Highly efficient catalysis of chalcopyrite with surface bonded ferrous species for activation of peroxymonosulfate toward degradation of bisphenol A: A mechanism study

Tremendously enhanced catalytic performance of Fe(III)/peroxymonosulfate process by trace Cu(II): A high-valent metals domination in organics removal

Dissolved copper and iron ions are regarded as friendly and economic catalysts for peroxymonosulfate (PMS) activation, however, neither Cu(II) nor Fe(III) shows efficient catalytic performance because of the slow rates of Cu(II)/Cu(I) and Fe(III)/Fe(II) cycles. Innovatively, we observed a significant enhancement on the degradation of organic contaminants when Cu(II) and Fe(III) were coupled to activate PMS in borate (BA) buffer. The degradation efficiency of Rhodamine B (RhB, 20 µmol/L) reached up to 96.3% within 10 min, which was higher than the sum of individual Cu(II)- and Fe(III)- activated PMS process. Sulfate radical, hydroxyl radical and high-valent metal ions (i.e., Cu(III) and Fe(IV)) were identified as the working reactive species for RhB removal in Cu(II)/Fe(III)/PMS/BA system, while the last played a predominated role. The presence of BA dramatically facilitated the reduction of Cu(II) to Cu(I) via chelating with Cu(II) followed by Fe(III) reduction by Cu(I), resulting in enhanced PMS activation by Cu(I) and Fe(II) as well as accelerated generation of reactive species. Additionally, the strong buffering capacity of BA to stabilize the solution pH was satisfying for the pollutants degradation since a slightly alkaline environment favored the PMS activation by coupling Cu(II) and Fe(III). In a word, this work provides a brand-new insight into the outstanding PMS activation by homogeneous bimetals and an expanded application of iron-based advanced oxidation processes in alkaline conditions.

Enhanced degradation of reactive black 5 via persulfate activation by natural bornite: influencing parameters, mechanism and degradation pathway

Reactive black 5 (RBk5) is a refractory azo dye that constitutes a serious threat to the environment and humans. Herein, natural bornite (Nbo) was utilized to activate persulfate (PDS) for the RBk5 removal. The particle size of the Nbo catalyst was optimized and the RBk5 degradation rate constant that responded positively to the particle size of the Nbo catalyst was exhibited. Then, the operational factors affecting RBk5 removal were comprehensively investigated. With the addition of 1.5 g L-1 Nbo and 1.5 mM PDS, 99.05% of the RBk5 (20 mg L-1) was removed in 150 min compared with 0.46% removal with PDS only, which was caused by the additional reactive oxygen species (ROS) produced by the synergistic action of Fe-Cu bimetallic metal and reductive sulfur species. The Nbo catalyst presented high stability and reusability toward RBk5 removal. Identification of reactive oxygen species revealed that SO 4 ⋅ - , ·OH, O 2 ⋅ - and 1O2 collectively participated in RBk5 removal. Additionally, a possible degradation pathway for RBk5 was proposed, including cleavage of the azo, C-S and S-O bonds, hydroxylation, hydrolyzation, direct oxidation and other pathways. This work developed a highly effective and low-cost natural mineral-based bimetallic sulfide material for PDS activation for the degradation of contaminants and environmental remediation.

Efficient removal of moxifloxacin through PMS activation by CuFeS2/MXene

Due to the frequent detection and potential toxicity of moxifloxacin (MOX), its removal technology had attracted attention in recent years. In this research, CuFeS2/MXene was prepared and used to activate peroxymonosulfate (PMS) to remove MOX. The degradation efficiencies, kinetics, influences, and reaction mechanism of MOX by CuFeS2/MXene/PMS were investigated. The synergistic effect of CuFeS2 and MXene significantly enhanced PMS activation, producing SO4•-, HO•, and 1O2 as the main active species. By adding 0.12 g/L CuFeS2/MXene and 0.12 mM PMS, MOX removal efficiency reached 99.1% within 40 min, with a rate constant of 0.1073 min-1. The composite ratios of CuFeS2/MXene impacted PMS activation more significantly than catalyst dosages and PMS concentrations. Acidic conditions were favorable for the degradation of MOX, while HCO3-, HPO42-, Mn2+, and HA had the inhibitory effects. Twelve major products were detected by HPLC-MS, and DFT was used to illustrate possible degradation pathways of MOX, including the removal of nitrogen-containing heterocycle and transformations of quinolone moieties. Toxicity analysis showed that the developmental toxicity, mutagenicity, and acute toxicity of degradation products tended to decrease. CuFeS2/MXene could exhibit excellent reusability, maintaining an average MOX degradation efficiency of 90.8% in the 7-cycle experiments.

Photo-assisted natural chalcopyrite activated peracetic acid for efficient micropollutant degradation

The effective activation of natural chalcopyrite (CuFeS2) on peracetic acid (PAA) to remove organic micropollutants was studied under visible light irradiation. Results showed than an effective sulfamethoxazole (SMX) degradation (95.0 %) was achieved under visible light irradiation for 30 min at pH 7.0. Quenching experiments, electron spin resonance analysis, and LC/MS spectrum demonstrated that HO• and CH3C(O)OO• were the main reactive species for SMX degradation, accounting for 43.3 % and 56.7 % of the contributions, respectively. Combined with X-ray photoelectron spectroscopy analysis, the photoelectrons generated on CuFeS2 activated by visible light enhanced the Fe3+/Fe2+ and Cu2+/Cu+ cycles on the surface, thereby activating PAA to generate HO•/CH3C(O)OO•. The removal rate of SMX decreased with the increase in wavelengths, due to the formation of low energy photons at longer wavelengths. Besides, the optimal pH for degradation of SMX by CuFeS2/PAA/Vis-LED process was neutral, which was attributed to the increasing easily activated anionic form of PAA during the increase in pH and the depletion of Fe species at alkaline conditions. Cl-, HCO3-, and HA slightly inhibited SMX degradation because of reactive species being quenched and/or shielding effect. Furthermore, the degradation efficiency of different pollutants by CuFeS2/PAA/Vis-LED was also measured, and the removal efficiency was different owing to the selectivity of CH3C(O)OO•. Finally, the process exhibited good applicability in real waters. Overall, this study provides new insight into visible light-catalyzed activation of PAA and suggests on further exploration of the intrinsic activation mechanism of PAA.

Facile synthesis of pyrite FeS2 on carbon spheres for high-efficiency Fenton-like reaction

Designing iron-based catalysts for Fenton-like reactions with peroxymonosulfate (PMS) as oxidants have attracted growing attentions. Herein, pyrite FeS2 supported on carbon spheres (FeS2@C) is synthesized by a facile low-temperature method. The FeS2@C/PMS system can degrade carbamazepine (CBZ) effectively in a wide pH range. Sulfate radicals (SO4·-), hydroxyl radicals (·OH), superoxide radical (O2·-), and singlet oxygen (1O2) are the responsible reactive oxygen species (ROSs) for CBZ degradation. Moreover, in the simulated fixed-bed reactor, the FeS2@C/PMS system can maintain a high CBZ removal ratio of >95% for than 8 h, exhibiting its excellent stability. The outstanding performance of FeS2@C/PMS system is attributed to the presence of carbon spheres and lattice S2-, which together promote the Fe(III)/Fe(II) redox cycle. The FeS2@C is a promising catalyst due to its facile synthesis, low cost, high efficiency, and excellent stability to activate PMS for organics degradation.

