Activation of peroxymonosulfate by iron oxychloride with hydroxylamine for ciprofloxacin degradation and bacterial disinfection

The synergistic effect of periodate/ferrate (VI) system on disinfection of antibiotic resistant bacteria and removal of antibiotic resistant genes: The dominance of Fe (IV)/Fe (V)

The proliferation of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARB) caused by antibiotic abuse has raised concerns about the global infectious-disease crisis. This study employed periodate (PI)/ferrate (VI) (Fe (VI)) system to disinfect Gram-negative ARB (Escherichia coli DH5α) and Gram-positive bacteria (Bacillus subtilis ATCC6633). The PI/Fe (VI) system could inactivate 1 × 108 CFU/mL of Gram-negative ARB and Gram-positive bacteria by 4.0 and 2.8 log in 30 min. Neutral and acidic pH, increase of PI dosage and Fe (VI) dosage had positive impacts on the inactivation efficiency of ARB, while alkaline solution and the coexistence of 10 mM Cl-, NO3-, SO42- and 20 mg/L humic acid had slightly negative impacts. The reactive species generated by PI/Fe (VI) system could disrupt the integrity of cell membrane and wall, leading to oxidative stress and lipid peroxidation. Intracellular hereditary substance, including DNA and ARGs (tetA), would leak into the external environment through damaged cells and be degraded. The electron spin resonance analysis and quenching experiments indicated that Fe (IV)/Fe (V) played a leading role in disinfection. Meanwhile, PI/Fe (VI) system also had an efficient removal effect on sulfadiazine, which was expected to inhibit the ARGs transmission from the source.

Influence mechanism of anions on iron doping into swine bone char: Promoting non-radical oxidation of acetaminophen in a Fenton-like system

The application of iron-doped biochar in peroxymonosulfate (PMS) activation systems has gained increasing attention due to their effectiveness and environmental friendliness in addressing environmental issues. However, the behavioral mechanism of iron doping and the detailed 1O2 generation mechanism in PMS activation systems remain ambiguous. Here, we investigated the effects of three anions (Cl-, NO3-and SO42-) on the process of iron doping into bone char, leading to the synthesis of three iron-doped bone char (Fe-ClBC, Fe-NBC and Fe -SBC). These iron-doped bone char were used to catalyze PMS to degrade acetaminophen (APAP) and exhibited the following activity order: Fe-ClBC > Fe-NBC > Fe-SBC. Characterization results indicated that iron doping primarily occurred through the substitution of calcium in hydroxyapatite within BC. In the course of the impregnation, the binding of SO42- and Ca2+ hindered the exchange of iron ions, resulting in lower catalytic activity of Fe-SBC. The primary reactive oxygen species in the Fe-ClBC/PMS and Fe-NBC/PMS systems were both 1O2. 1O2 is produced through O2•- conversion and PMS self-dissociation, which involves the generation of metastable iron intermediates and electron transfer within iron species. The presence of oxygen vacancies and more carbon defects in the Fe-ClBC catalyst facilitates 1O2 generation, thereby enhancing APAP degradation within the Fe-ClBC/PMS system. This study is dedicated to in-depth exploration of the mechanisms underlying iron doping and defect materials in promoting 1O2 generation.

Ascorbic acid enhanced the circulation between Fe(II) and Fe(III) in peroxymonosulfate system for fluoranthene degradation

In this research, ascorbic acid (AA) was used to enhance Fe(II)/Fe(III)-activated permonosulfate (PMS) systems for the degradation of fluoranthene (FLT). AA enhanced the production of ROS in both PMS/Fe(II) and PMS/Fe(III) systems through chelation and reduction and thus improved the degradation performance of FLT. The optimal molar ratio in PMS/Fe(II)/AA/FLT and PMS/Fe(III)/AA/FLT processes were 2/2/4/1 and 5/10/5/1, respectively. In addition, the experimental results on the effect of FLT degradation under different groundwater matrixes indicated that PMS/Fe(III)/AA system was more adaptable to different water quality conditions than the PMS/Fe(II)/AA system. SO4·- was the major reactive oxygen species (ROS) responsible for FLT removal through the probe and scavenging tests in both systems. Furthermore, the degradation intermediates of FLT were analyzed using gas chromatograph-mass spectrometry (GC-MS), and the probable degradation pathways of FLT degradation were proposed. In addition, the removal of FLT was also tested in actual groundwater and the results showed that by increasing the dose and pre-adjusting the solution pH, 88.8 and 100% of the FLT was removed for PMS/Fe(II)/AA and PMS/Fe(III)/AA systems. The above experimental results demonstrated that PMS/Fe(II)/AA and PMS/Fe(III)/AA processes have a great perspective in practice for the rehabilitation of FLT-polluted groundwater.

