Efficient degradation of sulfamethazine in simulated and real wastewater at slightly basic pH values using Co-SAM-SCS /H2O2 Fenton-like system

Co-catalysis strategy for low-oxidant-consumption Fenton-like chemistry: From theoretical understandings to practical applications and future guiding strategies

Recently, great effects have been made for the co-catalysis strategy to solve the bottlenecks of Fenton system. A series of co-catalysis strategies using various inorganic metal co-catalysts and organic co-catalysts have been developed in various oxidant (i.e., hydrogen peroxide (H2O2) and persulfate) systems with significantly promotion of catalytic performances and lower oxidant consumption (only 5-10 % of conventional Fenton/Fenton-like systems). However, the developments of these co-catalysis strategies from theoretical understandings to practical applications and future guiding strategies were overlooked, which was an essential problem that must be considered for the future scale-up applications of co-catalysis systems. In this paper, these co-catalysis strategies with low-oxidant-consumption characteristics have been reviewed by the comparison of their co-catalysis mechanisms, as well as their advantages and disadvantages. We also discussed the recent developments of amplifying devices based on the co-catalysis systems. The scale-up performances of co-catalysis strategies based on these amplifying devices have also been assessed. In addition, future guiding strategies for the development of co-catalysis strategy with low-oxidant-consumption characteristics have also been first time outlined by the combination of the technical-economic analysis (TEA), life cycle assessment (LCA) and machine learning (ML). Finally, the paper systematically discusses the development opportunities, technical bottlenecks and future development directions of co-catalysis strategies with the prospect of large-scale applications. Basically, this work provides a systematic review on co-catalysis strategy with low-oxidant-consumption characteristic from theoretical understandings to practical applications and future guiding strategies.

A comprehensive review of Co3O4 nanostructures in cancer: Synthesis, characterization, reactive oxygen species mechanisms, and therapeutic applications

Nanotechnology involves creating, analyzing, and using tiny materials. Cobalt oxide nanoparticles (Co3O4 NPs) have several medicinal uses due to their unique antifungal, antibacterial, antioxidant, anticancer, larvicidal, anticholinergic, antileishmanial, wound healing, and antidiabetic capabilities. Cobalt oxide nanoparticles (Co3O4 NPs) with attractive magnetic properties have found widespread use in biomedical applications, including magnetic resonance imaging, magnetic hyperthermia, and magnetic targeting. The high surface area of Co3O4 leads to unique electrical, optical, catalytic, and magnetic properties, which make it a promising candidate for biomedical bases. Additionally, cobalt nanoparticles with various oxidation states (i.e., Co2+, Co3+, and Co4+) are beneficial in numerous utilizations. Co3O4 nanoparticles as a catalyzer accelerate the conversion rate of hydrogen peroxide (H2O2) to harmful hydroxyl radicals (•OH), which destroy tumor cells. However, it is also possible to enhance the generation of reactive oxygen species (ROS) and successfully treat cancer by combining these nanoparticles with drugs or other nanoparticles. This review summarizes the past concepts and discusses the present state and development of using Co3O4 NPs in cancer treatments by ROS generation. This review emphasizes the advances and current patterns in ROS generation, remediation, and some different cancer treatments using Co3O4 nanoparticles in the human body. It also discusses synthesis techniques, structure, morphological, optical, and magnetic properties of Co3O4 NPs.

Removal of Sb(V) from complex wastewater of Sb(V) and aniline aerofloat using Fe3O4-CeO2 absorbent enhanced by H2O2: Efficiency and mechanism

Effective elimination of heavy metals from complex wastewater is of great significance for industrial wastewater treatment. Herein, bimetallic adsorbent Fe3O4-CeO2 was prepared, and H2O2 was added to enhance Sb(V) adsorption by Fe3O4-CeO2 in complex wastewater of Sb(V) and aniline aerofloat (AAF) for the first time. Fe3O4-CeO2 showed good adsorption performance and could be rapidly separated by external magnetic field. After five adsorption/desorption cycles, Fe3O4-CeO2 still maintained good stability. The maximum adsorption capacities of Fe3O4-CeO2 in single Sb(V), AAF + Sb(V), and H2O2+AAF + Sb(V) systems were 77.33, 70.14, and 80.59 mg/g, respectively. Coexisting AAF inhibited Sb(V) adsorption. Conversely, additional H2O2 promoted Sb(V) removal in AAF + Sb(V) binary system, and made the adsorption capacity of Fe3O4-CeO2 increase by 14.90%. H2O2 could not only accelerate the reaction rate, but also reduce the optimal amount of adsorbent from 2.0 g/L to 1.2 g/L. Meanwhile, coexisting anions had little effect on Sb(V) removal by Fe3O4-CeO2+H2O2 process. The adsorption behaviors of Sb(V) in three systems were better depicted by pseudo-second-order kinetics, implying that the chemisorption was dominant. The complexation of AAF with Sb(V) hindered the adsorption of Sb(V) by Fe3O4-CeO2. The complex Sb(V) was oxidized and decomposed into free state by hydroxyl radicals produced in Fe3O4-CeO2+H2O2 process. Then the free Sb(V) was adsorbed by Fe3O4-CeO2 mostly through outer-sphere complexation. This work provides a new tactic for the treatment of heavy metal-organics complex wastewater.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

