Superoxide radical mediated Mn(III) formation is the key process in the activation of peroxymonosulfate (PMS) by Mn-incorporated bacterial-derived biochar

A facile method for preparing the CeMnO3 catalyst with high activity and stability of toluene oxidation: The critical role of small crystal size and Mn3+-Ov-Ce4+ sites

Volatile organic compounds (VOCs) cause severe environmental pollution and are potentially toxic to humans who have no defense against exposure. Catalytic oxidation of these compounds has thus become an interesting research topic. In this study, microcrystalline CeMnO3 catalysts were prepared by a precipitant-concentration-induced strategy and evaluated for the catalytic oxidation of toluene/benzene. The effect of crystal size on catalytic performance was confirmed by XRD, TEM, N2 adsorption-desorption, XPS, Raman, H2-TPR, and TPSR. The CeMnO3 catalyst with more Mn3+-Ov-Ce4+ active sites exhibited enhanced VOCs catalytic oxidation performance, lowest active energy, and highest turnover frequency, which was attributed to its larger surface area, lower crystal size, higher low-temperature reducibility, and presence of more oxygen defects. In-situ FTIR results suggested more oxygen vacancies can profoundly promote the conversion of benzoate to maleate species, the rate-determining step of toluene oxidation. The work provides a convenient and efficient strategy to prepare single-metal or multi-metal oxide catalysts with smaller crystal sizes for VOC oxidation or other oxidation reactions.

Role of biochar in superoxide-dominated dye degradation in catalyst-activated peroxymonosulphate process

In recent times, the application of biochar (BC) as an upcoming catalyst for the elimination of recalcitrant pollutants has been widely explored. Here, an iron loaded bamboo biochar activated peroxymonosulphate (PMS) process was tested for removing Congo red (CR) dye from water medium. The catalyst was synthesized using a green synthesis method using neem extracts and characterized using SEM, FTIR, and XRD. The effects of various operating parameters, including solution pH, catalyst dosage, and pollutant dosage, on dye degradation efficiency were examined. The results showed that at the optimized conditions of 300 mg L-1 PMS concentration, 200 mg L-1 catalyst dosage, and pH 6, about 89.7% of CR dye (initial concentration 10 ppm) was removed at 60 min of operation. Scavenging experiments revealed the significant contribution of O2•-, •OH, and 1O2 for dye degradation, with a major contribution of O2•-. The activation of PMS was mainly done by biochar rather than iron (loaded on biochar). The catalyst was highly active even after four cycles.

Mechanical insights into desulfurization by peroxymonosulfate oxidation via a non-reactive oxygen species pathway

Air pollution by sulfur dioxide (SO2) remains a pressing concern for both the environment and human health. Desulfurization enhanced by persulfate based advanced oxidation processes (PS-AOPs) has been proven to be a feasible method. However, the inherent contradiction between the rapid diffusion mass transfer of SO2 in the "gas-liquid-gas" phase and the limited lifespan of reactive oxygen species (ROS) can not be ignored. Excessive investment in PS is required to sustainably generate ROS to achieve continuous desulfurization performance, which may lead to excessive PS consumption. To address this issue, whether PS can achieve the oxidation absorption of SO2 via a non-reactive oxygen species pathway was investigated. Experimental and computational results demonstrated that peroxymonosulfate (PMS) instead of peroxydisulfate (PDS) had a great SO2 removal performance, the utilization of PS could be effectively achieved by maintaining a 1:1 molar ratio of PMS and removed SO2. The presence of HOO bonds in the PMS introduced a partial positive charge to the oxygen atom, making the PMS polar and more susceptible to be attacked by the nucleophile HSO3-. So SO2 underwent a series of processes including dissolution, dissociation, one-oxygen atom transfer, and ionization before ultimately being converted into SO42- ions, effectively achieving its removal from flue gas. This study may presents a novel approach for achieving high-efficiency flue gas desulfurization.

