Production of Hydroxyl Radical via the Activation of Hydrogen Peroxide by Hydroxylamine

Iron coupled with hydroxylamine turns on the "switch" for free radical degradation of organic pollutants under high pH conditions

Reducing iron by hydroxylamine (HA) can promote the generation of reactive oxygen species (ROS) in the Fenton reaction and play a crucial role in the degradation of organic pollutants. However, the performance of this system at wider environmental thresholds is still not sufficiently understood, especially in the highly alkaline environments resulting from human activities. Here, we assessed the impact of solution pH on organic pollutant degradation by goethite with the addition of HA and H2O2. The solid phase variation and ROS generation were analyzed using Mössbauer spectroscopy, X-ray absorption near edge structure spectroscopy, and electron paramagnetic resonance analysis. This study found that under alkaline conditions, the system can continuously scavenge organic pollutants through oxygen-mediated generation of free radicals. At lower pH levels, organic pollutant decomposition, exemplified by the breakdown of bisphenol A (BPA), is primarily driven by the Fenton reaction facilitated by iron. As pH increases, hydroxyl radical (•OH) production decreases, accompanied by decreased BPA removal efficiency. However, the removal efficiency of BPA increased significantly at pH > 9. At pH 12, the removal of BPA exceeded that of the acidic condition after one hour, which is consistent with observations in soil system studies. Unlike the Fenton reaction, which is not sensitive to oxygen content, the removal of BPA under alkaline conditions occurs only under aerobic conditions. H2O2 is hardly involved in the reaction, and the depletion of HA becomes a critical factor in the decomposition of BPA. Importantly, in contrast to acidic conditions, where the dramatic decomposition of BPA occurs mainly in the first 10 min, the decomposition of BPA under alkaline conditions continued to occur over the 2 h of observation until complete removal. For natural systems, the remediation of pollutants depends more on the active time of ROS than on their reactivity. Therefore, this idea can reference pollution remediation strategies in anthropogenically disturbed environments.

Decolorization and degradation of crystal violet dye by electron beam radiation: Performance, degradation pathways, and synergetic effect with peroxymonosulfate

Ionizing radiation (mainly including gamma ray and electron beam) technology provides a more efficient and ecological option for dye-containing wastewater treatment, which is supported by its successful achievements in industrial-scale applications. However, the degradation pathway of triphenylmethane dyes by radiation technology is still unclear. In this study, crystal violet (CV) was selected as representative cationic triphenylmethane dye, the decolorization and degradation performance by electron beam radiation technology was systematically evaluated. The results showed that CV can be efficiently decolorized and mineralized by radiation, and its degradation kinetics followed the first-order kinetic model. The effect of inorganic anions and chelating agents commonly existed in dye-containing wastewater on CV decolorization and total organic carbon (TOC) removal was explored. Quenching experiments, density functional theory (DFT) calculation and high performance liquid chromatography mass spectrometry (HPLC-MS) analysis were employed to reveal CV decolorization and degradation mechanism and pathway, which mainly included N-demethylation, triphenylmethane chromophore cleavage, ring-opening of aromatic products and further oxidation to carboxylic acid, and mineralization to CO2 and H2O. Additionally, electron beam radiation/PMS process was explored to decrease the absorbed dose required for decolorization and degradation, and the synergetic effect of radiation with PMS was elucidated. More importantly, the findings of this study would provide the support for treating actual dyeing wastewater by electron beam radiation technology.

Molecular mechanism of the metal-independent production of hydroxyl radicals by thiourea dioxide and H2O2

It is well-known that highly reactive hydroxyl radicals (HO•) can be produced by the classic Fenton system and our recently discovered haloquinone/H2O2 system, but rarely from thiol-derivatives. Here, we found, unexpectedly, that HO• can be generated from H2O2 and thiourea dioxide (TUO2), a widely used and environmentally friendly bleaching agent. A carbon-centered radical and sulfite were detected and identified as the transient intermediates, and urea and sulfate as the final products, with the complementary application of electron spin-trapping, oxygen-18 isotope labeling coupled with HPLC/MS analysis. Density functional theory calculations were conducted to further elucidate the detailed pathways for HO• production. Taken together, we proposed that the molecular mechanism for HO• generation by TUO2/H2O2: TUO2 tautomerizes from sulfinic acid into ketone isomer (TUO2-K) through proton transfer, then a nucleophilic addition of H2O2 on the S atom of TUO2-K, forming a S-hydroperoxide intermediate TUO2-OOH, which dissociates homolytically to produce HO•. Our findings represent the first experimental and computational study on an unprecedented new molecular mechanism of HO• production from simple thiol-derived sulfinic acids, which may have broad chemical, environmental, and biomedical significance for future research on the application of the well-known bleaching agent and its analogs.

Electrochemical production of hydroxylamine from nitrate on metal electrodes: A comparative study of selectivity and efficiency

Despite the great potential of electrochemical nitrate reduction as a hydroxylamine production method, this strategy has not been sufficiently examined, and the effects of electrode material type on the selectivity and efficiency of this reduction remain underexplored. To bridge this gap, the present study evaluated six metals (Ag, Cu, Ni, Sn, Ti, and Zn) as cathode materials for the electrochemical reduction of nitrate to hydroxylamine, showing that the selectivity of hydroxylamine production was maximal for Sn, while the corresponding faradaic and energy utilization efficiencies were maximal for Ti. Although all tested materials favored nitrate reduction over hydrogen evolution, the disparity in the onset potentials of these reactions did not adequately explain the variations in nitrate removal efficiency, which was found to be influenced by material resistance and charge-transfer properties. The rate constants of elementary nitrate reduction steps determined from the time-dependent concentrations of nitrate and its reduction products (nitrous acid, hydroxylamine, and ammonium) were used to calculate the selectivity and efficiency of hydroxylamine production for each electrode. In turn, these selectivities and efficiencies were correlated with the density functional theory-computed adsorption energies of a key hydroxylamine precursor on different electrodes to afford a volcano-type plot with Ti and Sn at its pinnacle. Thus, this study introduces valuable descriptors and methods for the further screening of electrocatalysts for hydroxylamine generation and the establishment of more environmentally friendly hydroxylamine production techniques utilizing sustainable electricity.

