Electrochemical Oxidation Of Phenol Research Articles

Energy‐Efficient Co‐production of Benzoquinone and H2 Using Waste Phenol in a Hybrid Alkali/Acid Flow Cell

AbstractIn both the manufacturing and chemical industries, benzoquinone is a crucial chemical product. A perfect and economical method for making benzoquinone is the electrochemical oxidation of phenol, thanks to the traditional thermal catalytic oxidation of phenol process requires high cost, serious pollution and harsh reaction conditions. Here, a unique heterostructure electrocatalyst on nickel foam (NF) consisting of nickel sulfide and nickel oxide (Ni9S8‐Ni15O16/NF) was produced, and this catalyst exhibited a low overpotential (1.35 V vs. RHE) and prominent selectivity (99 %) for electrochemical phenol oxidation reaction (EOP). Ni9S8‐Ni15O16/NF is beneficial for lowering the reaction energy barrier and boosting reactivity in the EOP process according to density functional theory (DFT) calculations. Additionally, an alkali/acid hybrid flow cell was successfully established by connecting Ni9S8‐Ni15O16/NF and commercial RuIr/Ti in series to catalyze phenol oxidation in an alkaline medium and hydrogen evolution in an acid medium, respectively. A cell voltage of only 0.60 V was applied to produce a current density of 10 mA cm−2. Meanwhile, the system continued to operate at 0.90 V for 12 days, showing remarkable long‐term stability. The unique configuration of the acid‐base hybrid flow cell electrolyzer provides valuable guidance for the efficient and environmentally friendly electrooxidation of phenol to benzoquinone.

Energy-Efficient Co-production of Benzoquinone and H2 Using Waste Phenol in a Hybrid Alkali/Acid Flow Cell.

In both the manufacturing and chemical industries, benzoquinone is a crucial chemical product. A perfect and economical method for making benzoquinone is the electrochemical oxidation of phenol, thanks to the traditional thermal catalytic oxidation of phenol process requires high cost, serious pollution and harsh reaction conditions. Here, a unique heterostructure electrocatalyst on nickel foam (NF) consisting of nickel sulfide and nickel oxide (Ni9S8-Ni15O16/NF) was produced, and this catalyst exhibited a low overpotential (1.35 V vs. RHE) and prominent selectivity (99 %) for electrochemical phenol oxidation reaction (EOP). Ni9S8-Ni15O16/NF is beneficial for lowering the reaction energy barrier and boosting reactivity in the EOP process according to density functional theory (DFT) calculations. Additionally, an alkali/acid hybrid flow cell was successfully established by connecting Ni9S8-Ni15O16/NF and commercial RuIr/Ti in series to catalyze phenol oxidation in an alkaline medium and hydrogen evolution in an acid medium, respectively. A cell voltage of only 0.60 V was applied to produce a current density of 10 mA cm-2. Meanwhile, the system continued to operate at 0.90 V for 12 days, showing remarkable long-term stability. The unique configuration of the acid-base hybrid flow cell electrolyzer provides valuable guidance for the efficient and environmentally friendly electrooxidation of phenol to benzoquinone.

Hexagonal boron nitride-doped carbon membrane as anode for the enhanced adsorption and electrochemical oxidation of phenol

An activated carbon membrane (ACM) doped with hexagonal boron nitride (h-BN) was fabricated by using activated carbon as the raw material and phenolic resin as the binder. The preparation process involves blending raw materials, ball milling, membrane pressing, and high-temperature carbonization. The conductive ACM was employed as an anode to constitute an electrochemical membrane reactor (EMR) for phenol removal. The effect of h-BN doping rate (0–5 wt%) on the properties of ACM was explored. Results showed that ACM1 (1 wt% h-BN) displayed a small pore size (20 nm), high porosity (41.6 %), large specific surface area (446.8 m2/g), and strong mechanical strength (15.4 MPa) compared to the pristine ACM0. The oxygen precipitation potential of ACM1 (2.11 V) was much higher than that of ACM0 (1.53 V), thus reducing oxygen generation at the anode in EMR for phenol degradation. The phenol removal rate of phenol obtained from EMR with ACM1 as the anode at 1.5 V was up to 95.6 %, which was much higher than that for ACM0 (39.3 %). Density functional theory (DFT) calculations and experimental results confirmed that h-BN-doping enhanced the adsorption active sites, and adsorption energy, leading to the high performance of EMR for phenol removal. In addition, the equilibrium adsorption capacity of ACM1 (10.2 mg/g) was much higher than that of ACM0 (3.7 mg/g). The C atoms adjacent to pyridine N in ACM1 were identified as the adsorption and active catalytic sites by X-ray photoelectron spectroscopy (XPS) and DFT calculations. Therefore, this study sheds light on the design and fabrication of conductive carbon membranes for enhanced performance in industrial wastewater treatment.