Characteristics of biological manganese oxides produced by manganese-oxidizing bacteria H38 and its removal mechanism of oxytetracycline

Oxytetracycline (OTC) is widely used in clinical medicine and animal husbandry. Residual OTC can affect the normal life activities of microorganisms, animals, and plants and affect human health. Microbial remediation has become a research hotspot in the environmental field. Manganese oxidizing bacteria (MnOB) exist in nature, and the biological manganese oxides (BMO) produced by them have the characteristics of high efficiency, low cost, and environmental friendliness. However, the effect and mechanism of BMO in removing OTC are still unclear. In this study, Bacillus thuringiensis strain H38 of MnOB was obtained, and the conditions for its BMO production were optimized. The optimal conditions were determined as follows: optimal temperature = 35 °C, optimal pH = 7.5, optimal Mn(Ⅱ) initial concentration = 10 mmol/L. The results show that BMO are irregular or massive, mainly containing MnCO3, Mn2O3, and MnO2, with rich functional groups and chemical bonds. They have the characteristics of small particle size and large specific surface area. OTC (2.5 mg/L) was removed when the BMO dosage was 75 μmol/L and the solution pH was 5.0. The removal ratio was close to 100 % after 12 h of culture at 35 °C and 150 r/min. BMO can adsorb and catalyze the oxidation of OTC and can produce ·O2-, ·OH, 1O2, and Mn(Ⅲ) intermediate. Fifteen products and degradation pathways were identified, and the toxicity of most intermediates is reduced compared to OTC. The removal mechanism was preliminarily clarified. The results of this study are convenient for the practical application of BMO in OTC pollution in water and for solving the harm caused by antibiotic pollution.

Peroxymonosulfate activation by CuMn-LDH for the degradation of bisphenol A: Effect, mechanism, and pathway

The remediation of water contaminated with bisphenol A (BPA) has gained significant attention. In this study, a hydrothermal composite activator of Cu3Mn-LDH containing coexisting phases of cupric nitrate (Cu(NO3)2) and manganous nitrate (Mn(NO3)2) was synthesized. Advanced oxidation processes were employed as an effective approach for BPA degradation, utilizing Cu3Mn-LDH as the catalyst to activate peroxymonosulfate (PMS). The synthesis of the Cu3Mn-LDH material was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). According to the characterization data and screening experiments, Cu3Mn-LDH was selected as the best experimental material. Cu3Mn-LDH exhibits remarkable catalytic ability with PMS, demonstrating good degradation efficiency of BPA under neutral and alkaline conditions. With a PMS dosage of 0.25 g·L-1 and Cu3Mn-LDH dosage of 0.10 g·L-1, 10 mg·L-1 BPA (approximately 17.5 μM) can be completely degraded within 40 min, of which the TOC removal reached 95%. The reactive oxygen species present in the reaction system were analyzed by quenching experiments and EPR. Results showed that sulfate free radicals (SO4•-), hydroxyl free radicals (•OH), superoxide free radicals (•O2-), and nonfree radical mono-oxygen were generated, while mono-oxygen played a key role in degrading BPA. Cu3Mn-LDH exhibits excellent reproducibility, as it can still completely degrade BPA even after four consecutive cycles. The degradation intermediates of BPA were detected by GCMS, and the possible degradation pathways were reasonably predicted. This experiment proposes a nonradical degradation mechanism for BPA and analyzes the degradation pathways. It provides a new perspective for the treatment of organic pollutants in water.

Highly efficient activation of periodate by a manganese-modified biochar to rapidly degrade methylene blue

In this study, the manganese oxide/biochar composites (Mn@BC) were synthesized from Phytolacca acinosa Roxb. The Mn@BC was analyzed via techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). The results show that MnOx is successfully loaded on the surface of BC, and the load of MnOx can increase the number of surface functional groups of BC. X-ray photoelectron spectroscopy (XPS) shows that MnOx loaded on BC mainly exists in three valence forms: Mn(Ⅱ), Mn(Ⅲ), and Mn(Ⅳ). The ability of Mn@BC to activate periodate (PI) was studied by simulating the degradation of methylene blue (MB) dye. The degradation experiment results showed that the MB removal rate by the Mn@BC/PI system reached 97.4% within 30 min. The quenching experiment and electron paramagnetic resonance (EPR) analysis confirmed that Mn@BC can activate PI to produce iodate (IO3•), singlet oxygen (1O2), and hydroxyl radical (•OH), which can degrade MB during the reaction. Response surface methodology (RSM) based on Box-Behnken Design (BBD) was used to determine the interaction between pH, Mn@BC and PI concentration in the Mn@BC/PI system, and the optimum technological parameters were determined. When pH = 5.4, Mn@BC concentration 0.56 mg/L, PI concentration 1.1 mmol/L, MB removal rate can reach 98.05%. The cyclic experiments show that Mn@BC can be reused. After four consecutive runs, the removal rate of MB by the Mn@BC/PI system is still 82%, and the Mn@BC/PI system also shows high performance in treating MB in actual water bodies and degrading other pollutants. This study provides a practical method for degrading dyes in natural sewage.

