New insights into FeS/persulfate system for tetracycline elimination: Iron valence, homogeneous-heterogeneous reactions and degradation pathways

Remediation of antibiotic pollution in the global environment by iron-based materials activating advanced oxidation processes: A systematic review

Antibiotic pollution and its associated resistance genes have emerged as a global environmental and health concern, with widespread detection in various environmental media such as water, soil, atmosphere, and sediment, as well as in organisms. Hence, it is imperative to develop effective remediation technologies for the targeted treatment of antibiotic pollution to mitigate its environmental and health risks. This paper reviews the status of antibiotic pollution in major countries, territories, and regions worldwide. Addressing the risks cause by antibiotics and their resistance genes and achieving efficient remediation of antibiotic pollutants. Additionally, the study explores the issue of antibiotic use and resistance in detail from a global perspective. It provides a critical scientific foundation for controlling global antibiotic resistance through multi-dimensional integrated analysis. In 2021, 4.71 million deaths globally were attributed to antibiotic resistance, with countries such as India and China being the most affected. It also examined the predominant types and sources of antibiotic pollutants, as well as key remediation technologies for addressing antibiotic contamination. Antibiotics such as amoxicillin and ciprofloxacin are commonly found in surface waters at concentrations ranging from 1 to 120 μg L-1. Furthermore, this paper highlighted the distinctive advantages of advanced oxidation processes (AOPs) in addressing antibiotic pollution, demonstrating removal efficiencies exceeding 90 % under optimal conditions. Our review underscored the pivotal role of iron-based materials and porous biochar in AOPs, showing promising results in various environmental settings. Future research should prioritize the development of multifunctional iron-based composites with improved catalytic stability, environmental compatibility, and recyclability. Moreover, expanding the field-scale application of these materials, particularly in low-resource or high-risk regions, will be essential to translate laboratory successes into global impact. This analysis is designed to inform and guide future initiatives to control and eliminate antibiotic contamination.

Temperature-induced atomic intrinsic sites evolution during waste dyeing sludge into the wealthy iron-based catalyst to sustainable decontamination

Although the worldwide spike in the production of dyeing sludge offers a tantalizing resource to be harnessed, effective waste-to-wealth strategies remain elusive due to its intricate toxic organic matter and metallic elements. Here, we developed a temperature-rebuilding strategy to transform discarded dyeing sludge into an iron-based catalyst with favorable charge transfer for the highly efficient and sustainable Fenton-like catalytic degradation of ppm-level contaminants in wash-tank water. Using X-ray diffraction, X-ray photoelectron spectroscopy, and synchrotron X-ray absorption spectroscopy, we could precisely track and identify the gradual formation of inherent sites (i.e., Fe2(SO4)3, FeOOH, and Fe1-xS) towards active sites (i.e., FeS and Fe0) at crystal, surface, and atomic levels. Benefiting from the reconstruction of iron sites, BC-800 effectively decomposed peroxymonosulfate into multiple radicals and nonradicals through electronic structure modulation, which enabled nearly 100 % degradation and over 60 % mineralization rate of common aromatic compounds within 30 min via ring-opening and dechlorination/substitution pathways. More delightedly, the BC-800 maintained excellent Fenton-like activity across a broad pH or multiple anions coexisted, and its device allowed extended parachlorophenol degradation for over 1 d. This work proposes a feasible "waste control by waste" approach to the reutilization of dyeing sludge, encouraging a potential solution for sustainable wastewater treatment.

Simultaneous oxidation of roxarsone and adsorption of released arsenic by FeS-activated sulfite

The conventional oxidation-adsorption methods are effective for the removal of roxarsone (ROX) but are limited by complicated operation, toxic residual oxidant and leaching of toxic metal ions. Herein, we proposed a new approach to improve ROX removal, i.e., using the FeS/sulfite system. Experimental results showed that approximately 100% of ROX (20 mg/L) was removed and more than 90% of the released inorganic arsenic (As(V) dominated) was adsorbed on FeS within 40 min. This FeS/sulfite system was a non-homogeneous activation process, and SO₄^·-, ·OH and ¹O₂ were identified as reactive oxidizing species with their contributions to ROX degradation being 48.36%, 27.97% and 2.64%, respectively. Based on density functional theory calculations and HPLC-MS results, the degradation of ROX was achieved by C-As breaking, electrophilic addition, hydroxylation and denitrification. It was also found that the released inorganic arsenic was adsorbed through a combination of outer-sphere complexation and surface co-precipitation, and the generated arsenopyrite (FeAsS), a precursor to ecologically secure scorodite (FeAsO₄·2H₂O), was served as the foundation for further inorganic arsenic mineralization. This is the first attempt to use the FeS/sulfite system for organic heavy metal removal, which proposes a prospective technique for the removal of ROX.