S vacancies-introduced chalcopyrite switch radical to non-radical pathways via peroxymonosulfate activation: Vital roles of S vacancies

Regulation of peroxymonosulfate (PMS) activation from radical to non-radical pathways is an emerging focus of advanced oxidation processes (AOPs) due to its superiority of anti-interference to complex wastewater. However, the detailed correlation mechanism between the defect structure of the catalyst and the regulation of radicals/non-radicals remains unclear. Herein, natural chalcopyrite (CuFeS2) with different levels of S vacancies created by a simple NaBH4 reduction process was employed to explore the above-mentioned underlying mechanism for constructing high efficiency and low cost of catalyst towards AOPs. With the assistance of simulated solar light, S-deficient chalcopyrite (Sv-NCP) exhibited prominent performance for PMS activation. More interestingly, the different degrees of S vacancies regulated the active species from radicals to non-radical 1O2, thus showing excellent purification of complex wastewater as well as actual pharmaceutical wastewater. Mechanistic analysis reveals that PMS tends to loss electrons on S vacancies sites and is dissociated into 1O2 rather than ·OH/SO4·- due to electron deficiency. Meanwhile, the improved adsorption performance makes the degradation sites of pollutants change from solution to surface. Most importantly, Sv-NCP presented excellent detoxication for antibiotic wastewater due to the high selectivity of 1O2. This work provides novel insights into the regulation of active species in Fenton-like reactions via defect engineering for high efficiency of pollutant degradation.

Photocatalytic activation of sulfite by maghemite (γ-Fe2O3) for iohexol degradation and alleviation effect of HCO3- on water acidification

Photo-catalyzing sulfite (S(IV)) for the generation of sulfate radical (SO4•-) has emerged as a novel advanced oxidation process (AOP) recently. However, both the potential of soil minerals as effective photocatalysts and the process of water acidification due to S(IV) oxidation have been overlooked. Herein, maghemite (γ-Fe2O3), a typical soil iron oxide with excellent photocatalytic reactivity like hematite and magnetic-collectible property like magnetite, was successfully used to activate S(IV) for iohexol degradation under visible light irradiation. As a result, 91.3% of iohexol was eliminated within 15 min at 0.1 g/L maghemite and 0.5 mM S(IV) under neutral conditions. The influencing factors, including initial pH, catalyst dosage, S(IV) amount, co-existing substances and water matrix, were systematically investigated. The maghemite/S(IV)/vis system exhibited superior performance in iohexol degradation at a wide pH range (3-10). It was found that the released proton via S(IV) oxidation led to severe water acidification. Interestingly, a low dose of HCO3- could evidently resist water acidification with little influence on iohexol elimination. Radical quenching experiments and electron spin resonance (ESR) analysis confirmed that SO4•-, •OH and •O2- were involved in iohexol abatement with SO4•- being the dominant reactive species. Compared with hydrogen peroxide, persulfate and peroxymonosulfate, the established maghemite/S(IV)/vis system achieved much more remarkable degradation performance. Furthermore, the reactivity of the catalyst was not obviously reduced even after 10 runs of reaction. This study expands the application of soil iron oxide mineral in S(IV) activation in water treatment and proposes an approach to regulate water acidification in S(IV)-based AOP.

Insights into structural and functional regulation of chalcopyrite and enhanced mechanism of reactive oxygen species (ROS) generation in advanced oxidation process (AOP): A review

Chalcopyrite, renowned for its distinctive mixed redox-couple characteristics, exhibits excellent electron transfer properties both on its surface and within its crystal structure. This unique characteristic has attracted significant attention in various fields, including optics, electronics, and magnetism, as well as demonstrated remarkable catalytic efficacy in the environmental field. The rapid and effective electron transfer capability of a catalyst is crucial for advanced oxidation processes (AOPs). However, the performance of CuFeS2 in AOPs is hindered by its low electron transfer efficacy. This review aims to summarize the key steps and mechanisms of chalcopyrite-induced AOPs and provide strategies for enhancing effective electron transfer efficacies by controlling the structure and function of synthetic/natural chalcopyrite. These strategies include enhancing the catalytic performance of chalcopyrite and constructing composites to enhance catalytic activity (e.g., chelating agents, heterojunctions). Additionally, the factors influencing the generation of reactive oxygen species in chalcopyrite-induced AOPs are investigated, such as the types and properties of oxidants (e.g., H2O2, peroxymonocarbonate), the microstructure of catalysts, and reaction conditions in catalytic systems (e.g., pH values, dosage, temperature). Future perspectives on the applications of chalcopyrite are presented at the end of this paper. Overall, this review assists in narrowing the scope of chalcopyrite studies in AOPs and aids researchers in optimizing synthetic/natural catalysts for contaminant treatment.

Chalcopyrite functionalized ceramic membrane for micropollutants removal and membrane fouling control via peroxymonosulfate activation: The synergy of nanoconfinement effect and interface interaction

This work developed a novel chalcopyrite (CuFeS2) incorporated catalytic ceramic membrane (CFSCM), and comprehensively evaluated the oxidation-filtration efficiency and mechanism of CFSCM/peroxymonosulfate (PMS) for organics removal and membrane fouling mitigation. Results showed that PMS activation was more efficient in the confined membrane pore structure. The CFSCM50/PMS filtration achieved almost complete removal of 4-Hydroxybenzoic acid (4-HBA) under the following conditions: pH = 6.0, CPMS = 0.5 mM, and C4-HBA = 10 mg/L. Meanwhile, the membrane showed good stability after multiple uses. During the reaction, SO4•- and •OH were generated in the CFSCM50/PMS system, and SO4•- was considered to be the dominant reactive species for pollutant removal. The roles of copper, iron, and sulfur species, as well as the possible catalytic mechanism were also clarified. Besides, the CFSCM50/PMS catalytic filtration exhibited excellent antifouling properties against NOM with reduced reversible and irreversible fouling resistances. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis showed an increased in repulsive energy at the membrane-foulant interface in the CFSCM50/PMS system. Membrane fouling model analysis indicated that standard blocking was the dominant fouling pattern for CFSCM50/PMS filtration. Overall, this work demonstrates an efficient catalytic filtration process for foulants removal and outlines the synergy of catalytic oxidation and interface interaction.

