high usage frequency and biodegradation resistance, have been comparatively degraded by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes using two kinds of activated carbon fiber (ACF) cathodes with different physical properties. These two ACFs shared similar pore volumes and pore diameters but varied BET surface areas, which were confirmed to be 0.5210 cm3 g−1, 2.26 nm and 921 m2 g−1 for ACF1, while 0.6508 cm3 g−1, 2.16 nm and 1206 m2 g−1 for ACF2, respectively. Their oxidation abilities were comparatively assessed in terms of degradation kinetics and mineralization rates, which increased in the order: ACF1-EF < ACF2-EF < ACF1-PEF < ACF2-PEF. These results confirmed the superiority of ACF with higher surface area, which was correlated to faster H2O2 and OH accumulation in more reaction sites provided. After 120 min electrolysis, ACF1 exhibited 1510 μM H2O2 and 37 μM OH accumulation, while ACF2 generated 1934 μM H2O2 and 85 μM OH. Moreover, ACF cathode with more developed pore structure also revealed faster formation of degradation by-products like inorganic ions (NH4+ and NO3− ions) and short-chain carboxylic acids (acetic, formic, oxamic and oxalic acids), as well as enhanced removal for partial acids. In order to gain a deeper understanding of degradation mechanisms for ACF2-PEF system, evolutions of six aromatic by-products generated from sulfoxidation, hydroxylation and decarboxylation were confirmed by UPLC-QTOF-MS/MS determination. Based on the above identifications of the degradation intermediates, a plausible reaction pathway for CLX removal was proposed.

Electro-Fenton degradation of antibiotic ciprofloxacin (CIP): Formation of Fe3+-CIP chelate and its effect on catalytic behavior of Fe2+/Fe3+ and CIP mineralization

This work investigated the effect of the chelation of Fe3+ with a fluoroquinolone (FQ) antibiotic ciprofloxacin (CIP) on the catalytic behavior of Fe3+/Fe2+ and the degradation and mineralization of CIP in electro-Fenton (EF) process using activated carbon fiber (ACF) felt cathode. First of all, effect of initial Fe2+ and Fe3+ concentrations on the degradation and mineralization of CIP in EF process was compared, while the optimal initial Fe2+ and Fe3+ contents were both verified to be 1.50mmoldm−3, in which 73% and 72% of initial TOC were eliminated after 360min electrolysis, respectively. Secondly, Fe3+-CIP chelate was produced during CIP degradation in EF process, whose predominant form was confirmed as 1:2 metal-ligand stoichiometry. The formation of Fe3+-CIP chelate had no obvious inhibition on the degradation and mineralization of CIP due to the efficient Fe3+ reduction on the ACF cathode with excellent catalytic feature. About 17% and 35% of initial 1.50mmoldm−3 Fe3+ were reduced to Fe2+ at 18mAcm−2 in ultrapure water and 200mgdm−3 CIP solutions during 30min pre-aeration of EF process, respectively, while higher Fe2+ concentration was maintained for initial 1.50mmoldm−3 Fe3+ during CIP degradation. Finally, the evolution of F−, NH4+ and NO3− ions released to the acidic medium were determined, as well as the formation of short-chain carboxylic acid (oxalic, oxamic and formic acids). Eight aromatic intermediates were identified using UPLC-QTOF-MS/MS, and a feasible mineralization pathway was proposed.

Photo assisted electro-peroxone to degrade 2,4-D herbicide: The effects of supporting electrolytes and determining mechanism

Abstract In this work, photoelectro-peroxone (PEP) was utilized for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The influential operating parameters were studied and their results showed that complete degradation took place at pH = 7.0, applied current of 350 mA, 42.3 mg/L O3 and 25 min reaction time. The first-order kinetic model was fitted for 2,4-D degradation with the rate constant of 0.169 min−1. PEP showed a synergistic performance compared to individual and binary systems. The results of effect of supporting electrolytes showed that chloride, dihydrogen phosphate, nitrate and bicarbonate had an inhibitory effect on 2,4-D degradation. The presence of transition metal especially ferrous ion enhanced the degradation rate constant significantly. Activated carbon fiber cathode exhibited high function in 2,4-D degradation and H2O2 electrogeneration compared to graphite felt and stainless steel. PEP performance in divided cell showed that the main reaction occurred at the cathode compartment. Scavenging experiments showed that hydroxyl radical and singlet oxygen participated in degradation reaction. The presence of UV and ferrous ion increased the role of hydroxyl radical in the degradation of 2,4-D. Mineralization study indicated that 58.9% of total organic carbon (TOC) was removed during 30 min electrolysis. This result proved that PEP process was an effective and promising process for the degradation of refractory organic pollutant.

