Novel visible light enhanced Pyrite-Fenton system toward ultrarapid oxidation of p-nitrophenol: Catalytic activity, characterization and mechanism

Low-toxicity natural pyrite on electro-Fenton catalytic reaction in a wide pH range

The resource utilization of natural pyrite not only reduces secondary pollution but also brings certain environmental benefits. However, the green and efficient use of pyrite presents certain challenges. In this study, a novel electro-Fenton (EF) system was constructed utilizing copper modified graphite felt (GF/Cu) as cathode and natural pyrite (com-FeS2) as catalyst. The results demonstrated that the system exhibited a remarkable stability over an extensive pH range (3.0-10.0) and remained effective even under adverse environmental conditions, such as high salinity or elevated antibiotic concentration. After optimizing the reaction conditions, 0.2 mM sulfamerazine (SMZ) was almost completely degraded within 1.5 h. The results highlighted the catalytic role of Fe(II) on the com-FeS2 surface. Combined with quenching experiments and quantitative analysis of reactive oxygen species (ROS), the removal of SMZ was primarily attributed to the generation of •OH, ordered by 1O2 > •O2- > •OHads, a possible degradation pathway was proposed by HR-LC-MS. The biological toxicity after the reaction was detected, and the introduction of polyvinylpyrrolidone (PVP) was beneficial to reduce the biological toxicity of iron dissolution. This work provides new insights into the green and efficient resource utilization of natural pyrite and significantly expands the pH applicability range of the Fenton process, demonstrating the large-scale industrial application potential of pyrite.

Higher efficiency of vanadate iron in heterogeneous Fenton-like systems to pretreat sugarcane bagasse and its enzymatic saccharification

Pretreatment is crucial for effective enzymatic saccharification of lignocellulose such as sugarcane bagasse (SCB). In the present study, SCB was pretreated with five kinds of heterogeneous Fenton-like systems (HFSs), respectively, in which α-FeOOH, α-Fe2O3, Fe3O4, and FeS2 worked as four traditional heterogeneous Fenton-like catalysts (HFCs), while FeVO4 worked as a novel HFC. The enzymatic reducing sugar conversion rate was then compared among SCB after different heterogeneous Fenton-like pretreatments (HFPs), and the optimal HFS and pretreatment conditions were determined. The mechanism underlying the difference in saccharification efficiency was elucidated by analyzing the composition and morphology of SCB. Moreover, the ion dissolution characteristics, variation of pH and Eh values, H2O2 and hydroxyl radical (·OH) concentration of FeVO4 and α-Fe2O3 HFSs were compared. The results revealed that the sugar conversion rate of SCB pretreated with FeVO4 HFS reached up to 58.25%, which was obviously higher than that under other HFPs. In addition, the surface morphology and composition of the pretreated SCB with FeVO4 HFS were more conducive to enzymatic saccharification. Compared with α-Fe2O3, FeVO4 could utilize H2O2 more efficiently, since the dissolved Fe3+ and V5+ can both react with H2O2 to produce more ·OH, resulting in a higher hemicellulose and lignin removal rate and a higher enzymatic sugar conversion rate. It can be concluded that FeVO4 HFP is a promising approach for lignocellulose pretreatment.

Neutral pH Fenton and photo-Fenton activity of Mo-doped iron-pyrite particles

Low H2O2 utilization efficiency for hydroxyl radical generation, acidic pH, and recyclability are critical limitations of heterogeneous Fenton and photo-Fenton catalysts. The present research shows that the optimum Mo doping of FeS2 particles can largely alleviate these catalysis constraints. A solvothermal protocol was followed to prepare polyvinyl pyrrolidone (PVP) stabilized FeS2 and Mo-doped FeS2 particles. XRD observations showed that Mo doping increases the lattice parameters of FeS2. The band gap of the Mo-doped FeS2 particles decreased to 1.58 eV from the 2.24 eV value exhibited by pure FeS2 particles. Structural and electronic structure DFT calculations support these results. The Fenton and photo-Fenton p-nitrophenol (PNP) degradation at neutral pH on PVP-stabilized Mo-doped FeS2 and FeS2 particles were examined. The photo-Fenton results were substantially better than under Fenton conditions. The best PNP degradation photo-Fenton turnover frequency (TOF) recorded was 254.50 μmol g-1 min-1 on the PVP stabilized 4% Mo-doped FeS2 sample. The Mo-doped FeS2 catalysts were stable under photo-Fenton recycling, and the H2O2 (1.66 mM) required for these reactions was significantly lower than most reports (30-6000 mM). Given the economic importance of the latter in Fenton/photo-Fenton reactions, H2O2 normalized turnover frequency (13.85 and 153.31 mg-1 min-1 L for Fenton and photo-Fenton) values were used to evaluate catalytic activities.