Kinetic Modeling Assisted Analysis of Vitamin C-Mediated Copper Redox Transformations in Aqueous Solutions

The kinetics of oxidation of micromolar concentrations of ascorbic acid (AA) catalyzed by Cu(II) in solutions representative of biological and environmental aqueous systems has been investigated in both the presence and absence of oxygen. The results reveal that the reaction between AA and Cu(II) is a relatively complex set of redox processes whereby Cu(II) initially oxidizes AA yielding the intermediate ascorbate radical (A•-) and Cu(I). The rate constant for this reaction was determined to have a lower limit of 2.2 × 104 M-1 s-1. Oxygen was found to play a critical role in mediating the Cu(II)/Cu(I) redox cycle and the oxidation reactions of AA and its oxidized forms. Among these processes, the oxidation of the ascorbate radical by molecular oxygen was identified to play a key role in the consumption of ascorbic acid, despite being a slow reaction. The rate constant for this reaction (A • - + O 2 → DHA + O 2 • - ) was determined for the first time with a calculated value of 54 ± 8 M-1 s-1. The kinetic model developed satisfactorily describes the Cu/AA/O2 system over a range of conditions including different concentrations of NaCl (0.2 and 0.7 M) and pH (7.4 and 8.1). Appropriate adjustments to the rate constant for the reaction between Cu(I) and O2 were found to account for the influence of the chloride ions and pH on the kinetics of the process. Additionally, the presence of Cu(III) as the primary oxidant resulting from the interaction between Cu(I) and H2O2 in the Cu(II)/AA system was confirmed, along with the coexistence of HO•, possibly due to an equilibrium established between Cu(III) and HO•.

Efficient transformation of hydroxylamine from wastewater after supplementation with sodium carbonate or calcium bicarbonate

Hydroxylamine is a highly reactive inorganic nitrogen compound that not only has a toxic effect on microorganisms, but also makes wastewater treatment more difficult, which in turn damages the environment and even endangers human health. This study reported a new method for converting of hydroxylamine by adding sodium carbonate or calcium bicarbonate to the hydroxylamine-polluted wastewater. The conversion efficiency of hydroxylamine was more than 99% in the presence of sodium carbonate or calcium bicarbonate under the reaction conditions of 25 °C, C/N ratio 15, and dissolved oxygen 7.4 mg/L. And its maximal conversion rate can reach 3.49 mg/L/h. This method overcomes various shortcomings of the reported hydroxylamine removal technologies that require a large material dosage and high cost. The technology in this report has many advantages: low cost, 'green' environmental protection, easy market promotion, and high economic benefits.

Pd nanocatalysts adsorbed onto silica nanoparticle coated indium tin oxide: a reusable nanozyme for glucose detection

Nanozymes are nanomaterials that exhibit enzyme-like activity upon exposure to a substrate solution. The use of noble and platinum group metals enhances enzyme-like catalytic activity. However, noble metals are obtained at a high cost; therefore, their recovery after use is of high importance. Herein, we report the fabrication of indium tin oxide-silica nanoparticles decorated with palladium nanoparticles (ITO-SiO2-prS-PdNPs). The ITO-SiO2-prS-PdNPs were evaluated for peroxidase-like activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. A colour change from clear or colourless TMB to blue colour (oxidized TMB products) was observed confirming the peroxidase-like activity. A typical Michaelis-Menten enzyme-like behaviour is observed with Km values of 0.68 mM for H2O2 and 0.47 mM for TMB, which are better than the reported values for horse-radish peroxidase (HRP) for the same substrate. The peroxidase-like activity of ITO-SiO2-prS-PdNPs was found to proceed via the electron-transfer mechanism. The ITO-SiO2-prS-PdNPs were cleaned successfully after each use by rinsing with water and ethanol solution thus making the surface simple and easy to recover and reuse. A reusable and highly selective colorimetric assay for glucose detection based on the peroxidase-like activity of ITO-SiO2-prS-PdNPs gave excellent results. ITO-SiO2-prS-PdNPs exhibited a good linear range of 5.0-30 μM, a low limit of detection (LOD) of 1.84 μM and a limit of quantification (LOQ) of 6.14 μM. Finally, the nanozyme (ITO-SiO2-prS-PdNPs) was successfully used to detect glucose in a complex newborn calf serum (NCS), representing a real sample.

Capture and Stabilization of the Hydroxyl Radical in a Uranyl Peroxide Cluster

Here we describe the synthesis and characterization of a new uranyl peroxide cluster (UPC), U60 Ox30 *, which captures and stabilizes oxygen-based free radicals for more than one week. These radical species were first detected with a nitroblue tetrazolium colorimetric assay and U60 Ox30 * was characterized by single crystal X-ray diffraction as well as infrared (IR), Raman, UV-Vis-NIR, and electron paramagnetic resonance (EPR) spectroscopies. Identification of the free radicals present in U60 Ox30 * was done via room temperature solid and solution state X-band EPR studies using spin trapping methods. The spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was definitive for identifying the free radicals in U60 Ox30 *, which are hydroxyl radicals (⋅OH) that are stable for up to ten days that also persist upon addition of the metalloenzymes catalase and superoxide dismutase. Addition of the spin trapping agent α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) further confirmed the radicals were oxygen based, and deuteration experiments showed that the origin of the free radicals was from the decomposition of H2 O2 in water. These results demonstrate that highly oxidizing species such as the ⋅OH radical can be stabilized in UPCs, which alters our understanding of the role of free radicals present in spent nuclear fuel.