Natural pyrite-stimulative periodate activation: efficiency and mechanism study

Natural pyrite (NP) is an alternative catalyst for wastewater purification via advanced oxidation processes (AOPs). However, the activation performance and mechanism of periodate (PI) by NP have not yet been revealed. Herein, this work examines the activation performance of NP towards PI and its application in the degradation of antibiotic wastewater. Interestingly, 95.69% of chlortetracycline (CTC) was degraded by NP within 20 min via PI activation. Besides, NP shows effective degradation of various pollutants such as rhodamine B (65.81%), sulfamethoxazole (89.04%), and sodium butylxanthate (99.77%) within 20 min. The active species quenching experiment suggested that the active species ∙ OH ,IO 3 ∙ , 1O2 and the active complex of PI bonded with NP surface participated in CTC degradation. In addition, Fe(II) on NP surface is the main active site for PI activation, while Sn2- species accelerates the reduction of Fe(III) to Fe(II) and promotes sustained PI activation. This work provides new ideas for the application of NP in environmental pollution control.

Insights into the mechanism of multiple Cu-doped CoFe2O4 nanocatalyst activated peroxymonosulfate for efficient degradation of Rhodamine B

The multiple metal catalyst as a promising nanomaterial has shown excellent activity in the peroxymonosulfate (PMS) activation for pollutant degradation. However, the role of special sites and in-depth understanding of the PMS activation mechanism are not fully studied. In this study, a Cu-doped CoFe2O4 nanocatalyst (0.5CCF) was synthesized by a sol-gel and calcination method, and used for PMS activation to remove Rhodamine B (RhB). The results showed that the Cu doping obviously enhanced the catalytic performance of CoFe2O4, with 99.70% of RhB removed by 0.5CCF while 74.91% in the CoFe2O4 within 15 min. Based on the X-ray photoelectron spectroscopy and electrochemical analysis, this could be ascribed to the more low valence of Co and Fe species generated on the 0.5CCF and faster electron transfers occurred in the 0.5CCF due to the Cu doping. In addition, Cu doping could provide more reaction sites for the 0.5CCF to activate PMS for RhB removal. The metal species and the surface hydroxyl were the reaction sites of PMS activation, and the surface hydroxyl played an important role in surface-bound reactive species generation. During the PMS activation, the Cu not only activated PMS to produce reactive oxygen species (ROS), but also regenerated Co2+ and Fe2+ to accelerate the PMS activation. The non-radical of 1O2 was the main ROS with a 99.35% of contribution rate, and the SO5•- self-reaction was its major source. This study provides a new insight to enhance the PMS activation performance of multiple metal catalysts by Cu doping in wastewater treatment.

Domain-limited thermal transformation preparation of novel graphitized carbon-supported layered double oxides for efficient tetracycline degradation

The resource utilization of industrial lignin to construct high-performance catalysts for wastewater treatment field is pioneering research. Herein, the novel graphitized carbon-supported CuCoAl-layered double oxides (LDOs-GC) were successfully designed by the domain-limited thermal transformation technology using sodium lignosulfonate (LS) self-assembled CuCoAl-layered double hydroxides as the precursor. The optimized LDOs-GC catalyst owned the excellent tetracycline (TC) degradation of 98.0% within 15 min by activated peroxymonosulfate (PMS) under optimal conditions (20 mg/L catalyst, 1.5 mM PMS, 30 mg/L TC). The density of metal ions in the catalyst and the synergistic interaction between graphitized carbon (GC) and metal ions played a major role in TC degradation. Based on a comprehensive analysis, the TC degradation in LDOs-GC/PMS system was proved to be accomplished by a combination of free radicals (SO4·- and HO·) and non-radicals (1O2). Meanwhile, the possible degradation pathways of TC were proposed by the analysis of TC degradation intermediates and a comprehensive analysis of the rational reaction mechanism for TC degradation by LDOs-GC/PMS system was also performed. This work provides a new strategy for developing novel high-performance catalysts from industrial waste, while offering a green, cheap and sustainable approach to antibiotic degradation.

Enhanced chalcopyrite-catalyzed heterogeneous Fenton oxidation of diclofenac by ABTS

The widely used 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) has gained growing attention in advanced oxidation processes (AOPs), whereas there was limited knowledge regarding the feasibility of ABTS in enhancing heterogeneous Fenton oxidation so far. Hereof, ABTS was introduced into the chalcopyrite (CuFeS2)- catalyzed heterogeneous Fenton oxidation process to degrade diclofenac (DCF), and the degradation efficiency was enhanced by 25.5% compared with CuFeS2/H2O2 process. The available reactive oxygen species (ROS) and the enhanced mechanism were elaborated. Experimental results uncovered that •OH was the dominant reactive species responsible for the DCF degradation in the CuFeS2/H2O2/ABTS process, and ABTS•+ was derived from both •OH and Fe(IV). The presence of ABTS contributed significantly to the redox cycle of surface Fe of CuFeS2, and the roles of reductive sulfur species and surface Cu(I) in promoting surface Fe cycling also could not be neglected. In addition, the effects of several influencing factors were considered, and the potential practicability of this oxidation process was examined. The results demonstrate that the CuFeS2/H2O2/ABTS process would be a promising approach for water purification. This study will contribute to the development of enhancing strategies using ABTS as a redox mediator for heterogeneous Fenton oxidation of pharmaceuticals.

CuFeS2 supported on dendritic mesoporous silica-titania for persulfate-assisted degradation of sulfamethoxazole under visible light

Sulfamethoxazole (SMX) is a prevalent sulfonamide antibiotic found in the environment, and it has a variety of detrimental effects on environmental sustainability and water safety. Recently, the combination of photocatalysis and sulfate radical-based advanced oxidation processes (SR-AOPs) has attracted a lot of interest as a viable technique for degradation of refractory pollutants. In this study, a visible light active CuFeS2 supported on dendritic mesoporous silica-titania (CuFeS2-DMST) photocatalyst was synthesized to improve the ability of TiO2 to activate persulfate (PS) by introducing CuFeS2 (Fe2+/Fe3+, Cu+/Cu2+ redox cycles). The CuFeS2-DMST/PS/Vis system demonstrated superior SMX degradation efficiency (88.9%, 0.0146 min-1) than TiO2 because of reduced e-/h+ recombination, excellent charge separation and mobility, and a greater surface area than TiO2. Furthermore, after four consecutive photocatalytic cycles, the system demonstrated moderate stability. From chemical quenching tests, O2●-, h+, 1O2, SO4●- and ●OH were found to be the main reactive oxidizing species. The formed intermediates during the degradation process were identified, and degradation mechanisms were proposed. This study proposes a viable technique for activating PS using a low-cost, stable, and high-surface-area TiO2-based photocatalyst, and this concept can be applied to design photocatalysts for water treatment.