A review of metallurgical slags as catalysts in advanced oxidation processes for removal of refractory organic pollutants in wastewater

With the rapid growth of the metallurgical industry, there is a significant increase in the production of metallurgical slags. The waste slags pose significant challenges for their disposal because of complex compositions, low utilization rates, and environmental toxicity. One promising approach is to utilize metallurgical slags as catalysts for treatment of refractory organic pollutants in wastewater through advanced oxidation processes (AOPs), achieving the objective of "treating waste with waste". This work provides a literature review of the source, production, and chemical composition of metallurgical slags, including steel slag, copper slag, electrolytic manganese residue, and red mud. It emphasizes the modification methods of metallurgical slags as catalysts and the application in AOPs for degradation of refractory organic pollutants. The reaction conditions, catalytic performance, and degradation mechanisms of organic pollutants using metallurgical slags are summarized. Studies have proved the feasibility of using metallurgical slags as catalysts for removing various pollutants by AOPs. The catalytic performance was significantly influenced by slags-derived catalysts, catalyst modification, and process factors. Future research should focus on addressing the safety and stability of catalysts, developing green and efficient modification methods, enhancing degradation efficiency, and implementing large-scale treatment of real wastewater. This work offers insights into the resource utilization of metallurgical slags and pollutant degradation in wastewater.

Tri-modified ferric alginate gel with high regenerative properties catalysts for efficient degradation of rhodamine B

Water pollution caused by dyes has become a focal point of attention. Among them, the heterogeneous Fenton reaction has emerged as an effective solution to this problem. In this study, we designed a ferric alginate gel (PAGM) tri-modified with poly(vinyl alcohol), graphene oxide, and MoS2 as a heterogeneous Fenton catalyst for organic dye degradation. PAGM addresses the drawbacks of alginate gel, such as poor mechanical properties and gel chain dissolution, thereby significantly extending the catalyst's lifespan. The removal rate of rhodamine B by PAGM reached 95.5 % within 15 min, which was 5.9 times higher than that of unmodified ferric alginate gel. Furthermore, due to the π-π interactions, PAGM exhibits unique adsorption properties for pollutants containing benzene rings. Additionally, PAGM can be regenerated multiple times through a simple soaking procedure without any performance degradation. Finally, the reaction column constructed with PAGM maintained an 83.5 % removal rate even after 319 h of continuous wastewater treatment. This work introduces a novel concept for the study of alginate-based gel catalysts in heterogeneous Fenton reactions.

Low-cost materials for swine wastewater treatment using adsorption and Fenton's process

Untreated swine wastewater (SW) discharge leads to serious consequences such as water quality decreasing related to eutrophication and proliferation of harmful algae containing cyanotoxins, which can cause acute intoxication in humans. The use of untreated pig farming effluent as fertilizer can lead to the accumulation of polluting compounds. Biological treatments can degrade organic matter but have the disadvantage of requiring large areas and high retention times and demonstrating low efficiencies in the degradation of refractory compounds such as pharmaceutical compounds. In this ambit, the performance of four low-cost materials was evaluated for treatment of a swine wastewater using physical-chemical processes such as adsorption and Fenton's process. The tested materials are two natural resources, red volcanic rock from Canary (RVR) Islands and black volcanic rock (BVR) from Azores, and two industry residues, red mud (RM) and iron filings (IF). Among the tested materials, only IFs are catalytically active for Fenton's peroxidation. Still, RVR, BVR, and RM were efficient adsorbents removing up to 67% of COD. The combination between adsorption followed by Fenton's process using IF as catalyst showed interesting results. When RM is applied as adsorbent in the diluted effluent, it was able to remove 67% and 90% of COD for adsorption and adsorption followed by IF Fenton, respectively. At those conditions, the resultant treated effluent accomplishes the requirements for direct discharge in the natural water courses as well as the parameters for water reusing.

Functional fungal pellets self-immobilized by mycelium fragments of Irpex lacteus WRF-IL for efficient degradation of sulfamethazine as the sole carbon source

In order to achieve an efficient microbial material with dual functions of self-immobilization and sulfamethazine (SMZ) degradation, this study explored the pelletization technique utilizing mycelium fragments of Irpex lacteus WRF-IL and systematically examined the pellets formation conditions and degradation capability. The Box-Behnken design results demonstrated that pure mycelium fragments, broken by frosted glass beads, could be rapidly self-immobilized to form white rot mycelial pellets (WRMPs) within 24 h, serving as the pelleting core. These WRMPs could completely remove SMZ as the sole carbon source within 20 h. The addition of sucrose expedited this process, achieving complete removal within only 14 h. Kinetic analysis showed that WRMPs could potentially remove SMZ at higher concentrations (>25 mg/L). Biodegradation was the primary pathway of SMZ removal. Seven intermediates were identified by QTOF LC/MS, and three transformation pathways initiated by SO₂ overflow, molecular rearrangement, and aniline moiety oxidation were deduced.

