Insights into the oxidation of organic contaminants by iron nanoparticles encapsulated within boron and nitrogen co-doped carbon nanoshell: Catalyzed Fenton-like reaction at natural pH

Magnetic raspberry-like CuCo nanoalloy-embedded carbon as an enhanced activator of Oxone to degrade azo contaminant: Cu-induced hollowed structure and boosted activities

Azo compounds, particularly azo dyes, are widely used but pose significant environmental risks due to their persistence and potential to form carcinogenic by-products. Advanced oxidation processes (AOPs) are effective in degrading these stubborn compounds, with Oxone activation being a particularly promising method. In this study, a unique nanohybrid material, raspberry-like CuCo alloy embedded carbon (RCCC), is facilely fabricated using CuCo-glycerate (Gly) as a template. With the incorporation of Cu into Co, RCCC is essentially different from its analogue derived from Co-Gly in the absence of Cu, affording a popcorn-like Co embedded on carbon (PCoC). RCCC exhibits a unique morphology, featuring a hollow spherical layer covered by nanoscale beads composed of CuCo alloy distributed over carbon. Therefore, RCCC significantly outperforms PCoC and Co3O4 for activating Oxone to degrade the toxic azo contaminant, Azorubin S (AS), in terms of efficiency and kinetics. Furthermore, RCCC remains highly effective in environments with high NaCl concentrations and can be efficiently reused across multiple cycles. Besides, RCCC also leads to the considerably lower Ea of AS degradation than the reported Ea values by other catalysts. More importantly, the contribution of incorporating Cu with Co as CuCo alloy in RCCC is also elucidated using the Density-Function-Theory (DFT) calculation and synergetic effect of Cu and Co in CuCo contributes to enhance Oxone activation, and boosts generation of SO4•-and •OH. The decomposition pathway of AS by RCCC + Oxone is also comprehensively investigated by studying the Fukui indices of AS and a series of its degradation by-products using the DFT calculation. In accordance to the toxicity assessment, RCCC + Oxone also considerably reduces acute and chronic toxicities to lower potential environmental impact. These results ensure that RCCC would be an advantageous catalyst for Oxone activation to degrade AS in water.

A novel 3D nitrogen-doped porous carbon supported Fe-Cu bimetallic nanoparticles composite derived from lignin: an efficient peroxymonosulfate activator for naphthalene degradation

A novel 3D nitrogen-doped porous carbon supported Fe-Cu bimetallic nanoparticles composite (Fe-Cu-N-PC) was prepared via direct pyrolysis by employing black liquor lignin as a main precursor, and it was utilized as a novel catalyst for PMS activation in degrading naphthalene. Under the optimum experimental conditions, the naphthalene degradation rate was up to 93.2% within 60 min in the Fe-Cu-N-PC/PMS system. The porous carbon framework of Fe-Cu-N-PC could facilitate the quick molecule diffusion of reactants towards the inner bimetallic nanoparticles and enriched naphthalene molecules from the solution by a specific adsorption, which increased the odds of contact between naphthalene and reactive oxygen species and improved the reaction efficiency. The quenching reaction proved that the non-free radical pathway dominated by 1O2 was the main way in naphthalene degradation, while the free radical pathway involving SO4·- and ·OH only played a secondary role. Moreover, owing to its high magnetization performance, Fe-Cu-N-PC could be magnetically recovered and maintained excellent naphthalene degradation rate after four degradation cycles. This research will offer a theoretical basis for the construction of facile, efficient, and green technologies to remediate persistent organic pollutants in the environment.

Insights into the efficient water treatment over N-doped carbon nanosheets with layered minerals as template: The role of interfacial electron tunneling and transfer

Peroxymonosulfate (PMS) oxidation reactions have been extensively studied recently. Due to the high material cost and low catalytic capability, PMS oxidation technology cannot be effectively applied in an industrial water treatment process. In this work, we developed a modification strategy based on enhancing the neglected electron tunneling effect to optimize the intrinsic electron transport process of the catalyst. The 2D nitrogen-doped carbon-based nanosheets with small interlayer spacing were prepared by self-polymerization of dopamine hydrochloride inserted into the natural layered bentonite template. Systematic characterizations confirmed that the smaller layer spacing in the 2D nitride-doped carbon-based nanosheets reduces the depletion layer width. The weak electronic shielding effect derived by the small layer spacing on the material subsurface enhanced the bulk electron tunneling effect. More bulk electrons could be migrated to the catalyst surface to activate PMS molecules. The PMS activation system showed ultrafast oxidation capability to degrade organic pollutants and strong ability to resist interference from environmental matrixes due to the optimized electron transfer process. Furthermore, the developed membrane reactor exhibited strong catalytic stability during the continuous degradation of P-Chlorophenol (CP).

Hollow-Structured N-doped carbon-embedded CoFe NanoAlloy for boosting activation of Monopersulfate: Engineered interface and heteroatom Doping-Induced enhancements

While transition metals are useful for activating monopersulfate (MPS) to degrade contaminants, bimetallic alloys exhibit stronger catalytic activities owing to several favorable effects. Therefore, even though Co is an efficient metal for MPS activation, CoFe alloys are even more promising heterogeneous catalysts for MPS activation. Immobilization/embedment of CoFe alloy nanoparticles (NPs) onto hetero-atom-doped carbon matrices appears as a practical strategy for evenly dispersing CoFe NPs and enhancing catalytic activities via interfacial synergies between CoFe and carbon. Herein, N-doped carbon-embedded CoFe alloy (NCCF) is fabricated here to exhibit a unique hollow-engineered nanostructure and the composition of CoFe alloy by using Co-ZIF as a precursor after the facile etching and Fe doping. The Fe dopant embeds CoFe alloy NPs into the hollow-structured N-doped carbon substrate, enabling NCCF to possess the higher mesoscale porosity, active N species as well as more superior electrochemical properties than its analogue without Fe dopants, carbon matrix-supported cobalt (NCCo). Thus, NCCF exhibits a considerably larger activity than NCCo and the benchmark catalyst, Co3O4 NP, for MPS activation to degrade an environmental hormone, dihydroxydiphenyl ketone (DHPK). Besides, NCCF + MPS shows an even lower activation energy for DHPK degradation than literatures, and retains its high efficiency for eliminating DHPK in different water media. DHPK degradation pathway and ecotoxicity assessment are unraveled based on the insights from the computational chemistry, demonstrating that DHPK degradation by NCCF + MPS did not result in the formation of toxic and highly toxic by-products. These features make NCCF a promising heterogeneous catalyst for MPS activation to degrade DHPK.