Underwater bubbling plasma assisted with persulfate activation for the synergistic degradation of tetracycline hydrochloride

The performance and mechanism of persulfate consisting of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by underwater bubbling plasma (UBP) for the synergistic removal of tetracycline hydrochloride (TCH) were comparatively investigated. Both PMS and PDS addition significantly promoted the removal of TCH in UBP system, indicating persulfate exhibited highly synergistic effect with UBP. Furthermore, enhancing the persulfate dosage, peak voltage and pulse frequency, as well as reducing initial TCH concentration were favorable for the elimination of TCH. Compared with neutral condition, acidic and alkaline condition were advantageous to TCH removal. The presence of coexisting substances including Cl-, SO42- and humic acid (HA) had an adverse effect on TCH degradation, while Fe2+ could improve the removal of TCH. The degradation of ciprofloxacin and metronidazole proved the applicability for other antibiotics degradation of the reaction system. SO4-·, ·OH, ·O2-, hydrated electrons, O3 and H2O2 were the active substances responsible for TCH removal. The reduction of aqueous O3 concentration and enhancement of H2O2 concentration were observed after persulfate addition. UV-vis spectra and TOC analysis illustrated the addition of PMS or PDS facilitated the degradation and mineralization of TCH. 3D-EEMF spectra visually displayed the degradation process of TCH. Plausible degradation routes were deduced based on LC-MS and the toxicities of TCH and its intermediates were evaluated by Toxicity Estimation Software Tool.

Carbon nanotube supported cobalt nickel sulphide nano-catalyst for degradation of chloroquine phosphate with peroxymonosulphate

Carbon nanotubes supported cobalt nickel sulphide nanoparticles (nano-NiCo2S4@CNTs) were successfully prepared by a hydrothermal method as heterogeneous catalyst which can be used as an activator of peroxymonosulphate (PMS) for the degradation of chloroquine phosphate (CQP). Based on characterisation techniques, the prepared catalyst has excellent surface properties and structural stability. When different concentrations of CQP were treated with 0.2 g/L nano-NiCo2S4@CNTs and 1.0 mM PMS, the highest degradation rate could reach 99.86% after 30 min. Under the interference of pH, common anions and humic acid in the water environment, the reaction system can still achieve high degradation efficiency, showing excellent anti-interference ability and practical applicability. Furthermore, in the nano-NiCo2S4@CNTs/PMS system, according to the identification results of reactive oxygen species, the free radical and non-free radical pathway are responsible for the degradation of CQP, and the PMS mechanism activation was comprehensively proposed. Twelve intermediate products were detected in the degradation process, and the possible degradation pathways of CQP were proposed. This toxicity analysis demonstrates that the intermediate products formed during CQP degradation pose lower environmental risks compared to the original pollutant. In addition, after using the catalyst four cycles, the removal efficiency of CQP remains above 80%, indicating the excellent reusability and low metal ion leaching characteristics. Therefore, the nano-NiCo2S4@CNTs synthesised in this research has broad application prospects in activating PMS for wastewater treatment.

Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation

CuFeS2 is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS2 micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS2 micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS2 for heterogeneous PS activation. SO4•- and •OH were identified in EG-CuFeS2/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO2] (the molar ratio of PMSO2 generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S2- promoted the cycling of Fe3+/Fe2+ and Cu2+/Cu+, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Chalcopyrite as an oxidants activator for organic pollutant remediation: A review of mechanisms, parameters, and future perspectives

Advanced oxidation processes (AOPs) based on oxidants have attracted attention for the degradation of organic pollutants. The combination of chalcopyrite with oxidants such as persulfate, peroxide, percarbonate, and others shows promise as a system due to its ability to activate through various pathways, leading to the formation of numerous radical and non-radical species. In this review, the generation of sulfate radical (SR) and hydroxyl radical (HR) in AOPs were summarized. The significance of chalcopyrite in various approaches including Fenton, photo-Fenton, and photo/Fenton-like methods, as well as its involvement in electrochemical Fenton-based processes was discussed. The stability and reusability, toxicity, catalyst mechanism, and effects of operational parameters (pH, catalyst dosage, and oxidant concentration) are evaluated in detail. The review also discusses the role of Fe2+/3+, Cu1+/2+, S2- and Sn2- present in CuFeS2 in the generation of free radicals. Finally, guidelines for future research are presented in terms of future perspectives.

Heterogeneous-Driven Glutathione Oxidation: Defining the Catalytic Role of Chalcopyrite Nanoparticles

Transition-metal nanocatalysis represents a novel alternative currently experiencing flourishing progress to tackle the tumor microenvironment (TME) in cancer therapy. These nanomaterials aim at attacking tumor cells using the intrinsic selectivity of inorganic catalysts. In addition, special attention to tune and control the release of these transition metals is also required. Understanding the chemical reactions behind the catalytic action of the transition-metal nanocatalysts and preventing potential undesired side reactions caused by acute cytotoxicity of the released ionic species represent another important field of research. Specifically, copper-based oxides may suffer from acute leaching that potentially may induce toxicity not only to target cancer cells but also to nearby cells and tissues. In this work, we propose the synthesis of chalcopyrite (CuFeS₂) nanostructures capable of triggering two key reactions for an effective chemodynamic therapy (CDT) in the heterogeneous phase: (i) glutathione (GSH) oxidation and (ii) oxidation of organic substrates using H₂O₂, with negligible leaching of metals under TME-like conditions. This represents an appealing alternative toward the development of safer copper-iron-based nanocatalytic materials with an active catalytic response without incurring leaching side phenomena.

Selective degradation of antibiotic in a novel Cu7S4/peroxydisulfate system via heterogeneous Cu(III) formation: Performance, mechanism and toxicity evaluation

Efficient degradation of antibiotic by peroxydisulfate (PDS)-based advanced oxidation processes in complex water environment is challenging due to the interference of impurities and the low activation efficiency of PDS caused by its symmetric structure. Herein, a novel Cu₇S₄/PDS system was developed, which can selectively remove tetracycline hydrochloride (TC) without interference of inorganic ions (e.g., Cl^- and HCO₃^-) and natural organic matter (e.g., humic acid). The results of quenching and probe experiments demonstrated that surface high-valent copper species (Cu(III)), rather than radicals and ¹O₂, are main active species for TC degradation. Cu(III) can be generated via Cu(I)/O₂ and Cu(II)/Cu(I)/PDS systems and the S species on the surface of Cu₇S₄ promotes the cycle of Cu(II)/Cu(I) and Cu(III)/Cu(II), resulting in continuous generation of Cu(III). In addition, the degradation pathways of TC were proposed based on product analysis and DFT theory calculations. The acute toxicity, developmental toxicity and mutagenicity of treated TC were significantly reduced according to the results of toxicity estimation software tool. This study shows a promising Cu₇S₄/PDS system for the degradation and detoxication of antibiotic in complex water environment, while also providing a comprehensive understanding of PDS activation by Cu₇S₄ to generate active Cu(III) species.