Facet Dependence of Biosynthesis of Vivianite from Iron Oxides by Geobacter sulfurreducens

Vivianite plays an important role in alleviating the phosphorus crisis and phosphorus pollution. The dissimilatory iron reduction has been found to trigger the biosynthesis of vivianite in soil environments, but the mechanism behind this remains largely unexplored. Herein, by regulating the crystal surfaces of iron oxides, we explored the influence of different crystal surface structures on the synthesis of vivianite driven by microbial dissimilatory iron reduction. The results showed that different crystal faces significantly affect the reduction and dissolution of iron oxides by microorganisms and the subsequent formation of vivianite. In general, goethite is more easily reduced by Geobacter sulfurreducens than hematite. Compared with Hem_{100} and Goe_L{110}, Hem_{001} and Goe_H{110} have higher initial reduction rates (approximately 2.25 and 1.5 times, respectively) and final Fe(II) content (approximately 1.56 and 1.20 times, respectively). In addition, in the presence of sufficient PO₄^3-, Fe(II) combined to produce phosphorus crystal products. The final phosphorus recoveries of Hem_{001} and Goe_H{110} systems were about 5.2 and 13.6%, which were 1.3 and 1.6 times of those of Hem_{100} and Goe_L{110}, respectively. Material characterization analyses indicated that these phosphorous crystal products are vivianite and that different iron oxide crystal surfaces significantly affected the size of the vivianite crystals. This study demonstrates that different crystal faces can affect the biological reduction dissolution of iron oxides and the secondary biological mineralization process driven by dissimilatory iron reduction.

ZnCo2O4 composite catalyst accelerated removal of phenylic contaminants containing of Cr(VI) in dielectric barrier discharge reactor: Process and mechanism study

The degradation of phenylic contaminants (phenol, hydroquinone, nitrobenzene, p-nitrophenol) containing Cr(VI) has been investigated in a dielectric barrier discharge (DBD) system using a ZnCo₂O₄ composite catalyst. The ZnCo₂O₄ nanowires combined with multi-walled carbon nanotubes (MWNTs) on a sponge substrate in the discharge system can induce a decrease in the corona inception voltage and discharge becomes more stable resulting in an improvement in the energy utilization efficiency. With the synergistic degradation of phenylic species containing Cr(VI), the total elimination efficiency was further improved. The active substances (H₂O₂ and O₃) were detected in the discharged solution, and some of them were consumed in the phenylic system. The effects of ·OH, O₂·^- and e^- were also verified using free radical trapping experiments in which ·OH exhibited the main oxidation effect for the degradation of phenylic pollutants, and e^-, H₂O₂ and H· affect the reduction of Cr(VI). The intermediate products were determined in order to analyze the degradation process of phenylic pollutants by the ZnCo₂O₄ composite catalyst in combination with the DBD system. The electron transfer process in the ZnCo₂O₄ composite catalyst during discharge was analyzed. Finally, the biotoxicity of the phenylic pollutants before and after degradation was compared.

Ceftriaxone sodium degradation by carbon quantum dots (CQDs)-decorated C-doped α-Bi2O3 nanorods

A novel carbon quantum dots decorated C-doped α-Bi₂O₃ photocatalyst (CBO/CQDs) was synthesized by solvothermal method. The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies. The ceftriaxone sodium degradation rate constant (k) of CBO/CQDs was 11.4 and 3.2 times that of pure α-Bi₂O₃ and C-doped α-Bi₂O₃, respectively. The interstitial carbon doping generated localized states above the valence band, which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes; the loading of CQDs improved the charge carrier separation and extended the visible light response; the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers. The •O₂ ^- and h⁺ were identified as the dominant reactive species in ceftriaxone sodium degradation, and the key role of •O₂ ^- was further investigated by NBT transformation experiments. The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack, and intermediates analysis was conducted to explore the possible degradation pathways. The toxicity evaluation revealed that some degradation intermediates possessed high toxicity, thus the contaminants require sufficient mineralization to ensure safe discharge. The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of α-Bi₂O₃, which provides references for future studies.

Constructing tunable coordinatively unsaturated sites in Fe-based metal-organic framework for effective degradation of pharmaceuticals in water: Performance and mechanism

Micropollutants are ubiquitously detected in the aqueous environment, which needs to be removed by novel materials effectively. Herein, we synthesized a photo-Fenton catalyst based on MIL-53 (Fe) to effectively degrade sulfadimidine, one of the micropollutants in water. Abundant Lewis acid active sites (54.26 μmol/g) were successfully constructed within the metal cluster using FeCl₃·6H₂O, 1,4-benzene dicarboxylate, and modulators. This study reports a strategy by effectively constructing tunable Lewis acid active sites within the cavities in MIL-53 (Fe) via a facile solvothermal reaction for sixteen micropollutants removal. The photo-Fenton degradation of sulfamethazine was completely removed (∼99%) within only 1 min with a small amount of hydrogen peroxide added. Both theoretical calculation and the experiment results prove that introducing the unsaturated coordinated/lewis acid sites can remarkably reduce the band gap energy and increase the charge-separation efficiency by changing the electron configuration with more distribution asymmetry of structures. The effective degradation of structurally diverse pharmaceuticals with environmentally relevant concentrations was studied by immobilizing MOF-catalyst into a PVDF support. This work advanced the development of effective approaches for emergency contaminants control.