Inhibition photooxidation of pyrite under illumination via altering photogenerated carrier migration pathways: Role of DTC-TETA surface passivation

The oxidation of pyrite is the main cause of acidic mine drainage (AMD), which is a very serious environmental problem in numerous mining areas around the world. Previous studies have shown that passivation agents create a hydrophobic film on the surface of pyrite, effectively isolating oxygen and water. However, the presence of abundant sulfide minerals in tailings ponds may exacerbate AMD when exposed to solar radiation, due to the semiconductor properties of pyrite. It remains uncertain whether the current surface passivation coating can effectively prevent the oxidation of pyrite under light conditions. This paper is the first to investigate the passivation effect as well as the mechanism of surface passivation coating on pyrite under illumination from the perspective of materials science. The results demonstrated that the triethylenetetramine-bisdithiocarbamate (DTC-TETA) passivation coating on pyrite almost completely suppressed the photooxidation of pyrite under illumination by changing the migration path of photogenerated charge carriers. The formation of NC(S)2-Fe chelating groups provides atomic-level interface channels for DTC-TETA to transfer electrons to pyrite and creates a favorable reduction environment for pyrite. Besides, DTC-TETA coating greatly improves the electron-hole pairs recombination efficiency of pyrite, which significantly inhibits the photogenerated electron reduction of oxygen to generate reactive oxygen species (ROS). Moreover, DTC-TETA coating captures the photogenerated holes, avoiding direct oxidation of pyrite by holes. Density functional theory (DFT) calculations revealed that the DTC-TETA coating increases the adsorption energy barrier for oxygen and water. The results extend the existing knowledge on passivation mechanisms on pyrite and hold significant implications for the future screening, evaluation, and practical application of surface passivating agents.

Hydroxyl radical production by abiotic oxidation of pyrite under estuarine conditions: The effects of aging, seawater anions and illumination

Pyrite is widely distributed in estuarine sediments as an inexpensive natural Fenton-like reagent, however, the mechanism on the hydroxyl radical (HO·) production by pyrite under estuarine environmental conditions is still poorly understood. The batch experiments were performed to investigate the effects of estuarine conditions including aging (in air, in water), seawater anions (Cl-, Br- and HCO3-) and light on the HO· production by pyrite oxidation. The one-electron transfer dominated the process from O2 to HO· induced by oxidation of pyrite. The Fe (oxyhydr)oxide coatings on the surface of pyrite aged in air and water consumed hydrogen peroxide while mediating the electron transfer, and the combined effect of the two resulted in a suppression of HO· production in the early stage of aging and a promotion of HO· production in the later stage of aging. Corrosion of the surface oxide layers by aggressive anions was the main reason for the inhibition of HO· production by Cl- and Br-, and the generation of Cl· and Br· may also play a role in the scavenging of HO·. HCO3- increased the average rate of HO· production through surface-CO2 complexes formed by adsorption on the surface of pyrite. The significant enhancement of HO· production under light was attributed to the formation of photoelectrons induced by photochemical reactions on pyrite and its surface oxide layers. These findings provide new insights into the environmental chemical behavior of pyrite in the estuary and enrich the understanding of natural remediation of estuarine environments.

Research on ferroptosis as a therapeutic target for the treatment of neurodegenerative diseases

Ferroptosis is an iron- and lipid peroxidation (LPO)-mediated programmed cell death type. Recently, mounting evidence has indicated the involvement of ferroptosis in neurodegenerative diseases, especially in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and so on. Treating ferroptosis presents opportunities as well as challenges for neurodegenerative diseases. This review provides a comprehensive overview of typical features of ferroptosis and the underlying mechanisms that contribute to its occurrence, as well as their implications in the pathogenesis and advancement of major neurodegenerative disorders. Meanwhile, we summarize the utilization of ferroptosis inhibition in both experimental and clinical approaches for the treatment of major neurodegenerative disorders. In addition, we specifically summarize recent advances in developing therapeutic means targeting ferroptosis in these diseases, which may guide future approaches for the effective management of these devastating medical conditions.

Harnessing the power of natural minerals: A comprehensive review of their application as heterogeneous catalysts in advanced oxidation processes for organic pollutant degradation

The release of untreated wastewater into water bodies has become a significant environmental concern, resulting in the accumulation of refractory organic pollutants that pose risks to human health and ecosystems. Wastewater treatment methods, including biological, physical, and chemical techniques, have limitations in achieving complete removal of the refractory pollutants. Chemical methods, particularly advanced oxidation processes (AOPs), have gained special attention for their strong oxidation capacity and minimal secondary pollution. Among the various catalysts used in AOPs, natural minerals offer distinct advantages, such as low cost, abundant resources, and environmental friendliness. Currently, the utilization of natural minerals as catalysts in AOPs lacks thorough investigation and review. This work addresses the need for a comprehensive review of natural minerals as catalysts in AOPs. The structural characteristics and catalytic performance of different natural minerals are discussed, emphasizing their specific roles in AOPs. Furthermore, the review analyzes the influence of process factors, including catalyst dosage, oxidant addition, pH value, and temperature, on the catalytic performance of natural minerals. Strategies for enhancing the catalytic efficiency of AOPs mediated by natural minerals are explored, mainly including physical fields, reductant addition, and cocatalyst utilization. The review also examines the practical application prospects and main challenges associated with the use of natural minerals as heterogeneous catalysts in AOPs. This work contributes to the development of sustainable and efficient approaches for organic pollutant degradation in wastewater.