Peroxymonosulfate activation by Fe-Mn Co-doped biochar for carbamazepine degradation

Antibiotics in aquatic environments present a serious threat to the ecological environment and human health. Activation of carbon-catalyzed persulfate is a prospective approach for oxidizing antibiotics. There is a pressing need for inexpensive carbon catalysts of high quality. In this study, biochar (BC) modified by Fe, Mn and Fe@Mn was employed to activate peroxymonosulfate (PMS) to degrade carbamazepine (CBZ) in water. The surface of Fe@Mn BC had a dense, stalactite-like morphology comprising a square chassis that was elliptical. The catalyst Fe@Mn-BC possessed the optimal degradation effect (99%) on CBZ at 100 min. Electron paramagnetic resonance spectroscopy and the quenching spectrum suggested that ˙O2- and 1O2 contributed to CBZ degradation.

Development of MoS2-stainless steel catalyst by 3D printing for efficient destruction of organics via peroxymonosulfate activation

Herein, a novel MoS2-stainless steel composite material was first synthetized via a 3D printing method (3DP MoS2-SS) for peroxymonosulfate (PMS) activation and organics degradation. Compared with MoS2-SS powder/PMS system (0.37 g/(m2/min)), 4.3-fold higher kFLO/SBET value was obtained in 3DP MoS2-SS/PMS system (1.60 g/(m2/min), resulting from the superior utilization of active sites. We observed that 3DP MoS2-SS significantly outperformed the 3DP SS due to the enhanced electron transfer rate and increased active sites. Moreover, Mo4+ facilitated the Fe2+/Fe3+ cycle, resulting in the rapid degradation of florfenicol (FLO). Quenching experiments and electron paramagnetic resonance spectra indicated that •OH, SO4•-, O2•- and 1O2 were involved in the degradation of FLO. The effect of influencing factors on the degradation of FLO were evaluated, and the optimized degradation efficiency of 98.69% was achieved at 1 mM PMS and pH of 3.0. Six degradation products were detected by UPLC/MS analyses and several possible degradation pathways were proposed to be the cleavage of C-N bonds, dechlorination, hydrolysis, defluorination and hydroxylation. In addition, 3DP MoS2-SS/PMS system also demonstrated superior degradation performance for 2-chlorophenol, acetaminophen, ibuprofen and carbamazepine. This study provided deep insights into the MoS2-SS catalyst prepared by 3DP technology for PMS activation and FLO-polluted water treatment.

Starch of oat derived nanostructured Fe/Mn bimetallic carbon materials for sulfamethoxazole degradation via peroxymonosulfate activation

Fe/Mn bimetallic carbon materials were synthesized by combining oat and urea, followed by and carbonization processes, the activity and mechanism of the obtained materials in activating peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation were determined. Data suggested that the obtained material (CN@FeMn-10-800) showed the optimal performance for SMX degradation under the1:8:0.05:0.05 mass ratios of oat/urea/Fe/Mn. Around 91.2 % SMX (10 mg L-1) was removed under the conditions of 0.15 g L-1 CN@FeMn-10-800 and 0.20 g L-1 PMS. The CN@FeMn-10-800 showed great adaptability under different conditions, satisfactory activation repeatability and versatility. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that core-shell structure with rich porous of CN@FeMn-10-800 was achieved. Quenching test and electron paramagnetic resonance (EPR) indicated that surface bound oxygen and singlet oxygen (1O2) were the dominate reactive groups in this system. X-ray photoelectron spectroscopy (XPS) suggested that graphite N, Fe0, Fe3C and Mn(II) were the dominant active sites. Through the work, a simple strategy could be found to make high-value use of biomass and use it to effectively purified wastewater.