Hollow-Architected Heteroatom-Doped Carbon-Supported Nanoscale Cu/Co as an Enhanced Magnetic Activator for Oxone to Degrade Toxicants in Water

Even though transition metals can activate Oxone to degrade toxic contaminants, bimetallic materials possess higher catalytic activities because of synergistic effects, making them more attractive for Oxone activation. Herein, nanoscale CuCo-bearing N-doped carbon (CuCoNC) can be designed to afford a hollow structure as well as CuCo species by adopting cobaltic metal organic frameworks as a template. In contrast to Co-bearing N-doped carbon (CoNC), which lacks the Cu dopant, CuCo alloy nanoparticles (NPs) are contained by the Cu dopant within the carbonaceous matrix, giving CuCoNC more prominent electrochemical properties and larger porous structures and highly nitrogen moieties. CuCoNC, as a result, has a significantly higher capability compared to CoNC and Co3O4 NPs, for Oxone activation to degrade a toxic contaminant, Rhodamine B (RDMB). Furthermore, CuCoNC+Oxone has a smaller activation energy for RDMB elimination and maintains its superior effectiveness for removing RDMB in various water conditions. The computational chemistry insights have revealed the RDMB degradation mechanism. This study reveals that CuCoNC is a useful activator for Oxone to eliminate RDMB.

Algae-derived metal-free boron-doped biochar acts as a catalyst for the activation of peroxymonosulfate toward the degradation of diclofenac

In this study, plain seaweed biochar (SW) and boron-doped seaweed biochar (BSW) were prepared through a simple pyrolysis process using Undaria pinnatifida (algae biomass) and boric acid. The BSW catalyst was utilized to degrade organic pollutants in aqueous environments by activating peroxymonosulfate (PMS). Surface characterization of the BSW demonstrated successful doping of boron into the biochar materials. BSW₆₀₀ exhibited greater catalytic activity than SW₆₀₀, as evidenced by the former's maximum adsorption capacity of diclofenac (DCF) onto BSW₆₀₀ (q_max = 30.01 mg g^-1) and the activation of PMS. Complete degradation of DCF was achieved in 30 min using 100 mg L^-1 BSW₆₀₀, 0.5 mM PMS, and 6.5 initial solution pH as critical parameters. The pseudo-first-order kinetic model accurately described the DCF degradation kinetics. The scavenger experiment displayed that radical and non-radical reactive oxygen species (ROS) formed in the BSW₆₀₀/PMS system. Furthermore, the generation of ROS in the BSW₆₀₀/PMS system was confirmed by electron spin resonance spectroscopy (ESR). The percentage contribution of ROS was assessed to be 10, 65, and 25% for HO^•, SO₄^•-, and ¹O₂, respectively. Additionally, the electron transfer pathway was also confirmed by electrochemical analysis. Moreover, the influence of water matrics on the BSW₆₀₀/PMS system was demonstrated. The co-existence of anions and humic acid (HA) did not affect the catalytic activity of the BSW₆₀₀/PMS system. The recyclability of BSW₆₀₀ was assessed by DCF removal (86.3%) after three cycles. Ecological structure-activity relationships software was used to assess by-product toxicity. This study demonstrates the efficacy of non-metallic heteroatom-doped biochar materials as eco-friendly catalysts in groundwater applications.

Layered double hydroxide/carbonitride heterostructure with potent combination for highly efficient peroxymonosulfate activation

Iron-based layered double hydroxides (LDHs) have drawn tremendous attention as a promising peroxymonosulfate (PMS) activators, but they still suffer from low efficiencies limited by electrostatic agglomeration and low electronic conductivity. Herein, a MgFeAl layered double hydroxide/carbonitride (LDH/CN) heterostructure was constructed via triggering the interlayer reaction of citric acid (CA) and urea. CA as a structure-directing agent regulated the interlayer anion of MgFeAl-LDH, which enabled an interfacial tuning in the process of coupling with CN. The obtained LDH/CN heterostructure, as an efficient PMS activator, achieved nearly 100% bisphenol A (BPA) removal rate in 10 min with high specific activity (0.146 L min^-1·m^-2). Electron paramagnetic resonance (EPR) tests, quenching experiments, electrochemical characterization and X-ray photoelectrons spectroscopy (XPS) tests were applied to clarify the mechanism of BPA degradation. The results unraveled that the activity of the catalyst originated from the heterostructure of LDH and CN with an efficient interfacial electron transfer, which promoted the fast generation of O₂^•- for rapid pollutant degradation. In addition, the catalyst exhibited excellent applicability in realistic wastewater. This work offered a rational strategy for forming a heterostructure catalyst with a fine interface engineering in actual environmental cleanup.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)‑carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3-11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k₁) of 98.7% and 0.087 min^-1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L^-1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl^-, HCO₃^- and H₂PO₄^-) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving ¹O₂ and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI‑carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron‑carbon based catalysts towards PMS.