Recent advances in advanced oxidation processes (AOPs) for the treatment of nitro- and alkyl-phenolic compounds

The presence of phenolic compounds in the aquatic environment has posed severe risks due to their toxicity. Among the phenolic families, nitro- and alkyl-phenolic compounds have been categorized as precedence contaminants by the United States Environmental Protection Agency (US EPA). Therefore, efficient treatment methods for wastewater containing nitro- and alkyl-phenolic compounds are urgently needed. Due to the advantages of creating reactive species and generating efficient degradation of hazardous contaminants in wastewater, advanced oxidation processes (AOPs) are well-known in the field of treating toxic contaminants. In this review paper, the recent directions in AOPs, catalysts, mechanisms, and kinetics of AOPs are comprehensively reviewed. Furthermore, the conclusion summarizes the research findings, future prospects, and opportunities for this study. The main direction of AOPs lies on the optimization of catalyst and operating parameters, with industrial applications remain as the main challenge. This review article is expected to present a summary and in-depth understanding of AOPs development; and thus, inspiring scientists to accelerate the evolution of AOPs in industrial applications.

Heterogeneous Electro-Fenton-Catalyzed Degradation of Rhodamine B by Nano-Calcined Pyrite

The use of natural pyrite as a catalyst for the treatment of recalcitrant organic wastewater by an electro-Fenton system (pyrite-EF) has recently received extensive attention. To improve the catalytic activity of natural pyrite (Py), magnetic pyrite (MPy), and pyrrhotite (Pyr), they were obtained by heat treatment, and the nanoparticles were obtained by ball milling. They were characterized by X-ray diffraction, X-ray electron spectroscopy, and scanning electron microscopy. The degradation performance of rhodamine B (Rhb) by heterogeneous catalysts was tested under the pyrite-EF system. The effects of optimal pH, catalyst concentration, and current density on mineralization rate and mineralization current efficiency were explored. The results showed that the heat treatment caused the phase transformation of pyrite and increased the relative content of ferrous ions. The catalytic performance was MPy > Py > Pyr, and the Rhb degradation process conformed to pseudo-first-order kinetics. Under the optimum conditions of 1 g L^-1 MPy, an initial pH of five, and a current density of 30 mA cm^-2, the degradation rate and TOC removal rate of Rhb wastewater reached 98.25% and 77.06%, respectively. After five cycles of recycling, the chemical activity of MPy was still higher than that of pretreated Py. The main contribution to Rhb degradation in the system was •OH radical, followed by SO4•-, and the possible catalytic mechanism of MPy catalyst in the pyrite-EF system was proposed.

Semiconducting mineral induced photochemical conversion of PAHs in aquatic environment: Mechanism study and fate prediction

Semiconducting minerals (such as iron sulfides) are highly abundant in surface water, but their influences on the natural photochemical process of contaminants are still unknown. By simulating the natural water environment under solar irradiation, this work comprehensively investigated the photochemical processes of anthracene (a typical Polycyclic Aromatic Hydrocarbons) in both freshwater and seawater. The results show that the natural pyrite (NP) significantly promotes the degradation of anthracene under solar illumination via 1) NP induced photocatalytic degradation of anthracene, and 2) Fenton reaction due to the NP induced photocatalytic generation of H₂O₂. The material characterization and theoretical calculation reveal that the natural impurity in NP enlarges its band gap, which limits the utilization of solar spectra to shorter wavelength. The contribution of generated reactive intermediates on anthracene degradation follows the order of ¹O₂ >OH > O₂^- in freshwater and O₂^- >¹O₂ >OH in seawater. The photochemically generated H₂O₂ is a vital source for OH generation (from Fenton reaction). The steady-state concentration of OH, ¹O₂ and O₂^- in freshwater were monitored as 3.0 × 10^-15 M, 1.1 × 10^-13 M, and 4.5 × 10^-14 M, respectively. However, the OH concentration in seawater can be negligible due to the quenching effects by halides, and the ¹O₂ and O₂^- concentrations are higher than that in freshwater. An anthracene degradation kinetic model was built based on the experimentally determined reactive intermediates concentration and its second order rate constant with anthracene. Moreover, the anthracene degradation pathway was proposed based on intermediates analysis and DFT calculation, and its toxicity evolution during the photochemical process was assessed by quantitative structure-activity relationship (QSAR) based prediction. This finding suggests that the natural semiconducting minerals can affect the fate and environmental risks of contaminants in natural water.