Resolving the Mechanism for H2O2 Decomposition over Zr(IV)-Substituted Lindqvist Tungstate: Evidence of Singlet Oxygen Intermediacy

The decomposition of hydrogen peroxide (H2O2) is the main undesired side reaction in catalytic oxidation processes of industrial interest that make use of H2O2 as a terminal oxidant, such as the epoxidation of alkenes. However, the mechanism responsible for this reaction is still poorly understood, thus hindering the development of design rules to maximize the efficiency of catalytic oxidations in terms of product selectivity and oxidant utilization efficiency. Here, we thoroughly investigated the H2O2 decomposition mechanism using a Zr-monosubstituted dimeric Lindqvist tungstate, (Bu4N)6[{W5O18Zr(μ-OH)}2] ({ZrW5}2), which revealed high activity for this reaction in acetonitrile. The mechanism of the {ZrW5}2-catalyzed H2O2 degradation in the absence of an organic substrate was investigated using kinetic, spectroscopic, and computational tools. The reaction is first order in the Zr catalyst and shows saturation behavior with increasing H2O2 concentration. The apparent activation energy is 11.5 kcal·mol-1, which is significantly lower than the values previously found for Ti- and Nb-substituted Lindqvist tungstates (14.6 and 16.7 kcal·mol-1, respectively). EPR spectroscopic studies indicated the formation of superoxide radicals, while EPR with a specific singlet oxygen trap, 2,2,6,6-tetramethylpiperidone (4-oxo-TEMP), revealed the generation of 1O2. The interaction of test substrates, α-terpinene and tetramethylethylene, with H2O2 in the presence of {ZrW5}2 corroborated the formation of products typical of the oxidation processes that engage 1O2 (endoperoxide ascaridole and 2,3-dimethyl-3-butene-2-hydroperoxide, respectively). While radical scavengers tBuOH and p-benzoquinone produced no effect on the peroxide product yield, the addition of 4-oxo-TEMP significantly reduced it. After optimization of the reaction conditions, a 90% yield of ascaridole was attained. DFT calculations provided an atomistic description of the H2O2 decomposition mechanism by Zr-substituted Lindqvist tungstate catalysts. Calculations showed that the reaction proceeds through a Zr-trioxidane [Zr-η2-OO(OH)] key intermediate, whose formation is the rate-determining step. The Zr-substituted POM activates heterolytically a first H2O2 molecule to generate a Zr-peroxo species, which attacks nucleophilically to a second H2O2, causing its heterolytic O-O cleavage to yield the Zr-trioxidane complex. In agreement with spectroscopic and kinetic studies, the lowest-energy pathway involves dimeric Zr species and an inner-sphere mechanism. Still, we also found monomeric inner- and outer-sphere pathways that are close in energy and could coexist with the dimeric one. The highly reactive Zr-trioxidane intermediate can evolve heterolytically to release singlet oxygen and also decompose homolytically, producing superoxide as the predominant radical species. For H2O2 decomposition by Ti- and Nb-substituted POMs, we also propose the formation of the TM-trioxidane key intermediate, finding good agreement with the observed trends in apparent activation energies.

Activation of the combined hydrogen peroxide and peroxymonosulphate by lepidocrocite for chloramphenicol removal: kinetics and mechanisms

The main compositions of pipe deposits from water distribution networks are potential iron resources, which can be used as catalysts to activate the combined hydrogen peroxide (HP) and peroxymonosulphate (PMS) system to produce reactive oxidative species (ROSs) to degrade pollutants. As a result, the degradation efficiency of chloramphenicol (CAP) in the HP/PMS dual-oxidant system could reach as high as 75.21% within 100 min with hydroxylamine (HA) assistance, and the dual-oxidant method had a wide pH applied range. To explore the mechanism of the dual-oxidant system in detail, several main affecting factors were investigated. In addition, the hydroxyl radical(•OH) was identified as the predominant radicals by Electron paramagnetic resonance (EPR) and the Radical scavenger test (RST). According to the competition kinetics experiment, the reaction rate of CAP with •OH was 1.933(± 0.052) × 10¹⁰ M^-1s^-1 in the HP/PMS dual-oxidant system, which was higher than the HP single oxidant system (6.10(± 0.036) × 10⁹ M^-1s^-1). And the role of HA was explored , including reduction and competition. Six degradation products were detected by the liquid chromatography-mass spectrometry (LC-MS) and their toxicity was analyzed by the ecological structure-activity relationship (ECOSAR) predictive model. These findings further provide a theoretical basis for the practical application of pipe deposits and advance the development of in-situ removal of pollutants in water distribution networks in the future promisingly.

Identifying the evolution of primary oxidation mechanisms and pollutant degradation routes in the electro-cocatalytic Fenton-like systems

Herein, electro-catalysis (EC) as the electron donor to accelerate the continuable Fe(III)/Fe(II) cycles in different inorganic peroxides (i.e., peroxymonosulfate (PMS), peroxydisulfate (PDS) and hydrogen peroxide (HP)) activation systems were established. These electro-cocatalytic Fenton-like systems exhibited an excellent degradation efficiency of sulfamethoxazole (SMX). A series of analytical and characterization methods including quenching experiments, probe experiments, and electron paramagnetic resonance spectrometry (EPR) were implemented to systematically sort out the source and yield of reactive oxygen species (ROS). A wide kind of ROS including hydroxyl radical (^•OH), singlet oxygen (¹O₂), and sulfate radical (SO₄^•-), which contributed 38%, 37%, and 24% were produced in EC/Fe(III)/PMS system, respectively. ^•OH was the dominant ROS in both EC/Fe(III)/PDS and EC/Fe(III)/HP processes. According to the analysis of SMX degradation routes and biotoxicity, abundant degradation pathways were identified in EC/Fe(III)/PMS process and lower environmental impact was achieved in EC/Fe(III)/HP process. The diversiform ROS of EC/Fe(III)/PMS system makes it exhibit greater environmental adaptability in complex water matrixes and excellent low-energy consumption performance in many organic pollutants degradation. Continuous flow treatment experiments proved that the three systems have great sustainability and practical application prospect. This work provides a strong basis for constructing suitable systems to achieve different treatment requirements.

Gamma Radiation-Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single-cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady-state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

Heterogeneous Fenton oxidation of 2,4-dichlorophenol catalyzed by PEGylated nanoscale zero-valent iron supported by biochar

The excessive use of herbicides and fungicides containing 2,4-dichlorophenol (2,4-DCP) has led to serious environmental water pollution; 2,4-DCP is chemically stable and difficult to be degraded effectively by biological and physical methods. And the degradation of 2,4-DCP using advanced oxidation techniques has been a hot topic. Biochar, polyethylene glycol, ferrous sulfate, and sodium borohydride were used to synthesize the heterogeneous catalyst PEGylated nanoscale zero-valent iron supported by biochar (PEG-nZVI@BC). The catalyst was characterized using scanning electron microscope (SEM) and other means to determine its physicochemical properties. Catalytic performance and mechanism of this catalyst with hydrogen peroxide for the oxidation of 2,4-DCP were investigated. The results showed that PEG-nZVI@BC had good dispersibility, stability, and inoxidizability; the degradation efficiency of 50 mg/L 2,4-DCP by PEG-nZVI@BC/H₂O₂ system 92.94%, 1.68 times higher than that of nZVI/H₂O₂ system; there are both free radical and non-free radical pathways in PEG-nZVI@BC/H₂O₂ system; the degradation process of 2,4-DCP includes hydroxylation, dechlorination, and ring-opening. Overall, PEG-nZVI@BC is a promising heterogeneous catalyst for the degradation of 2,4-DCP.