Rapid degradation of p-arsanilic acid and simultaneous removal of the released arsenic species by Co-Fe@C activated peroxydisulfate process

In this study, a bimetallic composite catalyst (Co-Fe@C) was fabricated with calcination at high temperature (800 °C) by using Co-MIL-101 (Fe) as the precursor. The characterization results showed that the resulted Co-Fe@C composite mainly consisted of carbon, FeCo alloys, Fe₃O₄, Co₃O₄ and FeO, and owned evident magnetism. In addition, the Co-Fe@C was employed to activate the peroxydisulfate (PDS) to degrade a representative organic pollutant (p-arsanilic acid, p-ASA) and the main factors were optimized, which involved 0.2 g L^-1 of catalyst dosage, 1.0 g L^-1 of PDS dosage and 5.0 of initial pH. Under the optimal condition, Co-Fe@C/PDS system could completely degrade p-ASA (20 mg L^-1) in 5 min. In the Co-Fe@C/PDS system, SO₄^-·, Fe(IV) and ·OH were the main species during p-ASA degradation. Under the attack of these species, p-ASA was first decomposed into phenols and then transformed into the organics acids and finally mineralized into CO₂ and H₂O through a series of reactions like hydroxylation, dearsenification, deamination and benzene ring opening. Importantly, most of the released inorganic arsenic species (93.40%) could be efficiently adsorbed by the catalyst.

A novel electrochemically enhanced homogeneous PMS-heterogeneous CoFe2O4 synergistic catalysis for the efficient removal of levofloxacin

A novel electrochemically enhanced homogeneous-heterogeneous catalytic system was constructed by placing the prepared heterogeneous catalyst (CoFe₂O₄/NF) in parallel between the anode and the cathode for peroxymonosulfate (PMS) activation to remove levofloxacin (LVF) in this work. Over 90% of LVF could be effectively removed by the constructed system after 40 min's degradation. And the electrical energy consumption was only 2.51 kWh/m³, which was lower than 54.5% of the traditional electrochemical advanced oxidation process. Besides, the system broadened the response range of pH and overcame the inhibitory effect of alkaline conditions on degradation. These activities were mainly due to the high generation ability of free radical (SO₄^·-, ·OH and O₂^·-) and non-radical (¹O₂). And the SO₄^·- was found to be the main radical for LVF degradation. The high SO₄^·- generation ability was demonstrated to be resulted from the dual effects of synergy of CoFe₂O₄/PMS and enhancement of electrochemistry in EC/CoFe₂O₄/PMS system. In detail, electrochemistry could effectively promote the continuous circulation of Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺ redox cycles on the surface of CoFe₂O₄ to enhance the activation of PMS, thereby generating SO₄^·-. This work can provide a promising and cost-effective approach to construct highly efficient organic pollutant degradation system.

Facile Synthesis of Carbon- and Nitrogen-Doped Iron Borate as a Highly Efficient Single-Component Heterogeneous Photo-Fenton Catalyst under Simulated Solar Irradiation

The development of a heterogeneous catalyst for use in environmental remediation remains a challenging and attractive research endeavor. Specifically, for Fenton reactions, most research approaches have focused on the preparation of iron-containing heterostructures as photo-Fenton catalysts that utilize visible light for enhancing the degradation efficiency. Herein, the synthesis and novel application of C,N-doped iron borates are demonstrated as single-component heterogeneous photo-Fenton catalysts with high Fenton activity under visible light. Under the optimal conditions, 10 mg of the catalyst is shown to achieve effective degradation of 10 ppm methylene blue (MB) dye, Rhodamine B (RhB) dye, and tetracycline (TC) under simulated solar irradiation with a first-order rate constant of k = 0.218 min^-1, 0.177 min^-1, and 0.116 min^-1, respectively. Using MB as a model system, the C,N-doped iron borate exhibits 10- and 26-fold increases in catalytic activity relative to that of the 50 nm hematite nanoparticles and that of the non-doped iron borate, respectively, in the presence of H₂O₂ under the simulated solar irradiation. Furthermore, the optimum reaction conditions used only 320 equivalents of H₂O₂ with respect to the concentration of dye, rather than the several thousand equivalents of H₂O₂ used in conventional heterogeneous Fenton catalysts. In addition, the as-prepared C,N-doped iron borate achieves 75% MB degradation after 20 min in the dark, thus enabling the continuous degradation of pollutants at night and in areas with poor light exposure. The stability and recyclability of C,N-doped iron borate for the oxidation of MB was demonstrated over three cycles with insignificant loss in photo-Fenton activity. The high Fenton activity of the C,N-doped iron borate is considered to be due to the synergistic action between the negatively-charged borate ligands and the metal center in promoting the Fenton reaction. Moreover, carbon and nitrogen doping are shown to be critical in modifying the electronic structure and increasing the conductivity of the catalyst. In view of its synthetic simplicity, high efficiency, low cost of reagents, and minimal cost of operation (driven by natural sunlight), the as-prepared heterogeneous single-component metal borate catalyst has potential application in the industrial treatment of wastewater.

A review on percarbonate-based advanced oxidation processes for remediation of organic compounds in water

Sodium percarbonate (SPC) is considered a potential alternative to liquid hydrogen peroxide (H₂O₂) in organic compounds contaminated water/soil remediation due to its regularly, transportable, economical, and eco-friendly features. The solid state of SPC makes it more suitable to remediate actual soil and water with a milder H₂O₂ release rate. Apart from its good oxidative capacity, alkaline SPC can simultaneously remediate acidized solution and soil to the neutral condition. Conventionally, percarbonate-based advanced oxidation process (P-AOPs) system proceed through the catalysis under ultraviolet ray, transition metal ions (i.e., Fe²⁺, Fe³⁺, and V⁴⁺), and nanoscale zero-valent metals (iron, zinc, copper, and nickel). The hydroxyl radical (^•OH), superoxide radical (^•O₂^-), and carbonate radical anion (^•CO₃^-) generated from sodium percarbonate could attack the organic pollutant structure. In this review, we present the advances of P-AOPs in heterogeneous and homogeneous catalytic processes through a wide range of activation methods. This review aims to give an overview of the catalysis and application of P-AOPs for emerging contaminants degradation and act as a guideline of the field advances. Various activation methods of percarbonate are summarized, and the influence factors in the solution matrix such as pH, anions, and cations are thoroughly discussed. Moreover, this review helps to clarify the advantages and shortcomings of P-AOPs in current scientific progress and guide the future practical direction of P-AOPs in sustainable carbon catalysis and green chemistry.