Application of sludge biochar nanomaterials in Fenton-like processes: Degradation of organic pollutants, sediment remediation, sludge dewatering

In today's society, wastewater sludge has become solid waste, and the preparation of wastewater sludge into sludge biochar nanomaterials (SBCs) for resource utilization has become a promising method. SBCs have advantages over other biomasses, including their complex composition, wide range of raw materials, and especially the presence of various transition metals with catalytic properties. Heterogeneous Fenton processes using SBCs as catalyst carriers have shown great potential in the removal of pollutants. In this review, the synthesis methods of SBCs are reviewed and the effects of different synthesis methods on their physicochemical properties are discussed. Furthermore, the successful applications of raw SBCs, metal-modified SBCs, and Fenton sludge-SBCs in organic pollutant degradation, sediment remediation, and sludge dewatering are reviewed. The mechanisms occurring with different metals as active sites are explored, and the review shows that the degradation efficiency and stability of SBCs are very satisfactory. We also provide an outlook on the future development of SBCs. We hope that this review will help readers gain a clearer and deeper understanding of SBCs and promote the development of SBCs.

The application of transition metal-modified biochar in sulfate radical based advanced oxidation processes

Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) is a very important chemical oxidation technology for the degradation of recalcitrant organic pollutants in water and has been well developed. Recently, transition metals or their oxides-modified biochar has been widely used as the catalyst to catalyze peroxymonosulfate (PMS) and peroxydisulfate (PS) in SR-AOPs due to their outstanding properties (e.g., large surface area, high stability, abound catalytic sites, and diversity of material design, etc.). These composite materials not only combine the respective beneficial characteristics of biochar and transition metals (or their oxides) but also often present synergistic effects between the components. In this review, we present the synthesis of different types of transition metal (or metal oxides)/biochar-based catalysts and their application in SR-AOPs. The catalytic mechanism, including the generation process of free radicals and other reaction pathways on the surface of the catalyst were also carefully discussed. Particular attention has been paid to the synergistic effects between the components that result in enhanced catalytic performance. At the end of this review, the future development prospects of this technology are proposed.

Adsorption Properties of Modified ATP-RGO Composite Aerogel for Removal of Malachite Green and Methyl Orange from Unitary and Binary Aqueous Solutions

In this paper, the modified attapulgite-reduced graphene oxide composite aerogel (ATP-RGO CA) was prepared by sol-gel method using modified attapulgite as silica source. The removal of the cationic dye malachite green (MG) and azo dye methyl orange (MO) onto ATP-RGO CA from unitary and binary systems was investigated. Morphology and microstructure studies of ATP-RGO CA were investigated by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and specific surface area and porosity analysis. Experiments were carried out as a function of pH, contact time, initial dye concentration, and temperature in unitary and binary systems. The adsorption kinetics, isotherms, thermodynamics, and dye desorption were studied in unitary and binary dye systems. The adsorption kinetics was modeled using the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations. The equilibrium adsorption data of MG and MO dyes on ATP-RGO CA were analyzed. Thermodynamic parameters of dye adsorption were obtained. In addition, the regeneration of ATP-RGO CA was studied using dye desorption in unitary and binary dye systems. The adsorption kinetics of the dyes followed pseudo-second-order kinetics. The results indicate that the Langmuir model provides the best correlation of the experimental data. The thermodynamic studies showed that the dye adsorption onto ATP-RGO CA was a spontaneous and endothermic reaction. High desorption of MG and MO showed the regeneration of ATP-RGO CA. It can be concluded that ATP-RGO CA is suitable as an adsorbent material to remove MG and MO dyes from unitary and binary systems.

Recent progress in Fenton/Fenton-like reactions for the removal of antibiotics in aqueous environments

The frequent use of antibiotics allows them to enter aqueous environments via wastewater, and many types of antibiotics accumulate in the environment due to difficult degradation, causing a threat to environmental health. It is crucial to adopt effective technical means to remove antibiotics in aqueous environments. The Fenton reaction, as an effective organic pollution treatment technology, is particularly suitable for the treatment of antibiotics, and at present, it is one of the most promising advanced oxidation technologies. Specifically, rapid Fenton oxidation, which features high removal efficiency, thorough reactions, negligible secondary pollution, etc., has led to many studies on using the Fenton reaction to degrade antibiotics. This paper summarizes recent progress on the removal of antibiotics in aqueous environments by Fenton and Fenton-like reactions. First, the applications of various Fenton and Fenton-like oxidation technologies to the removal of antibiotics are summarized; then, the advantages and disadvantages of these technologies are further summarized. Compared with Fenton oxidation, Fenton-like oxidations exhibit milder reaction conditions, wider application ranges, great reduction in economic costs, and great improved cycle times, in addition to simple and easy recycling of the catalyst. Finally, based on the above analysis, we discuss the potential for the removal of antibiotics under different application scenarios. This review will enable the selection of a suitable Fenton system to treat antibiotics according to practical conditions and will also aid the development of more advanced Fenton technologies for removing antibiotics and other organic pollutants.

