Search Results (128)

The precise synthesis of non-precious metal single-atom electrocatalysts is crucial for enhancing the yield of highly active reactive oxygen species (ROSs). Conventional oxidation methods, such as Fenton or NaClO processes, suffer from poor efficiency, high energy demand, and secondary pollution. In contrast, heterogeneous electro-Fenton systems based on cascade oxygen reduction reactions (ORRs), which require low operational voltage and cause pollutant degradation through both direct electron transfer and ROS generation, have emerged as a promising alternative. Recent studies showed that carbon cathodes decorated with atomically dispersed transition metals can effectively integrate the excellent conductivity of carbon supports with the tunable surface chemistry of metal centers. However, the electronic structure of active sites intrinsically hinders the simultaneous achievement of high activity and selectivity in cascade ORRs. This review summarizes the advances, specifically from 2020 to 2025, in understanding the mechanism of cascade ORRs and the synthesis of transition metal-based single-atom catalysts in cathode electrocatalysis for efficient wastewater treatment, and discusses the key factors affecting treatment performance. While employing atomically engineered cathodes is a promising approach for energy-efficient wastewater treatment, future efforts should overcome the barriers in active site control and long-term stability of the catalysts to fully exploit their potential in addressing water pollution challenges. Full article

Fenton oxidation can contribute to meeting effluent standards for COD in actual wastewater treatment plant effluents. However, Fenton oxidation is prone to produce iron sludge waste. The application of heterogeneous Fenton-like systems based on Fenton iron mud carbon in wastewater treatment plants is essential for Fenton iron mud reduction and recycling. In this study, a Fenton iron mud carbon catalyst/Ferrate salts/H₂O₂ (FSC/Fe(VI)/H₂O₂) system was developed to remove chemical oxygen demand (COD) from secondary effluents at the pilot scale. The results showed that the FSC/Fe(VI)/H₂O₂ system exhibited excellent COD removal performance with a removal rate of 57% under slightly neutral conditions in laboratory experiments. In addition, the effluent COD was stabilized below 40 mg·L⁻¹ for 65 days at the pilot scale. Fe(IV) and ¹O₂ were confirmed to be the main active species in the degradation process through electron paramagnetic resonance (EPR) and quenching experiments. C=O, O-C=O, N sites and Fe⁰ were responsible for the generation of Fe(IV) and ¹O₂ in the FSC/Fe(VI)/H₂O₂ system. Furthermore, the cost per ton of water treated by the pilot-scale FSC/Fe(VI)/H₂O₂ system was calculated to be only 0.6209 USD/t, further confirming the application potential of the FSC/Fe(VI)/H₂O₂ system. This study promotes the engineering application of heterogeneous Fenton-like systems for water treatment. Full article

In this study, the degradation of Nile Blue dye was investigated using homogeneous and heterogeneous photocatalytic methods based on the photo-Fenton reaction. More specifically, for homogeneous photocatalysis, the classical photo-Fenton (UV/Fe²⁺/H₂O₂) and modified photo-Fenton-like (UV/Fe²⁺/S₂O₈²⁻) systems were studied, while for heterogeneous photocatalysis, a commercial MOF catalyst, Basolite F300, and a natural ferrous mineral, geothite, were employed. Various parameters—including the concentrations of the oxidant and catalyst, UV radiation, and pH—were investigated to determine their influence on the reaction rate. In homogeneous systems, an increase in iron concentration led to an enhanced degradation rate of the target compound. Similarly, increasing the oxidant concentration accelerated the reaction rate up to an optimal level, beyond which radical scavenging effects were observed, reducing the overall efficiency. In contrast, heterogeneous systems exhibited negligible degradation in the absence of an oxidant; however, the addition of oxidants significantly improved the process efficiency. Among the tested processes, homogeneous techniques demonstrated a superior efficiency, with the conventional photo-Fenton process achieving complete mineralization within three hours. Kinetic analysis revealed pseudo-first-order behavior, with rate constants ranging from 0.012 to 0.688 min⁻¹ and correlation coefficients (R²) consistently above 0.90, confirming the reliability of the applied model under various experimental conditions. Nevertheless, heterogeneous techniques, despite their lower degradation rates, also achieved high removal efficiencies while offering the advantage of operating at a neutral pH without the need for acidification. Full article