High-efficiency degradation of p-arsanilic acid and arsenic immobilization with iron encapsulated B/N-doped carbon nanotubes at natural solution pH

p-arsanilic acid (p-ASA) is still widely applied as feed additive in many countries. Accompanied with chemical reactions in the environment, p-ASA will release more toxic inorganic arsenic. In order to safely and efficiently treat p-ASA flow washing into the environment, iron encapsulated B/N-doped carbon nanotubes (Fe@C-NB) were fabricated and used as the catalyst for the degradation of p-ASA. The calcination temperature and the dose of the iron salt have significant effects on the structure and properties of the catalysts. We have produced a series of catalysts of the same type to facilitate the degradation of p-ASA. Under optimal conditions of material (Fe@C-NB) syntheses, both 95% degradation of p-ASA and 86% total arsenic immobilization can be obtained with oxidant (Peroxymonosulfate, PMS) and catalyst (Fe@C-NB) treatment after 60 min. The effects of oxidant types (peroxydisulfate (PDS), PMS, hydrogen peroxide (H₂O₂)), amount, initial solution pH, inorganic anion, and other reaction conditions were studied in the p-ASA removal. In this Fenton-like reaction, the Fe@C-NB exhibits high efficiency and excellent stability without complex preparation methods; besides, the advantages of short reaction time and natural reaction conditions in Fe@C-NB/PMS system will promote the practical application of Fenton-like.

Carbon coating enhances single-electron oxygen reduction reaction on nZVI surface for oxidative degradation of nitrobenzene

Research on the in-situ generation of hydrogen peroxide (H₂O₂) using nano zero-valent iron (nZVI) has received more and more attention in recent years. However, the low utilization rate of nZVI, strict production conditions, and high energy consumption limit the application of this technology in actual environmental pollution remediation. In this study, carbon-coated nZVI (Fe⁰@C) was used to synthesize H₂O₂ in situ and realize the mineralization of nitrobenzene (NB). The results showed that the composite removed 91% of NB through adsorption, reduction, and oxidation within 120 min, of which oxidation accounts for 42.92%. Not only that, the composite material could achieve effective mineralization of NB under the wide pH range of 3-7. Quantitative experiments of hydroxyl radicals (HO) showed that the composite could generate 185.64 μM HO in 120 min without any extra energy consumption. The carbon-coated structure effectively inhibits the formation of the passivation layer on the surface of the nZVI, thereby ensuring the high activity of the Fe⁰. In addition, the carbon coating strengthens the sequential single-electron transfer process by changing the oxygen reduction pathway on the surface of the nZVI, so that the Fe⁰ can efficiently generate HO through the superoxide radical (O₂^-) pathway under neutral conditions. This study provides a fundamental understanding of the in-situ synthesis of H₂O₂ to mineralize NB by carbon-coated nZVI.

Clinoptilolite mediated activation of peroxymonosulfate through spherical dispersion and oriented array of NiFe2O4: Upgrading synergy and performance

Inspired by the features of both transition metal oxide and natural clinoptilolite (flaky structure with suitable pore diameter and open skeleton structure), we adopted a robust strategy by immobilization of nickel ferrite nanoparticles (NiFe₂O₄) on the clinoptilolite surface via typical citric acid combustion method. The hybrid catalyst exhibited enhanced peroxymonosulfate (PMS) activation efficiency and bisphenol A (BPA) degradation performance. Calculated by effective equivalent of NiFe₂O₄, it is found that the reaction rate constant (k) of NiFe₂O₄/clinoptilolite/PMS system (0.1859 min^-1) was 11.9 times higher than that of bare NiFe₂O₄/PMS system (0.0156 min^-1), which demonstrated that catalyst would be conjugated to PMS or contaminant efficiently and renders the rapid degradation and mineralization in the presence of clinoptilolite. After comprehensive characterization analysis and DFT simulations, natural mineral carrier effect (i.e. decreased crystalline size, increased oxygen vacancy content, etc.), abundant surface-bonded and structural hydroxyl groups as well as effective bonding with iron or nickel ions charged for the potential activation mechanism of PMS by NiFe₂O₄/clinoptilolite composite. And it is indicated that not only ^•OH and SO₄^•-, but also ¹O₂ was involved into series reactions. Overall, this study put forward a green and promising technology for high-toxic wastewater treatment.

Manganese ferrite modified biochar from vinasse for enhanced adsorption of levofloxacin: Effects and mechanisms

The primitive biochar (BC) and NiFe₂O₄/biochar composites (NFBC), biological adsorbents prepared from vinasse wastes, possess the environmental application in levofloxacin (LEV) removal. In this study, the efficient adsorption of LEV onto biochar synthesized by pyrolysis of vinasse wastes from aqueous environment was investigated. The influencing factors (i.e., pH, reaction time, and temperature) of adsorption process were also well studied. The results indicated that the maximum adsorption capacities of both BC and NFBC were occurred in mildly acidic condition (pH 6). In addition, the biochar adsorption capacities were obviously increased in higher temperature (25-45 °C). The chemistry adsorption and monolayer homogeneous dominated adsorption process of LEV onto BC and NFBC. The adsorption process was spontaneous and endothermic by thermodynamic analysis. The SEDA (site energy distribution analysis) explained that the adsorption effectivity increased by increasing site energy of biochar surface. The SEDA revealed the more energy heterogeneity in NFBC, fitting the characterization result of Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electron-donor-acceptor (EDA) interactions and hydrogen bonds is suggested as the major adsorption mechanism. And as for the adsorption of the various biowaste recycled synthetic, this study can be referred in discussion of performance analysis and optimal condition.