Simultaneous recovery of phosphate and degradation of antibiotics by waste sludge-derived biochar

Recovery of phosphorus (P) from wastewater has led to growing public concern considering its scarcity and future availability as well as its detrimental environmental impacts. However, the recovered P is inevitably contaminated with co-existing antibiotics like tetracycline (TC) and sulfamethazine (SMT) which will pose serious risks to the health of human and animals after being spread to the environment. In this study, we propose a novel scheme that can recover P from synthetic wastewater and at the same time degrade the co-existing antibiotics. To achieve such a goal, a series of biochar (BC) were prepared from calcination of waste sludge and were used both as the adsorbent for P recovery and as the catalyst for peroxymonosulfate (PMS) activation and antibiotic degradation. Results showed that the sludge source (i.e. S_m: municipal sludge, S_p: paper mill sludge), calcination atmosphere (i.e. air-deficient, N₂, vacuum) and temperature (i.e. 600 and 800 °C) exhibited significant influence on P adsorption capacity. Generally, the BC calcined in N₂ showed better P uptake, and increase of calcination temperature from 600 °C to 800 °C could further improve P uptake. Though BC_p-N-600 (prepared from S_p in N₂ at 600 °C) showed faster and higher P uptake (56.3 mg/g) than its counterpart BC_m-N-600 (33.2 mg/g), BC_m-N-600 showed stronger catalytic activity and more stable performance in the complex pollutant system (P + SMT). It was proposed that P was recovered primarily through the chemisorption and precipitation mechanism, while SMT was nearly completely degraded primarily by the ROS generated from PMS activation.

Construction of Bi2WO6/CoAl-LDHs S-scheme heterojunction with efficient photo-Fenton-like catalytic performance: Experimental and theoretical studies

The photo-Fenton-like catalytic process has shown great application potential in environmental remediation. Herein, a novel photo-Fenton-like catalyst of Bi₂WO₆ nanosheets decorated hortensia-like CoAl-layered double hydroxides (Bi₂WO₆/CoAl-LDHs) was synthesized via hydrothermal process. The optimized Bi₂WO₆/CoAl-LDHs composite performed the high-efficiency photo-Fenton-like catalytic performance for oxytetracycline (OTC) removal (98.47%) in the mediation of visible-light and H₂O₂. The comparative experiment, technical characterization and density functional theory calculation results indicated that the efficient photo-Fenton-like catalytic performance of Bi₂WO₆/CoAl-LDHs was attributed to the synergistic action of the Fenton-like process of cobalt ions in CoAl-LDHs, an internal electric field and the S-scheme heterojunction form between Bi₂WO₆ and CoAl-LDHs, which could significantly promote the active substance formation and the photocatalytic process in the catalytic system. This study will stimulate the new inspiration of designing the efficient catalytic system for environmental remediation and other fields.

Mechanism for biodegradation of sulfamethazine by Bacillus cereus H38

Degradation of sulfonamides (SAs) by microorganisms has become a focus of current research. Sulfamethazine (SMZ) is a type of SA widely used in the livestock and poultry industry. However, understanding the intermediate products, degradation pathways and mechanism of SMZ biodegradation is limited at present. In this study, a SMZ degrading bacterium Bacillus cereus H38, which can use SMZ as its only carbon source, was isolated from farmland soil. The bacterium was gram-positive with rod-shaped cells. The effects of initial SMZ concentration, pH, temperature and amount of inoculation on the biodegradation of SMZ were investigated by a single factor experiment. The results showed that the maximum degradation rate of SMZ was achieved in the environmental conditions at an initial SMZ concentration of 5 mg/L, pH of 7.0, temperature of 25 °C and inoculation amount of 5%. Under these optimum degradation conditions, strain H38 can completely degrade SMZ within 3 days. The effects of intracellular enzymes, extracellular enzymes and periplasmic enzymes on the SMZ degradation process were compared. It was found that intracellular enzymes contributed the most to the biodegradation of SMZ, and the degradation rate approached 70%. Three possible intermediates were identified by LC-MS/MS, and two degradation pathways were proposed. Whole genome sequencing results showed that the genome size of strain H38 was 5,477,631 bp, including 5599 coding sequences (CDSs), and the GC content was 35.21%. In addition, functional annotation of CDSs was performed to analyze the metabolic pathways of nitrogen and sulfur in strain H38 combining genomics and bioinformatics. This study proposes new insights into the mechanism for biodegradation of SAs and will inform future research.

In-situ constructing nanostructured magnesium ferrite on steel slag for Cr(VI) photoreduction

An innovative method is created for transforming iron-rich RO phase (MgO_0.239FeO_0.761) on steel slag surface into nanostructured Mg_0.04Fe_2.96O₄ layer. The phase change process is investigated, and it is found that salicylic acid modification and alkaline roasting procedures remarkably increase the specific surface area from 0.46 m²/g (raw steel slag) to 69.5 m²/g (Mg_0.04Fe_2.96O₄), and the generation of Mg_0.04Fe_2.96O₄ enhances the absorption of visible light and Cr(VI) conversion with 2-times increasement than raw steel slag. Surface complexation between H₂C₂O₄ ligands and Fe metal moiety on Mg_0.04Fe_2.96O₄ induces the intramolecular electron transfer under visible light irradiation based on a ligand-to-metal charge transfer mechanism, thus resulting in Cr(VI) photoreduction, and the catalytic efficiency is above 90% for Cr(VI) (40 mg/L) under inherent pH= 5.5 conditions. Moreover, recyclability tests based on magnetic separation show that the photoreactivity is closely related to Mg content of Mg_0.04Fe_2.96O₄ layer where Mg leaching occurs and finally generates cubic spinel configuration Fe₃O₄. This work highlights the importance of surface functionalization in post-use phases of steel slag in which surface reactivity and application potential can be greatly altered by chemical exposure history and surface transformations. It also provides valuable references for studying the metastable state mechanism of magnesium ferrite photocatalysts.