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

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

Electrochemical oxidation of phenol in chloride containing electrolyte using a carbon-coated Ti4O7 anode

Magnéli-phase Ti4O7 is an excellent anode material for electrochemical advanced oxidation process (EAOP). However, the development of Ti4O7 electrodes is always limited by the high cost and high energy consumption in their preparation process. In this study, the carbon-coated Ti4O7 electrode was successfully synthesized by an in-situ pyrolysis method, which exhibited high specific surface area (143.8 m2 g−1) and efficient electron transfer (47.3 Ω). The accelerated service life was measured to be 102.5 h, demonstrating its excellent stability. EAOP performance of the C-coated Ti4O7 electrode was evaluated under various operating conditions. The result showed that a complete degradation of phenol (100 mg L−1) was obtained in 60 min, under the condition of 0.1 M NaCl electrolyte and 20 mA cm−2 current density. Owing to the high oxygen evolution potential (OEP, 2.25 V vs. RHE) of the C-coated Ti4O7 electrode, high TOC removal ratio (68.9%) and low energy consumption (113.8 kWh kg−1TOC) were achieved under the optimal condition. Moreover, the mechanism of phenol degradation was investigated by linear sweep voltammetry (LSV) and free radical scavenging experiments. The results indicated that the degradation of phenol can be mainly attributed to the synergistic effects between adsorbed ·OH (M(·OH)) and Cl−, rather than the direct electron transfer process (DET) on the surface of the C-coated Ti4O7 electrode. This study provides an efficient strategy for the mineralization of phenolic wastewater by the C-coated Ti4O7 electrode.

전해산화를 위한 양극 전극제조 및 페놀 제거 특성

Recently, the electrochemical oxidation of refractory organic materials has received significant research attention. In this research, titanium electrodes coated with iridium and tin were prepared using pyrolysis and dip-coating, respectively, and the surface and chemical composition of the fabricated electrodes were determined using scanning electron microscopy and X-ray diffraction analysis. Following this, the elimination routes for the contaminants in phenol wastewater treated with the fabricated electrodes were examined. Phenols have complex degradation mechanisms making it difficult to determine their reaction pathways and produce stable discharge concentrations. In the electrochemical oxidation of phenols, several intermediate species such as benzoquinone and carboxylic acids are produced. Benzoquinone is known to be more harmful to the ecosystem than carboxylic acids. Therefore, in the present study, the partial degradation of phenols was investigated under electrochemical anodic oxidation in the presence of NaCl during wastewater treatment using the Ti/SnO₂ and Ti/IrO₂. electrodes. The presence of NaCl in the electrolyte catalyzed the oxidation of phenols only with the Ti/IrO₂ anode. This catalytic action of NaCl was attributed to the participation of electro generated ClO^- in the oxidation of phenols and their oxidation products near to the anode or/and in the bulk of the electrolyte. The phenol removal rate was excellent when the phenol concentration was low and the electrolyte concentration and cell potential were higher. In particular, the removal rate was 99.8% after 30 min when the phenol and electrolyte concentrations were 1,000 mg/L and 0.4%, respectively. The reaction velocity of electrolysis exhibited first order for the phenol concentration.

Preparation and characterization of a novel blue-TiO2/PbO2-carbon nanotube electrode and its application for degradation of phenol

In this study, we fabricated a blue-TiO2/PbO2-carbon nanotube (CNT) electrode in which blue TiO2 nanotube arrays (blue-TNA) served as the substrate for PbO2-CNT eletrodeposition. Scanning electron microscope (SEM) showed compact surface structure of the electrode. The β-PbO2 crystal structure was detected by X-ray diffraction (XRD). The distribution of Pb, O, C, and Na elements on the electrode surface have been confirmed by X-ray photoelectron spectroscopy (XPS). Blue-TiO2/PbO2-CNT electrode had higher response current (213.12 mA), larger active surface area and lower charge transfer resistance (2.22 Ω/cm2) than conventional TiO2/PbO2-CNT electrode. The influences of current density, initial phenol concentration, initial solution pH, and Na2SO4 concentration on the electrochemical oxidation of phenol have been analyzed. The results showed that the 100 mg/L phenol could be destroyed completely after 210 min, and chemical oxygen demand (COD) removal rate was 89.3% within 240 min. Additionally, the electrode showed long actual lifetime (5468.80 hr) and low energy consumption (0.08 kWh/gCOD). A phenol degradation mechanism was proposed by analyzing the intermediate products with high-performance liquid chromatography-mass spectrometry (HPLC-MS). Importantly, the blue-TiO2/PbO2-CNT electrode exhibited superior stability and high degradation efficiency after 15 times reuse, demonstrating its promising application potential on phenol-containing wastewater treatment.