Synchronous decomplexation and mineralization of copper complexes by activating peroxymonosulfate with magnetic bimetallic biochar derived from municipal sludge

Efficient removal of copper complexes is a challenging issue due to their robust stability and solubility. In this study, CoFe2O4-Co0 loaded sludge-derived biochar (MSBC), a magnetic heterogeneous catalyst, was prepared to activate peroxymonosulfate (PMS) for the decomplexation and mineralization of some typical copper complexes (including Cu(Ⅱ)-EDTA, Cu(Ⅱ)-NTA, Cu(Ⅱ)-citrate, and Cu(Ⅱ)-tartrate). The results showed that abundant cobalt ferrite and cobalt nanoparticles were decorated in the plate-like carbonaceous matrix, making it a higher degree of graphitization, better conductivity and more excellent catalytic activity than the raw biochar. Cu(Ⅱ)-EDTA was chosen as the representative copper complex. Under the optimum condition, the decomplexation and mineralization efficiency of Cu(Ⅱ)-EDTA in MSBC/PMS system were 98% and 68% within 20 min, respectively. The mechanistic investigation confirmed that the activation of PMS by MSBC followed both a radical pathway contributed by SO4•- and •OH and a nonradical pathway contributed by 1O2. In addition, the electron transfer pathway between Cu(Ⅱ)-EDTA and PMS facilitated the decomplexation of Cu(Ⅱ)-EDTA. Jointly, CO, Co0, and the redox cycles of Co(Ⅲ)/Co(Ⅱ) and Fe (Ⅲ)/Fe (Ⅱ) were found to play a critical role in the decomplexation process. Overall, the MSBC/PMS system provides a new strategy for efficient decomplexation and mineralization of copper complexes.

Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes

Urbanization and industrialization have exerted significant adverse effects on water quality, resulting in a growing need for reliable and eco-friendly treatment technologies. Persulfate (PS)-based advanced oxidation processes (AOPs) are emerging as viable technologies to treat challenging industrial wastewaters or remediate groundwater impacted by hazardous wastes. While the generated reactive species can degrade a variety of priority organic contaminants through radical and nonradical pathways, there is a lack of systematic and in-depth comparison of these pathways for practical implementation in different treatment scenarios. Our comparative analysis of reaction rate constants for radical vs. nonradical species indicates that radical-based AOPs may achieve high removal efficiency of organic contaminants with relatively short contact time. Nonradical AOPs feature advantages with minimal water matrix interference for complex wastewater treatments. Nonradical species (e.g., singlet oxygen, high-valent metals, and surface activated PS) preferentially react with contaminants bearing electron-donating groups, allowing enhancement of degradation efficiency of known target contaminants. For byproduct formation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimated electrical energy per order of reaction (EE/O) parameter and show significantly higher energy requirements for the nonradical pathways. Overall, these critical comparisons help prioritize basic research on PS-based AOPs and inform the merits and limitations of system-specific applications.

Enhanced mechanism of copper doping in magnetic biochar for peroxymonosulfate activation and sulfamethoxazole degradation

Magnetic biochar is excellent for separation and peroxymonosulfate (PMS) activation. Copper doping could improve the catalytic capability of magnetic biochar significantly. In this study, cow dung biochar is applied to investigate the effects of copper doping on the magnetic biochar, focusing on the specific influence on the consumption of active sites, the production of oxidative species and the toxicity of degradation intermediates. The results showed that copper doping promoted the uniform distribution of iron sites on the biochar surface and reduced iron aggregation. At the same time, copper doping interpreted the biochar with larger specific surface area, which was beneficial to the adsorption and degradation of sulfamethoxazole (SMX). The SMX degradation kinetic constant with copper-doped magnetic biochar was 0.0403 min^-1, which was 1.45 times than that of magnetic biochar. Besides, copper doping might accelerate the consumption of CO, Fe⁰, Fe²⁺ sites and hinder the activation of PMS at copper-related sites. Furthermore, copper doping promoted the PMS activation by magnetic biochar through accelerated electron transfer. For the oxidative species, copper doping accelerated the production of hydroxyl radicals, singlet oxygen, and superoxide radicals in solution and inhibited the generation of sulfate radicals. In addition, SMX could be directly decomposed into less toxic intermediates in the copper-doped magnetic biochar/PMS system. In conclusion, this paper provides insight and analysis of the advantages of copper doping on the magnetic biochar, which helps to facilitate the design and practical application of bimetallic biochar.