Stable and recyclable FeS-CMC-based peroxydisulfate activation for effective bisphenol A reduction: performance and mechanism

In this study, a novel material, iron sulfide modified by sodium carboxymethyl cellulose (FeS-CMC), was successfully synthetized for peroxydisulfate (PDS) activation to remove bisphenol A (BPA). Characterization results showed that FeS-CMC had more attachment sites for PDS activation due to its higher specific surface area. A stronger negative potential contributed to preventing nanoparticles from reuniting in the reaction and improving the interparticle electrostatic interactions of the materials. Fourier transform infrared spectrometer (FTIR) analysis of FeS-CMC suggested that the coordination of the ligand for combining sodium carboxymethyl cellulose (CMC) with FeS was monodentate. A total of 98.4% BPA was decomposed by the FeS-CMC/PDS system after 20 min under optimized conditions (pH = 3.60, [FeS-CMC] = 0.05 g/L and [PDS] = 0.88 mM). The isoelectric point (pH_pzc) of FeS-CMC is 5.20, and FeS-CMC contributed to reducing BPA under acidic conditions but showed a negative effect under basic conditions. The presence of HCO₃^-, NO₃^- and HA inhibited BPA degradation by FeS-CMC/PDS, while excess Cl^- accelerated the reaction. FeS-CMC exhibited excellent performance in oxidation resistance with a final removal degree of 95.0%, while FeS was only 20.0%. Furthermore, FeS-CMC showed excellent reusability and still reached 90.2% after triple reusability experiments. The study confirmed that the homogeneous reaction was the primary part of the system. Surface-bound Fe(II) and S (-II) were found to be the major electron donors during activation, and the reduction of S (-II) contributed to the cycle of Fe(III)/Fe(II). Sulfate radicals (SO₄^•-), hydroxyl radicals (•OH), superoxide radicals (O₂^•-) and singlet oxygen (¹O₂) were produced at the surface of FeS-CMC and accelerated the decomposition of BPA. This study offered a theoretical basis for improving the oxidation resistance and reusability of iron-based materials in the presence of advanced oxidation processes.

Significant roles of surface functional groups and Fe/Co redox reactions on peroxymonosulfate activation by hydrochar-supported cobalt ferrite for simultaneous degradation of monochlorobenzene and p-chloroaniline

CoFe₂O₄/hydrochar composites (FeCo@HC) were synthesized via a facile one-step hydrothermal method and utilized to activate peroxymonosulfate (PMS) for simultaneous degradation of monochlorobenzene (MCB) and p-chloroaniline (PCA). Additionally, the effects of humic acid, Cl^-, HCO₃^-, H₂PO₄^-, HPO₄^2- and water matrices were investigated and degradation pathways of MCB and PCA were proposed. The removal efficiencies of MCB and PCA were higher in FeCo@HC140-10/PMS system obtained under hydrothermal temperature of 140 °C than FeCo@HC180-10/PMS and FeCo@HC220-10/PMS systems obtained under higher temperatures. Radical species (i.e., SO₄^•-, •OH) and nonradical pathways (i.e., ¹O₂, Fe (IV)/Co (IV) and electron transfer through surface FeCo@HC140-10/PMS* complex) co-occurred in the FeCo@HC140-10/PMS system, while radical and nonradical pathways were dominant in degrading MCB and PCA respectively. The surface functional groups (i.e., C-OH and CO) and Fe/Co redox cycles played crucial roles in the PMS activation. MCB degradation was significantly inhibited in the mixed MCB/PCA solution over that in the single MCB solution, whereas PCA degradation was slightly promoted in the mixed MCB/PCA solution. These findings are significant for the provision of a low-cost and environmentally-benign synthesis of bimetal-hydrochar composites and more detailed understanding of the related mechanisms on PMS activation for simultaneous removal of the mixed contaminants in groundwater.

Application of FeS-activated persulfate oxidation system for the degradation of tetracycline in aqueous solution

Tetracycline (TC), an antibiotic used to treat bacterial infectious diseases, is easily transferred to environmental matrixes and then sparks environmental concerns. In this study, TC was selected as a target pollutant to investigate the degradation performance of persulfate (PS) based advanced oxidation processes (AOPs) using FeS as the activator (FeS/PS). The results showed that with optimal PS and FeS concentrations of 1 mM and a pseudo-second-order rate constant (k₂) of 3.45 L mmol^-1 min^-1, 91.39% of TC, was effectively removed within 60 min. From the perspective of degradation rate, apart from CO₃^2-, TC decompositions by FeS/PS were hardly disturbed by the coexistence of different concentrations of Cl^-, NO₃^-, SO₄^2-, and humin acid. The degradation of TC under the O₂ bubbling, N₂ bubbling, and light-proof conditions also had limited effects on these AOPs. In addition, FeS exhibited excellent stability and recyclability when used as a PS activator for TC removal. The PS activated by old FeS and used FeS showed nearly identical performances on TC removal compared with the fresh FeS. It is suggested that homogeneous and heterogeneous reactions are jointly responsible for TC oxidation by FeS/PS. With the contributions of the generated, highly reactive SO₄^-•, and, in particular, •OH, TC enabled the mineralization of inorganic products eventually. Therefore, FeS/PS is highly recommended as an alternative AOPs in the future for TC-contaminated wastewater purification.

