Activation of peroxymonosulfate by Fe0@Fe3O4 core-shell nanowires for sulfate radical generation: Electron transfer and transformation products

Enhanced dewaterability of sludge by Fe(II)-sludge biochar activate persulfate

Sludge biochar supported Fe(II) (Fe(II)-SBC) was successfully prepared using waste activated sludge as peroxydisulfate (PDS) activator to condition sludge for deep dewatering. The experimental results showed that Fe(II)-SBC with FeO on it could effectively active PDS to produce SO 4 - ⋅ and HO ⋅ . The radicals could destroy the structure of sludge cells and extracellular polymeric substance (EPS), transformed the hydrophilic and tightly bound EPS into soluble-EPS, degrade partial proteins and polysaccharides and released bound water. The negatively charged groups on sludge floc were dripped off by SO 4 - ⋅ /HO ⋅ or neutralized with Fe2+, Fe3+, H+, or Fe(II)-SBC, leading to an increase in zeta potential to -2.24 mV and sludge destabilization. The residual Fe(II)-SBC served as a skeleton builder that decreased the compression coefficient of the sludge cake to 0.75. Under the combined functions, the CST and SRF were reduced by 70% and 82.7%, respectively, and Wc was reduced to 72.4%. The byproducts of Fe3+ and SO42- finally remained in sludge cake in the form of NaFeSi2O6 and CaSO4.

Enhanced degradation of chloramphenicol via heterogeneous activation of peroxymonosulfate by Fe3O4 and gallic acid

In this study, we demonstrated the effective degradation of wide-spectrum antibiotic chloramphenicol (CAP) by Fe3O4/peroxymonosulfate (PMS) system modified by gallic acid (GA). GA/Fe3O4/PMS showed a substantially higher degradation rate (77.6%) than Fe3O4/PMS (8.3%). The active components were detected by electron spin-resonance spectroscopy (ESR) and the quenching experiments. The results showed that the hydroxyl radical (HO•) was the main reason for the degradation of CAP. In the GA/Fe3O4/PMS system, the trace amount of dissolved iron ion were not the main species that activated PMS. Surface characterization and theoretical simulations showed that Fe atoms on Fe3O4 were responsible for PMS activation rather than a homogenous reaction. Five probable CAP degradation pathways were identified by density functional theory (DFT) calculations and liquid-phase mass spectrometry. Finally, the reusability of Fe3O4 was measured, and the GA/Fe3O4/PMS system maintained high efficiency after 5 times applications. The total organic carbon (TOC) removal rate reached 46.5% after reacting for 12 h. The gallic acid effectively promotes the circulation of Fe(II)/Fe(III) on solid surfaces and enhanced the degradation capacity of the original system. The research proposed a new way of directly employing plant polyphenols to boost the degradation ability of contaminants in heterogeneous systems.

Textile dye removal in wastewater by peroxymonosulfate (PMS) activation on a zero-valent iron nanoparticle-modified ultrafiltration catalytic membrane (nZVI@PES)

The use of the nano zero-valent iron (nZVI) nanoparticle-based advanced oxidation systems in conjunction with an activator such as peroxymonosulfate (PMS) to generate hydroxyl and sulfate radicals for the degradation of organic pollutants has been extensively used in recent studies. In this study, a nZVI-modified polyethersulfone (PES) membrane (nZVI@PES) was produced successfully by attaching the nZVI catalytic nanoparticles on the surface of a commercial microporous polymeric membrane material using a simple and easy filter press coating method. The presence of nZVI nanoparticles on the nZVI@PES membrane was confirmed by XRD, SEM, and EDS analyses. The nZVI@PES membrane was applied in the dead-end filtration system in the presence of the PMS activator to treat the reactive black 5 (RB5) dye solution. The effect of catalyst loading, RB5 dye concentration, PMS dosage, and pH level on the nZVI@PES membrane/PMS system was investigated. Quenching experiments were carried out to identify the reactive species responsible, and reusability tests were conducted on the membrane. The highest decolorization efficiency (96.8%) was obtained at 20 mg/L RB5 dye solution, initial pH of 3, the nZVI loading of 5 mg/cm2, and the PMS dosage of 300 mg/L at the end of a reaction time of 30 min. The formation of HO•, [Formula: see text], [Formula: see text] and, 1O2 was confirmed by quenching experiments. The results indicate that the nZVI@PES membrane/PMS system could successfully treat wastewater contaminated with an organic dye.