Heterogeneous electro-Fenton (HEF) technology utilizing iron-based cathode catalysts has emerged as an efficient advanced oxidation process for wastewater treatment, demonstrating outstanding performance in degrading emerging organic contaminants (EOCs) while maintaining environmental sustainability. The performance of this technology is governed by two critical processes: the accumulation of H₂O₂ and the electron transfer mechanisms governing the Fe(III)/Fe(II) redox cycle. This review comprehensively summarizes recent advances in understanding the electron transfer mechanisms in iron-based HEF systems and their applications for EOC degradation. Five representative catalyst categories are critically analyzed, including zero-valent iron/alloys, iron oxides, iron-carbon/nitrogen-doped carbon composites, iron sulfides/phosphides, and iron-based MOFs, with a particular focus on their structural design, catalytic performance, and electron transfer mechanisms. A particular focus is placed on strategies enhancing Fe(III)/Fe(II) cycling efficiency and the interplay between radical (^•OH) and non-radical (¹O₂) oxidation pathways, including their synergistic effects in complex wastewater systems. Major challenges, including catalyst stability, pH adaptability, and selective oxidation in complex matrices, are further discussed. Potential solutions to these limitations are also discussed. This review provides fundamental insights for designing high-efficiency iron-based HEF catalysts and outlines future research directions to advance practical applications. Full article

In recent years, the rapid development of industry has led to the discharge of large quantities of pollutants, including harmful dyes, into water sources, thereby posing potential threats to human health and the environment. FeOCl and biochar have their own shortcomings as a mediator in the heterogeneous Fenton process. To make both materials useful, FeOCl supported on bamboo biochar (FeOCl/BC) was prepared by calcination using FeCl₃·6H₂O and bamboo powder as raw materials, and the composite’s catalytic activities were explored with acid orange II (AO-II) as the target pollutant. The degradation efficiency of FeOCl/BC composites on AO-II was determined by testing the mass ratio of FeOCl and BC, initial pH, temperature, H₂O₂ concentration, catalyst addition, addition of coexisting inorganic anions, and natural organic matter. The addition of biochar to FeOCl increased the activation of H₂O₂ to generate •OH for the removal of AO-II and accelerated the cycle of Fe³⁺/Fe²⁺. The removal rate of AO-II by the Fe₁C_0.2 composite was 97.1% when the mass ratio of FeOCl and BC was 1:0.2 (Fe₁C_0.2), which was higher than that of the pure components (FeOCl or BC) at pH = 6.1. Moreover, after five reuses, the Fe₁C_0.2 composite still showed high degradation activity for AO-II, with 83.3% degradation and low activity loss. The capture experiments on the active material showed that the removal of AO-II by the Fe₁C_0.2 composite was mainly dominated by •OH; however, •O₂⁻ and h⁺ played minor roles. The synthesized Fe₁C_0.2 composite could be applied for organic contaminants such as AO-II with high removal efficiency. Full article

Organic pollutants released into water bodies have posed a serious threat to aquatic ecosystems. The elimination of organic pollutants from water through the photo-Fenton process has attracted extensive attention. Among various photo-Fenton catalysts, iron oxides have been intensively studied due to their environmentally benign characteristics and abundance. However, the rapid recombination of photogenerated charge carriers (e⁻–h⁺) and slow Fe(III)/Fe(II) cycling of iron oxides restrict their catalytic performance. Thus, this state-of-the-art review focuses on the recent research development regarding iron oxide-based heterojunctions with enhanced catalytic performance to eliminate organic pollutants. This review provides a fundamental understanding of the iron-based heterogeneous photo-Fenton reaction. In addition, various heterojunctions for photocatalytic applications are comprehensively summarized. A thorough discussion is held on the material design for iron oxide-based heterojunctions with improved photo-Fenton catalytic performance. Ultimately, the challenges and prospects of iron oxide-based heterojunction catalysts for photo-Fenton water decontamination are outlined. Full article