Phycoremediation integrated approach for the removal of pharmaceuticals and personal care products from wastewater - A review

Pharmaceuticals and personal care products (PPCPs) are of emerging concerns because of their large usage, persistent nature which promised their continuous disposal into the environment, as these pollutants are stable enough to pass through wastewater treatment plants causing hazardous effects on all the organisms through bioaccumulation, biomagnification, and bioconcentration. The available technologies are not capable of eliminating all the PPCPs along with their degraded products but phycoremediation has the advantage over these technologies by biodegrading the pollutants without developing resistant genes. Even though phycoremediation has many advantages, industries have found difficulty in adapting this technology as a single-stage treatment process. To overcome these drawbacks recent research studies have focused on developing technology that integrated phycoremediation with the commonly employed treatment processes that are in operation for treating the PPCPs effectively. This review paper focuses on such research approaches that focused on integrating phycoremediation with other technologies such as activated sludge process (ASP), advanced oxidation process (AOP), Up-flow anaerobic sludge blanket reactor (UASBR), UV irradiation, and constructed wetland (CW) with the advantages and limitations of each integration processes. Furthermore, augmenting phycoremediation by co-metabolic mechanism with the addition of sodium chloride, sodium acetate, and glucose for the removal of PPCPs has been highlighted in this review paper.

MXene-based designer nanomaterials and their exploitation to mitigate hazardous pollutants from environmental matrices

MXenes are a rapidly expanding and large family of two-dimensional (2D) materials that have recently garnered incredible research interests for diverse applications domains in various industrial sectors. Owing to unique inherent structural and physicochemical characteristics, such as high surface area, biological compatibility, robust electrochemistry, and high hydrophilicity, MXenes are appraised as a prospective avenue for environmental-clean-up technologies to detect and mitigate an array of recalcitrant hazardous contaminants from environmental matrices. MXene-based nanoarchitectures are thought to mitigate inorganic pollutants via interfacial chemical transformation and sorption, while three different mechanisms, including i) surface complexation and sorption (ii) catalytic activation and removal and (iii) radical's generation-based photocatalytic degradation, are involved in the removal of organic contaminants. Considering the application performance of MXenes on the incessant rise to expansion, in this review, we discuss the wide-spectrum applicability of diverse MXenes-based hybrid nanocomposites in environmental remediation. A brief description related to environmental pollutants, structural properties, chemical abilities, and synthesis route of MXenes is delineated at the start. Afterwards, the adsorption and degradative robustness of MXene-based designer nanomaterials for various contaminants including organic dyes, toxic heavy metals, pesticide residues, phenolics, antibiotics, radionuclides, and many others are thoroughly vetted to prove their potentiality in the arena of wastewater purification and remediation. Lastly, challenges and trends in assessing the wide-range applicability and scalability of MXenes are outlined. Seeing encouraging outcomes in plenty of reports, it can be concluded that MXenes-based nanostructures could be considered the next-generation candidates for water sustainability.

Preparation of a Gangue-Based X-type Zeolite Molecular Sieve as a Multiphase Fenton Catalyst and Its Catalytic Performance

In this study, a series of X-type zeolite molecular sieve catalysts, modified with copper (Cu-X), were prepared by an alkali fusion-hydrothermal synthesis using coal gangue from Inner Mongolia. These catalysts were used in the degradation of the methylene blue dye by a Fenton-like reaction. Characterization results showed that Cu is considered to be present in the surface structure of the zeolite in the form of doped Cu ions and metal oxide. It is believed that Cu2+ is the main active site involved in the Fenton reaction. The X-ray photoelectron spectroscopy (XPS) spectra indicated that Cu2+ and Cu+ coexist in the catalysts and participate together in the Fenton reaction. The degradation of methylene blue by the Cu-X catalysts was investigated to determine the optimal catalytic conditions in terms of six aspects: catalyst dosage, initial solution concentration, initial pH of the solution, H2O2 dosage, copper loading, and reaction temperature. The experimental results showed that CX-1.0 had excellent activity and stability for the degradation and decolorization of the methylene blue dye, which could completely degrade the dye within 90 min, and the total organic carbon removal rate reached as high as 97.8%. Electron spin resonance (ESR) and radical capture experiments showed that •OH played a dominant role in the Fenton-like reaction. Combined with XPS, ESR, and catalytic tests, the redox cycle of Cu+/Cu2+ was found to be accelerating the generation of reactive radicals in the Fenton system.

A Review of Modified Steel Slag Application in Catalytic Pyrolysis, Organic Degradation, Electrocatalysis, Photocatalysis, Transesterification and Carbon Capture and Storage

As a by-product of the iron and steel industry, steel slag is rich in catalytically active substances and can therefore be used as a solid catalyst. Many studies have shown that the application potential of steel slag in catalysis is huge, which provides new development space for its application, thereby increasing its additional utilization value. This article primarily reviews the research progress in catalytic fields such as catalytic pyrolysis, organic degradation, electrocatalysis, photocatalysis, transesterification, and carbon capture and storage, as well as the modification methods of steel slag. The catalytic performance of the modified steel slag has been further improved, and it has the meaningful characteristics of high efficiency, cleanliness, and low costs.