Transformation of graphene oxide affects photodegradation of imidacloprid in the aquatic environment: Mechanism and implication

Graphene oxide (GO) is a representative novel carbonaceous nanomaterial, and neonicotinoid insecticides (NEOs) are currently the insecticides with the highest market share in the world. Their widespread application deservedly leads to their release to the environment. Thus, the complex interactions of these two types of organic compounds have attracted extensive attention. In this study, the effects of GO and its derivatives, reduced GO (RGO) and oxidized GO (OGO), on the photolysis of imidacloprid (IMD) (a typical NEO) under ultraviolet (UV) irradiation were systematically investigated. The results showed that the presence of the graphene-based nanomaterials (GNs) largely depressed the photodegradation of IMD, and the inhibition degree followed the order of RGO > GO > OGO. This was because the sp² π-conjugated structure in the GNs caused light-shielding effect and attenuated the direct photolysis of IMD, even though the GNs-generated reactive oxygen species (ROS) promoted the indirect photodegradation of IMD to a certain extent. Additionally, the rich O-functionalized GO and OGO altered the photolysis pathway of IMD and induced more toxic intermediate products. These results highlight the implication of carbonaceous nanomaterials on the behavior, fate and potential risk of NEOs in aqueous systems.

The debatable role of singlet oxygen in persulfate-based advanced oxidation processes

Singlet oxygen (¹O₂) attracts much attention in persulfate-based advanced oxidation processes (PS-AOPs), because of its wide pH tolerance and high selectivity toward electron-rich organics. However, there are conflicts about the ¹O₂ role in PS-AOPs on several aspects, including the formation of different key reactive oxygen species (ROS) at similar active sites, pH dependence, broad-spectrum activity, and selectivity in the elimination of organic pollutants. To a large degree, these conflicts root in the drawbacks of the methods to identify and evaluate the role of ¹O₂. For example, the quenchers of ¹O₂ have high reactivity to other ROS and persulfate as well. In addition, electron transfer process (ETP) also selectively oxidizes organics, having a misleading effect on the identification of ¹O₂. Therefore, in this review, we summarized and discussed some basic properties of ¹O₂, the debatable role of ¹O₂ in PS-AOPs on multiple aspects, and the methods and their drawbacks to identify and evaluate the role of ¹O₂. On the whole, this review aims to better understand the role of ¹O₂ in PS-AOPs and further help with its reasonable utilization.

Effective degradation of 2,4,4'-trichlorodiphenyl by Fe3C@Fe-800 activated peroxymonosulfate: Superoxide radical and singlet oxygen-dominated advanced oxidation process

Polychlorinated biphenyls (PCBs) degradation by peroxymonosulfate (PMS) activation through •OH and SO₄^•- radical oxidation process was the effective technology in the last decades; however, there were few research focusing on removing PCBs by O₂^•- and ¹O₂ induced by PMS activation. In this work, 90.86% of 2,4,4-trichlorodiphenyl (PCB 28) was degraded by 0.3 g/L Fe₃C@Fe-800 activated 0.5 mM PMS system under the synergistic action of O₂^•- and ¹O₂. The structures of Fe₃C@Fe-800 were identified by Scanning electron microscope (SEM), High resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), Raman spectra and Fourier transform infrared (FT-IR) spectra. Electron paramagnetic resonance (EPR) measurements and quenching tests verified that O₂^•- and ¹O₂ were the primary reactive species in Fe₃C@Fe-800/PMS/PCB 28 ternary reaction system. Density functional theory (DFT), Linear sweep voltammetry (LSV), and chronoamperometry test revealed that electron-deficient Fe atoms on Fe₃C were the main active sites in Fe₃C@Fe-800 for PMS activation to generate ¹O₂. Unlike the reported •OH and SO₄^•- mediated degradation induced by the iron-based catalyst, both O₂^•- and ¹O₂ contributed to PCB 28 degradation： nucleophilic dichlorination reaction by O₂^•- and then ring-open oxidation process by ¹O₂. Fe₃C@Fe-800/PMS system had excellent catalytic performance under different reaction conditions and possessed desirable inorganic salt and natural organic matter resistance. This work elucidated the important role of Fe₃C in PMS activation to generate O₂^•- and ¹O₂ for PCB 28 decontamination by nonradical way and provided a clue to design rationally catalysts in polychlorinated biphenyl pollution remediation.