Visible-light-driven iron-based heterogeneous photo-Fenton catalysts for wastewater decontamination: A review of recent advances

Visible-light-driven heterogeneous photo-Fenton process has emerged as the most promising Fenton-derived technology for wastewater decontamination, owing to its prominent superiorities including the potential utilization of clean energy (solar light), and acceleration of ≡Fe(II)/≡Fe(III) dynamic cycle. As the core constituent, catalysts play a pivotal role in the photocatalytic activation of H₂O₂ to yield reactive oxidative species (ROS). To date, all types of iron-based heterogeneous photo-Fenton catalysts (Fe-HPFCs) have been extensively reported by the scientific community, and exhibited satisfactory catalytic performance towards pollutants decomposition, sometimes even exceeding the homogeneous counterparts (Fe(II)/H₂O₂). However, the relevant reviews on Fe-HPFCs, especially from the viewpoint of catalyst-self design are extremely limited. Therefore, this state-of-the-art review focuses on the available Fe-HPFCs in literatures, and gives their classification based on their self-characteristics and modification strategies for the first time. Two classes of representative Fe-HPFCs, conventional inorganic semiconductors of Fe-containing minerals and newly emerging Fe-based metal-organic frameworks (Fe-MOFs) are comprehensively summarized. Moreover, three universal strategies including (i) transition metal (TMs) doping, (ii) construction of heterojunctions with other semiconductors or plasmonic materials, and (iii) combination with supporters were proposed to tackle their inherent defects, viz., inferior light-harvesting capacity, fast recombination of photogenerated carriers, slow mass transfer and low exposure and uneven dispersion of active sites. Lastly, a critical emphasis was also made on the challenges and prospects of Fe-HPFCs in wastewater treatment, providing valuable guidance to researchers for the reasonable construction of high-performance Fe-HPFCs.

Molecular Oxygen Activation by Citric Acid Boosted Pyrite-Photo-Fenton Process for Degradation of PPCPs in Water

Pyrite has been used in photo-Fenton reactions for the degradation of pollutants, but the application of photo-Fenton processes with extra H₂O₂ in real water/wastewater treatment has still been limited by the economic cost of H₂O₂ and artificial light sources. Herein, citric acid (CA) and simulated/natural sunlight are used to develop a pyrite-based photo-Fenton system (pyrite-CA-light) in situ generating H₂O₂ through the enhanced activation of molecular oxygen. The degradation of pharmaceuticals and personal care products (PPCPs), especially acetaminophen (APAP) as the main target pollutant, in the pyrite-CA-light system was investigated. The effects of influencing factors such as various organic acids, APAP concentration, pH, pyrite dosage, CA concentration and co-existing anions (HCO₃^-, Cl^-, NO₃^-, SO₄^2- and H₂PO₄^-) were examined. At a pyrite dosage of 0.1 g L^-1, CA concentration of 0.6 mM and an initial pH of 6.0, the degradation efficiency of APAP (30 μM) was 99.1% within 30 min under the irradiation of xenon lamp (70 W, λ ≥ 350 nm). Almost the same high efficiency of APAP degradation (93.9%) in the system was achieved under natural sunlight irradiation (ca. 650 W m^-2). The scavenging experiments revealed that the dominant active species for degrading APAP was hydroxyl radical (HO^•). Moreover, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants (k_obs) was established with a high significance (R² = 0.932, p = 0.001) by using three descriptors: octanol-water partition coefficient (logKow), dissociation constant (pK_a) and highest occupied molecular orbital (HOMO). This work provides an innovative strategy of the photo-Fenton process for the degradation of PPCPs using natural minerals and ordinary carboxylic acid under sunlight.

Recyclable Fe/S co-doped nanocarbon derived from metal-organic framework as a peroxymonosulfate activator for efficient removal of 2,4-dichlorophenol

In this study, a recyclable Fe/S co-doped nanocarbon (Fe/S-NC) was successfully prepared by the pyrolysis of ZIF-8 confined with Fe(II) and added S. Characterization showed that a highly graphitized carbon-based material co-doped with sulfur and iron was successfully prepared. This Fe/S-NC can efficiently activate PMS to remove organic pollutants in water. The effect of different synthesis conditions on the degradation efficiency of 2,4-DCP was studied by orthogonal experiments. The optimized Fe/S-NC/PMS system exhibited excellent catalytic performance and could degrade more than 99.7% of 2,4-DCP within 30 min. Even after 5 cycles, the degradation efficiency could still be maintained above 96.3%, which proved that the catalytic system had good cycle performance. In addition, the effect of pH on catalytic performance showed that the degradation rate of 2,4-DCP exceeds 96.7% in the pH range of groundwater (pH = 5-9). We had confirmed that the free radicals that caused 2,4-DCP degradation were SO₄^·-, ·OH, O₂^·-, and ¹O₂, which played important roles in degrading organic pollutants. These research results show that the Fe/S-NC/PMS system can be used as an efficient, stable, and environmentally friendly system to treat organic pollutants in groundwater.

Multi-catalysis of glow discharge plasma coupled with FeS2 for synergistic removal of antibiotic

Fe-based composites improved the energy utilization efficiency of plasma for removing contaminants through multi-catalysis have received much attention. However, the energy efficiency and catalytic activity are compromised by the slow transformation from Fe (Ⅲ) to Fe (Ⅱ). Here, given the electron-donating ability of reducing sulfur species, as well as the acidic environment generated by FeS₂, single FeS₂ was introduced into the glow discharge plasma (GDP) reactor for the removal of tylosin (TYL). The results showed that a significant synergistic effect between FeS₂ and GDP improved the energy efficiency of plasma and the removal efficiency of TYL (99.7%). FeS₂ boosted the generation of radicals (·OH, ·O₂^-) and nonradicals (h⁺, e^-) rather than H₂O₂ and O₃, which played an important role in TYL abatement. Moreover, the electrons donating sulfur and iron species from FeS₂ can accelerate the conversion of Fe(III) to Fe(II), which was conducive to the generation of radicals. Besides, acid solution self-adjustment resulted from the oxidation of FeS₂ improved heterogeneous Fenton reaction, the oxidation potential of ·OH and adsorption of positive charged TYL. The plausible degradation pathways of TYL were proposed in GDP/FeS₂ system. In summary, enhanced removal of TYL was mainly attributed to the catalytic pathway altered by FeS₂ through high-energy electrons, photocatalysis, heterogeneous Fenton and O₃ catalysis in the GDP system simultaneously. The strategy of integrating GDP with FeS₂ proposed in this work is expected to offer a feasible and potential technique for organic wastewater treatment.