Enhanced Fenton-like efficiency by the synergistic effect of oxygen vacancies and organics adsorption on FexOy-d-g-C3N4 with Fe‒N complexation

d-g-C₃N₄-Fe composites was prepared via a self-assembly and calcination process. According to measurements and density functional theory (DFT) computations, the complexation of iron and pyridinic N of g-C₃N₄ (Fe‒N) occurred with Fe(III)-π interaction, causing more oxygen vacancies (OVs) with more electrons in iron oxides. In the catalyst air-saturated suspension, the adsorbed pollutants complexed surface Fe(III) through their hydroxyl group donated electrons to around OVs, reducing the surface Fe(III) to Fe(II) and were destructed by Fe(III)-π interaction of the complexation. The addition of H₂O₂ mainly acted as acceptor being reduced ^•OH at the OV centers, causing higher degradation rate of pollutants due to both ^•OH and the surface reaction. However, for the adsorbed hydrophobic pollutants onto the sites of peripheral structure in g-C₃N₄, H₂O₂ was mainly decomposed into O₂ by the synergistic effect of iron species and OVs. Therefore, the catalyst exhibited high Fenton-like efficiency for the degradation of hydroxyl-containing pollutants and hydrophobic pollutants mixing with the former. Our results demonstrate that the Fe(III)-π interaction could carry out the oxidation of pollutants on the catalyst surface, decreasing the consumption of H₂O₂, and the role of OVs depends on pollutant adsorption patterns.

Catalyst-free activation of permanganate under visible light irradiation for sulfamethazine degradation: Experiments and theoretical calculation

In this study, visible light (VL) was adopted for permanganate (PM) activation without additional catalyst, where sulfamethazine (SMT) was selected as the probe compound. Experiment results showed that the VL/PM system can effectively degrade SMT through pseudo-first-order reaction kinetics. Influencing factors including PM dosage, solution pH, humid acid (HA) and coexisting anions (CO₃^2-, SO₄^2-, Cl^- and NO₃^-) which affect SMT photo-degradation were also examined. Pyrophosphate (PP) had an inhibitory effect on SMT degradation due to the complexation of PP with Mn (III). Electron spin resonance (ESR) spectrometry and UV-Vis spectrophotometer proved that VL can activate PM to generate ·O₂^- and Mn (III) reactive species. Furthermore, based on the active site prediction, intermediates identification and Density Functional Theory (DFT) calculation, two main degradation pathways involving SMT molecular rearrangement and cleavage of S-N bond were proposed. Moreover, the energy barriers of the two degradation pathways were also calculated. This study offers a novel approach for aqueous SMT removal and deepens our understanding of the degradation mechanism of SMT through DFT calculation, which hopes to shed light on the future development of VL/PM treatment.

Enhanced Fenton-like degradation of sulfadiazine by single atom iron materials fixed on nitrogen-doped porous carbon

The use of single-atom iron catalysts in heterogeneous Fenton-like reactions has demonstrated tremendous potential for antibiotic wastewater treatment. In this study, single-atom iron fixed on nitrogen-doped porous carbon materials (Fe-ISAs@CN) was synthesised using a metal organic framework (MOF) as a precursor. Fe-ISAs@CN was applied as a heterogeneous Fenton catalyst to activate H₂O₂ for the degradation of sulfadiazine (SDZ) in an aqueous solution. The physical and chemical properties of Fe-ISAs@CN were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disk electrode (RDE) measurements. The results of our degradation experiments indicated that Fe-ISAs@CN exhibited remarkable activity and stability for the degradation of SDZ over a wide pH range; even after five cycles, Fe-ISAs@CN retained a high catalytic efficiency (>80%). The 5,5-dimethyl-1-oxaporphyrin-n-oxide (DMPO)-X signal captured by electron paramagnetic resonance (EPR) spectroscopy indicated that a large amount of hydroxyl radicals (OH) was produced in the reaction system. Quench tests indicated that the OH was the main active substance in the degradation of SDZ. The degradation products of the reaction were analysed by High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS), and possible degradation pathways for the SDZ degradation were proposed.

Faster electron injection and higher interface reactivity in g-C3N4/Fe2O3 nanohybrid for efficient photo-Fenton-like activity toward antibiotics degradation

Two different morphologies of Fe₂O₃ involving nanodots and nanosheets were deposited on g-C₃N₄ nanosheets by simple in-situ deposition and impregnation-hydrothermal methods, respectively. Structural effect of Fe₂O₃ on photo-Fenton-like activity and charge transfer at the interface in these two g-C₃N₄/Fe₂O₃ hybrids were studied. Detail characterizations on charge transfer kinetics revealed that g-C₃N₄/nanodot-Fe₂O₃ structure showed faster electron injection rate and higher injection efficiency (≈0.084 ns^-1 and ≈27.5%) than g-C₃N₄/nanosheet-Fe₂O₃ counterpart (≈0.054 ns^-1 and ≈19.5%). Stronger intimate junction between g-C₃N₄ nanosheets and Fe₂O₃ nanodots was believed to be the reason for faster and more efficient electron injection. In addition, stronger interaction with tetracycline and higher reactivity with H₂O₂ at the interface were observed for g-C₃N₄/nanodot-Fe₂O₃ compared with g-C₃N₄/nanosheet-Fe₂O₃. Thereby, under visible light stimulation, g-C₃N₄/nanodot-Fe₂O₃ demonstrated higher photo-Fenton-like tetracycline removal efficiency and rate (≈87% and ≈0.037 min^-1) than g-C₃N₄/nanosheet-Fe₂O₃ (≈57% and ≈0.016 min^-1). Furthermore, g-C₃N₄/nanodot-Fe₂O₃ junction can remain robust catalytic performance under various conditions (recycle experiment, real environment, different initial pHs and temperatures, anion coexistence, and other contaminants removal) and possible tetracycline degradation pathways were proposed. This study provided deep insights into structure-activity relationship and electron transfer between g-C₃N₄ and nanostructured Fe₂O₃, which can open a new avenge to develop Fe₂O₃-based photo-Fenton catalysts with high efficiencies for antibiotic wastewaters remediation.