Chemical Cyclic Amplification: Hydroxylamine Boosts the Fenton Reaction for Versatile and Scalable Biosensing

Nucleic acid detection is undoubtedly one of the most important research fields to meet the medical needs of genetic disease diagnosis, cancer treatment, and infectious disease prevention. However, the practical detection methods based on biological amplification are complex and time-consuming and require highly trained operators. Herein, we report a simple, rapid, and sensitive method for the nucleic acid assay by fluorescence or naked eye using chemical cyclic amplification. The addition of hydroxylamine (HA) during the Fenton reaction can continuously generate hydroxyl radicals (^•OH) via Fe³⁺/Fe²⁺ cycle, termed as "hydroxylamine boosts the Fenton reaction (Fenton-HA system)". Meanwhile, the reducing substances, such as terephthalic acid or o-phenylenediamine, react with ^•OH to generate oxidized substances that can be recognized by the naked eye or detected by fluorescence so as to realize the detection of Fe³⁺. The concentration of Fe³⁺ has a good linear relationship with fluorescence intensity in the range of 0.1 to 100 nM, and the limit of detection is calculated to be 0.03 nM (S/N = 3). Subsequently, Fe was introduced into the nucleic acid hybridization system after the Fe source was transformed into Fe³⁺, and the nucleic acids were indirectly determined by this method. This Fenton-HA system was used for sensing HIV-DNA and miRNA-21 to verify the validity of this method in nucleic acid detection. The detection limits were as low as 2.5 pM for HIV-DNA and 3 pM for miRNA-21. We believe that our work has unlocked an efficient signal amplification strategy, which is expected to develop a new generation of highly sensitive chemical biosensors.

New insights into the degradation of micro-pollutants in the hydroxylamine enhanced Fe(II)/peracetic acid process: Contribution of reactive species and effects of pH

The hydroxylamine-enhanced Fe(II)/peracetic acid (PAA) process is a promising advanced oxidation process (AOP) with the generation of reactive species (RS) including RO•, •OH and Fe(IV). Nevertheless, it is still challenging to identify which RS is the major intermediate oxidant, and the reasons why the optimal condition is pH 4.5 rather than 3.0 are also unclear. Herein, the generation of RS and their contribution to the degradation of three micro-pollutants were explored. The quenching experiments and pseudo first-order kinetic model demonstrated that RO• rather than the other two RS were predominant. Then the overall generation and evolution pathways of RS were depicted. The elevation of pH (3.0-4.5) would accelerate the Fe(II)/Fe(III) redox cycle through the enhanced reduction of Fe(III) by hydroxylamine and induce the conversion of Fe(IV) to RO•, which benefited naproxen degradation. While the adverse Fe(III) precipitation would dominate the reduced degradation performance with the solution pH higher than 4.5. The elevation of PAA and Fe(II) dosages sped up the PAA activation, while excess hydroxylamine could consume the formed RS and exhibited an inhibitory effect. This study helps further understand the role of HA and differentiate the contribution of RS in the emerging PAA-based AOPs.

Multiscale modelling of the radical-induced chemistry of acetohydroxamic acid in aqueous solution

Acetohydroxamic acid (AHA) is a small organic acid with a wide variety of industrial, biological, and pharmacological applications. A deep fundamental molecular level understanding of the mechanisms responsible for the radical-induced reactions of AHA in these environments is necessary to predict and control their behaviour and elucidate their interplay with other attendant chemical species, for example, the oxidative degradation products of AHA. To this end, we present a comprehensive, multiscale computer model for interrogating the radical-induced degradation of AHA in acidic aqueous solutions. Model predictions were critically evaluated by a systematic experimental radiation chemistry investigation, leveraging time-resolved electron pulse irradiation techniques for the measurement of new radical reaction rate coefficients, and steady-state gamma irradiations for the identification and quantification of AHA degradation products: acetic acid, hydroxylamine, nitrous oxide, and molecular hydrogen, with formic acid and methane as minor products. Excellent agreement was achieved between calculation and experiment, indicating that this fundamental model can accurately predict the degradation pathways of AHA under irradiation in acidic aqueous solutions.

A comprehensive multiscale model determines the fundamental reaction mechanisms of the radical-induced degradation of acetohydroxamic acid in acidic aqueous solutions.

Goethite and lepidocrocite catalyzing different double-oxidant systems to degrade chlorophenol

Goethite and lepidocrocite, as the main compositions of pipe deposits in the water distribution network, could be used as a catalyst for advanced oxidation processes (AOPs). This research utilizes them to activate PDS/H₂O₂ and PMS/H₂O₂ degrading the 2,4,6-trichlorophenol, respectively. To describe the incomplete degradation of pollutants and reflect the induction period, a modified first-order model has been proposed and used to analyze degradation differences under several key affecting factors. The results revealed that the PDS/H₂O₂ system has a synergy effect in the 2,4,6-trichlorophenol degradation process. The possible degradation pathways and intermediate products were confirmed by gas chromatograph-mass spectrometry (GC-MS). The paper provides a new idea for the effective use of pipe deposits to remove chlorophenols from drinking water, which is of great significance to ensure water quality safety.

Verifying the relationships of defect site and enhanced photocatalytic properties of modified ZrO2 nanoparticles evaluated by in-situ spectroscopy and STEM-EELS

Base treatment and metal doping were evaluated as means of enhancing the photocatalytic activity of ZrO₂ nanoparticles (NPs) via the generation of oxygen vacancies (O_vS), and the sites responsible for this enhancement were identified and characterized by spectroscopic and microscopic techniques. We confirmed that O_vS produced by base treatment engaged in photocatalytic activity for organic pollutant degradation, whereas surface defects introduced by Cr-ion doping engaged in oxidative catalysis of molecules. Moreover, we verified that base-treated ZrO₂ NPs outperformed their Cr-ion doped counterparts as photocatalysts using in situ X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS). Thus, our study provides valuable information on the origin of the enhanced photocatalytic activity of modified ZrO₂ NPs and demonstrates the practicality of in situ spectroscopy and STEM-EELS for the evaluation of highly efficient metal oxide photocatalysts.