Activated carbon fiber (ACF) enhances the UV/EF system to remove nitrobenzene in water

Abstract Activated carbon fiber (ACF) was used to enhance the UV/Electro-Fenton (UV/EF) system to remove nitrobenzene (NB). Comparative removal of NB by ACF adsorption, electrolysis, and UV photolysis was investigated, which indicated ACF can significantly enhance the UV/EF (ACF) system to remove NB. By using ACF cathode, 98% of NB removal was achieved after 20 min, which was much higher than Ti cathode by 60%. The UV/EF (ACF) system was proved to have the feasibility of mineralization of nitrobenzene by the 90% of TOC removal after 5 h. ACF reuse experiments were carried, and the results showed ACF cathode could be reused for successive 4 runs with just 5% declination of NB removal. The impacts of several key influence factors (current intensity, electrolyte, and O2 flux) were explored. Three different kinds of ACF (ACF0: original ACF; ACFN: treated by ammonia; ACFH: treated by nitric acid), methanol, tert-butyl (TBA) alcohol, phenol, and catalase were involved in the system to study the mechanism of the UV/EF (ACF) system. The results showed the combination of ACF and the UV/EF system could significantly improve the H2O2 production and NB removal. Finally, the comparison of the electrical energy per order (EE/O) values between the UV/EF (ACF) and UV/EF (Ti) system showed that ACF can significantly improve the current efficiency of the UV/EF system.

An activated carbon fiber cathode for the degradation of glyphosate in aqueous solutions by the Electro-Fenton mode: Optimal operational conditions and the deposition of iron on cathode on electrode reusability

An activated carbon fiber (ACF) cathode was fabricated and used to treat glyphosate containing wastewater by the Electro-Fenton (EF) process. The results showed that glyphosate was rapidly and efficiently degraded and the BOD5/COD ratio was increased to >0.3 implying the feasibility of subsequent treatment of the treated wastewater by biological methods. The results of ion chromatography and HPLC measurements indicated that glyphosate was completely decomposed. Effective OH generation and rapid recycling/recovery of the Fe2+ ions at the cathode were responsible primarily for the high performance of the ACF-EF process. Factors such as inlet oxygen gas flow rate, Fe2+ dosage, initial glyphosate concentration, applied current intensity, and solution pH that may affect the efficiency of the ACF-EF process were further studied and the optimum operation condition was established. Results of SEM/EDX, BET and XPS analysis showed the deposition of highly dispersed fine Fe2O3 particles on the ACF surface during the EF reaction. The possibility of using the Fe2O3-ACF as iron source in the EF process was assessed. Results showed that the Fe2O3-ACF electrode was effective in degrading glyphosate in the EF process. The deposition of Fe2O3 particles on the ACF electrode had no adverse effect on the reusability of the ACF cathode.

Effective adsorption/electrocatalytic degradation of perchlorate using Pd/Pt supported on N-doped activated carbon fiber cathode

In this work, Pd/Pt supported on N-doped activated carbon fiber (Pd/Pt-NACF) was employed as the electrode for electrocatalytic degradation of perchlorate through adsorption/electroreduction process. Perchlorate in solution was firstly adsorbed on Pd/Pt-NACF and then reduced to non-toxic chloride by the catalytic function of Pd/Pt at a constant current (20mA). Compared with Pd/Pt-ACF, the adsorption capacity and electrocatalytic degradation efficiency of Pd/Pt-NACF for perchlorate increased 161% and 28%, respectively. Obviously, positively charged N-functional groups on NACF surface enhanced the adsorption capacity of Pd/Pt-NACF, and the dissociation of hydrogen to atomic H* by the Pd/Pt nanostructures on the cathode might drastically promote the electrocatalytic reduction of perchlorate. The role of atomic H* in the electroreduction process was identified by tertiary butanol inhibition test. Meanwhile, the perchlorate degradation performance was not substantially lower after three successive adsorption/electrocatalytic degradation experiments, demonstrating the electrochemical reusability and stability of the as-prepared electrode. These results showed that Pd/Pt-NACF was effective for electrocatalytic degradation of perchlorate and had great potential in perchlorate removal from water.

