Iron-doped cathodes for electro-Fenton implementation: Application for pymetrozine degradation

Hydrogen peroxide electrogeneration from O2 electroreduction: A review focusing on carbon electrocatalysts and environmental applications

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

New Insights on Designing the Next-Generation Materials for Electrochemical Synthesis of Reactive Oxidative Species Towards Efficient and Scalable Water Treatment: A Review and Perspectives

Electrochemical water remediation technologies offer several advantages and flexibility for water treatment and degradation of contaminants. These technologies generate reactive oxidative species (ROS) that degrade pollutants. For the implementation of these technologies at an industrial scale, efficient, scalable, and cost-effective in-situ ROS synthesis is necessary to degrade complex pollutant mixtures, treat large amount of contaminated water, and clean water in a reasonable amount of time and cost. These targets are directly dependent on the materials used to generate the ROS, such as electrodes and catalysts. Here, we review the key design aspects of electrocatalytic materials for efficient in-situ ROS generation. We present a mechanistic understanding of ROS generation, including their reaction pathways, and integrate this with the key design considerations of the materials and the overall electrochemical reactor/cell. This involves tunning the interfacial interactions between the electrolyte and electrode which can enhance the ROS generation rate up to ~ 40% as discussed in this review. We also summarized the current and emerging materials for water remediation cells and created a structured dataset of about 500 electrodes and 130 catalysts used for ROS generation and water treatment. A perspective on accelerating the discovery and designing of the next generation electrocatalytic materials is discussed through the application of integrated experimental and computational workflows. Overall, this article provides a comprehensive review and perspectives on designing and discovering materials for ROS synthesis, which are critical not only for successful implementation of electrochemical water remediation technologies but also for other electrochemical applications.

Heterogeneous electro-Fenton system using Fe-MOF as catalyst and electrocatalyst for degradation of pharmaceuticals

In recent years, heterogeneous electro-Fenton processes have gained considerable attention as an alternative to homogeneous processes. In this context, the aim of this study is the use of a commercial iron metal-organic framework (Fe-MOF), Basolite® F-300, as a base material for the design of a heterogeneous electro-Fenton treatment system for the removal of antipyrine. Initially, the catalyst was applied as powder in aqueous solution and three key parameters of the electro-Fenton process (pH, Fe-MOF concentration and current density) were evaluated and optimized by a Central Composite Design Face Centred (CCD-FC) using antipyrine removal and energy consumption as response functions. Near complete antipyrine removal (94%) was achieved under optimal conditions: pH 3, Fe-MOF 157.78 mg/L and current density 6.67 mA/cm2, obtaining an energy consumption of 0.29 W·h per mg of antipyrine removed. Later, two electrocatalysts (Fe-MOF functionalized cathodes), prepared by different Fe-MOF immobilisation approaches (composite of carbon black/polytetrafluoroethylene or by electrospinning on Ni foam), were synthesized. Their characterisation showed notable Fe-MOF incorporation into the material and favourable properties as electrocatalysts. Both Fe-MOF functionalized cathodes were evaluated in the removal of antipyrine at different pH (acidic and natural) and current density (27.78 and 55.56 mA/cm2), achieving in the best conditions removal levels around 80% in 1 h without any operational problems. In addition, several intermediates generated during the treatment were identified and their toxicity estimated. According to the obtained results, the degradation compounds have less toxicity than the parent compounds, confirming the effectiveness of the treatment.