Current progress in degradation and removal methods of polybrominated diphenyl ethers from water and soil: A review

The widespread of polybrominated diphenyl ethers (PBDEs) in the environment has caused rising concerns, and it is an urgent endeavor to find a proper way for PBDEs remediation. Various techniques such as adsorption, hydrothermal and thermal treatment, photolysis, photocatalytic degradation, reductive debromination, advanced oxidation processes (AOPs) and biological degradation have been developed for PBDEs decontamination. A comprehensive review of different PBDEs remediation techniques is urgently needed. This work focused on the environmental source and occurrence of PBDEs, their removal and degradation methods from water and soil, and prospects for PBDEs remediation techniques. According to the up-to-date literature obtained from Web of Science, it could be concluded that (i) photocatalysis and photocatalytic degradation is the most widely reported method for PBDEs remediation, (ii) BDE-47 and BDE-209 are the most investigated PBDE congeners, (iii) considering the recalcitrance nature of PBDEs and more toxic intermediates could be generated because of incomplete degradation, the combination of different techniques is the most potential solution for PBDEs removal, (iv) further researches about the development of novel and effective PBDEs remediation techniques are still needed. This review provides the latest knowledge on PBDEs remediation techniques, as well as future research needs according to the up-to-date literature.

γ-ray induced formation of oxygen vacancies and Ti3+ defects in anatase TiO2 for efficient photocatalytic organic pollutant degradation

Oxygen vacancies and Ti³⁺ defects in anatase TiO₂ have attracted great attention to address the insufficient optical absorption and photoinduced charge-carrier separation in photocatalysis. In this study, we demonstrate a superficial and innovative approach for synthesizing anatase TiO₂ nanoparticles with abundant oxygen vacancies via γ-ray irradiation reduction at room temperature. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) confirm that oxygen vacancies and Ti³⁺ defects can be quantitatively and extensively obtained by merely regulating the irradiation dosage. Photoelectrochemical measurements suggest that oxygen vacancies and Ti³⁺ defects promoted the separation of electron-hole pairs and then enhanced the photocatalytic degradation performance for organic pollutant. In comparison with TiO₂ (no irradiation), the sample (49.5 kGy irradiation) exhibited a 20.0-fold enhancement in visible-light decomposition of phenol. In addition, the results of scavenge experiments and mechanism analysis revealed that O₂^- are the dominant active species. The excited electrons generated at the conduction band and oxygen vacancy level of TiO_2-x-49.5 conspicuously contributes to generate much more ·O₂^- species. This novel study shows at room temperature, the γ-ray approach of irradiation leads to faster formation and quantification of oxygen vacancies in the semiconductor materials.

Simultaneous degradation of p-arsanilic acid and inorganic arsenic removal using M-rGO/PS Fenton-like system under neutral conditions

In this study, magnetic material based reduced graphene oxide (M-rGO) was prepared through co-precipitation and displayed high catalytic efficiency together with persulfate (PS) for simultaneous p-arsanilic acid (p-ASA) decomposition and arsenic removal. Linear sweep voltammetry and chronoamperometric measurements with M-rGO revealed that PS was effectively bound to M-rGO surface and probably formed charge transfer complex, in which M-rGO was pivotal in mediating facile electron transfer. The effects of pH, temperatures, anions, p-ASA concentration, PS, and M-rGO dosages on p-ASA decomposition were studied in the system. Excellent degradation of p-ASA was carried out at a wide range of pH values, which was unattainable by other Fenton-like processes. Under optimal conditions, M-rGO exhibited prominent removal of both p-ASA (98.8 %) and inorganic arsenic (89.8 %). M-rGO had reasonably excellent repeatability and stability, and 77.7 % p-ASA degraded in the third recovered catalyst. The advantages of environmental friendliness, short reaction time, and straightforward synthesis of M-rGO will facilitate the development of heterogeneous Fenton-like catalysts under neutral conditions.

Iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon as an efficient peroxymonosulfate activator to degrade 1-naphthol

A novel iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon (Fe-N-S-MPC) was proposed by one-pot pyrolysis strategy to activate peroxymonosulfate (PMS) to degrade 1-naphthol using low-cost lignin as precursors. The Fe-N-S-MPC was characterized for structure and properties by different characterizations. The obtained materials had the morphology of iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon with rich functional groups and large specific surface area, which made the materials have a good catalytic property. It was proved that the doping of nitrogen and sulfur is pivotal for improving the catalytic performance. The radical quenching experiment confirmed that sulfate radical (SO₄^-) and hydroxyl radical (OH) are two major reactive oxygen groups. The reaction had phenomenon of the free radicals upsurge in the early stage and the shortage in the later stage. Therefore, a mathematical model was put forward to represent the two-stage reaction kinetics. By adding oxidants in batches, the degradation effect could reach nearly 100% within 30 min. The Fe-N-S-MPC were applied to the degradation of 1-naphthol in soil and showed high degradation performance. This work provided a new type of catalytic material by the high-value utilization of waste for the degradation of organic pollutants.

Defective, oxygen-functionalized multi-walled carbon nanotubes as an efficient peroxymonosulfate activator for degradation of organic pollutants

Herein, the defects and surface oxygen functionalities of multi-walled carbon nanotubes (MWCNTs) derived from a solid state reaction are demonstrated to be effective in the activation of peroxymonosulfate (PMS) for organic pollutant degradation. The catalytic activity of defective, oxygen-functionalized CNTs (dCNTs) is much better than bare CNTs, which stems from many active sites on the CNT surface, including structural defects and carbonyl functional groups, and excellent electrical conductivity. Furthermore, the effect of several operational factors and water conditions on the degradation rate of the targeted pollutant and material stability are comprehensively evaluated for the practical application of the dCNT/PMS-coupled process. The underlying catalytic mechanism in dCNTs is expected to take place via nonradical pathway and radical-induced oxidation where surface-bound radicals play a more dominant role than free radicals. The defect and oxygen functional group tuning strategy provides an effective methodology for the development of advanced carbon catalysts in Fenton-like reactions.