Cyanide oxidation by singlet oxygen generated via reaction between H2O2 from cathodic reduction and OCl− from anodic oxidation

Cyanide is widely present in electroplating wastewater or metallurgical effluents. In the present study, the electrochemical destruction of cyanide with various anode and cathode compositions under alkaline conditions was investigated. The results indicated that the electrochemical system using RuO2/Ti as anode and activated carbon fiber (ACF) as cathode in the presence of sodium chloride was efficient for the cyanide removal. In this system, in situ generation of HClO by anodic oxidation of Cl− at RuO2/Ti anode occurred with the H2O2 generation by O2 reduction at ACF cathode. As confirmed by the electron spin resonance technique, the reaction between HClO and H2O2 led to the generation of singlet oxygen, which was responsible for the cyanide removal. Further experiment indicated that the cyanide removal efficiency increased with the increase of the current density or the sodium chloride concentration. Cyanate was identified as main product in the system. Besides, the system exhibited good stability for the cyanide removal, which was beneficial to its practical application.

Electric field induced activated carbon fiber (ACF) cathode transition from an initiator/a promoter into an electrocatalyst in ozonation process

Removal of nitrobenzene (NB), a carcinogenic and refractory pollutant, in aqueous solution by adsorption, ozonation, electrolysis, and electro-peroxone (E-peroxone) with activated carbon fiber (ACF) was investigated, respectively. Kinetic analyses of NB removal by all the processes followed pseudo-first-order kinetics and the Kapp of E-peroxone-ACF was 14.90×10−2min−1, which was much higher than the others. Besides, the Kapp of E-peroxone-ACF process reduces slightly to 12.18×10−2min−1 even after 100 times of ACF recycle, showing a sustainable activity. Moreover, according to the pore texture characteristics, surface functional groups, FTIR, and SEM images, E-peroxone process does not considerably alter the ACF surface, whereas ozone alone can cause substantial damage to it. These results suggested that ACF was induced from an initiator/a promoter into an electrocatalyst in ozonation by free electrons injection. Moreover, comparing with titanium cathode, ACF can remarkably improve the removal of NB in E-peroxone due to the synchronous adsorption of pollutants and ozone as well as the enhancement of H2O2 generation. It indicates that the ACF cathode is a promising material for organic pollutants removal in the E-peroxone process.

Photoperoxi-coagulation using activated carbon fiber cathode as an efficient method for benzotriazole removal from aqueous solutions: Modeling, optimization and mechanism

In this research, benzotriazole (BTA) was removed from aqueous solution using photoperoxi-coagulation (PPC) in which activated carbon fiber (ACF) was used as a cathode. Box-Behnken design was used to optimize and analyze four parameters i.e. time, applied current, initial BTA concentration and UV light power. According to the results, the R-squared and adjusted R-squared were 0.982 and 0.964, respectively, implying that the model was statistically suitable. It was shown that under the optimal condition for BTA removal i.e. 60 mg/L initial BTA concentration, 50 min time, 200 mA applied current and UV light power of 12W, the efficiency of the PPC process was maximum (97.8%). The removal mechanisms were determined and their results showed that the oxidation mechanism of photoperoxi-coagulation process had a more contribution in BTA removal in comparison with coagulation mechanism. The results of scavenging experiments also confirmed the determined removal mechanisms. Synergistic effect was observed in PPC while first order rate constant of PPC was 2.7 fold more than that of sum of each mechanism. The removals of TOC and COD were 64.5% and 76.3% respectively. Average oxidation state and carbon oxidation state of BTA solution were increased after PPC process indicating biodegradability improvement indirectly.

Complete bromate and nitrate reduction using hydrogen as the sole electron donor in a rotating biofilm-electrode reactor

Simultaneous reduction of bromate and nitrate was investigated using a rotating biofilm-electrode reactor (RBER) with graphite carbon (GC) rods as anode and activated carbon fiber (ACF) bonded with steel ring as cathode. In RBER, the community of denitrifying bacteria immobilized on the cathode surface could completely utilize hydrogen (H2) as the electron donor, which was internally produced by the electrolysis of water. The short-term test confirmed that the RBER system could reduce 150–800μg/L bromate to below 10μg/L under autotrophic conditions. The reduced bromate was considered to be roughly equivalent to the amount of bromide in effluent, indicating that bromate was completely reduced to bromide without accumulation of by-products. The long-term test (over 120 days) showed that the removal fluxes of bromate and nitrate could be improved by increasing the electric current and decreasing the hydraulic retention time (HRT). But nitrite in effluent was significantly accumulated when the electric current was beyond 10mA and the HRT was less than 6h. The maximum bromate reduction rate estimated by the Monod equation was 109.12μg/Lh when the electric current was 10mA and HRT was 12h. It was proposed that the electron transfer process in RBER produced H2 on the surface of the ACF cathode, and the microbial cultures attached closely on the cathode which could completely utilize H2 as electron donors for reduction of bromate and nitrate.