Fast degradation of macro alkanes through activating indigenous bacteria using biosurfactants produced by Burkholderia sp

Soil bacteria that produce biosurfactants can use total petroleum hydrocarbons (TPHs) as a carbon source. This study demonstrated that biosurfactants produced by Burkholderia sp. enhanced the recovery and synergism of soil microbial community, resulting in fast degradation of macro alkanes. Experiments were carried out by applying bio-stimulation after pre-oxidation to investigate the effects of nutrient addition on biosurfactant production, TPH degradation, and microbial community succession in the soil. The results presented that bio-stimulation could produce biosurfactants in high C/N (32.6) and C/H (13.3) conversion after pre-oxidation and increased the total removal rate of TPH (10.59-46.71%). The number of total bacteria had a rapid increase trend (2.94-8.50 Log CFU/g soil). The degradation rates of macro alkanes showed a 4.0-fold (48.07 mg/kg·d^-1 versus 186.48 mg/kg·d^-1) increase, and the bioremediation time of degrading macro alkanes saved 166 days. Further characterization revealed that the biosurfactants produced by Burkholderia sp. could activate indigenous bacteria to degrade macro alkanes rapidly. A shift in phylum from Actinomycetes to Proteobacteria was observed during bioremediation. The average relative abundance of the microbial community increased from 36.24 to 64.96%, and the predominant genus tended to convert from Allorhizobium (8.57%) to Burkholderia (15.95%) and Bacillus (15.70%). The co-occurrence network and Pearson correlation analysis suggested that the synergism of microbial community was the main reason for the fast degradation of macro alkanes in petroleum-contaminated soils. Overall, this study indicated the potential of the biosurfactants to activate and enhance the recovery of indigenous bacteria after pre-oxidation, which was an effective method to remediate petroleum-contaminated soils.

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)-Oxo Species

Four-nitrogen-coordinated transitional metal (MN₄) configurations in single-atom catalysts (SACs) are broadly recognized as the most efficient active sites in peroxymonosulfate (PMS)-based advanced oxidation processes. However, SACs with a coordination number higher than four are rarely explored, which represents a fundamental missed opportunity for coordination chemistry to boost PMS activation and degradation of recalcitrant organic pollutants. We experimentally and theoretically demonstrate here that five-nitrogen-coordinated Mn (MnN₅) sites more effectively activate PMS than MnN₄ sites, by facilitating the cleavage of the O-O bond into high-valent Mn(IV)-oxo species with nearly 100% selectivity. The high activity of MnN₅ was discerned to be due to the formation of higher-spin-state N₅Mn(IV)═O species, which enable efficient two-electron transfer from organics to Mn sites through a lower-energy-barrier pathway. Overall, this work demonstrates the importance of high coordination numbers in SACs for efficient PMS activation and informs the design of next-generation environmental catalysts.