Wood induced preparation of Fe3C decorated biochar for peroxymonosulfate activation towards bisphenol a degradation with low ion leaching

Heterogeneous iron/persulfate system suffers from the problems of high ion leaching, severe catalyst surface corrosion and low performance stability. Herein, a series of iron compound incorporated N doped biochar composite catalysts were prepared from pyrolyzing wood powder and ferric ferrocyanide mixture, which were used for bisphenol A (BPA) degradation in water through peroxymonosulfate (PMS) activation. It was found that the reducing gases released from wood powder at different pyrolysis temperature significantly affected the crystalline phase of the iron compound in the catalyst, in which pure phase iron carbide (Fe₃C) decorated N doped biochar was obtained at pyrolysis temperature of 600 °C or higher. Wood powder was introduced as both Fe₃C formation inductive agent and biochar precursor. Fe₃C/biochar exhibited optimal BPA degradation performance, in which 0.5 g/L of catalyst could completely degrade 0.05 mM BPA within 30 min. Radical, high valent iron-oxo, and non-radical species were all generated in the reaction system by both Fe₃C and N doped biochar, respectively. Moreover, the multi-valence nature of Fe in Fe₃C enabled the reaction system with remarkably reduced Fe ion leaching and negligible iron sludge production since Fe₃C could activate PMS through a heterogeneous mechanism. Having multiple active species generated for BPA degradation, the prepared catalyst also showed promising adaptability and recyclability. This study can provide a new solution for the design of iron based catalyst/PMS system for organic pollutant degradations with low ion release.

Enhancement of Fenton processes at initial circumneutral pH for the degradation of norfloxacin with Fe@FeS core-shell nanowires

The disadvantages of narrow working pH range (2.5-4.0), accumulation of iron sludge and incomplete degradation have hindered the practical application of the traditional homogeneous Fenton technique. In this research, Fe@FeS core-shell nanowires were synthesised and the innovative Fe@FeS/Fe2+/H2O2 system was adopted for norfloxacin (NOR) degradation at an initial circumneutral pH. More than 95% NOR has been removed in the Fe@FeS/Fe2+/H2O2 system within 30 min at pH 7. After investigating the concentration change of total iron, Fe2+ and H2O2 during the degradation process, NOR degradation in the Fe@FeS/Fe2+/H2O2 system might be attributed to the combined effect of homogeneous Fenton reaction and heterogeneous Fenton process. Besides that, the added Fe@FeS has accelerated Fe3+/Fe2+ redox cycle with extremely high degree. The generated reactive ●OH has been identified by electron paramagnetic resonance spectrometer results, possible degradation intermediates have also been proposed according to Gas chromatography-mass spectrometry analysis results. Moreover, Fe@FeS core-shell nanowires showed excellent reusability, it is a promising heterogeneous Fenton catalyst that is applicable for practical application.

In-situ preparation of yeast-supported Fe0@Fe2O3 as peroxymonosulfate activator for enhanced degradation of tetracycline hydrochloride

Nano zero-valent iron (nZVI) is extensively used as a peroxymonosulfate (PMS) activator but suffers from the ease of oxidation and agglomeration due to its high surface energy and inherent magnetism. Here, green and sustainable yeast was selected as a support material to firstly in-situ prepare yeast-supported Fe⁰@Fe₂O₃ and used for activating PMS to degrade tetracycline hydrochloride (TCH), one of the common antibiotics. Due to the anti-oxidation ability of the Fe₂O₃ shell and the support effect of yeast, the prepared Fe⁰@Fe₂O₃/YC exhibited a superior catalytic activity for the removal of TCH as well as some other typical refractory contaminants. The chemical quenching experiments and EPR results demonstrated SO₄^•- was the main reactive oxygen species while O₂^•-, ¹O₂ and ^•OH played a minor role. Importantly, the crucial role of the Fe²⁺/Fe³⁺ cycle promoted by the Fe⁰ core and surface iron hydroxyl species in PMS activation was elucidated in detail. The TCH degradation pathways were proposed by LC-MS and density functional theory (DFT) calculation. In addition, the outstanding magnetic separation property, anti-oxidation ability, and high environmental resistance of the catalyst were demonstrated. Our work may inspire the development of green, efficient, and robust nZVI-based materials for wastewater treatment.