Electrochemical treatment of leachate containing highly concentrated phenol and ammonia using a Pt/Ti anode at different current densities

Abstract The electrochemical oxidation of phenol in leachate was evaluated at current densities of 50, 100, and 150 mA/cm2 using a Pt/Ti anode electrode in a single-chambered reactor. The feasibility of electrochemical treatment for leachate containing phenol was determined in terms of phenol, chemical oxygen demand (COD), ammonia degradation rate, gas generation, energy consumption, and current efficiency. Phenol was removed within the first-hour of treatment in all study conditions. Galvanostatic electrolysis at a current density of 150 mA/cm2 removed COD and ammonia faster than the other conditions, possibly due to the formation of chloride-oxychloride radicals, which are strong oxidizing agents. The COD removal rate at 150 mA/cm2 was 1.73 h − 1 , which is 2.5–5 times higher than the values (0.35 h − 1 ) at 50 and (0.68 h − 1 ) at 100 mA/cm2. For ammonia removal, the electrochemical process at 150 mA/cm2 achieved a maximum removal rate of 438.6 M/h, which is at least two times higher than at the other current densities. Gas analysis during the electrolysis indicates that H 2 is generated as a valuable product of the reaction. This study reveals that electrochemical oxidation using the Pt/Ti electrode is promising for the treatment of landfill effluents containing toxic and low biodegradable contaminants and for efficient nutrient removal.

Comparison on efficiency of electrochemical phenol oxidation in two different supporting electrolytes (NaCl and Na2SO4) using Pt/Ti electrode

Abstract The electrochemical oxidation of phenol was evaluated with two different electrolytes using a Pt/Ti anode electrode in a single-chambered reactor. The bulk electrolysis was conducted at a fixed current density of 9.6 mA cm−2, and the average applied potential difference was 6 V (anode potential 4 V; cathode potential -2 V). The feasibility of electrochemical treatment of phenol contaminated water was determined in terms of phenol degradation rate, byproduct formation, pH stability, and current efficiency. Galvanostatic electrolysis with NaCl electrolyte removed phenol and chemical oxygen demand (COD) faster than with Na2SO4 electrolyte, possibly due to the formation of chloride–oxychloride radicals, which are strong oxidation agents. The phenol and COD removal rates with NaCl were 2.26 × 10 − 2 and 3.00 × 10 − 4 min−1, which was 9.5 and 1.5 times higher respectively than with Na2SO4. Energy consumption and current efficiency during the electrolysis suggested that chloride ions hinder the oxygen-evolution reaction, causing a growth in current efficiency and a decrease in energy consumption. This result clearly indicated that the presence of chloride in the solution was an important parameter for the efficient electrochemical oxidation of phenol-contaminated water.

Preparation and Characterization of Graphite Substrate Manganese Dioxide Electrode for Indirect Electrochemical Removal of Phenol

Manganese dioxide rotating cylinder electrode prepared by anodic deposition on a graphite substrate using MnSO4 solution in the presence of 0.918 M of H2SO4. The influence of different operational parameters (MnSO4 concentration, current density, time, and rotation speed) on the structure, and morphology of MnO2 deposit film was examined widely. The structure and crystal size determined by X-ray diffraction (XRD), the morphology examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The γ-MnO2 obtained as the main product of the deposition process. It found that the four parameters have a significant influence on the structure, morphology, and roughness of the prepared MnO2 deposit. The crystal size increases with MnSO4 concentration, current density, and rotation speed, and decreasing with time, while the roughness decreases with increasing all of four parameters. It found that the optimum conditions used in preparing MnO2 rotating electrode that gave the smallest crystal size, low roughness and less cracking were 0.33 M of MnSO4, 6 mA/cm2, 2 h, and 200 rpm. Electrochemical oxidation of phenol in a batch reactor was carried out in the presence of NaCl to examine the performance of the prepared MnO2 electrode for degrading phenol and any organic byproducts at different current densities. The results indicate that as the current density increased from 25 to 100 mA/cm2, the chemical oxygen demand (COD) removal efficiency was increased from 59.26 to 99.90%. Kinetics and the effect of temperature on the COD disappearance have been studied. It was clear that COD decreases with time and as the temperature increases, and the value of reaction order equals to 1 as has been found.

