Open research questions in Advanced oxidation water treatment

What the literature leaves open

• The gap between commercially mature technologies and emerging research-stage technologies in advanced oxidation processes. The need for more selective, efficient, and operationally relevant technologies for environmental protection. The limited scalability of some advanced oxidation processes due to catalyst stability and regeneration issues.

  From Oxidation Chemistry to Intelligent Water Systems: Emerging Directions in Process Optimization and Environmental Engineering · 2026 · DOI

• The reliance on simplified aqueous matrices and unresolved long-term stability of single-atom catalysts. The difficulty in demonstrating the practical process advantages of non-radical pathways in catalytic ozonation. The need to consider wastewater complexity, reactor-scale performance, and operational durability in evaluating catalytic ozonation strategies.

  Non-Radical Catalytic Ozonation for Wastewater Treatment: Evidence Standards, Bromate Trade-Offs, and Scale-Up Constraints · 2026 · DOI

• The lack of rigorous demonstration of practical process advantages for non-radical pathways in catalytic ozonation. The need for a critical review to evaluate the evidence supporting mechanistic claims. The importance of considering wastewater complexity and reactor-scale performance in evaluating catalytic ozonation strategies.

  Non-Radical Catalytic Ozonation for Wastewater Treatment: Evidence Standards, Bromate Trade-Offs, and Scale-Up Constraints · 2026 · DOI

• Sluggish interfacial charge transfer limiting the catalytic efficiency of Co3O4. Potential inhibition of the Cl-Co3O4/PMS system by high-concentration anions like NO3- and Cl-. The need to identify the major reactive species and propose a catalytic mechanism. The challenge of achieving efficient and sustainable BPA degradation using the Cl-Co3O4/PMS system.

  Chlorine-Doped Co3O4 Accelerates Interfacial Charge Transfer for Efficient Peroxymonosulfate Activation: Radical-Dominated Bisphenol A Degradation · 2026 · DOI

• Conventional water treatment processes are ineffective in eliminating micropollutants like BPA. Traditional advanced oxidation processes are hindered by catalyst instability and potential toxic by-products. There is a need for efficient and sustainable treatment technologies for BPA degradation.

  Chlorine-Doped Co3O4 Accelerates Interfacial Charge Transfer for Efficient Peroxymonosulfate Activation: Radical-Dominated Bisphenol A Degradation · 2026 · DOI

• Optimization must increasingly be linked to realistic matrices, lifecycle performance, and techno-economic constraints

  From Oxidation Chemistry to Intelligent Water Systems: Emerging Directions in Process Optimization and Environmental Engineering · 2026 · DOI

• However, there is an insufficient understanding of the effect of oxidant dosage on the reaction pathway, and the tuning of the reaction pathway between mineralization and polymerization has not yet been reported.

  Reaction Pathway Tuning between Electron Transfer-Mediated Degradation and Polymerization in Fe-MoS 2 -Based Persulfate Activation System · 2026 · DOI

• However, how contaminants adsorbed on sediment surfaces are degraded at oxic-anoxic interfaces remains unclear.

  Production of Surface-Bound Hydroxyl Radicals on Sediments for Adsorbed Contaminant Transformation at Oxic–Anoxic Interfaces · 2026 · DOI

• However, earlier reported treatment systems mostly suffer from side reactions against efficient and cost-effective production of 1 O 2, together with insufficient utilization of 1 O 2 limited by the extremely short diffusion length.

  Confinement-Modulated Singlet-Oxygen Nanoreactors for Water Decontamination · 2025 · DOI

• However, the roles of coexisting hydrogen peroxide (H 2 O 2 ) remain insufficiently explored.

  New Insights into Natural Polyphenol-Enhanced Fe(III)/Peracetic Acid System under Acidic pH Conditions: The Overlooked Role of Coexisting Hydrogen Peroxide · 2025 · DOI

• However, the efficiency of the conventional bulk-phase UV/H 2 O 2 system is limited by the low yield and utilization of • OH, in turn necessitating high UV energy input and long purification period.