Sulfur defect and Fe(III) (hydr)oxides on pyrite surface mediate tylosin adsorption in lake water: effect of solution chemistry and dissolved organic matter

Pyrite affects the adsorption of tylosin (TYL) due to their coexistence in the lake system. As well as the reactivity groups of S-S-H, S-OH, and Fe-OH, defects also have the possibilities to influence the adsorption of organic contaminants. However, the role of these active sites in antibiotic adsorption on pyrite has not been deeply studied. Besides, pH, N, P, dissolved oxygen, and dissolved organic matter (DOM) fluctuate greatly in lake at different seasons, which may change the surface characteristics of pyrite. Hence, the adsorption of TYL on natural pyrite considered solution chemistry and DOM in lake water was explored in this study. The fitting results of the kinetic and isotherm models showed that the adsorption included physical and chemical interactions. The neutral initial solution pH was conductive to TYL adsorption owing to the combined result of electrostatic and cover of Fe-oxyhydroxide. NO₃^- and NH₄⁺ had no effect on TYL adsorption, whereas H₂PO₄^- promoted adsorption by forming flocculent Fe(H₂PO₄)₃ precipitates. The dissolved oxygen increased adsorption. This is due to the co-promotion of the pyrite oxidation by oxygen and sulfur defects. The Fe(II)-DOM complex caused by pyrite surface oxidation reduced the concentration of TYL in solution by gathering. Except for the surface charge, reactivity groups on pyrite significantly influenced the adsorption of TYL. The bond fracture of S-S resulted in sulfur defects that contributed to pyrite oxidation. As a result, Fe(III)/Fe(II) on the surface of pyrite or in solution produced a complex Fe(III)/Fe(II) with anions and DOM. In addition, Fe(III)-S on sulfur defects interacted with the O-H of TYL through hydrogen bonding. Furthermore, the Fe-O-C bond is formed by the interaction of C-OH on TYL and Fe(III) (hydr)oxides on the surface of pyrite. The study provides a deep insight into the effect of pyrite surface active sites on amphoteric antibiotic adsorption. It helps to understand antibiotic migration and interactions with widespread pyrite in the real environment.

Synergistic improving photo-Fenton and photo-catalytic degradation of carbamazepine over FeS2/Fe2O3/organic acid with H2O2in-situ generation

Herein, a heterogeneous photo-Fenton and photo-catalytic system was constructed using oxide pyrite (FeS₂/Fe₂O₃) mineral and organic acids including tartaric acid (TA), ascorbic acid (AA), and citric acid (CA). In the proposed system, FeS₂/Fe₂O₃ can be successfully activated through irradiation to generate photogenerated carriers, which generated H₂O₂in-situ through the reduction reactions between e^- and O₂. The addition of organic acids enhanced the dissolution of iron from FeS₂/Fe₂O₃. Based on the iron and in-situ generated H₂O₂, •OH was produced through a photo-Fenton reaction. Furthermore, h⁺, e^-, and •O₂^-, which were generated through the photo-catalytic activation of FeS₂/Fe₂O₃, also played a certain role in the degradation of carbamazepine (CBZ). Therefore, the synergistic photo-Fenton and photo-catalytic reaction improved the degradation of CBZ, with the degradation efficiencies of 86%, 62%, and 68% in FeS₂/Fe₂O₃/TA, FeS₂/Fe₂O₃/AA, and FeS₂/Fe₂O₃/CA systems, respectively. This investigation provides an innovative strategy for the removal of organic pollutants using natural minerals.

Simultaneous Removal of Antibiotic Resistant Bacteria, Antibiotic Resistance Genes, and Micropollutants by FeS2@GO-Based Heterogeneous Photo-Fenton Process

The co-occurrence of various chemical and biological contaminants of emerging concerns has hindered the application of water recycling. This study aims to develop a heterogeneous photo-Fenton treatment by fabricating nano pyrite (FeS₂) on graphene oxide (FeS₂@GO) to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and micropollutants (MPs). A facile and solvothermal process was used to synthesize new pyrite-based composites. The GO coated layer forms a strong chemical bond with nano pyrite, which enables to prevent the oxidation and photocorrosion of pyrite and promote the transfer of charge carriers. Low reagent doses of FeS₂@GO catalyst (0.25 mg/L) and H₂O₂ (1.0 mM) were found to be efficient for removing 6-log of ARB and 7-log of extracellular ARG (e-ARG) after 30 and 7.5 min treatment, respectively, in synthetic wastewater. Bacterial regrowth was not observed even after a two-day incubation. Moreover, four recalcitrant MPs (sulfamethoxazole, carbamazepine, diclofenac, and mecoprop at an environmentally relevant concentration of 10 μg/L each) were completely removed after 10 min of treatment. The stable and recyclable composite generated more reactive species, including hydroxyl radicals (HO^•), superoxide radicals (O₂^• -), singlet oxygen (¹O₂). These findings highlight that the synthesized FeS₂@GO catalyst is a promising heterogeneous photo-Fenton catalyst for the removal of emerging contaminants.