Degradation of Rhodamine B in Wastewater by Iron-Loaded Attapulgite Particle Heterogeneous Fenton Catalyst

The water pollution caused by industry emissions makes effluent treatment a serious matter that needs to be settled. Heterogeneous Fenton oxidation has been recognized as an effective means to degrade pollutants in water. Attapulgite can be used as a catalyst carrier because of its distinctive spatial crystal structure and surface ion exchange. In this study, iron ions were transported on attapulgite particles to generate an iron-supporting attapulgite particles catalyst. BET, EDS, SEM and XRD characterized the catalysts. The particle was used as a heterogeneous catalyst to degrade rhodamine B (RhB) dye in wastewater. The effects of H2O2 concentration, initial pH value, catalyst dosage and temperature on the degradation of dyes were studied. The results showed that the decolorization efficiency was consistently maintained after consecutive use of a granular catalyst five times, and the removal rate was more than 98%. The degradation and mineralization effect of cationic dyes by granular catalyst was better than that of anionic dyes. Hydroxyl radicals play a dominant role in RhB catalytic degradation. The dynamic change and mechanism of granular catalysts in catalytic degradation of RhB were analyzed. In this study, the application range of attapulgite was widened. The prepared granular catalyst was cheap, stable and efficient, and could be used to treat refractory organic wastewater.

Hydroxylamine mediated Fenton-like interfacial reaction dynamics on sea urchin-like catalyst derived from spent LiFePO4 battery

Herein, we converted spent LiFePO₄ battery to the sea urchin-like material (SULM) with a highly efficient and environment-friendly method, which can contribute to building a zero-waste city. With SULM as a Fenton-like catalyst, a highly-efficient degradation process was realized for organic pollutants with interface and solution synergistic effect. In our SULM+NH₂OH+H₂O₂ Fenton-like system, NH₂OH can effectively promote the interface iron (Fe(Ⅲ)/Fe(Ⅱ)) and solution iron (Fe(Ⅲ)/Fe(Ⅱ)) redox cycle, thus promoting the generation of reactive oxygen species (ROS). However, the ROS generation process and organic pollutants degradation pathway with the presence of NH₂OH remains a puzzle. Here the detailed ROS generation mechanism and pollutants degradation pathway have been illustrated carefully based on experimental exploration and characterization. Therein, hydroxyl radicals (·OH) and singlet oxygen (¹O₂) are the main ROS for oxidizing and degrading organic pollutants. Notably, ¹O₂ can be converted from superoxide radicals (·O₂) in SULM+NH₂OH+H₂O₂ system. This study not only demonstrates the strategy of "trash-to-treasure" and "waste-to-control-waste" to simultaneously reduce the hazardous release from industrial solid waste and organic wastewater, it also provides new mechanistic insights for NH₂OH mediated Fenton-like redox system.

Coupling electrode aeration and hydroxylamine for the enhanced Electro-Fenton degradation of organic contaminant: Improving H2O2 generation, Fe3+/Fe2+ cycle and N2 selectivity

To improve H2O2 generation and Fe3+/Fe2+ cycle simultaneously for enhancing Electro-Fenton performance, the electrode aeration (EA) and hydroxylamine sulfate (HA) were coupled. With dimethyl phthalate (DMP) as main target contaminant, combination of HA and EA greatly accelerated the degradation of DMP and exhibited a synergy in the pH of 2.0-6.9 through promoting the key reactions, including electrochemical two-electron reduction of O2 into H2O2 and redox cycles of Fe3+/Fe2+, which then improved the generation of hydroxyl radicals (·OH). The coupling EA and HA reduced the use of HA and converted most of HA into environment-friendly N2 (60.1-62.1% of HA products), while HA/solution aeration(SA) system consumed HA rapidly and the generated N2 only accounted for 5.8-6.7% of HA products. Furthermore, compared with HA/SA and EA Electro-Fenton systems, enhancement degree of DMP degradation in HA/EA Electro-Fenton process was higher in actual waterbody than in ultrapure water. The coupling EA and HA in the Electro-Fenton process could solve the low Fe3+/Fe2+ cycle efficiency and low H2O2 production simultaneously, and improve the N2 selectivity of HA transformation, which advanced its application in practical environmental remediation.

Hydroxylamine promoted Fe(III) reduction in H2O2/soil systems for phenol degradation

Production of hydroxyl radicals (•OH) upon the oxidation of solid Fe(II) by O₂ or H₂O₂ in soils and sediments has been confirmed, which benefits in situ remediation of contaminants. However, Fe(III) reduction by H₂O₂ is rate-limiting. Accelerating the Fe(III)/Fe(II) cycle could improve the efficiency of remediation. This study intended to use hydroxylamine to promote Fe(III)/Fe(II) cycle during 100 g/L soil oxidation by H₂O₂ for phenol degradation. The removal of phenol was 76% in 3 h during soil oxidation with 1 mM H₂O₂ in the presence of 1 mM hydroxylamine but was negligible in the absence of hydroxylamine. Fe(III) in the soil was reduced to 0.21 mM Fe(II) by 1 mM hydroxylamine in 30 min. The accelerated cycle of Fe(III)/Fe(II) in the soil by hydroxylamine could effectively decompose H₂O₂ to produced •OH, which was responsible for the effective enhancement of phenol degradation during soil oxidation. Under the conditions of 1 mM H₂O₂ and 100 g/L soil, the pseudo-first-order kinetic constant of phenol degradation increased proportionally from 0.0453 to 0.0844 min^-1 with the increase of hydroxylamine concentrations from 0.5 to 1 mM. The kinetic constant also increased from 0.0041 to 0.0111 min^-1 with H₂O₂ concentration increased from 0.5 to 2 mM, while it decreased from 0.0100 to 0.0051 min^-1 with soil dosage increased from 20 to 200 g/L. In addition, column experiments showed that phenol (10 mg/L) degradation ratio kept at about 48.7% with feeding 2 mM hydroxylamine and 2 mM H₂O₂ at 0.025 PV/min. Column experiments suggested an optional application of hydroxylamine and H₂O₂ for in situ remediation. The output of this study provides guidance and optional strategies to enhance contaminant degradation during soil oxidation.