Metal-carbon hybrid materials induced persulfate activation: Application, mechanism, and tunable reaction pathways

Proper wastewater treatment has always been the focus of human society, and many researchers have been working to find efficient and stable wastewater treatment technologies. Persulfate-based advanced oxidation processes (PS-AOPs) mainly rely on persulfate activation to form reactive species for pollutants degradation and are considered to be one of the most effective wastewater treatment technologies. Recently, metal-carbon hybrid materials have been diffusely used for PS activation because of their high stability, abundant active sites, and easy applicability. Metal-carbon hybrid materials can successfully overcome the shortcomings of onefold metal catalysts and carbon catalysts by combing the complementary advantages of the two components. This article reviews recent studies about metal-carbon hybrid materials-mediated PS-AOPs for wastewater decontamination. The interactions of metal and carbon materials, as well as the active sites of metal-carbon hybrid materials, are introduced first. Then, the application and mechanism of metal-carbon hybrid materials-mediated PS activation are presented in detail. Lastly, the modulation methods of metal-carbon hybrid materials and their tunable reaction pathways were discussed. The prospect of future development directions and challenges is proposed to facilitate metal-carbon hybrid materials-mediated PS-AOPs to take a step further for practical application.

Engineering active heterojunction architecture with oxygenated-Co, Mo bimetallic sulfide heteronanosheet and graphene oxide for peroxymonosulfate activation

Bimetallic sulfides have distinctive catalytic property in activating peroxymonosulfate (PMS) for water remediation. Polyoxometalates as potential precursors have rarely been reported for the catalytic degradation of refractory organic pollutants. Herein, a composite catalyst of Co-Mo bimetallic sulfides supported onto graphene oxide (O-CoMoS/GO) with a heterojunction architecture was synthesized through a hydrothermal strategy with polyoxometalates ((NH₄)₄[Co^IIMo₆O₂₄H₆]·6H₂O) as the precursor and applied in the PMS activation. This material showed a superior performance for the catalytic degradation of the model organic pollutant, 4-chlorophenol (rapidly removed within 10 min with an apparent reaction rate constant of 0.5458 min^-1). O-CoMoS/GO outperformed most of the reported catalysts in terms of activity and had a strong tolerance towards common organic and inorganic compounds in water, and could perform well in different real water systems. Experimental and theoretical results indicated that the introduction of GO could achieve the enrichment of electrons on the metals and reduce the d band center (ε_d) of Co close to the Fermi level (ε_F), thereby facilitating the interfacial electron transfer process. The activation mechanism was due to the as-prepared bimetallic sulfides and the formation of heterojunction structure with GO, where Co(II) as the active center could be regenerated by the adjacent Mo element (as co-catalyst) and by gathering electrons from GO through the Co/Mo-O-C coupling. This work provides insights into the design of bimetallic sulfide catalysts in activating PMS for water remediation.

Activity and mechanism of vanadium sulfide for organic contaminants oxidation with peroxymonosulfate

Transition metal sulfides have been demonstrated to be effective for peroxymonosulfate (PMS) activation towards wastewater treatment. However, the activity of vanadium sulfide (VS₄) and the role of the chemical state of V have not been revealed. Here, three types of VS₄ with various morphologies and chemical states of V were synthesized by using methanol (M-VS₄, nanosphere composed of nanosheets), ethanol (E-VS₄, sea urchin like nanosphere) and ultrapure water (U-VS₄, compact nanosphere) as hydrothermal solvent, respectively, and used as heterogeneous catalysts to activate PMS for the degradation of refractory organic pollutants. The effects of PMS concentration, temperature, pH, inorganic ions, and humic acid (HA) on the degradation efficiency of VS₄/PMS system were investigated systematically. The results indicated that the highest specific surface area and lowest ratio of V⁵⁺ enable E-VS₄/PMS system possessed the highest performance in degrading tetracycline hydrochloride (TCH), in which 100% TCH was removed after operating 10 min (0.805 min^-1) under a relatively low concentration of PMS (1 mM) and catalyst (100 mg/L). It also revealed that the system exhibited a typical radical process in TCH degradation, which could be attributed to the redox cycles between V⁵⁺, V⁴⁺ and V³⁺ in the presence of PMS to generate various radicals. This radical process enabled the E-VS₄/PMS system with a high activity in wide reaction conditions and high mineralization ratios in degrading various refractory organic pollutants within 10 min. In addition, the E-VS₄/PMS system exhibited favorable reusability and stability with very less V and S ions leaching, and showed excellent performance in real water purification.

Enhanced activation of H2O2 by bimetallic Cu2SnS3: A new insight for Cu (II)/Cu (I) redox cycle promotion

HYPOTHESIS

Despite that the development of Cu₂SnS₃ (CTS) catalyst has attracted increasing interests, few study has reported to investigate its heterogeneous catalytic degradation of organic pollutants in a Fenton-like process. Furthermore, the influence of Sn components towards Cu (II)/Cu (I) redox cycling in CTS catalytic systems remains a fascinating research.

EXPERIMENTS

In this work, a series of CTS catalysts with controlled crystalline phases were prepared via a microwave-assisted pathway and applied in the H₂O₂ activation for phenol degradation. The efficiency of phenol degradation in CTS-1/H₂O₂ system (CTS-1: the molar ratio of Sn (copper acetate) and Cu (tin dichloride) is determined to be Sn:Cu = 1:1) was systematically investigated by controlling various reaction parameters including H₂O₂ dosage, initial pH and reaction temperature. We discovered that Cu₂SnS₃ exhibited superior catalytic activity to the contrast monometallic Cu or Sn sulfides and Cu (I) acted as the dominant active sites. The higher Cu (I) proportions conduce to the higher catalytic activities of CTS catalysts. Quenching experiments and electron paramagnetic resonance (EPR) further proved that the activation of H₂O₂ by CTS catalyst produces reactive oxygen species (ROS) and subsequently leads to degradation of the contaminants. A reasonable mechanism of enhanced H₂O₂ activation in Fenton-like reaction of CTS/H₂O₂ system was proposed for phenol degradation by investigating the roles of copper, tin and sulfur species.

FINDINGS

The developed CTS acted as a promising catalyst in Fenton-like oxidation progress for phenol degradation. Importantly, the copper and tin species contribute to a synergetic effect for the promotion of Cu (II)/Cu (I) redox cycle, which thus enhanced the activation of H₂O₂. Our work may offer new insight on the facilitation of Cu (II)/Cu (I) redox cycle in Cu-based Fenton-like catalytic systems.