Adsorption and Oxidation of Pnenol on Metal Oxide Electrodes

The article investigates kinetics of electrocatalytic oxidation of phenol in the solution of sodium sulfate on a platinum electrode in the presence of dispersed oxides of metals of varied valence. It is shown that the degree of phenol oxidation in the presence of oxides increase by 10–15%. The most active catalysts include oxides of cobalt, chromium, copper and titanium, whose catalytic activity diminishes in the series Co3O4 > Cr2O3 > Cr2O3 > TiO2 > CuO; the rate of electrooxidation of phenol increases at a decrease of anolyte. It was shown that a limiting stage of electrochemical oxidation of phenol in aqueous solutions with the concentration 50 mg/dm3 is a diffusion of the substance to the electrode.

Effect of Adsorption and Passivation Phenomena on the Electrochemical Oxidation of Phenol and 2-Chlorophenol at Carbon Black Diamond Composite Electrode

This work reports on the importance of adsorption and passivation phenomena during the electro-oxidation of phenolic mixture. A case study of the anodic oxidation of phenol and 2-chlorophenol was performed. A carbon black–diamond electrode with 20% carbon black (20CBD electrode) was used as the anode. The anodic oxidation behaviors of 100 mg/L phenol and 100 mg/L 2-chlorophenol on the 20CBD electrode were investigated using cyclic voltammetry in aqueous solutions of 0.25 M Na2SO4. The electrochemical impedance technique was used to investigate the effects of electrode passivation and the adsorption of phenol and 2-chlorophenol through the electrochemical degradation process. The results showed that oxidation of 2-chlorophenol was easier than that of phenol. Even in a 1:1 mixture of 2-chlorophenol and phenol, each at 100 mg/L, the removal rate of 2-chlorophenol was higher than that of phenol. After 6 h, up to 94% of the 2-chlorophenol had degraded, whereas only 20% of the phenol had degraded in the same ti...

Influence of expanded graphite coming from the electrochemical oxidation of phenol on cement-polymer matrix

Abstract In presented article the polymer-modified cement mortars with expanded graphite covered by the oligomer film, being a by-product of phenol electro-oxidation, were investigated. The changes in the morphology of EG and EG/oligomer as well as in the microstructure of cement-polymer composites modified with EG/oligomer were verified using the scanning electron microscopy (SEM). The evaluation of adhesion between EG/oligomer and cement-polymer mortar based on the mechanical tests, especially their flexural behavior. It was shown that the oligomer film formed on EG surface made graphite flakes more durable and resistant to bending. Moreover, the oligomer due to the interaction with polymer network in cement-polymer mortar led to the improvement of flexural toughness of composite.

Electrochemical oxidation behavior of some hazardous phenolic compounds in acidic solution

The electrochemical oxidation of phenol, resorcinol and pyrogallol was investigated in sulfuric acid solution. Cyclic voltammetry and electrochemical impedance spectroscopy, EIS, were used. The mechanism of the electrochemical oxidation process was proposed and discussed. The process includes a selective oxidation and PtOx formation. EIS measurements were carried out to further examine the reaction kinetics involved in the phenolic compounds electro-oxidation. The EIS responses were found to be strongly dependent on electrode potentials. The result showed the presence of an oxidation peak in the region around 1V vs SCE to all conditions evaluated. In cyclic voltammetric experiments a gradual decrease of the oxidation peak with the number of cycles was observed. This suggests the deactivation or blockage of the electrode surface by the adsorption of substances and/or phenoxy radical polymerization.

The influence of anode materials on the kinetics toward electrochemical oxidation of phenol

Electrode performances of IrO2-Ta2O5/Ti and PbO2/Ti anodes were investigated by electrochemical measurements and phenol oxidation. The cyclic voltammetry (CV), polarization and electrochemical impedance spectroscopy (EIS) conducted in phenol solution indicate the oxidation ability of PbO2/Ti anode is higher than that of IrO2-Ta2O5/Ti electrode because it can reduce oxygen evolution and thus increase effective current. A novel parameter, γ, associated with anode materials was proposed to quantitatively describe the effective current applied to main reactions and its value could be achieved through EIS fitted data of the components in equivalent electrical circuits (EEC). The suitability of the used EEC was checked by consistency of the exchange current density between Tafel plots and EIS data. With involvement of the novel parameter (γ) into organics oxidation, a universal kinetics was thereafter presented to predict variations of chemical oxygen demand, average current efficiency and power consumption. The results of regression analysis and F-test show higher agreement between the experimental and model estimation during phenol oxidation, verifying necessity of the parameter γ in characterizing effective current for anodic reactions and rationality of the kinetics in describing organics oxidation by different electrodes.