Advances in application of g-C3N4-based materials for treatment of polluted water and wastewater via activation of oxidants and photoelectrocatalysis: A comprehensive review

Recently, graphitic carbon nitride (g-C₃N₄) has received significant attention as a non-metallic, visible-light-activated photocatalyst for treating water and wastewater by degrading contaminants. Accordingly, previous review articles have focused on the photocatalytic properties of g-C₃N₄-based materials. However, g-C₃N₄ has several other notable features, such as high adsorption affinity towards aromatic substances and heavy metals, high thermal and chemical resistances, good compatibility with various materials, and easily scalable synthesis; therefore, in addition to simple photocatalysis, it can be widely used in other decontamination systems based on activation of oxidants and electrocatalysis. This critical review provides a comprehensive summary of recent advancements in g-C₃N₄-based materials and their use in treating polluted water and wastewater via the following routes (1) activation of oxidizing agents (e.g., hydrogen peroxide, ozone, peroxymonosulfate, and persulfate): and (2) photoelectrocatalysis using fabricated g-C₃N₄-based photocathodes and photoanodes. For each route, we briefly summarize the primary mechanisms, distinctive features, and performances of various water treatment systems using g-C₃N₄-based catalysts. We also highlight the specific roles of g-C₃N₄ in improving the efficiencies of these treatment processes. The advantages and limitations of previously reported water treatment systems using g-C₃N₄-based materials are also described and compared in this review. Finally, we discuss the challenges and prospects of improving g-C₃N₄-based water purification applications.

Formation of nitrosated and nitrated aromatic products of concerns in the treatment of phenols by the combination of peroxymonosulfate and hydroxylamine

Recently, the combination of peroxymonosulfate (PMS) and hydroxylamine (HA) has been proposed as a green and efficient sulfate radical ()-based advanced oxidation process (AOP) for eliminating organic contaminants. However, we found that toxic nitrosated and nitrated aromatic compounds were generated during the treatment of phenolic compounds by PMS/HA system, indicating the involvement of reactive nitrogen species (RNS) during the interaction of PMS with HA. Specifically, considerable production of p-nitrosophenol (p-NSP) and mononitrophenol were obtained when phenol was oxidized by PMS/HA system under various conditions. At the molar ratio between HA and PMS of 1.0 and pH 5.0, sum of the yields of p-NSP and nitrophenols reached their maxima (around 50%). Moreover, production of p-NSP was inhibited while that of nitrophenols was promoted when applied NH₂OH1/2H₂SO₄ was replaced by NH₂OHHCl, which was possibly related to the formation of secondary reactive species induced by the reaction of with chloride ion. Further, formation of undesirable nitrosated and nitrated aromatic products was obtained in the treatment of other phenolic compounds including acetaminophen, bisphenol A, and bisphenol S by PMS/HA system. Considering the toxicity of nitrosated and nitrated aromatic compounds, practical application of PMS/HA system for environmental decontamination should be scrutinized.

Reactive Oxygen Species in Acute Lymphoblastic Leukaemia: Reducing Radicals to Refine Responses

Acute lymphoblastic leukaemia (ALL) is the most common cancer diagnosed in children and adolescents. Approximately 70% of patients survive >5-years following diagnosis, however, for those that fail upfront therapies, survival is poor. Reactive oxygen species (ROS) are elevated in a range of cancers and are emerging as significant contributors to the leukaemogenesis of ALL. ROS modulate the function of signalling proteins through oxidation of cysteine residues, as well as promote genomic instability by damaging DNA, to promote chemotherapy resistance. Current therapeutic approaches exploit the pro-oxidant intracellular environment of malignant B and T lymphoblasts to cause irreversible DNA damage and cell death, however these strategies impact normal haematopoiesis and lead to long lasting side-effects. Therapies suppressing ROS production, especially those targeting ROS producing enzymes such as the NADPH oxidases (NOXs), are emerging alternatives to treat cancers and may be exploited to improve the ALL treatment. Here, we discuss the roles that ROS play in normal haematopoiesis and in ALL. We explore the molecular mechanisms underpinning overproduction of ROS in ALL, and their roles in disease progression and drug resistance. Finally, we examine strategies to target ROS production, with a specific focus on the NOX enzymes, to improve the treatment of ALL.

How Organic Substances Promote the Chemical Oxidative Degradation of Pollutants: A Mini Review

The promotion of pollutant oxidation degradation efficiency by adding organic catalysts has obtained widespread attention in recent years. Studies have shown that organic substances promote the process of traditional oxidation reactions by accelerating the redox cycle of transition metals, chelating transition metals, activating oxidants directly to generate reactive oxygen species such as hydroxyl and sulfate radical, or changing the electron distribution of the target pollutant. Based on the promotion of typical organic functional groups on the chemical oxidative process, a metal-organic framework has been developed and applied in the field of chemical catalytic oxidation. This manuscript reviewed the types, relative merits, and action mechanisms of common organics which promoted oxidation reactions so as to deepen the understanding of chemical oxidation mechanisms and enhance the practical application of oxidation technology.

Efficient cyclic oxidation of macro long-chain alkanes in soil using Fenton oxidation with recyclable Fe

Recyclable Fe in soil was prepared by using fermented food waste supernatant. The efficient cyclic oxidation of long-chain alkanes in oil-contaminated soils could be achieved by Fenton oxidation with the recyclable Fe. The oxidation efficiency of macro long-chain alkanes (C₂₇-C₃₀) from the first cycle (63.4%) to the last cycle (60.1%) showed no significant decrease during three-cycle Fenton oxidation with the recyclable Fe. However, for the oil-absorbing Fe prepared by HA and Fe-SOM prepared by Cs, the oxidation efficiency of C₂₇-C₃₀ could not be efficiently cyclic oxidized during three-cycle Fenton oxidation. Further analysis showed that the proportion of Fe(III) in the recyclable Fe was higher than that in the oil-absorbing Fe or the Fe-SOM, where the iron content was similar. Moreover, more fulvic-like acid and humic-like acid were found in the recyclable Fe, and thus many Fe(III) ions simultaneously combined with the fulvic-like acid and humic-like acid through -C-O-C and C˭O bonds in the recyclable Fe. It was the recyclable Fe with such a stable structure that could still maintain high catalytic activity and efficiently cyclic oxidize macro long-chain alkanes during three-cycle Fenton oxidation, which is valuable for its repeated use.