Pyrite-mediated advanced oxidation processes: Applications, mechanisms, and enhancing strategies

Proper treatment of wastewater is one of the key issues to the sustainable development of human society, and people have been searching for high-efficiency and low-cost methods for wastewater treatment. This article reviews recent studies about pyrite-mediated advanced oxidation processes (AOPs) in removing refractory organics from wastewater. The basic information of pyrite and its characteristics for AOPs are first introduced. Then, the performance and mechanisms of pyrite-mediated Fenton oxidation, electro-Fenton oxidation, and persulfate oxidation processes are carefully reviewed and presented. Natural pyrite is an abundant low-cost heterogeneous catalyst for AOPs, and the slow release of Fe²⁺ and the self-regulation of solution pH are highlighted characteristics of pyrite-mediated AOPs. In AOPs, the interaction between Fe³⁺ and pyrite facilitates the Fe²⁺ regeneration and the Fe²⁺/Fe³⁺ cycle. Making pyrite into nanoparticles, assisting by ultrasound and light irradiation, and adding exogenous Fe³⁺, organic chelating agents, or biochar is effective to enhance the performance of pyrite-mediated AOPs. Based on the analyses of those pyrite-mediated AOPs and their enhancing strategies, the future development directions are proposed in the aspects of toxicity research, mechanism research, and technological coupling.

p-nitrophenol degradation by hybrid advanced oxidation process of heterogeneous Fenton assisted hydrodynamic cavitation: Discernment of synergistic interactions and chemical mechanism

The present study has investigated p-nitrophenol (PNP) degradation by hybrid advanced oxidation process (AOP) of hydrodynamic cavitation with heterogenous Fe₃O₄ nanoparticles. 78.8 ± 1.2% of PNP degradation was obtained at optimum operational conditions: inlet pressure = 8 atm, pH = 3, initial concentration of PNP = 20 mg L^-1, Fe₃O₄:H₂O₂ = 1:100. PNP degradation profiles were analyzed using a kinetic model based on the reaction network. The closest match between the simulated and experimental degradation profiles was obtained for the initial concertation of [H₂O₂] = 0.6 M, which was far higher than concentration of externally added H₂O₂. This was attributed to in-situ generation of H₂O₂ through transient cavitation. Intense shear and turbulence generated in cavitating flow caused surface leaching of Fe₃O₄ particles that released Fe²⁺/Fe³⁺ ions. The synergy in the hybrid AOP was in-situ Fenton reactions between leached Fe²⁺/Fe³⁺ ions and H₂O₂ present in the reaction mixture. The mechanism in ^•OH mediated oxidative degradation of PNP was further explored with Density Functional Theory (DFT) simulations. Both ^•OH addition on benzene ring and H-abstraction reactions were simulated to identify the possible pathways for the degradation. On the basis of activation free energy analysis, degradation pathways initiating with both ^•OH addition and H abstraction were determined to be feasible. The ortho-C of benzene ring was the most favourable site for ^•OH addition, while H atom of phenolic hydroxyl group was more susceptible (or more reactive) for H-atom abstraction route.

Trimethylamine functionalized radiation-induced grafted polyamide 6 fibers for p-nitrophenol adsorption

The method of pre-irradiation grafting was used with the aid of electron beam (EB) accelerator to accomplish the grafting of polyamide 6 fibers (PA6) with glycidyl methacrylate (GMA). The extent to which GMA was grafted on PA6 was found to be markedly influenced by the absorbed dose of radiation and the reaction time of grafting. Trimethylamine (TMA) was afterwards employed for the functionalization of GMA-grafted fibers (PA6-g-GMA). A range of analyses (e.g., FTIR, FESEM, XRD, BET, and pHpzc) were carried out to determine the physiochemical and morphological properties of the fibrous adsorbent. p-Nitrophenol (PNP) adsorption from aqueous solution was conducted with the resulting TMA-(PA6-g-GMA) adsorbent. The adsorption behaviour of PNP on the fibrous adsorbent was clarified by investigating the adsorption kinetics and isotherm. According to the results, the adsorption of PNP on TMA-(PA6-g-GMA) reflected the pseudo-second order model. Meanwhile, the isotherm analysis revealed that the best description of the equilibrium data was provided by Redlich-Peterson model, followed closely by Langmuir isotherm model. The achieved adsorption capacity was highest at 176.036 mg/g. Moreover, the adsorption was indicated by the thermodynamic analysis to be spontaneous and exothermic. Regeneration and recycling of the adsorbent was possible for a minimum of five cycles with no reduction in adsorption capacity. It was concluded that the fibrous adsorbent could have applications for the removal of PNP at industrial pilot scale.