Electrochemical Oxidation of Phenol for Wastewater Treatment Using Ti/PbO2 Electrode

AbstractThe electrochemical oxidation of phenol was studied using a Ti/PbO2 electrode prepared by the electrodeposition method with PbO2 coated on Ti. The structural and morphological activity of Ti/PbO2 was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and intermediates formed after degradation of phenol were quantitatively assessed by high-pressure liquid chromatography (HPLC). Optimization of various parameters such as current density, initial phenol concentration, initial solution pH, and different temperature and dose of Fe2+ on electrochemical degradation of phenol using Ti/PbO2 were investigated. Complete removal of phenol (250 mgL−1) was observed at 50°C, potential difference (5 V), and at pH 2. Experimental results showed that the phenol removal rate increased with increasing current intensity along with significant reduction in total organic carbon (TOC). Fundamental kinetic data obtained for the degradation of phenol by Ti/PbO2 was found to follow in accordance wi...

Beneficial effect of Ni in pillared bentonite based electrodes on the electrochemical oxidation of phenol

The influence of Ni on the electrochemical performance of Fe containing bentonite-based electrode materials was investigated in the electrochemical oxidation of phenol in acidic solution. Clay originated from Mečji Do, Serbia, was submitted to pillaring. Mixed pillaring solutions containing Al3+ and Fe3+ or Al3+, Fe3+ and Ni2+ were used for this purpose. The XRD, chemical and FTIR analysis and nitrogen physisorption at -196°C were used for sample characterization. The electrochemical behavior of the pillared clay-based electrodes was tested by cyclic voltammetry. The results confirmed that the pillaring was successful. The presence of Ni in the electrode material enhanced the electrode stability. It is possible that the presence of Ni restricted the electrode fouling caused by the formation of polymeric products during the electrooxidation of phenol.

Cyclic voltammetry of phenol

The possibility of phenol determination by cyclic voltammetry (CVA) on electrochemically modified glassy-carbon electrodes (GCE) was studied. The effect of the rate of linear potential sweep on the sensitivity of phenol determination was investigated. The adsorption nature of the analytical signal of phenol was revealed. The formation of the hydroquinone-quinone couple by the electrochemical oxidation of phenol was proved by CVA.

Time Varying Toxicity of Effluents from the Electrochemical Oxidation of Phenol

The Microtox® test was used to quantify the impact of holding time on toxicity of compounds formed in the electrochemical treatment of phenol. Phenol was treated in the presence of a sodium chloride (NaCl) or sodium sulfate (Na2SO4) electrolyte using either a boron-doped diamond anode/stainless steel cathode, or graphite anode/SS cathode. The intermediates from both oxidative and chlorine-substitution pathways were measured concurrently using HPLC immediately after the application of constant current was stopped and at time intervals up to 18 days. The toxicity of the samples were measured using the Microtox® basic test protocol at each of these time points as well. Chlorine-substitution pathway effluents, consisting mainly of chlorinated phenols, exhibited little toxicity change over the 18 day storage period considered in the study. Oxidative pathway effluents, however, consisting of quinone products, most notably the highly toxic benzoquinone, exhibited significant toxicity loss over the time period of the study. Over a period of 18 days, a 0.092 mM solution of benzoquinone alone lost over 92% of its initial toxicity. Over a 13 day period, an electrochemical effluent from conditions conducive to the oxidative pathway and benzoquinone formation also lost over 96% of its initial toxicity.

Electrochemical degradation of phenol in aqueous solution using PbO2 anode

The PbO2 electrode was prepared by electrodeposition method in this paper. The electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The electrochemical oxidation of phenol in aqueous solution was studied by galvanostatic electrolysis using PbO2 electrode as anode. UV spectroscopy, total organic carbon (TOC) and chemical oxygen demand (COD) measurements were conducted to study the kinetics of phenol electrochemical degradation and the mineralization efficiency under different current densities. The experimental results showed that the applied current density had a positive influence on the degradation of phenol and removal of TOC, but a higher current density led to lower current efficiency and higher energy consumption. The phenol degradation always followed a pseudo-first-order kinetics. In addition, aromatic intermediates and general carboxylic acids generated in the degradation of phenol have been indentified using high-performance liquid chromatography (HPLC) and a general pathway for the electrochemical degradation of phenol on PbO2 anode was proposed.