Nitrosoarene-Catalyzed HFIP-Assisted Transformation of Arylmethyl Halides to Aromatic Carbonyls under Aerobic Conditions

A rare metal-free nucleophilic nitrosoarene catalysis accompanied by highly hydrogen-bond-donor (HBD) solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), organocatalytically converts arylmethyl halides to aromatic carbonyls. This protocol offers an effective means to access a diverse array of aromatic carbonyls with good chemoselectivity under mild reaction conditions. The activation of arylmethyl halides by HFIP to generate stable carbocation and autoxidation of in situ generated hydroxylamine to nitrosoarene in the presence of atmospheric O₂ are the keys to success.

Enhancing iron redox cycling for promoting heterogeneous Fenton performance: A review

Conventional water treatment methods are difficult to remove stubborn pollutants emerging from surface water. Advanced oxidation processes (AOPs) can achieve a higher level of mineralization of stubborn pollutants. In recent years, the Fenton process for the degradation of pollutants as one of the most efficient ways has received more and more attention. While homogeneous catalysis is easy to produce sludge and the catalyst cannot be cycled. In contrast, heterogeneous Fenton-like reaction can get over these drawbacks and be used in a wider range. However, the reduction of Fe (III) to Fe(II) by hydrogen peroxide (H₂O₂) is still the speed limit step when generating reactive oxygen species (ROS) in heterogeneous Fenton system, which restricts the efficiency of the catalyst to degrade pollutants. Based on previous research, this article reviews the strategies to improve the iron redox cycle in heterogeneous Fenton system catalyzed by iron materials. Including introducing semiconductor, the modification with other elements, the application of carbon materials as carriers, the introduction of metal sulfides as co-catalysts, and the direct reduction with reducing substances. In addition, we also pay special attention to the influence of the inherent properties of iron materials on accelerating the iron redox cycle. We look forward that the strategy outlined in this article can provide readers with inspiration for constructing an efficient heterogeneous Fenton system.

Iodometric spectrophotometric determination of peroxydisulfate in hydroxylamine-involved AOPs: 15 min or 15 s for oxidative coloration?

In this study, iodometric spectrophotometry, the most-used method for detecting peroxydisulfate (PDS), was modified by increasing the concentration of potassium iodide (KI) for realizing the immediate PDS determination and avoiding the interference of hydroxylamine. Kinetic studies showed that the reaction between PDS and I^- to generate the yellow-colored I₃^- followed the kinetic equation as [Formula: see text] . Detection time of the iodometric spectrophotometry was shortened from 15 min to 15 s when KI concentration was increased from 0.6 M to 4.8 M. Different with the previous iodometric spectrophotometry, the modified method using 4.8 M KI as the indicator was well tolerable to the interference of hydroxylamine at acidic pH conditions. The calibration curve of the modified method showed a well linear relationship (R² = 0.999) between the absorbance of I₃^- at 352 nm and PDS concentration in the range of 0-80 μM. The modified method was highly sensitive with the absorptivity of 2.5 × 10⁴ M^-1 cm^-1 and the limit of detection of 0.11 μM. Moreover, the modified method was successfully applied for monitoring the change of PDS concentration during the degradation of diclofenac with four different PDS-based AOPs, the calculated reaction stoichiometric efficiency (RSE(%)=DiclofenacdegradedPDSconsumed×100%) followed the order as heat/PDS system > hydroxylamine/Fe²⁺/PDS system > hydroxylamine/Cu²⁺/PDS system > Fe²⁺/PDS system.

Degradation of norfloxacin by hydroxylamine enhanced fenton system: Kinetics, mechanism and degradation pathway

This study demonstrated a fast and efficient degradation of a typical antibiotic norfloxacin (NOR) in a hydroxylamine enhanced Fenton (HA-Fenton) system, which showed a higher catalytic activity over a wider pH range (3.0-9.0). The removal efficiency of NOR was 96% at following conditions: 10 mg/L NOR, 10 μM Fe²⁺, 1.0 mM H₂O₂, 0.4 mM HA and pH 5.0. The degradation rate of NOR in the HA-Fenton system (0.23 min^-1) was 10.9 times of that (0.021 min^-1) in Fenton system. The addition of HA to Fenton system accelerated the conversion of Fe³⁺ to Fe²⁺, leading to the high concentration of ·OH in the HA-Fenton system. Ten degradation transformation products were detected by ultra-performance liquid chromatography tandem quadrupole time of flight mass spectrometer (UPLC-QTOF-MS), consequently, three main degradation steps were proposed, including defluorination, quinolone group transformation, and defluorination and piperazinyl ring opening. Further analyses of NO₃^-, NO₂^- and F^- after the reaction indicated that defluorination process was the crucial degradation step. The HA-Fenton system might offer an efficient alternative for degradation of antibiotics in wastewater.

Pyrite/H2O2/hydroxylamine system for efficient decolorization of rhodamine B

To improve the efficiency of the Fe(II)/Fe(III) cycle and continuous reactivity of pyrite, a pyrite/H₂O₂/hydroxylamine (HA) system was proposed to treat rhodamine B (RhB). The results showed that near-complete decolorization and 52.8% mineralization 50 mg L^-1 RhB were achieved under its optimum conditions: HA 0.8 mM, H₂O₂ 1.6 mM, pyrite 0.4 g L^-1, and initial pH 4.0. The degradation reaction was dominated by an •OH radical produced by the reaction of Fe²⁺ with H₂O₂ in solution. HA primarily had two roles: in solution, HA could accelerate the Fe(II)/Fe(III) cycle through its strong reducibility to enhance RhB decolorization; on the pyrite surface, HA could improve the continuous reactivity of pyrite by inhibiting the oxidation of pyrite. In addition, the dosing manner of HA had a significant effect on RhB decolorization. In addition, the high decolorization and mineralization efficiency of other dye pollutants suggested that the pyrite/H₂O₂/HA system might be widely used in textile wastewater treatment.

