Electrochemical oxidation of aniline using Ti/RuO2-SnO2 and Ti/RuO2-IrO2 as anode

Electrochemical oxidation of Florfenicol in aqueous solution with mixed metal oxide electrode: Operational factors, reaction by-products and toxicity evaluation

Veterinary antibiotics have become an emerging pollutant in water and wastewater sources due to excess usage, toxicity and resistance to traditional water and wastewater treatment. The present study explored the degradation of a model antibiotic- Florfenicol (FF) using electrochemical oxidation (EO) with Ti-RuO2/IrO2 anode. The anode material was characterized using SEM-EDS studies expressing stable structure and optimal interaction of the neighboring metal oxides with each other. The EDS results showed the presence of Ru, Ir, Ti, O and C elements with 6.44%, 2.57%, 9.61%, 52.74% and 28.64% atomic weight percentages, respectively. Optimization studies revealed pH 5, 30 mA cm-2 current density and 0.05 M Na2SO4 for 5 mg L-1 FF achieved 90% TOC removal within 360 min treatment time. The degradation followed pseudo-first order kinetics. LC-Q-TOF-MS studies revealed six predominant byproducts illustrating hydroxylation, deflourination, and dechlorination to be the major degradation mechanisms during the electrochemical oxidation of FF. Ion chromatography studies revealed an increase in Cl-, F- and NO3- ions as treatment time progressed with Cl- decreasing after the initial phase of the treatment. Toxicity studies using Zebrafish (Danio rerio) embryo showed the treated sample to be toxic inducing developmental disorders such as pericardial edema, yolk sac edema, spinal curvature and tail malformation at 96 h post fertilization (hpf). Compared to control, delayed hatching and coagulation were observed in treated embryos. Overall, this study sets the stage for understanding the effect of mixed metal oxide (MMO) anodes on the degradation of veterinary antibiotic-polluted water and wastewater sources using electrochemical oxidation.

Development of an environmentally sustainable technique to minimize the sludge production in the textile effluent sector through an electrokinetic (EK) coupled with electrooxidation (EO) approach

This study presents an environmentally sustainable method for minimizing sludge production in the textile effluent sector through the combined application of electrokinetic (EK) and electrooxidation (EO) processes. AAS and XRF analyses reveal that utilizing acidic electrolytes in the EK method successfully eliminates heavy metals (Cu, Mn, Zn, and Cr) from sludge, demonstrating superior efficiency compared to alkaline conditions. In addition, the total removal efficiency of COD contents was calculated following the order of EK-3 (60%), EK-1 (51%) and EK-2 (34%). Notably, EK-3, leveraging pH gradient fluctuations induced by anolyte in the catholyte reservoir, outperforms other EK systems in removing COD from sludge. The EK process is complemented by the EO process, leading to further degradation of dye and other organic components through the electrochemical generation of hypochlorite (940 ppm). At an alkaline pH of 10.0, the color and COD removal were effectively achieved at 98 and 70% in EO treatment, compared to other mediums. In addition, GC-MS identified N-derivative residues at the end of the EO. This study demonstrates an integrated approach that effectively eliminates heavy metals and COD from textile sludge, combining EK with EO techniques.

Vanadium nitride decorated carbon cloth anode promotes aniline degradation and electricity generation of MFCs by efficiently enriching electroactive bacteria and promoting extracellular electron transfer

To increase the colonization of electroactive bacteria and accelerate the rate of extracellular electron transfer, a simple coated anode of microbial fuel cell was designed. Here, we took advantage of vanadium nitride (VN) particles to modify the carbon cloth (VN@CC). Compared with bare carbon cloth, the designed VN@CC bioanodes exhibited a larger electrochemically active area, better biocompatibility, and smaller charge transfer impedance. The MFC with VN@CC bioanodes achieved the maximum power density of 3.89 W m-2 and chemical oxygen demand removal rate of 84% when 1000 mg L-1 aniline was degraded, which were about 1.88 and 2.8 times that of CC. The morphology of biofilm and 16s rRNA gene sequence analysis proved that the VN@CC bioanodes facilitated the enrichment of electroactive bacteria (99.02%) and increased the ratio of fast electron transfer in the extracellular electron transfer, thus enhancing the MFC performance of aniline degradation and power output. This work disclosed that it was feasible to increase the overall performance of MFC by enhancing the EET efficiency and presented valuable insights for future work.