Enhanced degradation of tetracycline over FeS-based Fenton-like process: Autocatalytic decomposition of H2O2 and reduction of Fe(III)

This study constructed a FeS-based Fenton-like process to explore the degradation of TTC in the presence of copper ions. The acidic condition of pH 3 was more favorable to the H₂O₂ decomposition and TTC degradation, and it was slightly enhanced by Cu(II). The production of •OH from H₂O₂ was revealed through radical scavenging and benzoic acid probe experiments, and the ratio of H₂O₂ decomposition to •OH production was about 1-1.5, which is comparatively consistent with the theoretical ratio. FeS-based Fenton process was proved to be a homogenous system, the slow release of Fe(II) source and the autocatalytic cycle of Fe(III) to Fe(II) resulting from the reductive species of TTC and dissolved S(-II) improved the production of •OH and the degradation of TTC, which was proved by comparing TTC degradation, TOC removal, H₂O₂ decomposition and Fe(II) concentration with different iron sources (FeS, Fe(II) and Fe(III)) and external addition of dissolved S(-II). The possible degradation pathways of TTC were subsequently inferred according to the detected products by LC-MS. Understanding these autocatalytic processes is essential to reveal the transformation of redox-active substances in environments and may have potential significance in applying FeS-based Fenton-like process for the treatment of wastewater containing reductive organic matters.

Performance investigation of electrochemical assisted HClO/Fe2+ process for the treatment of landfill leachate

The feasibility of removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) from landfill leachate by an electrochemical assisted HClO/Fe2+ process is demonstrated for the first time. The performance of active chlorine generation at the anode was evaluated in Na2SO4/NaCl media, and a higher amount of active chlorine was produced at greater chloride concentration and higher current density. The probe experiments confirmed the coexistence of hydroxyl radical (•OH) and Fe(IV)-oxo complex (FeIVO2+) in the HClO/Fe2+ system. The influence of initial pH, Fe2+ concentration, and applied current density on COD and NH4+-N abatement was elaborately investigated. The optimum pH was found to be 3.0, and the proper increase in Fe2+ dosage and current density resulted in higher COD removal due to the accelerated accumulation of •OH and FeIVO2+ in the bulk liquid phase, whereas, the NH4+-N oxidation was significantly affected by the applied current density because of the effective active chlorine generation at higher current but was nearly independent of Fe2+ concentration. The reaction mechanism of electrochemical assisted HClO/Fe2+ treatment of landfill leachate was finally proposed. The powerful •OH and FeIVO2+, in concomitance with active chlorine and M(•OH), were responsible for COD abatement, and active chlorine played a key role in NH4+-N oxidation. The proposed electrochemical assisted HClO/Fe2+ process is a promising alternative for the treatment of refractory landfill leachate.

Efficient Degradation of Iopromide by Using Sulfite Activated with Mackinawite

Iopromide (IOP), an iodinated X-ray contrast medium (ICM), is identified as a precursor to iodide disinfection byproducts that have high genotoxicity and cytotoxicity to mammals. ICM remains persistent through typical wastewater treatment processes and even through some hydroxyl radical-based advanced oxidation processes. The development of new technologies to remove ICMs is needed. In this work, mackinawite (FeS)-activated sulfite autoxidation was employed for the degradation of IOP-containing water. The experiment was performed in a 500 mL self-made temperature-controlled reactor with online monitoring pH and dissolved oxygen in the laboratory. The effects of various parameters, such as initial pH values, sulfite dosages, FeS dosages, dissolved oxygen, and inorganic anions on the performance of the treatment process have been investigated. Eighty percent of IOP could be degraded in 15 min with 1 g L-1 FeS, 400 μmol L-1 sulfite at pH 8, and high efficiency on the removal of total organic carbon (TOC) was achieved, which is 71.8% via a reaction for 1 h. The generated hydroxyl and oxysulfur radicals, which contributed to the oxidation process, were identified through radical quenching experiments. The dissolved oxygen was essential for the degradation of IOP. The presence of Cl- could facilitate IOP degradation, while NO3- and CO32- could inhibit the degradation process. The reaction pathway involving H-abstraction and oxidative decarboxylation was proposed, based on product identification. The current system shows good applicability for the degradation of IOP and may help in developing a new approach for the treatment of ICM-containing water.