Development of 3-dimensional Co3O4 catalysts with various morphologies for activation of Oxone to degrade 5-sulfosalicylic acid in water

Since 5-sulfosalicylic acid (SFA) has been increasingly released to the environment, SO₄^--based oxidation processes using Oxone have been considered as useful methods to eliminate SFA. As Co₃O₄ has been a promising material for OX activation, the four 3D Co₃O₄ catalysts with distinct morphologies, including Co₃O₄-C (with cubes), Co₃O₄-P (with plates), Co₃O₄-N (with needles) and Co₃O₄-F (with floral structures), are fabricated for activating OX to degrade SFA. In particular, Co₃O₄-F not only exhibits the highest surface area but also possesses the abundant Co²⁺ and more reactive surface, making Co₃O₄-F the most advantageous 3D Co₃O₄ catalyst for OX activation to degrade SFA. The mechanism of SFA by this 3D Co₃O₄/OX is also investigated and the corresponding SFA degradation pathway has been elucidated. The catalytic activities of Co₃O₄ catalysts can be correlated to physical and chemical properties which were associated with particular morphologies to provide insights into design of 3D Co₃O₄-based catalysts for OX-based technology to degrade emerging contaminants, such as SFA.

Nitrogen-doped porous carbon encapsulating iron nanoparticles for enhanced sulfathiazole removal via peroxymonosulfate activation

Developing novel catalyst with both high efficiency and stability presents an enticing prospect for peroxymonosulfate (PMS) activation. In this paper, nitrogen-doped porous carbon encapsulating iron nanoparticles (CN-Fe) was fabricated by a facile carbothermal reduction process using polyaniline (PANI) and α-Fe₂O₃ as the precursors. The stubborn antibiotics, sulfathiazole (STZ), was employed as a target pollutant, demonstrating that CN-Fe coupled with PMS could achieve 96% removal efficiency and even 57% mineralization rate of STZ within 40 min. More importantly, the rate constant of CN-Fe was calculated to be 0.07665 min^-1, which was 6 times higher than that of the commercial α-Fe₂O₃ catalyst. Furthermore, CN-Fe also presented a favorable catalytic performance for removing other organic pollutants including phenolic compounds and organic dyes. Interestingly, the catalytic activity of the used CN-Fe catalyst could be regenerated after thermal treatment (600 °C) and the as-synthesized CN-Fe catalyst exhibited excellent long-term stability with almost no loss of activity after storage for three months. The catalytic mechanism in the CN-Fe/PMS system was elucidated by electron paramagnetic resonance (EPR), linear sweep voltammetry (LSV), radical and electron trapping tests, which confirmed that sulfate radicals (SO₄^-), hydroxyl radicals (OH), superoxide radicals (O₂^-) and singlet oxygen (¹O₂) were generated in the oxidation process with the assistance of electron transfer between PMS and catalyst. To our knowledge, this was the first attempt for the application of PANI-derived CN-Fe hybrid materials as PMS activators and the findings would provide a simple and promising strategy to fabricate highly efficient and environment-benign catalysts for wastewater remediation.

Sustainable Catalytic Processes Driven by Graphene-Based Materials

In the recent two decades, graphene-based materials have achieved great successes in catalytic processes towards sustainable production of chemicals, fuels and protection of the environment. In graphene, the carbon atoms are packed into a well-defined sp2-hybridized honeycomb lattice, and can be further constructed into other dimensional allotropes such as fullerene, carbon nanotubes, and aerogels. Graphene-based materials possess appealing optical, thermal, and electronic properties, and the graphitic structure is resistant to extreme conditions. Therefore, the green nature and robust framework make the graphene-based materials highly favourable for chemical reactions. More importantly, the open structure of graphene affords a platform to host a diversity of functional groups, dopants, and structural defects, which have been demonstrated to play crucial roles in catalytic processes. In this perspective, we introduced the potential active sites of graphene in green catalysis and showcased the marriage of metal-free carbon materials in chemical synthesis, catalytic oxidation, and environmental remediation. Future research directions are also highlighted in mechanistic investigation and applications of graphene-based materials in other promising catalytic systems.

Removal mechanism of mitoxantrone by a green synthesized hybrid reduced graphene oxide @ iron nanoparticles

Anti-tumor drugs, due to their non-specific toxicity will cause long-term delayed toxicity to organisms and humans when discharged into the environment. In this study, reduced graphene oxide @ iron nanoparticles (rGO@Fe NPs) were successfully prepared using green tea extract as reductant and subsequently used for mitoxantrone (MTX) removal. SEM and Raman spectroscopy showed that 30-60 nm sized Fe NPs were loaded on rGO and green tea extract successfully reduced GO to rGO. The removal efficiency of MTX by the hybrid material was higher (98.5%) than either rGO (77.5%) or Fe NPs (53.1%) alone. In addition, the removal efficiency of MTX by the hybrid material was as high as 95% within 5 min, MTX adsorption followed both a pseudo-second-order kinetic model and the Langmuir isotherm, and it is a spontaneous adsorption. Recycling experiments showed that the removal efficiency of MTX decreased from 99.9 to 76.8% after six cycles, and could be as high as 99% in both municipal and medical wastewater. Scanning electron microscopy (SEM), Fourier transform infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and High performance liquid chromatography (HPLC) were all used to characterize and analyze the hybrid material, and possible adsorption mechanisms which revealed that MTX adsorption probably involved a combination of π-π stacking interaction, hydrogen bonding, electrostatic interaction and pore-filling.