Copper sulphide/cuprous sulphide doped zero-valent iron@carbon (ZVI@C/CuS/Cu2S) activate PMS for rapid and effective decomposition of Ni-EDTA

Ni-EDTA is widely present in electroplating effluents. It cannot be effectively removed by traditional wastewater treatment methods due to its chemical stability. In this study, copper sulphide/cuprous sulphide doped zero-valent iron@carbon (ZVI@C/CuS/Cu₂S) was prepared to active peroxymonsulphate (PMS) to decomposition Ni-EDTA. The ZVI@C/CuS/Cu₂S + PMS process shows excellent performance under neutral or even alkaline conditions. This is due to the acceleration of ZVI electron transport by CuS/Cu₂S, the autocatalysis of CuS/Cu₂S itself, and the synergistic effect of CuS/Cu₂S and Ni-EDTA. The removal efficiency of 50 ppm Ni-EDTA electroplating effluents reached 99.53% at 10 min, and the discharge water can meet the Chinese emission standard. The influences of the main parameters such as initial pH value, catalyst, PMS and initial Ni-EDTA concentration on removal efficiency was systematically investigated.

Insight into mechanism of peroxydisulfate activation by natural pyrite: Participation of Fe(IV) and regulation of Fe(III)/Fe(II) cycle by sulfur species

In this study, natural pyrite (NP) was used to activate peroxydisulfate (PDS) for imidacloprid (IMD) degradation. NP was characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Effects of key reaction parameters (NP dosage, PDS concentration and initial pH) and co-existing ions on IMD degradation in the NP/PDS system were investigated. Quenching experiments and electron spin resonance (ESR) tests identified the existence of sulfate radical (SO₄^•-), hydroxyl radical (^•OH), singlet oxygen (¹O₂) and superoxide radical (O₂^•-). The cumulative concentration of SO₄^•- and ^•OH were quantified by the formation of benzoquinone (BQ) and p-hydroxybenzoic acid (HBA), respectively. Meanwhile, more than 60% of methylphenyl sulfoxide (PMSO) was selectively converted to methylphenyl sulfone (PMSO₂), revealing that Fe(IV) was dominant in the NP/PDS system. The order of contribution of the three reactive species in the NP/PDS system was Fe(IV) > ^•OH > SO₄^•- (contributions of ¹O₂ and O₂^•- were negligible). Fe(II) released from NP played a crucial role in PDS activation, and sulfur species in NP could also boost Fe(III)/Fe(II) cycle and contribute to the generation of reactive species. Further, the possible degradation pathways of IMD have been proposed based on the detected intermediates using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the toxicity (including acute toxicity, developmental toxicity and mutagenicity) of these intermediates have been predicted using Toxicity Estimation Software Tool (T.E.S.T). Moreover, NP/PDS system was applied in four natural water bodies and IMD degradation efficiency reached more than 97% after adjusting the pH to 3. The fluorescence excitation-emission matrix (EEM) spectra showed that in addition to IMD, NP/PDS system could also remove other impurities.

Development of Bi2WO6 and Bi2O3 - ZnO heterostructure for enhanced photocatalytic mineralization of Bisphenol A

Present study proposed the synthesis of mixed p-type and n-type nanocomposite heterostructures by co-precipitation method. The as-synthesized heterostructures were characterized through different characterization techniques. The as-synthesized Bi₂WO₆ and Bi₂O₃-ZnO heterostructures were tested as photocatalysts during the photodegradation of Bisphenol A (BPA). The Bi₂O₃-ZnO heterostructure nanocomposite was found to be a more effective photocatalyst than Bi₂WO₆. The effect of operating parameters including catalytic dose (0.02-0.15 gL^-1), initial BPA concentration (5-20 mgL^-1), temperature change (5-20 °C) and solution pH changes (4, 5, 7, and 8) were evaluated with Bi₂O₃-ZnO under UV-light irradiation by selecting a 300 W Xe lamp. More than 90% BPA was degraded with 0.15 gL^-1 Bi₂O₃-ZnO, keeping 1.0 mM H₂O₂ concentration fixed in 250 mL of reaction suspension. The HPLC and GC-MS were used to detect the reaction intermediates and final products. A plausible degradation pathway was proposed on the basis of the identification of reaction intermediates. Repeatability test analysis confirmed that the as-synthesized catalyst showed superb catalytic performance on its removal trend. The kinetics of degradation of BPA were well fitted by the power laws model. With the order of reaction being 0.6, 0.9, 1.2, and 1.3 for different operating parameters, i.e., catalyst dose, initial pH, temperature, and initial BPA concentration.

Peroxymonosulfate activation through ferromagnetic bimetallic spinel sulfide composite (Fe3O4/NiCo2S4) for organic pollutant degradation

Spinel sulfides are a good candidate as heterogeneous catalysts for wastewater treatment through peroxymonosulfate (PMS) activation. In this paper, magnetic Fe₃O₄/NiCo₂S₄ composite was successfully synthesized by hydrothermal method. Catalyst screening displayed that the composite catalyst with a Fe₃O₄:NiCo₂S₄ molar ratio of 1:3 (i.e.,0.33-Fe₃O₄/NiCo₂S₄) is the most optimal. The results showed that 0.33-Fe₃O₄/NiCo₂S₄ composite catalyst had superior catalytic activity, achieving 99.8%,65.1% and 40.7% of RhB, COD and TOC removals within 30 min with 180 m g/L PMS and 75 mg/L catalyst. We proposed a potential catalytic mechanism of PMS activation by Fe₃O₄/NiCo₂S₄ in two aspects. On the one hand, sulfur species such as S^2- and S₂^2- enhance the Co³⁺/Co²⁺, Ni³⁺/Ni²⁺ and Fe³⁺/Fe²⁺ cycles on Fe₃O₄/NiCo₂S₄ surface. On the other hand, there is the synergistic effect of Co³⁺/Co²⁺, Ni³⁺/Ni²⁺ and Fe³⁺/Fe²⁺ cycles in activating PMS. Overall, owing to its excellent catalytic activity, reusability, and easy recovery, Fe₃O₄/NiCo₂S₄ is a potentially useful catalyst for remediation of contaminated water.

Photo-assisted reductive cleavage and catalytic hydrolysis-mediated persulfate activation by mixed redox-couple-involved CuFeS2 for efficient trichloroethylene oxidation in groundwater

Persulfate (PS, S₂O₈^2-) activation through transition metal sulfides (TMS) has gained increasing attention since it can decompose a wide variety of refractory halogenated organic compounds in groundwater and wastewater. However, the processes of PS activation by TMS and particularly the formation of •OH radical under anoxic and acidic conditions (pH ∼2.8) remain elusive. Herein, by employing mixed redox-couple-involved chalcopyrite (CuFeS₂) (150 mg/L) nanoparticles for PS (3.0 mM) activation, 96% of trichloroethylene was degraded within 120 min at pH 6.8 under visible light irradiation. The combination of experimental studies and theoretical calculations suggested that the Cu(I)/Fe(III) mixed redox-couple in CuFeS₂ plays a crucial role to activate PS. Cu(I) acted as an electron donor to transfer electron to Fe(III), then Fe(III) served as an electron transfer bridge as well as a catalytic center to further donate this received electron to the O-O bond of PS, thus yielding SO₄^•- for trichloroethylene oxidation. Moreover, for the first time, •OH radicals were found to form from the catalytic hydrolysis of PS onto CuFeS₂ surface, where S₂O₈^2- anion was hydrolyzed to yield H₂O₂ and these ensuing H₂O₂ were further transformed into •OH radicals via photoelectron-assisted O-O bond cleavage step. Our findings offer valuable insights for understanding the mechanisms of PS activation by redox-couple- involved TMS, which could promote the design of effective activators toward PS decomposition for environmental remediation.