Treatment of aniline-containing wastewater by electrochemical oxidation using Ti/RuO2 anode: the influence of process parameters and reaction mechanism

Aniline detected in many industrial wastewater is a refractive organic pollutant with strong biological toxicity to aquatic organisms and humans. In this research, electrochemical oxidation process with Ti/RuO2 as the anode has been used to degrade aniline-containing wastewater on a laboratory scale. The influence of anode materials, electrolyte, NaCl concentration, current density, and aniline initial concentration on COD removal, ICE, and Ep were studied. The results showed that Cl- addition in the electrolyte is essential to promote aniline degradation efficiency and avoid the anode being passivated. Furthermore, decreasing the current density, increasing Cl- concentration, and initial aniline concentration are beneficial to increase current efficiency and reduce energy consumption. Although the addition of SO42- has a restriction on the active chlorine evolution process, the conductivity increased, which resulted in the reduction of energy consumption. At last, the aniline degradation mechanism in the presence of chloride ions was summed up and proposed based on the literature.

From black water to flushing water: potential applications of chlorine-mediated indirect electrooxidation for ammonia removal

Removing ammonia from black water is one of the most urgent issues before it can be recycled as flushing water. In this study, an electrochemical oxidation (EO) process with commercial Ti/IrO₂-RuO₂ anodes to treat black water could remove 100% of different concentrations of ammonia by adjusting the dosage of chloride. Through the relationship between ammonia, chloride, and corresponding the pseudo-first-order degradation rate constant (K_obs), we could determine the chloride dosage and predict the kinetics of ammonia oxidation based on initial ammonia concentration in black water. The optimal N/Cl molar ratio was 1:1.8. The difference between black water and the model solution in terms of ammonia removal efficiency and oxidation products was explored. A higher chloride dosage was beneficial for removing ammonia and shortening the treatment cycle, but it also led to the generation of toxic by-products. Especially HClO and ClO₃^- generated in black water were 1.2 and 1.5 times more than the synthesized model solution under 40 mA cm^-2. Through SEM characterization of electrodes and repeated experiments, the electrodes always maintained a high treatment efficiency. These results demonstrated the potential of the electrochemical process as a treatment method for black water.

Romo AI, Pudar S, Putnam ST, Bustos E, Rodríguez-López J. Real-Time Detection of Hydroxyl Radical Generated at Operating Electrodes via Redox-Active Adduct Formation Using Scanning Electrochemical Microscopy

The hydroxyl radical (•OH) is one of the most attractive reactive oxygen species due to its high oxidation power and its clean (photo)(electro)generation from water, leaving no residues and creating new prospects for efficient wastewater treatment and electrosynthesis. Unfortunately, in situ detection of •OH is challenging due to its short lifetime (few ns). Using lifetime-extending spin traps, such as 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to generate the [DMPO-OH]• adduct in combination with electron spin resonance (ESR), allows unambiguous determination of its presence in solution. However, this method is cumbersome and lacks the necessary sensitivity and versatility to explore and quantify •OH generation dynamics at electrode surfaces in real time. Here, we identify that [DMPO-OH]• is redox-active with E0 = 0.85 V vs Ag|AgCl and can be conveniently detected on Au and C ultramicroelectrodes. Using scanning electrochemical microscopy (SECM), a four-electrode technique capable of collecting the freshly generated [DMPO-OH]• from near the electrode surface, we detected its generation in real time from operating electrodes. We also generated images of [DMPO-OH]• production and estimated and compared its generation efficiency at various electrodes (boron-doped diamond, tin oxide, titanium foil, glassy carbon, platinum, and lead oxide). Density functional calculations, ESR measurements, and bulk calibration using the Fenton reaction helped us unambiguously identify [DMPO-OH]• as the source of redox activity. We hope these findings will encourage the rapid, inexpensive, and quantitative detection of •OH for conducting informed explorations of its role in mediated oxidation processes at electrode surfaces for energy, environmental, and synthetic applications.