Antibiotic removal from synthetic and real aqueous matrices by peroxymonosulfate-based advanced oxidation processes. A review of recent development

The widespread use of antibiotics for the treatment of bacteriological diseases causes their accumulation at low concentrations in natural waters. This gives health risks to animals and humans since it can increase the damage of the beneficial bacteria, the control of infectious diseases, and the resistance to bacterial infection. Potent oxidation methods are required to remove these pollutants from water because of their inefficient abatement in municipal wastewater treatment plants. Over the last three years in the period 2021-September 2023, powerful peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have been developed to guaranty the effective removal of antibiotics in synthetic and real waters and wastewater. This review presents a comprehensive analysis of the different procedures proposed to activate PMS-producing strong oxidizing agents like sulfate radical (SO4•-), hydroxyl radical (•OH, radical superoxide ion (O2•-), and non-radical singlet oxygen (1O2) at different proportions depending on the experimental conditions. Iron, non-iron transition metals, biochar, and carbonaceous materials catalytic, UVC, photocatalytic, thermal, electrochemical, and other processes for PMS activation are summarized. The fundamentals and characteristics of these procedures are detailed remarking on their oxidation power to remove antibiotics, the influence of operating variables, the production and detection of radical and non-radical oxidizing agents, the effect of added inorganic anions, natural organic matter, and aqueous matrix, and the identification of by-products formed. Finally, the theoretical and experimental analysis of the change of solution toxicity during the PMS-based AOPs are described.

Iron-doped swine bone char as hydrogen peroxide activator for efficient removal of acetaminophen in water

Bone char is a functional material obtained by calcining animal bones and is widely used for environmental remediation. In this work, iron was inserted into porcine bone-derived bone char via ion exchange to synthesize iron-doped bone char (Fe-BC) for efficient catalysis of hydrogen peroxide. This is the first time that Fe-BC has been used as a catalyst for the activation of H2O2. The effectiveness of the Fe-BC catalyst was influenced by the annealing temperature and the amount of iron doping. The results showed that the activation of H2O2 by the Fe-BC catalyst with the best catalytic performance could achieve 97.6% of APAP degradation within 30 min. Insights from electron paramagnetic resonance (EPR), free radical scavenging experiments and linear sweep voltammetry (LSV) proposed a reaction mechanism based on free radicals dominated degradation pathways (OH and O2-). Iron served as the primary active site in Fe-BC, with defect sites and oxygen-containing groups in the catalyst also contributing to the removal of pollutants. The Fe-BC/H2O2 system demonstrated resilience to interference from common anions (Cl-, NO3-, SO42- and HCO3-) in water, but was less effective against humic acid (HA). Based on the detection of intermediates produced during APAP degradation, possible degradation pathways of APAP were proposed and the toxicity of intermediates was evaluated. This work provides fresh insights into the use of heterogeneous Fenton catalysts for the removal of organic pollutants from water.

Insight into iron oxychloride composite bone char for peroxymonosulfate activation: Mechanism of singlet oxygen evolution for selective degradation of organic pollutants

The activity of iron-based catalysts in advanced oxidation processes (AOPs) is limited by the redox cycle of Fe(III) and Fe(II). In this work, iron oxychloride (FeOCl) with a unique layered structure was loaded on the bone char (BC) to enhance the activation of peroxymonosulfate (PMS). Characterization of the FeOCl-BC catalyst reveals that the loading of FeOCl changed the composition and structure of BC and BC reduced the bond gap of FeOCl. Acetaminophen (APAP) as a target pollutant could be almost completely degraded at neutral pH, and the removal rate reached 0.6597 min^-1. APAP could also be selectively oxidized by FeOCl-BC/PMS system in the presence of some inorganic anions (SO₄^2-, NO₃^-, and Cl^-) and humic acid. Quenching experiments, electron paramagnetic resonance (EPR), chemical probes, and linear sweep voltammetry (LSV) confirm that the primary oxidation mechanism of the FeOCl-BC/PMS system was dominated by ¹O₂. The ¹O₂ was generated from the conversion of O₂^•- and the self-dissociation of PMS, involving the formation of metastable iron intermediates and the redox cycle of Fe(III) and Fe(II). The unique structure of FeOCl, the transport of lattice oxygen and the enrichment of electrons by carbon defects play an essential role in generating reactive species. In this work, the limitation of the redox cycle of Fe(III) and Fe(II) was broken by loading FeOCl on the surface of BC, and a new catalytic mechanism was proposed. This work provides a new perspective for the construction of efficient iron-based catalysts and the practical application of PMS-based AOPs.

Tungsten disulfide (WS2) is a highly active co-catalyst in Fe(III)/H2O2 Fenton-like reactions for efficient acetaminophen degradation

The most important factor that restricts the decomposition of H₂O₂ in the Fe³⁺/H₂O₂ reaction is the slow cycling efficiency of reducing Fe³⁺ to Fe²⁺. In this study, the addition of tungsten disulfide (WS₂) as a co-catalyst achieved a rapid cycling of the reaction rate-limiting step and a significant enhancement of H₂O₂ decomposition, which resulted in the effective degradation of acetaminophen (APAP). Results show that 99.6% of APAP (5 mg L^-1) could be degraded by H₂O₂/Fe³⁺/WS₂ system within 2.5 min. The conversion of Fe³⁺ to Fe²⁺ occurred mainly on the surface of WS₂ due to the redox reaction of the exposed W⁴⁺ active sites with Fe³⁺ after the unsaturated S atoms were bound to protons. Electron paramagnetic resonance (EPR) and radical quenching experiments evaluated the contribution of hydroxyl radical (•OH) and superoxide radical (O₂^•-) in the degradation of pollutants. WS₂ showed good recoverability after four cycles of the reaction. This study provides a new perspective to improve the efficiency of Fe³⁺/H₂O₂ and provides a reference for the involvement of transition metal sulfides in advanced oxidation processes (AOPs).