Morphology regulation of zero-valent iron nanosheets supported on microsilica for promoting peroxymonosulfate activation

Combing the assisted dispersion strategy of support with the wet chemical reduction method, a novel nano-zero valent iron/microsilica (nZVI/M) composite was successfully fabricated, where the 2D nZVI nanosheets were uniformly anchored and covered on the surface of microsilica. The introduction of microsilica notably relieved the agglomeration effect of nZVI nanosheets, which induced the improvement of specific surface area (45.68 m²/g) and pore volume (0.172 cm³/g), and thereby exposing more active sites for bisphenol A (BPA) removal. The optimized nZVI/M-0.6 displayed the superior catalytic performance in the presence of peroxymonosulfate (PMS) with the degradation rate of BPA reached above 97% within 3 min and a higher constant rate of 0.659 min^-1, which was approximately 3.9 times as high as that of nZVI/PMS system. The homogeneously dispersion of nZVI nanosheets on microsilica benefited for the assembly of the pollutants and boosting the kinetics of the catalytic degradation process. As a highly efficient PMS activator, it could well maintain the catalytic activity in different real water samples. The quenching experiments verified that SO₄^•- played the dominate role for BPA removal. This work offered novel insights for designing and preparing iron-based persulfate activator for wastewater treatment.

Surface-bound hydroxyl radical-dominated degradation of sulfamethoxazole in the amorphous FeOOH/ peroxymonosulfate system: The key role of amorphous structure enhancing electron transfer

In this study, activation of peroxymonosulfate (PMS) by amorphous FeOOH to degrade sulfamethoxazole (SMX) was investigated. The amorphous FeOOH showed a better performance in the decomposition of PMS and the degradation of SMX than the crystallized α-FeOOH and β-FeOOH. The quenching experiments and EPR measurements suggested that the mechanism of PMS activation by amorphous FeOOH was mainly the surface-bound radicals (^●OH and SO₄^●-). Basically, the surface-bound ^●OH radicals were the dominate reactive oxide species in this system, which were mainly generated via the decomposition of amorphous FeOOH-PMS complexes. The degradation of SMX was significantly inhibited with the presence of H₂PO₄^-, and this adverse impact was negligibly affected by the increase of H₂PO₄^- concentration, implying that the inhibition of SMX degradation was caused by competitive adsorption. Consequently, the Fe-OH bonds on the amorphous FeOOH were proposed as the reactive sites for forming amorphous FeOOH-PMS complexes. Besides, the amorphous FeOOH showed a better performance in the degradation of SMX in the acid conditions than that in the base conditions due to the surface charge of amorphous FeOOH. More importantly, the reduction efficiency of Fe(III) was significantly enhanced due to the excellent conductivity of amorphous FeOOH.

Enhancing Brackish Water Desalination using Magnetic Flow-electrode Capacitive Deionization

Flow-electrode capacitive deionization (FCDI) is viewed as a potential alternative to the current state-of-the-art electrodriven technology for the desalination of brackish water. However, the key shortcoming of the FCDI is still the discontinuous nature of the electrode conductive network, resulting in low electron transport efficiency and ion adsorption capacity. Here, a novel magnetic field-assisted FCDI system (termed magnetic FCDI) is proposed to enhance brackish water desalination, simply by using magnetic activated carbon (MAC) as flow electrodes. The results show that the assistance from the magnetic field enables a 78.9% - 205% enhancement in the average salt removal rate (ASRR) compared with that in the absence of a magnetic field, which benefits from the artificial manipulation of the flow electrode transport behavior. In long-term tests, the stable desalination performance of magnetic FCDI was also demonstrated with a stable ASRR of 0.70 μmol cm^-2 min^-1 and energy-normalized removed salt (ENRS) of 8.77 μmol J^-1. In addition, magnetic field also enables the regeneration of the electrode particles from the concentrated electrolyte. In summary, the findings indicate that the magnetic FCDI is an energy-efficient and operation convenient technology for brackish water desalination.