  Accelerated Pollutant Degradation by UV/H 2 O 2 at the Air–Water Interface of Microdroplets · 2025 · DOI

• The type of active oxidant generated can be tailored by the structure of peroxides, yet the underlying mechanism remains to be uncovered.

  Peroxide Directing the Iron Cycling for Tailored Generation of Active Oxidants in Aqueous Fenton Reactions · 2025 · DOI

• Heterogeneous catalytic ozonation (HCO) is a promising strategy for removing organic pollutants from wastewater, but its practical deployment is limited by the scavenging effects of coexisting constituents (e.

  Single-Atom Copper@Carbon Nanospheres for Catalytic Ozonation: Parallel Dual Surface Oxidation Pathways for Broad-Spectrum Water Pollutant Removal · 2025 · DOI

• Dissolved black carbon (DBC) displays strong photochemical effects in surface Earth systems through reactive oxygen species production, yet the role of redox minerals during this process has been poorly characterized.

  Synergistic Photochemistry of Dissolved Black Carbon Mediated by Iron: A Critical Pathway for Enhancing Hydroxyl Radical Generation · 2025 · DOI

• , amine, amide) in persulfate activation remains unexplored due to their thermal instability during pyrolysis.

  Intrinsic Roles of Conjugated and Nonconjugated Nitrogen on Graphene Aerogels in Electron Transfer Activation of Persulfates · 2025 · DOI

• Pyrogenic carbon (PyC) has been widely known to mediate electron transfer, yet a quantitative relationship between the active functional groups within PyC and •OH production remains lacking.

  Dual Roles of Phenolic Groups in Pyrogenic Carbon as Mediators and Quenchers for Hydroxyl Radical Production · 2025 · DOI

• Aqueous Fe(IV) is a crucial oxidant in iron-mediated oxidation processes relevant to water purification and atmospheric aqueous systems; yet, its chemical behavior under environmentally relevant pH conditions remains poorly understood.

  Formation and Decay of Aqueous Fe(IV) during Fe(II) Ozonation under Acidic Conditions: Kinetics and Mechanistic Insights into pH-Dependent Behavior · 2025 · DOI

• However, it is rarely reported for Fe IV ═O generation in the H 2 O 2 -based Fenton-like process.

  Boosting Fe Atom Density and Forming Fe(IV) via Fe–N 5 Generation in the Catalyst for H 2 O 2 -Based Fenton Reaction · 2025 · DOI

• Nevertheless, its practical implementation was limited by the high energy consumption of microwaves and the poor sustainable reactivity of catalysts.

  Enhanced peroxymonosulfate activation for degradation of iodinated contrast media by microwave-induced bimetallic carbon-based catalysts: Insight into the synergistic mechanism between microwaves and bimetallic sites · 2024 · DOI

• Abstract Precise modulation of the axial coordination microenvironment in single‐atom catalysts (SACs) to enhance peroxymonosulfate (PMS) activation represents a promising yet underexplored approach.

  Unraveling the Fundamentals of Axial Coordination FeN 4+1 Sites Regulating the Peroxymonosulfate Activation for Fenton‐Like Activity · 2024 · DOI

• Furthermore, a systematic understanding of the generation and contributions of organic radicals remains lacking.

  Comprehensive Insight into the Common Organic Radicals in Advanced Oxidation Processes for Water Decontamination · 2024 · DOI

• Alkoxy radicals including CH 3 COO • and CH 3 COOO • are primary reactive species in PAA-AOP systems; however, their reaction mechanism on attacking organic pollutants still remains controversial.

  Unraveling Different Reaction Characteristics of Alkoxy Radicals in a Co(II)-Activated Peracetic Acid System Based on Dynamic Analysis of Electron Distribution · 2024 · DOI

• However, it remains unclear how this process relates to organic radicals generated from reactions between the NOM and oxidants.

  Overlooked Roles and Transformation of Carbon-Centered Radicals Produced from Natural Organic Matter in a Thermally Activated Persulfate System · 2024 · DOI

• Passage of vent gases through an alkaline spray has been proposed for scrubbing SF, but base hydrolysis is insufficiently fast and generates equal yields of fluoride and fluorosulfate, the latter of unknown environmental hazard.