A review of electrochemical oxidation technology for advanced treatment of medical wastewater

Antibiotics widely exist in medical wastewater, which seriously endanger human health. With the spread of the COVID-19 and monkeypox around the world, a large number of antibiotics have been abused and discharged. How to realize the green and efficient treatment of medical wastewater has become a hot research topic. As a common electrochemical water treatment technology, electrochemical oxidation technology (EOT) could effectively achieve advanced treatment of medical wastewater. Since entering the 21st century, electrochemical oxidation water treatment technology has received more and more attention due to its green, efficient, and easy-to-operate advantages. In this study, the research progress of EOT for the treatment of medical wastewater was reviewed, including the exploration of reaction mechanism, the preparation of functional electrode materials, combining multiple technologies, and the design of high-efficiency reactors. The conclusion and outlook of EOT for medical wastewater treatment were proposed. It is expected that the review could provide prospects and guidance for EOT to treat medical wastewater.

Performance Optimization and Toxicity Effects of the Electrochemical Oxidation of Octogen

Octogen (HMX) is widely used as a high explosive and constituent in plastic explosives, nuclear devices, and rocket fuel. The direct discharge of wastewater generated during HMX production threatens the environment. In this study, we used the electrochemical oxidation (EO) method with a PbO2-based anode to treat HMX wastewater and investigated its degradation performance, mechanism, and toxicity evolution under different conditions. The results showed that HMX treated by EO could achieve a removal efficiency of 81.2% within 180 min at a current density of 70 mA/cm2, Na2SO4 concentration of 0.25 mol/L, interelectrode distance of 1.0 cm, and pH of 5.0. The degradation followed pseudo-first-order kinetics (R2 > 0.93). The degradation pathways of HMX in the EO system have been proposed, including cathode reduction and indirect oxidation by •OH radicals. The molecular toxicity level (expressed as the transcriptional effect level index) of HMX wastewater first increased to 1.81 and then decreased to a non-toxic level during the degradation process. Protein and oxidative stress were the dominant stress categories, possibly because of the intermediates that evolved during HMX degradation. This study provides new insights into the electrochemical degradation mechanisms and molecular-level toxicity evolution during HMX degradation. It also serves as initial evidence for the potential of the EO-enabled method as an alternative for explosive wastewater treatment with high removal performance, low cost, and low environmental impact.

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L^-1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO₂-TiO₂ anode prepared using a CO₂ laser heating and an ionic liquid is compared with Ti/RuO₂-TiO₂-IrO₂ and Ti/IrO₂-Ta₂O₅ commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na₂SO₄, and NaClO₄) and current density (15, 30, and 50 mA cm^-2) on the iohexol degradation is also studied. The Ti/RuO₂-TiO₂ laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min^-1) with the lowest energy consumption per order (0.21 kWh m^-3order^-1), using NaCl solution as the electrolyte and applying 15 mA cm^-2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO₂-TiO₂ is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO₂-TiO₂ anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO₂-TiO₂ active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.

Electrocatalytic oxidation of low concentration cefotaxime sodium wastewater using Ti/SnO2-RuO2 electrode: Feasibility analysis and degradation mechanism

In this research, Ti/SnO₂-RuO₂ stable anode was successfully prepared by thermal decomposition method, and low concentration cefotaxime sodium (CFX) was degraded by green and sustainable electrocatalytic oxidation technology. The electrocatalytic activity and stability of the Ti/SnO₂-RuO₂ coating electrode were studied according to the polarization curve of oxygen and chlorine evolution. The effects of current density, initial concentration, pH, electrolyte concentration, and other technological parameters on the degradation efficiency were discussed. Orthogonal experiment results indicated that when the current density was 25 mA cm^-2, concentration of electrolyte was 5 mM and the pH value was 7, the best CFX removal rate of 86.33% could be obtained. The degradation efficiency of electrocatalytic oxidation was discussed through electrochemical analysis. Fourier transform infrared spectroscopy was used to analyze the different inlet and outlet stages before and after the degradation of CFX, and the possible degradation process was discussed. Therefore, the electrocatalytic oxidation of Ti/SnO₂-RuO₂ electrode was a clean and efficient technology, which could be widely used in the treatment of CFX wastewater.