The increasing presence of persistent pollutants in industrial wastewater underscores the shortcomings of conventional treatment methods, prompting the adoption of advanced oxidation processes (AOPs) for sustainable water remediation. This review examines the development of AOPs, focusing on their ability to produce hydroxyl radicals and reactive oxygen species (ROS) to mineralize complex pollutants. Homogeneous systems such as Fenton’s reagent show high degradation efficiency. However, challenges like pH sensitivity, catalyst recovery issues, sludge generation, and energy-intensive operations limit their scalability. Heterogeneous catalysts, such as TiO₂-based photocatalysts and Fe₃O₄ composites, offer improved pH adaptability, visible-light activation, and recyclability. Emerging innovations like ultraviolet light emitting diode (UV-LED)-driven systems, plasma-assisted oxidation, and artificial intelligence (AI)-enhanced hybrid reactors demonstrate progress in energy efficiency and process optimization. Nevertheless, key challenges remain, including secondary byproduct formation, mass transfer constraints, and economic feasibility for large-scale applications. Integrating AOPs with membrane filtration or biological treatments enhances treatment synergy, while advances in materials science and computational modeling refine catalyst design and reaction mechanisms. Addressing barriers in energy use, catalyst durability, and practical adaptability requires multidisciplinary collaboration. This review highlights AOPs as pivotal solutions for water security amid growing environmental pollution, urging targeted research to bridge gaps between laboratory success and real-world implementation. Full article

Herein, a heterogeneous Fenton-like catalyst was designed by immobilizing iron oxide (FeS) and nickel sulfide (NiS) on the surface of β-cyclodextrin (β-CD), creating a NiS/FeS@β-CD composite for degrading triphenylmethane cresol red dye. Varied instruments were used to study the physical and chemical characteristics of the NiS/FeS@β-CD catalyst. The appropriate catalytic conditions of the Fenton-like degradation of cresol red by NiS/FeS@β-CD were identified, clarifying that the higher degradation % fulfilled 99.86% with an adsorption % of 27.44% at a cresol red concentration = 50 mg/L, NiS/FeS@β-CD dose = 0.01 g, pH = 3, processing temperature = 30 °C, H₂O₂ concentration = 100 mg/L, and H₂O₂ volume = 1 mL. The kinetic assessments depicted the preference of the second order to represent the Fenton-like degradation of cresol red by NiS/FeS@β-CD. The mechanistic proposition of the adsorption/Fenton-like degradation of cresol red was understood using a quenching test and XPS analysis. Finally, to confirm the durability of NiS/FeS@β-CD, a reusability test was proceeded on the catalyst for five adsorption/Fenton-like degradation runs, with identifying the leaching concentrations of nickel and iron from the catalyst by ICP-OES after each run. Full article

The process of hydrogen peroxide decomposition, facilitated by copper oxide nanoparticles, produces reactive oxidants that possess the ability to oxidize multiple pollutants. CuO/Cu₂O hybrid nanoparticles were successfully synthesized through a thermal decomposition route and applied as a heterogeneous catalytic oxidant for a fluorescent dye, namely Basic Violet 10 (BV10) dye. The microstructure and morphology of the prepared catalyst were evaluated via X-ray diffraction (XRD) and a field-emission scanning electron microscope (FE-SEM), respectively. The produced nanoparticles (NPs) were induced through ultraviolet light as a green photodecomposition technology. The system parameters were investigated, and the optimal initial NP concentration, H₂O₂ concentration, and pH were assessed. The highest removal rate corresponding to 82% was achieved when 40 and 400 mg/L of NPs and H₂O₂ were introduced, respectively. The system could operate at various pH values, and the alkaline pH (8.0) was efficient in proceeding with the oxidation system that overcomes the limitation of the homogeneous acidic Fenton catalyst. The introduced catalyst demonstrated consistent sustainability, achieving a notable removal rate of 68% even after six consecutive cycles of use. This innovative technique’s accomplishment examines the feasibility of utilizing copper as a replacement for iron in the Fenton reaction, demonstrating efficacy over an extended pH range. Finally, the temperature effectiveness of the reaction showed that the reaction is exothermic in nature, working at a low energy barrier (20.4 kJ/mol) and following the pseudo-second-order kinetic model. Full article