Effect of metal doping (Me = Zn, Cu, Co, Mn) on the performance of bismuth ferrite as peroxymonosulfate activator for ciprofloxacin removal

In this study, a facile hydrothermal method was employed to prepare Me-doped Bi₂Fe₄O₉ (Me = Zn, Cu, Co, and Mn) as peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) degradation. The characteristics of the Me-doped bismuth ferrites were investigated using various characterization instruments including SEM, TEM, FTIR and porosimeter indicating that the Me-doped Bi₂Fe₄O₉ with nanosheet-like square orthorhombic structure was successfully obtained. The catalytic activity of various Me-doped Bi₂Fe₄O₉ was compared and the results indicated that the Cu-doped Bi₂Fe₄O₉ at 0.08 wt.% (denoted as BFCuO-0.08) possessed the greatest catalytic activity (k_app = 0.085 min^-1) over other Me-doped Bi₂Fe₄O₉ under the same condition. The synergistic interaction between Cu, Fe and oxygen vacancies are the key factors which enhanced the performance of Me-doped Bi₂Fe₄O₉. The effects of catalyst loading, PMS dosage, and pH on CIP degradation were also investigated indicating that the performance increased with increasing catalyst loading, PMS dosage, and pH. Meanwhile, the dominant reactive oxygen species was identified using the chemical scavengers with SO₄^•-, ^•OH, and ¹O₂ playing a major role in CIP degradation. The performance of BFCuO-0.08 deteriorated in real water matrix (tap water, river water and secondary effluent) due to the presence of various water matrix species. Nevertheless, the BFCuO-0.08 catalyst possessed remarkable stability and can be reused for at least four successive cycles with >70% of CIP degradation efficiency indicating that it is a promising catalyst for antibiotics removal.

Degradation of 4-chlorophenol using MnOOH and γ-MnOOH nanomaterials as porous catalyst: Performance, synergistic mechanism, and effect of co-existing anions

Transition metal catalysts have been proven to be a highly-potent catalyst for peroxymonosulfate (PMS) activation. The present work aimed to synthesizes the γ-MnOOH and MnOOH based on the one-pot hydrothermal method as PMS activators for efficient degradation of 4-chlorophenol (4-CP). The effect of operational parameters including solution pH, γ-MnOOH and MnOOH dose, PMS dose, 4-CP concentration, and also mixture media composition was elaborated. The results showed that the combination of MnOOH and γ-MnOOH with PMS noticeably creates a synergistic effect (SF) in 4-CP degradation by both PMS/MnOOH and PMS/γ-MnOOH process, with a SF value of 48.14 and 97.42, respectively. In both systems, the removal of 4-CP decreased in severely alkaline and acidic conditions, while no significant changes were observed in pH 5 to 9. Also, coexisting PO₄³- significantly reduced the removal efficiency of both systems. In addition, the effect of humic acid (HA) as a classical scavenger was investigated and showed that presence of 4 mg/L HA reduced the removal efficiency of 4-CP in the PMS/MnOOH process from 97.44% to 79.3%. The three consecutive use of both catalysts turned out that MnOOH has better stability than γ-MnOOH with lower Mn ions leaching. More importantly, quenching experiment showed that both non-radical (¹O₂ and O₂^-) and radical (SO₄^- and OH) pathways are involved in 4-CP degradation and non-radical pathway was the dominant one in both systems.

Heterogeneous activation of H2O2/Na2S2O8 with iron ore from water distribution networks for pollutant removal

In this study, we investigated using the main composition of pipe deposits from water distribution networks as catalyst to activate dual-oxidant H₂O₂/Na₂S₂O₈ system to produce radicals for perchloroethylene and chloramphenicol removal. According to the results, the degradation efficiency of perchloroethylene by H₂O₂/Na₂S₂O₈ system was 92.05% within 8 h. Due to the slow conversion between ≡Fe³⁺ and ≡Fe²⁺, the hydroxylamine was introduced to reduce reaction time. As for the results, the degradation efficiency of chloramphenicol in the H₂O₂/Na₂S₂O₈ system with hydroxylamine assistance was 73.31% within 100 min. Meanwhile, several key affecting factors and the kinetic models were investigated. The primary radicals were identified by electron paramagnetic resonance and radical scavenging tests. Eleven degradation products were confirmed by high-resolution liquid chromatography-mass spectrometry. The result of this study provided the theoretical basis for resource utilization of pipe deposits in water treatment in case of emerging contamination events.