Improving Wastewater Treatment by Triboelectric-Photo/Electric Coupling Effect

The ability to meet higher effluent quality requirements and the reduction of energy consumption are the biggest challenges in wastewater treatment worldwide. A large proportion of the energy generated during wastewater treatment processes is neglected and lost in traditional wastewater treatment plants. As a type of energy harvesting system, triboelectric nanogenerators (TENGs) can extensively harvest the microscale energies generated from wastewater treatment procedures and auxiliary devices. This harvested energy can be utilized to improve the removal efficiency of pollutants through photo/electric catalysis, which has considerable potential application value in wastewater treatment plants. This paper gives an overall review of the generated potential energies (e.g., water wave energy, wind energy, and acoustic energy) that can be harvested at various stages of the wastewater treatment process and introduces the application of TENG devices for the collection of these neglected energies during wastewater treatment. Furthermore, the mechanisms and catalytic performances of TENGs coupled with photo/electric catalysis (e.g., electrocatalysis, photoelectric catalysis) are discussed to realize higher pollutant removal efficiencies and lower energy consumption. Then, a thorough, detailed investigation of TENG devices, electrode materials, and their coupled applications is summarized. Finally, the intimate coupling of self-powered photoelectric catalysis and biodegradation is proposed to further improve removal efficiencies in wastewater treatment. This concept is conducive to improving knowledge about the underlying mechanisms and extending applications of TENGs in wastewater treatment to better solve the problems of energy demand in the future.

Ultralong-lifetime Ti/RuO2-IrO2@Pt anodes with a strong metal-support interaction for efficient electrochemical mineralization of perfluorooctanoic acid

Electrocatalytic oxidation is regarded as an effective technique for decomposing refractory organic compounds like perfluorooctanoic acid (PFOA). However, achieving highly efficient and long-life electrodes is still a great challenge. Herein, Ti/RuO₂-IrO₂@Pt anodes consisting of Pt⁴⁺ and Pt⁰ species were fabricated by combining modified microemulsion technology with a calcination process, in which Pt nanoparticles were highly dispersed and encapsulated in Ru-Ir composite oxides to form a strong metal-support interaction (SMSI) structure. The as-constructed SMSI layer on the Ti/RuO₂-IrO₂@Pt anode resulted in the improvement of the charge transfer capability and also increased the degradation (99.30%) and mineralization (91.32%) of PFOA during the electrochemical oxidation process. Notably, the service lifetime of Ti/RuO₂-IrO₂@Pt anodes was remarkably improved from 24 to 42.3 h compared to commercial Ti/RuO₂-IrO₂ anodes. Moreover, the possible degradation mechanism of PFOA was also speculated through the detection of short-chain perfluorocarboxylic acids and reactive radicals. These results not only revealed that the concept and methodology of SMSI could be an effective way for constructing highly efficient and stable electrocatalysts but also greatly advanced fundamental understanding.

A review on the landfill leachate treatment technologies and application prospects of three-dimensional electrode technology

With the expansion of urbanisation, the total amount of solid waste produced by urban residents has been increasing, and the problem of municipal solid waste disposal has also been aggravated. Landfill leachate treatment technologies could be divided into three categories: biological, physical and advanced oxidation treatment technology. Among them, advanced oxidation treatment technology has a good effect on the treatment of landfill leachate with little secondary pollution and has excellent application potential. Three-dimensional (3D) electrode technology, as a new type of advanced oxidation technology, could remove refractory pollutants in water and has attracted considerable attention. This article aims to (1) compare existing landfill leachate treatment technologies, (2) summarise 3D electrode technology application scenarios, (3) discuss the advantages of 3D electrode technology in landfill leachate treatment and (4) look ahead the future directions of 3D electrode technology in landfill leachate treatment. We hope that this article will be helpful to researchers who are interested in the field of landfill leachate treatment.