A comprehensive review on BPA degradation by heterogeneous Fenton-like processes

Synthetic organic pollutants emanating continuously in the ecosystem have become a global concern because of their toxicity and persistent nature. Bisphenol A (BPA) is one such pollutant which threatens public health and safety. It is a monomer used in manufacturing plastics, polycarbonate resins, epoxy resins and is a well-recognised endocrine disruptor mimicking estrogen. BPA leaches into food and beverages stored in containers causing contamination issues. Its widespread exposure and potential toxicity is an environmental health concern. In this review, a systematic investigation has been carried out on the heterogeneous catalysts used for Fenton-like processes for BPA degradation. The Fenton-like reaction is one such reaction that is used for wastewater remediation purposes. The reaction advances through the generation of powerful oxidizing radicals like •OH and SO₄^•- in the presence of a suitable catalyst. The application of various Fenton catalysts, with their distinguished morphological characteristics, oxidizing properties, toxicity analysis, and the present state of the art of BPA degradation by these catalysts, have been documented in the current work. This review also highlights a few challenges and prospects for analysing degradation products of landfill leachate.

Facile synthesis of CoFe2O4@BC activated peroxymonosulfate for p-nitrochlorobenzene degradation: Matrix effect and toxicity evaluation

p-Nitrochlorobenzene (p-NCB) is widely used in industry and poses a potential threat to the public health due to its persistence, carcinogenicity and mutagenicity. Herein, magnetic catalyst CoFe₂O₄@Biochar (CoFe₂O₄@BC) was synthesized by a facile sol-gel method, efficiently activating peroxymonosulfate (PMS) to degrade p-NCB. The synergistic effect of Fe and Co in well-dispersed CoFe₂O₄ and the electron transfer promote the production of reactive oxygen species (ROS) (OH, SO₄^- and O₂^-), efficiently removing p-NCB enriched by CoFe₂O₄@BC. Under optimum conditions, the CoFe₂O₄@BC/PMS system could remove 89% of p-NCB from water, and the degradation efficiency could reach 80% in soil. Toxic chlorinated intermediates appeared during the degradation process and thus efficient dechlorination process can lower the toxicity of the reaction solution, which was also proved by the oxygen uptake inhibition experiment as well as zebrafish toxicity experiments. Furthermore, p-NCB degradation efficiency could be inhibited by Cl^-, HCO₃^-, HPO₄^2- and humic acid (HA) through quenching effect or occupation of CoFe₂O₄@BC surface active sites while HPO₄^2- could also improve the efficiency by directly activating PMS. The CoFe₂O₄@BC/PMS system can be efficiently applied in the remediation of p-NCB pollution in water and soil.

Enhanced Cr(VI) reduction on natural chalcopyrite mineral modulated by degradation intermediates of RhB

Wastewater with complex compositions of both heavy metals and organic pollutants is of critical environmental and socioeconomic threat worldwide, which urgently requires feasible remediation technologies to target this challenge. In this study, natural chalcopyrite (CuFeS₂, NCP), the most abundant copper-based mineral in the Earth's crust, has been discovered to be a heterogeneous catalyst that can activate peroxydisulfate (PDS) for the simultaneous degradation of organic pollutant Rhodamine B (RhB) and reduction of hexavalent chromium (Cr(VI)). Batch experimental results indicate that both RhB and Cr(VI) could be simultaneously removed under a near-neutral condition in NCP/PDS combined system. The radicals SO₄^•- and ^•OH generated from PDS activation are the main oxidative species detected by electron paramagnetic resonance (EPR) spectroscopy. SO₄^•- acted as a predominant role in RhB degradation, while Cr(VI) reduction is mainly attributed to the oxidization of S^2- and S₂^2- species on NCP surface, as well as the photoreduction performance of NCP, which could be enhanced by the intermediates generated from RhB degradation. Density functional theory (DFT) calculation results disclose that Fe is the critical catalytic site for PDS activation. This work demonstrates a user-friendly strategy for remediation of complex wastewater containing both heavy metal and organic pollutants by combining photoreduction and advanced oxidation processes (AOPs) with natural minerals. It paves a way for wastewater treatment by utilizing low-cost natural abundant minerals as catalysts.

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.

Efficient degradation of minocycline by natural bornite-activated hydrogen peroxide and persulfate: kinetics and mechanisms

Natural bornite (NBo), a sulfide mineral of copper and iron, is one of the main mineral raw materials for copper extraction. In this study, NBo-activated hydrogen peroxide (H₂O₂) and persulfate processes (PS) for the degradation of minocycline (MNC) in aqueous solution were systemically investigated and compared. The MNC removal rates with the NBo/PS and NBo/H₂O₂ processes were 86.40% and 87.50%, respectively. The mineralization rate of NBo/PS (33.96%) was higher than that of NBo/H₂O₂ (29.94%) after reaction for 180 min. The effects of oxidant and activator dosage, pH, common inorganic anions (i.e., Cl^-, NO₃^-, and HCO₃^-), and water composition on MNC degradation were systematically evaluated. In addition, the degradation of MNC in natural water matrix and toxicity evaluation was also studied to better evaluate the feasibility of practical application of those two processes. The results of free radical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) showed that HO· was the main activated species in the NBo/H₂O₂ system, while SO₄^·- and HO· were the main activated species in the NBo/PS system. The degradation of MNC in the NBo/PS system was achieved through electron transfer, while the degradation of MNC in the NBo/H₂O₂ system was mainly achieved through free radical addition. The degradation pathway mainly included deamidation reactions, C-C bond breakage and hydroxylation. Reusability of NBo showed that NBo was considerably stable in activating PS and H₂O₂ for degradation of MNC, which was cost-effective activator. This work provides a new perspective on the degradation mechanism of pollutants by Fe-Cu bimetallic sulfide activation of PS and H₂O₂.