Solar irradiation induced oxidation and adsorption of arsenite on natural pyrite

The migration and bioavailability of toxic elemental arsenic (As) are influenced by the adsorption and redox processes of sulfide minerals in waters around mining areas. Pyrite is the most abundant sulfide mineral in the Earth's crust and exhibits certain photochemical activity. However, the adsorption and redox behaviors of arsenite (As(III)) on pyrite surface under solar irradiation remain unclear. Here, the interaction between As(III) and natural pyrite was investigated under light irradiation. The results indicated that solar irradiation promotes As(III) oxidation and adsorption on pyrite surface due to reactive oxygen species (ROS) intermediates. The reactions between H₂O/O₂ and hole-electron pairs (h_vb⁺-e_cb^-) on excited pyrite and the oxidation of Fe²⁺ released from pyrite by dissolved O₂ contributed much to the generation of OH^•, O₂^•- and H₂O₂ under light irradiation. ROS production and As(III) oxidation were accelerated by dissolved O₂. An increase in pH within 5.0 to 9.0 decreased the concentration of OH^• but increased that of H₂O₂ and the amount of oxidized As(III). In weakly acidic and neutral environments, OH^• was mainly responsible for As(III) oxidation, while H₂O₂ contributed much to As(III) oxidation in weakly alkaline environments. Partial arsenate (As(V)) was adsorbed on pyrite and newly formed ferrihydrite. The present work enriches the understanding of As migration and transformation in the waters around mining areas, and provides a potential method for As(III) removal by using pyrite under solar irradiation.

A green solar photo-Fenton process for the degradation of carbamazepine using natural pyrite and organic acid with in-situ generated H2O2

Pyrite is widely used in Fenton reaction for degradation of pollutants and exhibits great potential for environmental remediation, however, its efficiency is greatly compromised by extra H₂O₂ and pH adjustment. Herein, a pyrite based green solar photo-Fenton system for carbamazepine (CBZ) treatment is constructed, involving the use of simulated sunlight and natural organic acids with in situ-generated H₂O₂ and without extra pH adjustment. The addition of organic acids including tartaric acid (TA), citric acid (CA), and ascorbic acid (AA) can form complex with iron in pyrite, which promotes the Fe(II) dissolution. Upon irradiation, pyrite could be excited to produce photoelectrons, which would reduce oxygen to produce H₂O₂ through a two-step route assisted by organic acids. The simulated sunlight and organic acids promoted the in-situ production of H₂O₂ and Fe(II) species, sustaining an efficient Fenton reaction. This produced massive hydroxyl radical (OH), as demonstrated by the active species capture experiment. Compared with no degradation of CBZ under pure pyrite, the degradation efficiency of CBZ reached to 70%, 60%, and 53% in pyrite/TA, pyrite/CA, pyrite/AA within 30 min under simulated solar light irradiation, respectively. This work reports the first use of natural pyrite, a typical Fe-mineral semiconductor, to produce OH for CBZ degradation through natural additive assisted Fenton reaction excluding the adding extra H₂O₂ and pH adjustment.

Synthesis of nano-FeS2 and its application as an effective activator of ozone and peroxydisulfate in the electrochemical process for ofloxacin degradation: A comparative study

In this work, nanopyrite particles (NP) were synthesized by ball mill method and used as a novel source of Fe²⁺ in the electro-activation of ozone and peroxydisulfate (PDS) for ofloxacin (OFX) removal. Fourier transform infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy analyzes were performed to characterize the as-made NP. Optimal values of operating parameters in NP/PDS and NP/O₃ processes were obtained. The OFX (10 mgL^-1) removal efficiency and molar ratio of OFX: oxidant in NP/PDS and NP/O₃processes were 92%, 0.1:11 and 89%, 0.1:9, respectively. Although the synergistic effect was observed in both systems, it was more significant in the NP/PDS. The results of free radical tracing showed that HO^•and SO₄^•- had the more contribution in NP/O₃ and NP/PDS systems for OFX degradation, respectively. In this way, the OFX removal mechanism was the effective release of Fe²⁺ from the NP in the electro-activation of O₃ and PDS. Moreover, the effect of electrocoagulation process on OFX removal was negligible. The as-made NP overcame the disadvantages of iron electrode corrosion and iron sludge production in the Fe-based classical electro-activation processes. Overall, the performance of the synthesized NP in the OFX oxidation was very successful in terms of sustainability, Fe²⁺distribution, removal efficiency, energy consumption and PDS or O₃ activation.