Improving the Fenton-like catalytic performance of MnOx-Fe3O4/biochar using reducing agents: A comparative study

In this work, a Fenton-like system with MnO_x-Fe₃O₄/biochar composite (FeMn/biochar) and reducing agents (RAs) was constructed for pollutant degradation, aiming to enhance Fenton-like performance from both degradation efficacy and operational cost aspects. Batch experiments revealed that five well-characterized RAs (sodium borohydride (SBH), sodium thiosulfate (STS), ascorbic acid (AA), hydroxylamine (HA) and oxalic acid (OA)) could impact performance of FeMn/biochar-H₂O₂ system through multiple mechanisms, including variation of solution pH, competition for H₂O₂, electrostatic attraction and acceleration of metal redox cycle. Significantly, only OA and HA obviously enhanced the catalytic capacity of Fenton-like process and HA increased ciprofloxacin degradation efficiency from 38.2% to 92.8% with a low economic consumption as 4.16 US$/m³, well in agreement with the accelerated Fe(III/II) cycle and Mn(III/II) cycle in FeMn/biochar-H₂O₂-HA system. The accelerated metal redox cycle could enhance the decomposition of H₂O₂ into •OH and •O₂^-, which were verified to be the main reactive oxygen species responsible for ciprofloxacin degradation by radical trapping experiments. Meanwhile, FeMn/biochar-H₂O₂-HA system could also work effectively in real wastewaters, and exhibited favorable catalytic performance towards oxytetracycline, tetracycline, methyl orange, methylene blue, Rhodamine B, and naphthalene, indicating the applicability of FeMn/biochar-H₂O₂-HA system in oxidizing refractory pollutants in wastewaters.

Enhanced degradation of sulfamethoxazole by a novel Fenton-like system with significantly reduced consumption of H2O2 activated by g-C3N4/MgO composite

Advanced oxidation processes (AOP) based on nonradicals have attracted growing attentions because nonradical systems require much less oxidants and have low susceptibility to radical scavengers. Herein, a novel Fenton-like system that utilizes nonradicals was explored. It was derived from g-C₃N₄/MgO activated H₂O₂, and can reduce the H₂O₂ stoichiometry from 0.94%-0.18% to 0.03%. Sulfamethoxazole (SMX), a widely used sulfonamide, was used as the model pollutant to evaluate the efficacy of the system. It was observed for the first time that organic pollutants can be degraded with singlet oxygen (¹O₂) through a nonradical pathway in the g-C₃N₄/MgOH₂O₂ system. The reduced H₂O₂ consumption was the net result of continuously-recycled H₂O₂ from the reactions between H₂O₂ and g-C₃N₄/MgO. Based on experimental results and theoretical calculations, the synthesis of g-C₃N₄ and MgO forms a N-Mg bond with strong ability to absorb electrons and the electron transfer of H₂O₂ to N-Mg bonding is accelerated, activation of H₂O₂ to generate ¹O₂. Experimental data showed that organic pollutants can be degraded rapidly over a wide pH range. Findings of this study point to a cyclical but stable Fenton-like system with reduced H₂O₂ requirement for cost-effective remediation and treatment of organic pollutants and toxic wastes.

Interfacial sites in platinum-hydroxide-cobalt hybrid nanostructures for promoting CO oxidation activity

Metal-oxide/hydroxide hybrid nanostructures provide an excellent platform to study the interfacial effects on tailoring the catalysis of metal catalysts. Herein, a hybrid nanostructure of Pt@Co(OH)2 supported on SiO2 was synthesized by incipient wetness impregnation of Co(OH)2 with the aid of H2O2 and successive urea-assisted deposition-precipitation of platinum nanoparticles. The Fenton-like reaction between Co2+ and H2O2 during the impregnation process facilitates the formation of active interfacial sites. This hybrid nanostructure exhibits much higher catalytic activity towards CO oxidation than Pt/SiO2 nanoparticles with a similar Pt loading and particle size. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to track the CO adsorption processes and to identify the reaction intermediates during CO oxidation. It shows that the OH species at the Pt-OH-Co interfacial sites could readily react with CO adsorbed on neighboring Pt to yield CO2 by forming *COOH intermediates and oxygen vacancies. Under the CO + O2 oxidation conditions, O2 molecules are activated by the oxygen vacancy and react with the CO molecules adsorbed on Pt to generate CO2, via forming the highly active *OOH intermediates as observed by DRIFTS.