Efficient degradation of Rhodamine B by magnetically recoverable Fe3O4-modified ternary CoFeCu-layered double hydroxides via activating peroxymonosulfate

Environment-friendly nano-catalysts capable of activating peroxymonosulfate (PMS) have received increasing attention recently. Nevertheless, traditional nano-catalysts are generally well dispersed and difficult to be separated from reaction system, so it is particularly important to develop nano-catalysts with both good catalytic activity and excellent recycling efficiency. In this work, magnetically recoverable Fe₃O₄-modified ternary CoFeCu-layered double hydroxides (Fe₃O₄/CoFeCu-LDHs) was prepared by a simple co-precipitation method and initially applied to activate PMS for the degradation of Rhodamine B (RhB). X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller method (BET), and vibrating sample magnetometer (VSM) were applied to characterize morphology, structure, specific surface area and magnetism. In addition, the effects of several key parameters were evaluated. The Fe₃O₄/CoFeCu-LDHs exhibited high catalytic activity, and RhB degradation efficiency could reach 100% within 20 min by adding 0.2 g/L of catalyst and 1 mmol/L of PMS into 50 mg/L of RhB solution under a wide pH condition (3.0-7.0). Notably, the Fe₃O₄/CoFeCu-LDHs showed good super-paramagnetism and excellent stability, which could be effectively and quickly recovered under magnetic condition, and the degradation efficiency after ten cycles could still maintain 98.95%. Both radicals quenching tests and electron spin resonance (ESR) identified both HO• and SO₄^•- were involved and SO₄^•- played a dominant role on the RhB degradation. Finally, the chemical states of the sample's surface elements were measured by X-ray photoelectron spectroscopy (XPS), and the possible activation mechanism in Fe₃O₄/CoFeCu-LDHs/PMS system was proposed according to comprehensive analysis.

Efficient degradation of sulfamethazine via activation of percarbonate by chalcopyrite

In this work, the novel application of chalcopyrite (CuFeS₂) for sodium percarbonate (SPC) activation towards sulfamethazine (SMT) degradation was explored. Several key influencing factors like SPC concentration, CuFeS₂ dosage, reaction temperature, pH value, anions, and humic acid (HA) were investigated. Experimental results indicated that SMT could be effectively degraded in the neutral reaction media by CuFeS₂/SPC process (86.4%, 0.054 min^-1 at pH = 7.1). The mechanism of SPC activation by CuFeS₂ was elucidated, which was discovered to be a multiple reactive oxygen species (multi-ROS) process with the coexistence of hydroxyl radical (^•OH), carbonate radical (CO₃^•-), superoxide radical (O₂^•-), and singlet oxygen (¹O₂), as evidenced by quenching experiments and electron spin resonance (ESR) tests. The generated ^•OH via the traditional heterogeneous Fenton-like process would not only react with carbonate ions to yield other ROS but also involve in SMT degradation. The abundant surface-bound Fe(II) was deemed to be the dominant catalytic active sites for SPC activation. Meanwhile, it was verified that the reductive sulfur species, the interaction between Cu(I) and Fe(III) as well as the available O₂^•- derived from the activation of molecular oxygen and the conversion of ^•OH favored the regeneration of Fe(II) on CuFeS₂ surface. Furthermore, the degradation intermediates of SMT and their toxicities were evaluated. This study presents a novel strategy by integrating transition metal sulfides with percarbonate for antibiotic-contaminated water treatment.

Critical review of natural iron-based minerals used as heterogeneous catalysts in peroxide activation processes: Characteristics, applications and mechanisms

Recently, an increasing number of works have been reported about iron-based materials applied as catalysts in peroxide activation processes to degrade pollutants in water. Iron-based catalysts include synthetic and natural iron-based materials. However, some synthetic iron-based materials are difficult to scale up in the practical applications due to high cost and serious secondary environmental pollution. In contrast, natural iron-based minerals are more available and cheaper, and also hold a great promise in peroxide activation processes for pollutant degradation. In this review, we classify different natural iron-based materials into two categories: iron oxide minerals (e.g., magnetite, hematite, and goethite,), and iron sulfide minerals (e.g., pyrite and pyrrhotite,). Their overview applications in peroxide activation processes for pollutant degradation in wastewaters are systematically summarized for the first time. Moreover, the peroxide activation mechanisms induced by natural minerals, and the influences of reaction conditions in different systems are discussed. Finally, the application prospects and existing drawbacks of natural iron-based minerals in the peroxide activation processes for wastewater treatment are proposed. We believe this review can shed light on the application of natural iron-based minerals in peroxide activation processes and present better perspectives for future researches.

Synthesis of novel erdite nanorods for the activation of peroxymonosulfate during p-nitrophenol wastewater treatment

Fe-bearing salt and minerals are common reagents used in activating peroxymonosulfate (PMS) for Fenton-like oxidation in wastewater treatment. Fe-bearing reagents are used in mass production, which generate abundant Fe-bearing waste sludge in the absence of a reductant for Fe³⁺/Fe²⁺ cycling. Herein, a novel Fe/S-bearing mineral, erdite, was synthesized with a one-step hydrothermal route. The material exerted an Fe/S synergetic effect for p-nitrophenol degradation upon PMS activation and showed a one-dimensional structure similar to that of (FeS₂)_n^n-. It contained short rods with diameters of 100 nm and lengths ranging from 200 to 400 nm. It grew radically to 0.8-2 μm in length upon the addition of MnO₂. Ps-0.5, prepared by adding MnO₂ in an Mn/Fe molar ratio of 0.5, showed optimal efficiency in removing approximately 99.4% of p-nitrophenol upon PMS activation. Only 3.3% of p-nitrophenol was removed without MnO₂. The efficiency of p-nitrophenol removal through Ps-0.5 activation was higher than that through FeSO₄, nanoscale zero-valent iron (nZVI), CuFeS₂, and MnSO₄ activation. The formed erdite rods were spontaneously hydrolyzed to Fe/S-bearing flocs, in which an electron was used by structural S to reduce Fe³⁺ to Fe²⁺ upon PMS activation. The reduction resulted in a high p-nitrophenol removal rate. This study provided new insight into the development of an effective PMS activator in wastewater treatment.

One-step synthesis of mixed valence FeOX nanoparticles supported on biomass activated carbon for degradation of bisphenol A by activating peroxydisulfate

A novel FeO_X nanoparticles supported biomass activated carbon (BAC/FeO_X) composite was prepared through one-pot calcination method with FeCl₃ and cherry stone powder as precursors. The carbonization of biomass, reduction of Fe³⁺, and FeO_X anchored on carbon substrate could be achieved at the same time. Characterization with transmission electron microscope (TEM) and scanning electron microscope indicated that nanoscale FeO_X distributed uniformly on carbon substrate, and X-ray photoelectron spectroscopy, X-ray diffraction, and high resolution TEM characterization proved that the loaded FeO_X was high crystallinity of Fe₃O₄ and α-Fe⁰. Bisphenol A (BPA) was used to investigate the degradation performance of BAC/FeO_X activating peroxydisulfate (PDS). The ratio of raw materials affected degradation efficiency of BPA intensively through the content, valence state, and dispersibility of FeO_X nanoparticles, and the optimal material could degrade 20 mg/L BPA completely in 5 min at 0.1 g/L in the presence of 1 g/L PDS. Free radical determination and quenching experiments indicated that both SO₄^•- and •OH were involved in BPA degradation. The degradation pathway was proposed based on the identification of degradation intermediates. The facile synthesis method, high activation efficiency, and low-cost and environmental friendly raw materials made the BAC/FeO_X-50 an alternative catalyst for organic pollution water treatment.