A novel strategy for enhancing heterogeneous Fenton degradation of dye wastewater using natural pyrite: Kinetics and mechanism

Hydrogen peroxide activation by pyrite for degradation of recalcitrant contaminants receives increasing attention. The improvement of catalytic efficiency of natural pyrite is still a challenging issue. This work provides a novel strategy of enhancing catalytic efficiency via pre-reaction between pyrite and hydrogen peroxide. Effects of process factors including pre-reaction time, hydrogen peroxide, solution pH and initial dye concentration were examined. Natural pyrite with low purity was characterized by Raman, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Reaction kinetic verifies tremendous improvement of the reaction rate through pre-reaction. Enhanced dye degradation is ascribed to hydroxyl radical production promoted by self-regulation of pH, Fe²⁺ releasing and Fe²⁺/Fe³⁺ cycle. The plausible mechanism was proposed based on multiple determinations. Dye degradation in different water matrix was efficiently obtained, as well as multicomponent dyes. Additionally, broad operation pH and good reusing performance make the developed process highly attractive for application. This work provides a solid step-forward of pyrite/hydrogen peroxide Fenton process for treatment of recalcitrant contaminants in wastewater.

Recent advances in waste water treatment through transition metal sulfides-based advanced oxidation processes

With the ever-growing water pollution issues, advanced oxidation processes (AOPs) have received growing attention due to their high efficiency in the removal of refractory organic pollutants. Transition metal sulfides (TMSs), with excellent optical, electrical, and catalytical performance, are of great interest as heterogeneous catalysts. These TMSs-based heterogeneous catalysts have been demonstrated to becapable and adaptable in water purification through advanced oxidation processes. The aim of this review is to conduct an exhaustive analysis and summary of recent progress in the application of TMSs-based AOPs for water decontamination. Firstly, the commonly used tuning strategies for TMSs-based catalysts are concisely introduced, including artificial size and shape control, composition control, doping, and heterostructure manufacturing. Then, a comprehensive overview of the current state-of-the-art progress on TMSs-based AOPs (i.e., Fenton-like oxidation, photocatalytic oxidation, and electro chemical oxidation processes) for wastewater treatment is discussed in detail, with an emphasis on their catalytic performance and involved mechanism. In addition, influencing factors of water chemistry, namely, pH, temperature, dissolved oxygen, inorganic species, and natural organic matter on the catalytic performance of established AOPs are analyzed. Furthermore, the reusability and stability of TMSs-based catalysts in these AOPs are also outlined. Finally, current challenges and future perspectives related to TMSs-based catalysts and their applications for AOPs wastewater treatment are proposed. It is expected that this review would shed some light on the future development of TMSs-based AOPs towards water purification.

Efficient transformation of diethyl phthalate using calcium peroxide activated by pyrite

In this study, pyrite (FeS₂) was used as a novel activator of calcium peroxide (CaO₂) for the degradation of diethyl phthalate (DEP) in both aqueous solution and soil. DEP (10 mg/L) in aqueous solution was completely degraded within 5.0 min by the FeS₂ (0.30 g/L)/CaO₂ (1.0 mM) system at pH 3.5. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), free radical quenching, and X-ray photoelectron spectroscopy (XPS) were used to elucidate the mechanism of the catalytic decomposition of CaO₂, radical formation and DEP degradation in the presence of by pyrite. The results show that hydroxyl radicals (OH) are the dominant active species responsible for DEP degradation. Surface or lattice Fe(II) of FeS₂ readily activates H₂O₂ generated by CaO₂ decomposition to produce OH, while the reducing sulfur species of FeS₂ promotes the regeneration of surface of Fe(II) that catalyzes the production of additional OH, leading to the efficiently oxidative degradation of DEP. Although high concentration of common anions, such as Cl^-, NO₃^-, SO₄^2-, and HCO₃^-, exert inhibitory effects on DEP degradation by pyrite/CaO₂, the reaction system can still efficiently degrade DEP in realistic soil. It was observed that 78% of DEP (25 mg kg^-1) was degraded by 2.5% CaO₂ (w/w) and 0.5% FeS₂ (w/w) within 24 h. These results provide new insight into the mechanistic processes of CaO₂ activation and OH formation by the novel FeS₂ catalyst, demonstrating a promising alternative to the traditional H₂O₂-base Fenton process for contaminated soil remediation.

Comparative time-based intermediates study of ozone oxidation of 4-chloro- and 4-nitrophenols followed by LCMS-TOF

Greater insights on the degradation pathways and intermediates formed during the oxidation of organics can be achieved by more suitable and compatible instrumentation. In our research, we sought to explore the relative advantages of the liquid chromatography coupled to a time of flight mass spectrometer (LCMS-TOF) technique for the comparative time-based degradation intermediates and pathways of 4-chlorophenol (4CP) and 4-nitrophenol (4NP). The ozonation of the analytes solution (100 mL of 2 x 10^-3 M) was done in a sintered glass reactor, with an ozone dose of 0.14 mg min^-1 (O₂/O₃ 10 mL/min). The comparative oxidation results revealed that the 4-chloro- and 4-nitrocatechol pathways via hydroxylation were the major degradation route for 4CP and 4NP. Catechol intermediate was present as a primary breakdown product for the two analytes. Hydroquinone was observed as transient degradation intermediate for 4CP, but was absent for 4NP. Rather, a novel ozonation intermediate 2, 4-dinitrophenol was identified which was further oxidized to 3,6-dinitrocatechol. Several dimer products were identified in the oxidation processes, favored by alkaline conditions with more versatility shown by 4CP. The study provided a great insight into the ozone degradation intermediates and pathways, with some intermediates scarce in literature identified.