Iron-based materials for simultaneous removal of heavy metal(loid)s and emerging organic contaminants from the aquatic environment: Recent advances and perspectives

The existence of heavy metals and emerging organic contaminants in wastewater produces serious toxic residues to the environment. Developing cheap and efficient materials to remove these persistent pollutants is crucial. Iron-based materials are cost-effective and environmentally friendly catalysts, and their applications in the environmental field deserve attention. This paper critically reviewed the removal mechanisms of heavy metals and emerging organic pollutants by different influencing factors. The removal of pollutants (heavy metals and emerging organic pollutants) in a multi-component system was analyzed in detail. The mechanisms of synergism, antagonism and non-interference were discussed. This paper had a certain reference value for the research of wastewater remediation technology which could simultaneously remove various pollutants by iron-based materials.

CoFe-LDO nanoparticles as a novel catalyst of peroxymonosulfate (PMS) for histidine removal

Dissolved organic nitrogen (DON) has been a research subject due to its potential to form nitrogenous disinfection byproducts (N-DBPs) in drinking water treatment. In our study, CoFe layered double oxide (CoFe-LDO) was selected as an effective catalyst for the removal of histidine by activation of peroxymonosulfate (PMS). The results investigated that the removal of DON and histidine within 1 h in the CoFe-LDO/PMS system were up to 61% and 72%, respectively. The influences of CoFe-LDO dosage, PMS dosage, and pH value for DON removal were also elucidated. The optimum pH was 8, and the optimal dosage of CoFe-LDO and PMS were 0.04 g/L and 0.5 mmol/L. It was found that SO₄^•- and •OH induced by the transformation of Co²⁺-Co³⁺ and Fe²⁺-Fe³⁺ on the catalyst surface were responsible for the degradation by ESR detection, in which SO₄^•- played a more important role. The degradation pathway of histidine indicated that it was partly oxidized to NH₄⁺-N in the 60 min and no evident generation of N₂ during the whole process. Furthermore, degradation products of histidine have also been revealed by the analysis of HPLC-MS. In addition, the generation potentials of two typical N-DBPs were also clarified. The formation potential of dichloroacetonitrile (DCAN) decreased, while that of dichloroacetamide (DCAcAm) increased firstly before declining.

Hydrothermal and Co-Precipitated Synthesis of Chalcopyrite for Fenton-like Degradation toward Rhodamine B

In this study, Chalcopyrite (CuFeS2) was prepared by a hydrothermal and co-precipitation method, being represented as H-CuFeS2 and C-CuFeS2, respectively. The prepared CuFeS2 samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy mapping (EDS-mapping), powder X-ray diffractometer (XRD), X-ray photoelectron spectrometry (XPS), and Raman microscope. Rhodamine B (RhB, 20 ppm) was used as the target pollutant to evaluate the degradation performance by the prepared CuFeS2 samples. The H-CuFeS2 samples (20 mg) in the presence of Na2S2O8 (4 mM) exhibited excellent degradation efficiency (98.8% within 10 min). Through free radical trapping experiment, the major active species were •SO4− radicals and •OH radicals involved the RhB degradation. Furthermore, •SO4− radicals produced from the prepared samples were evaluated by iodometric titration. In addition, one possible degradation mechanism was proposed. Finally, the prepared H-CuFeS2 samples were used to degrade different dyestuff (rhodamine 6G, methylene blue, and methyl orange) and organic pollutant (bisphenol A) in the different environmental water samples (pond water and seawater) with 10.1% mineral efficiency improvement comparing to traditional Fenton reaction.

Facile fabrication of Fe/Fe3C embedded in N-doped carbon nanofiber for efficient degradation of tetracycline via peroxymonosulfate activation: Role of superoxide radical and singlet oxygen