Activity and stability of bifunctional perovskite/carbon-based electrodes for the removal of antipyrine by electro-Fenton process

Bifunctional perovskite/carbon-black(CB)/polytetrafluoroethylene(PTFE) electrodes for electro-generation and catalytic decomposition of hydrogen peroxide to oxidizing hydroxyl radicals have been fabricated. These electrodes were tested for electroFenton (EF) removal of antipyrine (ANT) as a model antipyretic and analgesic drug. The influence of the binder loading (20 and 40 wt % PTFE) and type of solvent (1,3-dipropanediol and water) was studied for the preparation of CB/PTFE electrodes. The electrode prepared with 20 wt % PTFE and water exhibited a low impedance and remarkable H₂O₂ electro-generation (about 1 g/L after 240 min, a production rate of ca. 6.5 mg/h·cm²). The incorporation of perovskite on CB/PTFE electrodes was also studied following two different methods: i) direct deposition on the CB/PTFE electrode surface and ii) addition in the own CB/PTFE/water paste used for the fabrication. Physicochemical and electrochemical characterization techniques were used for the electrode's characterization. The dispersion of perovskite particles in the own electrode matrix (method ii) exhibited a higher EF performance than the immobilisation onto the electrode surface (method i). EF experiments at 40 mA/cm² and pH 7 (non-acidified conditions) showed ANT and TOC removals of 30% and 17%, respectively. The increase of current intensity up to 120 mA/cm² achieved the complete removal of ANT and 92% of TOC mineralisation in 240 min. The bifunctional electrode also proved high stability and durability after 15 h of operation.

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Sulfidised nanoscale zerovalent iron-modified pitaya peel-derived carbon for enrofloxacin degradation and swine wastewater treatment: Combination of electro-Fenton and bio-electro-Fenton process

In this study, a new Fenton system combining electro-Fenton and bio-electro-Fenton (EF-BEF) processes was proposed for ENR degradation and swine wastewater treatment, and pitaya peel-derived carbon modified with sulfidised nanoscale zerovalent iron (SnZVI) was developed as a catalyst for the system. The as-prepared PPC-800 carbon displayed a hierarchical porous structure (693.5 m²/g), abundant oxygen-containing groups, and carbon defects, which endowed it with a good adsorption capacity, high H₂O₂ generation capacity (151.9 ± 10.5 mg/L) during the EF period, and good power production performance (194.3 ± 12.50 mW/m²) during the BEF period. When modified with SnZVI, despite the decrease in the adsorption capacity and power output (102.05 ± 4.05 mW/m²), the SnZVI@PPC-2 exhibited the best ENR removal performance with that of 98.9 ± 0.2% in the EF period and 86.2 ± 5.6% during the BEF period. An increase in the current intensity and air flow rate promoted ENR degradation. Finally, swine wastewater was treated using the SnZVI@PPC-2 EF-BEF system, and 97.9 ± 1.3% of the TOC was removed using the combined system.

Peroxymonosulphate Activation by Basolite® F-300 for Escherichia coli Disinfection and Antipyrine Degradation

In this study, the removal of persistent emerging and dangerous pollutants (pharmaceuticals and pathogens) in synthetic wastewater was evaluated by the application of heterogeneous Advanced Oxidation Processes. To do that, a Metal-Organic Framework (MOF), Basolite^® F-300 was selected as a catalyst and combined with peroxymonosulfate (PMS) as oxidants in order to generate sulphate radicals. Several key parameters such as the PMS and Basolite^® F-300 concentration were evaluated and optimized using a Central Composite Experimental Design for response surface methodology for the inactivation of Escherichia coli. The assessment of the degradation of an analgesic and antipyretic pharmaceutical, antipyrine, revealed that is necessary to increase the concentration of PMS and amount of Basolite^® F-300, in order to diminish the treatment time. Finally, the PMS-Basolite^® F-300 system can be used for at least four cycles without a reduction in its ability to disinfect and degrade persistent emerging and dangerous pollutants such as pharmaceuticals and pathogens.