Prussian Blue Analogue-derived co/fe bimetallic nanoparticles immobilized on S/N-doped carbon sheet as a magnetic heterogeneous catalyst for activating peroxymonosulfate in water

While Co is the most effective metal for activating PMS, extensive efforts are made to develop Co/Fe species (CF) (e.g., CoFe₂O₄) for imparting magnetic properties and facilitating recovery of catalysts. When carbon substrates are doped with heteroatoms (e.g., S and N) and CF is embedded within the heteroatom-doped carbon matrix, synergies can occur to boost catalytic activities. This study proposes an alternative CF-bearing carbonaceous composite, a cobalt-containing Prussian Blue Analogue (PBA) (Co₃[Fe(CN)₆]₂) is employed as a precursor for preparing CF species embedded in N-doped carbon matrix and immobilized on S/N-co-doped carbon (SNC). Specifically, PBA in-situ grows on SNC by a heat treatment of trithiocyanuric acid to form PBA@SNC, which is then carbonized into CF species@SNC (CF@SNC). By adopting Amaranth degradation as a model reaction, CF@SNC shows a higher catalytic activity (k_app = 0.230 min^-1) than CF (k_app = 0.152 min^-1) and SNC (k_app = 0.016 min^-1) for activating PMS. In comparison with Co₃O₄, CF@SNC exhibits a higher catalytic activity for PMS activation. CF@SNC renders a relatively low E_a value (53 kJ/mol) for Amaranth degradation in comparison to other reported catalysts. These comparisons demonstrate the advantageous features of CF@SNC as a magnetic and efficient catalyst for PMS activation.

Activation of persulfate by stability-enhanced magnetic graphene oxide for the removal of 2,4-dichlorophenol

A stability-enhanced magnetic catalyst, composed of α-Fe₂O₃@Fe₃O₄ shell-core magnetic nanoparticles and graphene oxide (MGO), was prepared and characterized by scanning electron micrope (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). Catalyst synthesis was used to efficiently activate persulfate for the removal of 2,4-dichlorophenol (2,4-DCP). A magnetic nanoparticle:GO mass ratio of 5 (MGO-5) exhibited a better catalytic efficiency and could be effectively reused four times. The influences of the pollutant, catalyst, and oxidant concentrations were investigated, and the intrinsic relationships among these factors and the degradation kinetic constant were evaluated by a fitting method. It was found that the catalytic degradation process in the MGO-5-persulfate-2,4-DCP system was most likely dominated by an interfacial catalytic reaction, with an activation energy of 13.88 kJ/mol. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis indicated that both sulfate radicals (SO₄^-) and hydroxyl radicals (OH) were responsible for 2,4-DCP removal, but surface-bounded SO₄^- played a greater role. Chloride ions at a concentration of 0-60 mg/L had no effect on 2,4-DCP removal. The proposed advanced oxidation technology has potential applications for the practical removal of aqueous organic pollutants.

Synergistic oxidation of Bisphenol A in a heterogeneous ultrasound-enhanced sludge biochar catalyst/persulfate process: Reactivity and mechanism

Recently, clean-up of resistant organic compounds has attracted growing attention. In this study, a novel heterogeneous ultrasound-enhanced sludge biochar catalyst/persulfate (BC/PS/US) process was firstly developed for the degradation of bisphenol A (BPA) in water. The results revealed that BC/PS/US process could successfully achieve a positively synergistic effect between sonochemistry and catalytic chemistry on the degradation of BPA compared to its corresponding comparative process. Nearly 98% of BPA could be degraded within 80 min at optimum reaction conditions. The coexisting substances including Cl^-, SO₄^2- and NO₃^- had no obvious inhibition on the BPA degradation, whereas HCO₃^- and humic acid (HA) had significant inhibition effects on that. PS decomposition of BC/PS/US process was superior to that of BC/PS or US/PS process. Both SO₄^- and HO participated in the degradation of BPA, but SO₄^- was predominant radical in the BC/PS/US process. A possible pathway of BPA degradation was proposed, and the BPA molecule was attacked by SO₄^- and degraded into five kinds of intermediate products through hydroxylation and demethylation processes. This study helps to comprehend the application of sludge biochar catalyst as a persulfate activator for the degradation of organic compounds under ultrasound irradiation, and provides a new strategy in wastewater treatment.

Bismuth impregnated biochar for efficient estrone degradation: The synergistic effect between biochar and Bi/Bi2O3 for a high photocatalytic performance

An innovative advanced oxidation process was successfully developed to photocatalytic-degradation of estrone through the synergistic effect of biochar and Bi/Bi₂O₃ in bismuth-containing photocatalytic biochar (BiPB). The highest reaction rate constant (k_obs) of estrone degradation by BiPB was 0.045 min^-1 under the conditions of initial concentration of estrone =10.4 μmol L^-1, [BiPB] =1 g L^-1, pH = 7.0. The k_obs was almost tenfold and more than 20 times than that of biochar without bismuth impregnation and pristine Bi/Bi₂O₃, respectively. The best photocatalytic performance of BiPB composites for the degradation of estrone was primarily attributed to generation of OH radicals. Impregnation of bismuth helped control the concentration of persistent free radicals (PFRs) and develop a hierarchical porous structure of biochar. The presence of biochar facilitated pre-concentration estrone on BiPB and improved the separation and transfer efficiency of charge carriers. The synergistic effect between biochar and Bi/Bi₂O₃ contributed to the generation of OH radicals for estrone degradation under neutral pH conditions. The transformation pathway of estrone was also proposed based on the measured transformation products in the presence of BiPB. The high efficiency of BiPB composites indicated that this easily-obtained material was promising for estrone-wastewater treatment applications as a low-cost composite photocatalyst.