In this study, the catalytic performance of the Fenton sludge iron-based biochar catalyst (Fe@BC700), generated during the Fenton process, was investigated regarding its role in oxidizing 2,4-dichlorophenol (2,4-DCP) and As(III) from aqueous solutions in peroxymonosulfate (PMS), peroxydisulfate (PDS), and hydrogen peroxide (H₂O₂) systems. The characteristics of the as-prepared catalyst, operational parameters of H₂O₂/UV/Fe@BC700, PDS/UV/Fe@BC700, and PMS/UV/Fe@BC700 systems, and the kinetics of 2,4-DCP degradation were evaluated. Fe@BC700 exhibited excellent capabilities for activating persulfate and an outstanding oxidant performance as a heterogeneous photocatalyst under UV irradiation. Among the tested systems, PMS/UV/Fe@BC700 showed the highest oxidation capabilities for both 2,4-DCP and As(III) within 40 min. The total organic carbon (TOC) removal efficiency for 2,4-DCP was up to 95.9% in the PMS/UV/Fe@BC700 system. The presence of free radicals in the PMS/PDS system included ·OH, SO₄^·−, and ·O₂⁻, which were facilitated by both UV irradiation and the catalyst. The by-products generated during the PMS/UV/Fe@BC700 treatment were identified via LC-MS analysis, which showed that catalytic degradation substantially reduced the chronic and acute toxicity of 2,4-DCP intermediates. The present study demonstrates that the iron-based biochar derived from Fenton sludge exhibited remarkable persulfate activation capabilities and was highly effective in removing 2,4-DCP and As(III). Full article

Fe-based heterogeneous catalytic advanced oxidation processes show great potential for treating wastewater. However, catalyst instability often hinders their practical use, mainly due to the slow regeneration of Fe²⁺ sites. Herein, we developed a Fe₃S₄/WO₃ catalyst, where the electron-rich Wx and Sx sites promoted efficient electron transfer, enabling continuous regeneration of Fe²⁺ active sites on the catalyst surface. The Fe₃S₄/WO₃ catalyst exhibited outstanding degradation efficiency for tetracycline (TC) in the peroxymonosulfate (PMS) system, achieving a 92.5% removal efficiency, significantly higher than its individual components of Fe₃S₄ (52.8%), WO₃ (43.1%), and WS₂ (53.2%). Moreover, the Fe₃S₄/WO₃/PMS system demonstrated a broad operational pH range (3.0–9.0), excellent degradation efficiency for various emerging pollutants, minimal interference from background electrolytes and organic matter, and strong stability in real water treatment. Chemical scavenger tests and electron paramagnetic resonance (EPR) analysis confirmed that the oxidative degradation of TC was driven by multiple reactive species, including SO₄^•−, ^•OH, ^•O₂⁻, and ¹O₂. This study provides a novel strategy for regulating active sites in Fe-based catalysts to ensure sustained performance, offering a pathway for the rational design of next-generation Fenton-like catalysts for efficient and sustainable micropollutant removal from wastewater. Full article

The suitability of steel shavings (SS) as a low-cost waste catalyst in catalytic ozonation and the heterogeneous Fenton process was evaluated. Three dyes were selected for the research: Indigo Carmine, Tartrazine, and Allura Red AC. Single processes (oxidation by H₂O₂, O₃, and heterogeneous Fenton process) and hybrid processes (O₃ + Fenton) were applied. The Fenton process had the highest efficiency at pH = 3 and with the highest dose of catalyst (5 mg of SS) and hydrogen peroxide (30 µL). More than 98% discoloration of the solution was observed in 10 min. Analyzing ozone-based processes, they can be ranked with the highest efficiency as follows: (O₃ + H₂O₂ + SS) > (O₃ + H₂O₂) > O₃ > (O₃ + SS). The combination of the Fenton process (5 mg of SS + 15 µL of H₂O₂) with ozonation accelerated the reaction rate in the case of Indigo Carmine. In the hybrid process, only 5 min were enough for complete decolorization, while more than 98% in the Fenton process was reached after 30 min. Kinetic studies revealed that the degradation of dyes in an aqueous solution through advanced oxidation processes followed first- and second-order reaction kinetics. The calculation of the energy requirement confirmed that the most economic process for removing Indigo Carmine was the O₃+Fenton process (SS dose = 5 mg, H₂O₂ dose = 15 µL, pH = 3). Full article