Heterogeneous Advanced Oxidation Processes: Current Approaches for Wastewater Treatment

Nowadays, water pollution is one of the most dangerous environmental problems in the world. The presence of the so-called emerging pollutants in the different water bodies, impossible to eliminate through conventional biological and physical treatments used in wastewater treatment plants due to their persistent and recalcitrant nature, means that pollution continues growing throughout the world. The presence of these emerging pollutants involves serious risks to human and animal health for aquatic and terrestrial organisms. Therefore, in recent years, advanced oxidation processes (AOPs) have been postulated as a viable, innovative and efficient technology for the elimination of these types of compounds from water bodies. The oxidation/reduction reactions triggered in most of these processes require a suitable catalyst. The most recent research focuses on the use and development of different types of heterogeneous catalysts, which are capable of overcoming some of the operational limitations of homogeneous processes such as the generation of metallic sludge, difficult separation of treated water and narrow working pH. This review details the current advances in the field of heterogeneous AOPs, Fenton processes and photocatalysts for the removal of different types of emerging pollutants.

Electrochemically-driven regeneration of iron (II) enhances Fenton abatement of pesticide cartap

Cartap is a carbamate insecticide intended to protect crops such as rice, tea, and sugarcane. Cartap in the environment presents a serious threat to non-target organisms through direct exposure or via biomagnification. Electro-assisted Fenton technology taps the potential of Fenton reagents to degrade cartap. Electrochemical reduction of iron accelerates catalyst regeneration. Cartap degradation was first investigated by varying reaction pH, as well as the initial H₂O₂ and Fe²⁺ dosage, followed by optimization studies using central composite design. Parametric results indicate the highest cartap removal of 98.10% was achieved at 1.6 pH, 3.0 mM Fe²⁺_, and 40 mM H₂O₂ at I = 1.0 A and t = 30 min. These results notoriously surpass conventional Fenton that only achieved 53.8% cartap removal under similar conditions. The hybridization of Fenton process through electrochemical regeneration enhances removal and increases degradation kinetic up to a pseudo-first-order rate constant value of 21.30 × 10^-4 s^-1. Effects of coexisting inorganic salts PO₄^3-, NO₃^-, and Cl^- at 1 mM and 10 mM concentrations were investigated. These results demonstrate that Fenton electrification as process intensification alternative can enhance the performance and competitiveness of conventional Fenton by ensuring higher availability of iron catalyst while minimizing sludge production.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

Heterogeneous Electro-Fenton-like Designs for the Disposal of 2-Phenylphenol from Water

The hunt for efficient and environmentally friendly degradation processes has positioned the heterogeneous advanced oxidation processes as an alternative more interesting and economical rather than homogenous processes. Hence, the current study lies in investigating the efficiency of different heterogeneous catalysts using transition metals in order to prevent the generation of iron sludge and to extend the catalogue of possible catalysts to be used in advanced oxidation processes. In this study, nickel and zinc were tested and the ability for radical-generation degradation capacity of both ions as homogeneous was evaluated in the electro-Fenton-like degradation of 2-phenylphenol. In both cases, the degradation profiles followed a first-order kinetic model with the highest degradation rate for nickel (1 mM) with 2-phenylphenol removal level of 90.12% and a total organic reduction near 70% in 2 h. To synthesise the heterogeneous nickel catalyst, this transition metal was fixed on perlite by hydrothermal treatment and in a biochar or carbon nanofibers by adsorption. From the removal results using the three synthesized catalysts, it is concluded that the best catalysts were obtained by inclusion of nickel on biochar or nanofibers achieving in both with removal around 80% before 1 h. Thus, to synthetize a nickel electrocatalyst, nickel doped nanofibers were included on carbon felt. To do this, the amount of carbon black, nickel nanofibers and polytetrafluoroethylene to add on the carbon felt was optimized by Taguchi design. The obtained results revealed that under the optimised conditions, a near-complete removal was achieved after 2 h with high stability of the nickel electrocatalyst that open the applicability of this heterogeneous system to operate in flow systems.