Spectrophotometric determination of hydrogen peroxide in water with peroxidase-catalyzed oxidation of potassium iodide and its applications to hydroxylamine-involved Fenton and Fenton-like systems

A spectrophotometric method for the rapid measurement of hydrogen peroxide (H₂O₂) in aqueous solutions was developed in this study. This method is based on a reaction catalyzed by peroxidase (POD) in which potassium iodide (KI) is oxidized to generate the stable yellow-colored I₃^- within 15 s. The absorbance of the generated I₃^- at both 350 nm and 400 nm had good linear relationships with H₂O₂ concentration in the range of 0-70 μM (R² > 0.999) with sensitivities of 2.34 × 10⁴ M^-1 cm^-1 and 5.30 × 10³ M^-1 cm^-1 respectively. Meanwhile, through calculation, the detection limits of the proposed POD-KI method at 350 nm and 400 nm were 0.09 μM and 0.33 μM, respectively. Even when the concentration of H₂O₂ was up to 350 μM, the absorbance of the generated I₃^- at 350 nm did not decrease observably. The generated I₃^- was found to be stable enough in ultrapure water, underground water, reservoir water and samples containing the strong reducing agent hydroxylamine. Moreover, the proposed POD-KI method was successfully used to analyze trace H₂O₂ in rainwater, and to monitor the change of H₂O₂ concentration in the Fenton, hydroxylamine/Fenton and hydroxylamine/Cu(II)/H₂O₂ systems. Overall, the POD-KI method could be adopted as a candidate method to determine H₂O₂ in Fenton and Fenton-like systems, and especially in those involving hydroxylamine.

New insights into the mechanisms of tartaric acid enhancing homogeneous and heterogeneous copper-catalyzed Fenton-like systems

The specific roles of tartaric acid (TA), as an eco-friendly ligand, in homogeneous and heterogeneous copper-catalyzed systems were systematically revealed and new mechanisms of TA enhancing the three Fenton-like processes were proposed to provide a theoretical significance in overcoming the deficiency of conventional Fenton processes. The results identified hydroxyl radical (•OH) as the main species responsible for the simultaneous decomposition of TA and metronidazole (MNZ) according to TOC removal. The ESR technique was used to detect superoxide radicals (•O₂^-), carbon-centered radical (•R) and hydrogen radical (•H) in the Cu²⁺/TA/H₂O₂ system, which contributed to the acceleration of the Cu²⁺/Cu⁺ redox cycle. The enhancing effect of TA on the homogeneous process was ascribed to the formation of a soluble complex with Cu²⁺, which favored the pH range extension, Cu⁺ oxidation, and radical generation. Moreover, the adsorption of TA on the catalysts surface promoted the consumption of H₂O₂, inducing •OH generation. The formed surface complex (≡Cu²⁺-TA) also accelerated the regeneration of ≡Cu⁺, which was confirmed by density functional theory (DFT) calculation and surface characterization analysis (SEM, XRD, and XPS). The possible degradation pathways of MNZ in TA-modified Fenton-like system were also clarified.

Staged assessment for the involving mechanism of humic acid on enhancing water decontamination using H2O2-Fe(III) process

Humic acid (HA) as a natural coordinating agent was employed to modify the Fenton-like process by promoting the redox cycle of Fe(III)/Fe(II) and enhancing the pH tolerance. However, the roles of coordinating stages of HA-Fe(III) and the dynamic changes of iron species remain unclear. In this study, HA was introduced into the H₂O₂-Fe(III) process to investigate the accelerating roles of coordinating stages and systematically reveal the mechanism via the reactive oxygen species (ROS) identification, HA-Fe(III)/Fe(II) redox cycles tracking, electrochemical and kinetic analysis. Results suggested that two reaction stages were separated concerning the enhancement for HA in H₂O₂-Fe(III) process, including coordinating stage (slow rate) and promoting the redox stage (fast rate). HA-Fe(III) was identified as the major contributor, along with hydroxyl radical (·OH) and superoxide radical (·O₂^-) as the dominant ROS with formation rates calculated as 7.0 × 10^-9 and 2.1 × 10^-3 M s^-1 via the steady-state model. Based on the density-functional theory (DFT) calculations and HPLC-MS/MS analysis, three degradation pathways of 2,4-Dichlorophenol were proposed with ten intermediate products identified, and the ecotoxicity was evaluated through Ecological Structure Activity Relationships (ECOSAR) program. This study unveiled the mechanism of HA on enhancing water decontamination via H₂O₂-Fe(III) process in stages.

Improving the Fenton-like catalytic performance of MnOx-Fe3O4/biochar using reducing agents: A comparative study

In this work, a Fenton-like system with MnO_x-Fe₃O₄/biochar composite (FeMn/biochar) and reducing agents (RAs) was constructed for pollutant degradation, aiming to enhance Fenton-like performance from both degradation efficacy and operational cost aspects. Batch experiments revealed that five well-characterized RAs (sodium borohydride (SBH), sodium thiosulfate (STS), ascorbic acid (AA), hydroxylamine (HA) and oxalic acid (OA)) could impact performance of FeMn/biochar-H₂O₂ system through multiple mechanisms, including variation of solution pH, competition for H₂O₂, electrostatic attraction and acceleration of metal redox cycle. Significantly, only OA and HA obviously enhanced the catalytic capacity of Fenton-like process and HA increased ciprofloxacin degradation efficiency from 38.2% to 92.8% with a low economic consumption as 4.16 US$/m³, well in agreement with the accelerated Fe(III/II) cycle and Mn(III/II) cycle in FeMn/biochar-H₂O₂-HA system. The accelerated metal redox cycle could enhance the decomposition of H₂O₂ into •OH and •O₂^-, which were verified to be the main reactive oxygen species responsible for ciprofloxacin degradation by radical trapping experiments. Meanwhile, FeMn/biochar-H₂O₂-HA system could also work effectively in real wastewaters, and exhibited favorable catalytic performance towards oxytetracycline, tetracycline, methyl orange, methylene blue, Rhodamine B, and naphthalene, indicating the applicability of FeMn/biochar-H₂O₂-HA system in oxidizing refractory pollutants in wastewaters.