The toxic metal ions leaching and metal nanoparticles agglomeration were the critical issues for metal-based carbon materials during the peroxymonosulfate (PMS) activation processes. Herein, a facile strategy was first proposed that zero-dimensional Fe/Fe₃C nanoparticles were embedded in one-dimensional N-doped carbon nanofiber (Fe/Fe₃C@NCNF) to solve the above challenges. The as-obtained Fe/Fe₃C@NCNF-800 possessed a low E_a value (11.7 kJ/mol) and exhibited high activity for activating PMS to degrade tetracycline (TC) in a wide range of pH 3-11. As expected, the iron ions leaching concentration of Fe/Fe₃C@NCNF-800 was very low (0.082 mg/L). Meanwhile, the Fe/Fe₃C@NCNF-800 was easily recovered from the reaction solution due to its magnetic properties. Both superoxide radicals (O₂^∙-) and non-radical of singlet oxygen (¹O₂) were the primary reactive oxygen species (ROS) in the Fe/Fe₃C@NCNF-800/PMS system via quenching tests and electron spin resonance spectroscopy (ESR). The catalytic mechanism suggested that the Fe/Fe₃C and graphitic N were the main active sites in the Fe/Fe₃C@NCNF-800 for PMS activation. This work provided a facile method for the preparation of Fe-based carbon materials with high catalytic ability, low metal leaching and easy recycling, showing a broad prospect for environmental applications.

Removal of organic compounds by nanoscale zero-valent iron and its composites

During the latest several decades, the continuous development of the economy and industry has brought more and more serious organic pollutants to the natural environment, which have inevitably aroused severe menace to human health and the environmental system. The nano zero-valent iron (NZVI) particles and NZVI-based materials have widely applied to remove organic pollutants. This article reviews the key advancements of different methods for the synthesis of NZVI and NZVI-based materials. Different modification methods (e.g., doped NZVI, encapsulated NZVI and supported NZVI) are also introduced detailedly for overcoming the defects of NZVI such as aggregation and easy oxidation. The removal of different organic pollutants including dyes, halogenated organic compounds, nitro-organic compounds, phenolic compounds, pesticides, and antibiotics are summarized. The interaction mechanisms, including adsorption, reduction, and active oxidation of organic pollutants by NZVI/NZVI-based composites, are discussed. The dyes are mainly removed by destroying their chromogenic group according to the reduction or the Fenton-like reaction with NZVI. The removal of halogenated organic compounds (HOCs) is realized by the dehalogenation process, including reductive elimination, hydrogenolysis, and hydrogenation. As for the nitro-organic compounds, three different reduction pathways as nitro-reduction (into amino), cleavage at the carbon‑nitrogen bond or denitration of the NO₂ group may take effect. The phenolic compounds can be mineralized into inorganic molecules, including CO₂ and H₂O, by Fenton oxidation. This review might provide the basis for future studies on developing more effective NZVI-based materials for the treatment of wastewaters contaminated by organic pollutants.

Peracids - New oxidants in advanced oxidation processes: The use of peracetic acid, peroxymonosulfate, and persulfate salts in the removal of organic micropollutants of emerging concern - A review

In recent years, there has been increasing interest in using of advanced oxidation processes in water and wastewater decontamination. As a new oxidants peracids, mainly peracetic acid (PAA) and peracid salts, i.e. peroxymonosulfate (PMS) and persulfate (PS) are used. The degradation process of organic compounds takes place with the participation of radicals, including hydroxyl (^•OH) and sulfate (SO₄^•-) radicals derived from the peracids activation processes. Peracids can be activated in homogeneous systems (UV radiation, d-electron metal ions, e.g. Fe²⁺, Co²⁺, Mn²⁺, base, ozonolysis, thermolysis, radiolysis), or using heterogeneous activation (metals with zero oxidation state, metal oxides, quinones, activated carbon, semiconductors). As a result of oxidation, products of a lower mass than the parent compounds, less toxic, and more susceptible to biodegradation are formed. An important task is to investigate the effect of the peracid activation method and matrix composition on the efficiency of contamination removal. The article presents the latest information about the application of peracids in the removal of organic micropollutants of emerging concern (mainly focuses on endocrine disrupted compounds). The most important information on peracetic acid, peroxymonosulfate and persulfate salts, and methods of their activation are presented. Current uses of these oxidants in organic micropollutants removal are also described. Information was collected on the factors influencing the oxidation process and the effectiveness of pollutant removal. This paper compares PAA, PMS and PS-based processes for the first time in terms of kinetics and efficiency.

Single-atom catalysis in advanced oxidation processes for environmental remediation

This review presents the recent advances in synthetic strategies, characterisation, and computations of carbon-based single-atom catalysts, as well as their innovative applications and mechanisms in advanced oxidation technologies.