Sulfonamides, including sulfadoxine (SDX), are widely used antibiotics, particularly for malaria treatment. However, their extensive use has led to environmental pollution, microbial resistance, and public health risks. Advanced Oxidation Processes (AOPs) offer promising methods to degrade such pollutants in water, though they may generate more toxic by-products. This study evaluates three AOPs with different hydroxyl radical generation principles: the Fenton reagent (H₂O₂/Fe²⁺), hydrogen peroxide photolysis (UV-C/H₂O₂), and heterogeneous photocatalysis (UV-A/TiO₂). Heterogeneous photocatalysis showed superior performance, achieving 100% degradation and 77% mineralization under optimized conditions. Further analysis explored the effects of UV dose, catalyst concentration, and pH on process efficiency. The influence of water matrices, including Ultrapure Water (UW), Tap Water (TW), and Surface Water (SW) from the Aliakmonas River, was also examined. High-Resolution Mass Spectrometry identified 11 SDX transformation products formed during photocatalysis, with their formation mechanisms reported for the first time. An ecotoxicity assessment using ECOSAR software revealed insights into the potential environmental impact of these by-products. Full article

In pursuit of overcoming Fenton oxidation limitations in wastewater treatment, an introduction of a heterogeneous photocatalyst was developed. In this regard, the current work introduces ZnO nanocrystals that were successfully prepared via a thermal decomposition technique and then capped with oleic acid (OA). The synthesized ZnO-OA and the pristine ZnO were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM). Then, the study introduces the application of such materials in advanced oxidation processes, i.e., a Fenton reaction to treat dye-containing wastewater. Synthetic wastewater that was prepared using Reactive Blue 4 (RB4) was used as a simulated textile wastewater effluent. Fenton’s oxidation was applied, and the system parameters were assessed using the modified Fenton’s system. The synthesized samples of ZnO were characterized by a recognized wurtzite hexagonal structure. The surface modification of ZnO with oleic acid (OA) resulted in an increase in crystallite size, lattice parameters, and cell volume. These modifications were linked to the efficient capping of ZnO nanoparticles by OA, which further improved the dispersion of the nanoparticles, as demonstrated through SEM imaging. The optimum conditions of ZnO- and ZnO-OA-synthesized modified Fenton composites showed 400 mg/L and 40 mg/L for H₂O₂ and the catalyst, respectively, at pH 3.0, and within 90 min under UV irradiation the maximal dye oxidation reached 93%. The catalytic performance at its optimal circumstances was in accordance with a pseudo-second-order kinetics model for both ZnO-OA- and the pristine ZnO-based Fenton’s systems. The thermodynamic parameters, including the enthalpy (ΔH′), the entropy (ΔS′), and Gibbs free energy (ΔG′) of activations, were also checked, and their values settled that both ZnO and ZnO-OA Fenton systems are non-spontaneous in nature. Furthermore, the reaction signified for processing at a low energy barrier condition (10.38 and 31.38 kJ/mol for ZnO-OA- and the pristine ZnO-based Fenton reactions, respectively). Full article

The limited utilization of H₂O₂ restricts the practical application of heterogeneous Fenton oxidation technology. In this study, the flower-shaped MnFe₂O₄@MoS₂ nanocomposite was prepared by two-step hydrothermal treatment, constructing MnFe₂O₄@MoS₂/H₂O₂ system for the degradation of tetracycline (TC). Under optimized conditions, MnFe₂O₄@MoS₂/H₂O₂ system fully degraded 20 mg·L⁻¹ of TC within 60 min, and the corresponding utilization of H₂O₂ was also as high as 95.7%. Meanwhile, this system not only exhibited excellent cycling stability for the degradation of TC but also had good anti-interference ability against actual water sources, inorganic cations and anions and natural organic compounds. The efficient activation of H₂O₂ in MnFe₂O₄@MoS₂/H₂O₂ system mainly relied on the redox cycling of Fe(II)/Fe(III) and Mn(II)/Mn(III) mediated by MoS₂; meanwhile, the oxygen vacancies caused by redox cycling also accelerated activation of H₂O₂, resulting in the production of a large number of active species (·OH, ·O₂⁻ and ¹O₂) for rapid degradation of pollutants. The vulnerable atomic sites of TC were confirmed through theoretical calculation, and four degradation pathways of TC in MnFe₂O₄@MoS₂/H₂O₂ system were proposed. Finally, the toxicity analysis confirmed that the toxicity of degradation intermediates was developing towards low toxicity. This study provided new insights into the wide application of heterogeneous Fenton systems in wastewater treatment. Full article