Fenton/Fenton-like processes with in-situ production of hydrogen peroxide/hydroxyl radical for degradation of emerging contaminants: Advances and prospects

Fenton processes based on the reaction between Fe²⁺ and H₂O₂ to produce hydroxyl radicals, have been widely studied and applied for the degradation of toxic organic contaminants in wastewater due to its high efficiency, mild condition and simple operation. However, H₂O₂ is usually added by bulk feeding, which suffers from the potential risks during the storage and transportation of H₂O₂ as well as its low utilization efficiency. Therefore, Fenton/Fenton-like processes with in-situ production of H₂O₂ have received increasing attention, in which H₂O₂ was in-situ produced through O₂ activation, then decomposed into hydroxyl radicals by Fenton catalysts. In this review, the in situ production of H₂O₂ for Fenton oxidation was introduced, the strategies for activation of O₂ to generate H₂O₂ were summarized, including chemical reduction, electro-catalysis and photo-catalysis, the influencing factors and the mechanisms of the in situ production and utilization of H₂O₂ in various Fenton/Fenton-like processes were analyzed and discussed, and the applications of these processes for the degradation of toxic organic contaminants were summarized. This review will deepen the understanding of the tacit cooperation between the in situ production and utilization of H₂O₂ in Fenton process, and provide the further insight into this promising process for degradation of emerging contaminants in industrial wastewater.

Optimization of pretreatment in pymetrozine production wastewater via reactive distillation and side-stream distillation methods with response surface methodology

Lots of highly concentrated saline organic wastewater is produced during the pymetrozine production process, causing environmental pollution and waste of resources if discharged directly. Research on actual pymetrozine wastewater treatment is quite scarce. Existing treatment methods of pesticide wastewater usually have disadvantages of long treatment time, low processing efficiency and low recovery rate. To solve these problems, a pretreatment process for pymetrozine wastewater was studied based on material recovery and pollutant degradation. The ammonia conversion process was experimentally investigated by reactive distillation. The reaction product vapor was neutralized and then separated by side-stream distillation. Aspen Plus and response surface methodology were employed to simulate and optimize the operating conditions. Box-Behnken design was used to investigate the individual and interaction effects on methanol purification and sodium acetate removal. Experimental study was carried out on the basis of theoretical simulation data. The result showed that the optimized methanol content on tower top was 99.28% with a yield of 99.95% and methanol content of side withdrawal was 0.01%. The process can be applied for pesticide wastewater treatment to recycle high purity chemical materials, and meets the national sewage comprehensive emission standard.

Preparation of a ZIF-67-modified magnetic solid phase extraction material and its application in the detection of pyridine ring insecticides

An advanced and reliable m-SPE material of a water-stable ZIF was developed for the determination of trace praziquantel and pymetrozine in spinach and broccoli.

Unravelling the Environmental Application of Biochar as Low-Cost Biosorbent: A Review

In this age, a key target for enhancing the competitiveness of the chemical, environmental and biotechnology industries is to manufacture high-value products more efficiently and especially with significantly reduced environmental impact. Under this premise, the conversion of biomass waste to a high-value added product, biochar, is an interesting approach under the circular economy principles. Thus, the improvements in the biochar production and its new and innovative uses are hot points of interest, which are the focus of vast efforts of the scientific community. Biochar has been recognized as a material of great potential, and its use as an adsorbent is becoming a reliable strategy for the removal of pollutants of different streams, according to its high adsorption capacity and potential to eliminate recalcitrant compounds. In this review, a succinct overview of current actions developed to improve the adsorption capability of biochar, mainly of heavy metal and organic pollutants (dyes, pharmaceuticals and personal care products), is summarized and discussed, and the principal adsorption mechanisms are described. The feedstock and the production procedure are revealed as key factors that provide the appropriate physicochemical characteristics for the good performance of biochar as an adsorbent. In addition, the modification of the biochar by the different described approaches proved their feasibility and became a good strategy for the design of selective adsorbents. In the last part of this review, the novel prospects in the regeneration of the biochar are presented in order to achieve a clean technology for alleviating the water pollution challenge.