Biochar-supported nanoscale zero-valent iron as an efficient catalyst for organic degradation in groundwater

High-efficiency and cost-effective catalysts are critical to completely mineralization of organic contaminants for in-situ groundwater remediation via advanced oxidation processes (AOPs). The engineered biochar is a promising method for waste biomass utilization and sustainable remediation. This study engineers maize stalk (S)- and maize cob (C)-derived biochars (i.e., SB300, SB600, CB300, and CB600, respectively) with oxygen-containing functional groups as a carbon-based support for nanoscale zero-valent iron (nZVI). Morphological and physiochemical characterization showed that nZVI could be impregnated within the framework of the synthesized Fe-CB600 composite, which exhibited the largest surface area, pore volume, iron loading capacity, and Fe⁰ proportion. Superior degradation efficiency (100% removal in 20 min) of trichloroethylene (TCE, 0.1 mM) and fast pseudo-first-order kinetics (k_obs =22.0 h^-1) were achieved via peroxymonosulfate (PMS, 5 mM) activation by the Fe-CB600 (1 g L^-1) under groundwater condition (bicarbonate buffer solution at pH = 8.2). Superoxide radical and singlet oxygen mediated by Fe⁰ and oxygen-containing group (i.e., CO) were demonstrated as the major reactive oxygen species (ROSs) responsible for TCE dechlorination. The effectiveness and mechanism of the Fe/C composites for rectifying organic-contaminated groundwater were depicted in this study.

Antimicrobial efficacy and mechanisms of silver nanoparticles against Phanerochaete chrysosporium in the presence of common electrolytes and humic acid

In this study, influences of cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺), anions (NO₃^-, Cl^-, and SO₄^2-), and humic acid (HA) on the antimicrobial efficacy of silver nanoparticles (AgNPs)/Ag⁺ against Phanerochaete chrysosporium were investigated by observing cell viability and total Ag uptake. K⁺ enhanced the antimicrobial toxicity of AgNPs on P. chrysosporium, while divalent cations decreased the toxicity considerably, with preference of Ca²⁺ over Mg²⁺. Impact caused by a combination of monovalent and divalent electrolytes was mainly controlled by divalent cations. Compared to AgNPs, however, Ag⁺ with the same total Ag content exhibited stronger antimicrobial efficacy towards P. chrysosporium, regardless of the type of electrolytes. Furthermore, HA addition induced greater microbial activity under AgNP stress, possibly originating from stronger affinity of AgNPs over Ag⁺ to organic matters. The obtained results suggested that antimicrobial efficacy of AgNPs was closely related to water chemistry: addition of divalent electrolytes and HA reduced the opportunities directly for AgNP contact and interaction with cells through formation of aggregates, complexes, and surface coatings, leading to significant toxicity reduction; however, in monovalent electrolytes, the dominating mode of action of AgNPs could be toxic effects of the released Ag⁺ on microorganisms due to nanoparticle dissolution.

Synergistic construction of green tea biochar supported nZVI for immobilization of lead in soil: A mechanistic investigation

Biochar-based nanocomposites with functional materials provide an excellent prospect in reactivity and stability. Most biochar reported have no reusability upon aging and offer the risk of release of immobilized components after short-term immobilization. To overcome this, we developed nano zero-valent iron (nZVI) impregnated magnetic green tea biochar (nZVI@GTBC) and studied its performance in immobilizing Pb and long-term effectiveness in the soil. The reactive nZVI units were obtained from iron oxide solution by reducing with polyphenol solution (green tea extract) and were successively stabilized by impregnation onto the remaining green tea waste matrix through co-precipitation technique. Finally, the magnetic biochar was developed from the above nZVI impregnated green tea waste through oven drying and slow pyrolysis technique in different temperature range (150-650 °C). The synthesized nZVI@GTBC biochar was characterized and studied by XRD, FTIR, Raman, UV-Vis, TG/DSC, XPS, SEM, and TEM. The nZVI@GTBC obtained with a particle size of 130 nm and surface charge of +2.8 C/m² at 450 °C. Moreover, colloidal stability and mobility experiments were considered to explain the transport behavior and stability of bare nZVI and magnetic nZVI@GTBC in the soil. The immobilization of Pb by pristine nZVI, GTBC, and nZVI@GTBC was compared and explained under different soil pH conditions. The bioavailability of Pb content before and after immobilization was investigated through leaching experiments. Further, thirty days of soil incubation were carried out to examine different species of Pb according to the Tessier sequential extraction scheme. The study suggested that nZVI@GTBC enhanced the immobilization efficiency by 19.38% in comparison with pristine nZVI and 57.14% in comparison with bare GTBC biochar.

A simple, cost-effective and selective analysis of glucose via electrochemical impedance sensing based on copper and nitrogen co-doped carbon quantum dots

Cu,N co-doped CQDs were prepared and employed as electrode modification materials for improving the efficiency of electron transfer. The Cu and N co-doped CQDs exhibited high electrocatalytic activity for glucose sensing in alkaline medium.

Mn-based catalysts for sulfate radical-based advanced oxidation processes: A review

Sulfate radical-based advanced oxidation processes (AOPs) have drawn increasing attention during the past two decades, and Mn-based materials have been proven to be effective catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS) to degrade many contaminants. This article presents a comprehensive review of various Mn-based materials to activate PMS and PDS. The activation mechanisms of different Mn-based catalysts (i.e., Mn oxides MnO_x, MnO_x hybrids, and MnO_x‑carbonaceous material composites) were first summarized and discussed in detail. Besides the commonly reported free radicals (SO₄^-• and ^•OH), non-radical mechanisms such as singlet oxygen and direct electron transfer have also been discovered for selected materials. The effects of pH, inorganic ions, natural organic matter (NOM), dissolved oxygen content, temperature, and the crystallinity of the materials on the catalytic reactivity were also discussed. Then, important instrumentations and technologies employed to characterize Mn-based materials and to understand the reaction mechanisms were concisely summarized. Three common overlooks in the experimental designs for examining the PMS/PDS-MnO_x systems were also discussed. Finally, future research directions were suggested to further improve the technology and to provide a guidance to develop cost-effective Mn-based materials to activate PMS/PDS.