  Hydrogen Peroxide-Assisted Alkaline Defluorination of the Fumigant and Potent Greenhouse Gas, Sulfuryl Fluoride: Hydrogen Peroxide as a Nucleophilic Reagent · 2024 · DOI

• However, the impact of common water constituents, including cations and dissolved organic matter (DOM), on this reaction is poorly understood.

  Influence of Divalent Cation Inhibition and Dissolved Organic Matter Enhancement on Phenol Oxidation Kinetics by Manganese Oxides · 2024 · DOI

Most-cited papers in Advanced oxidation water treatment

• Assessing the Use of Probes and Quenchers for Understanding the Reactive Species in Advanced Oxidation Processes · Environmental Science & Technology · 2023 · 609 citations
• Critical review of electrochemical advanced oxidation processes for water treatment applications · Environmental Science Processes & Impacts · 2014 · 578 citations
• Water decontamination via nonradical process by nanoconfined Fenton-like catalysts · Nature Communications · 2023 · 483 citations
• Can the commonly used quenching method really evaluate the role of reactive oxygen species in pollutant abatement during catalytic ozonation? · Water Research · 2022 · 457 citations
• Key Points of Advanced Oxidation Processes (AOPs) for Wastewater, Organic Pollutants and Pharmaceutical Waste Treatment: A Mini Review · ChemEngineering · 2022 · 423 citations
• Generating dual-active species by triple-atom sites through peroxymonosulfate activation for treating micropollutants in complex water · Proceedings of the National Academy of Sciences · 2023 · 412 citations
• Aqueous Iron(IV)–Oxo Complex: An Emerging Powerful Reactive Oxidant Formed by Iron(II)-Based Advanced Oxidation Processes for Oxidative Water Treatment · Environmental Science & Technology · 2022 · 387 citations
• Heterogeneous activation of persulfate by metal and non-metal catalyst for the degradation of sulfamethoxazole: A review · Chemical Engineering Journal · 2022 · 331 citations
• Overlooked Formation of H 2 O 2 during the Hydroxyl Radical-Scavenging Process When Using Alcohols as Scavengers · Environmental Science & Technology · 2022 · 327 citations
• Fenton-like activity and pathway modulation via single-atom sites and pollutants comediates the electron transfer process · Proceedings of the National Academy of Sciences · 2024 · 325 citations

Most recent work

• One-step fabrication of CuFe2O4/CuAl2O4 Fenton-like catalytic ceramic membranes using coal fly ash for synergistic filtration-catalysis · Journal of Cleaner Production · 2026
• Reaction Pathway Tuning between Electron Transfer-Mediated Degradation and Polymerization in Fe-MoS 2 -Based Persulfate Activation System · Environmental Science & Technology · 2026
• Research Directions for Promoting Applications of Advanced Oxidation Processes in Water Remediation · Environmental Science & Technology · 2026
• Production of Surface-Bound Hydroxyl Radicals on Sediments for Adsorbed Contaminant Transformation at Oxic–Anoxic Interfaces · Environmental Science & Technology · 2026
• UiO-66 as a multifunctional catalyst for photocatalytic degradation of dyes and pharmaceuticals and biodiesel production: advancing energy and environmental sustainability · Coordination Chemistry Reviews · 2026
• Fenton-like Catalysts Based on Supported Cu for Dyes’ and Pharmaceuticals’ Removal Using Only H 2 O 2 and/or O 2 as Oxidants: A Review Focused on the Last 10 years · ACS Omega · 2026
• Regulating Phenolic Pollutant Polymerization from Oligomers to Multimers via Carbon Nanotubes in Permanganate Systems · Environmental Science & Technology · 2026
• Synergistic MOF-on-MOF S-scheme heterojunction for highly efficient peroxomonosulfate activation toward tetracycline degradation · Environmental Research · 2026
• Optimizing Electrocoagulation-Adsorption Treatment System for Comprehensive Water Quality Improvement in Olive-Mill-Wastewater (OMW): Synergy of EC Utilizing Al Electrodes and Olive Stones Biochar as a Sustainable Adsorbent · Water · 2026
• Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems · Water · 2026

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