Hydrothermal synthesis of sewage sludge biochar for activation of persulfate for antibiotic removal: Efficiency, stability and mechanism

The use of biochar materials as catalysts to activate persulfate (PS) for the degradation of antibiotics has attracted much attention. In this study, a carbonaceous material (Cu/Zn-SBC) was prepared from sewage sludge by hydrothermal modification. The efficiency of PS activation by Cu/Zn-SBC was investigated using tetracycline (TC) as the model antibiotic. In the Cu/Zn-SBC + PS system, the TC removal rate reached 90.13% at 10 min and exceeded 99% within 4 h. This not only met the requirement of removing large amounts of pollutants in a short time but also achieved the complete removal of pollutants in the subsequent time. Additionally, the Cu/Zn-SBC + PS system was found to be dominated by radical and nonradical pathways. Cu, hydroxyl and carboxyl groups on the surface of Cu/Zn-SBC promoted the production of free radicals and non-free radicals. Under several changes in reaction conditions and water environment factors, the TC removal rate remained above 85% within 10 min. Furthermore, the removal rate of TC was still 85.79% when Cu/Zn-SBC combined with PS was reused twice and 77.14% when reused four times. This study provides an ideal solution for the treatment of sewage sludge, and offers a stable and efficient material for removing antibiotics from wastewater.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Single atom Mn anchored on N-doped porous carbon derived from spirulina for catalyzed peroxymonosulfate to degradation of emerging organic pollutants

Highly efficient single atom catalysts are critical to substantially promote for peroxymonosulfate (PMS) activation to organic pollutant degradation, but it remains a challenge at present. Herein, single atom Mn anchored on N-doped porous carbon (SA-Mn-NSC) was synthesized by ball milling of Mn-doped carbon nitride and spirulina biochar to dominantly activate PMS. The precursor of carbon nitride and spirulina possessed a strong coordinating capability for Mn(II), facilitating the formation of highly dispersed nitrogen-coordinated Mn sites (Mn-N₄). The SA-Mn-NSC catalyst exhibited high activity and stability in the heterogeneous activation of PMS to degrade a wide range of pollutants within 10 min, showing an outstanding degradation rate constant of 0.31 min^-1 in enrofloxacin (ENR) degradation. The high surface density of Mn-N₄ sites and abundant interconnected meso-macro pores were highly favorable for activating PMS to produce ¹O₂ and high-valent manganese (Mn(IV)) for pollutant degradation. This work offers a new pathway of using a low-cost and easily accessible single-atom catalysts (SACs) and could inspire more catalytic oxidation strategies.

Cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts as peroxymonosulfate activator for rapid removal of chloramphenicol

Chloramphenicol (CAP) is a typical kind of antibiotics, which has posed a severe threat to nature and human beings due to its wide application. In this study, cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts (Co-Bi@CCB) was prepared to activate peroxymonosulfate (PMS) for the removal of CAP. Our results demonstrated Co-Bi@CCB not only possessed excellent catalytic performance, but also significantly limited metal ions dissolution. Over 98% of CAP (10 mg/L) was degraded in the presence of Co-Bi@CCB (0.05 g/L) and PMS (1 mM) within 20 min at pH = 7. Quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that SO₄^•-, ^•OH, and ¹O₂ led to the rapid decomposition of CAP. Combined with X-ray photoelectron spectroscopy (XPS) of Co-Bi@CCB before and after reaction, the mechanism of PMS activation was deduced. Finally, the possible pathways of CAP degradation was further speculated according to the intermediates determination by high-performance liquid chromatography equipped with high resolution mass spectrometer (HPLC-HRMS). Thus, the present study provides a new strategy to utilize discarded cigarette butts (recycled materials) as a carrier to fabricate novel and efficient catalysts to activate PMS for the removal of organic contaminants.

Efficient electro-catalyzed PMS activation on a Fe-ZIF-8 based BTNAs/Ti anode: An in-depth investigation on anodic catalytic behavior

Phenanthrene (PHE), mainly released from coal tar and petroleum distillation, is an important kind of prevalent polycyclic aromatic hydrocarbons (PAHs) contamination in China (up to 2.38 ± 0.02 mg/kg in soil and 8668 ng/L in surface water) and other countries in the world. Metal-organic frameworks (MOFs) show promising application prospects in the decontamination field, however, suffering from the intrinsic fragility and fine powder forms. Therefore, macroscopic MOFs architecture-sandwich-like Fe-ZIF-8/blue TiO₂ nanotube arrays (BTNAs)/Ti substrate (FBTT) anode with strong interfacial bonding (Fe-O-Ti and Fe-2-MIM-Ti coordination) was constructed using innovative in situ growth, condensation-crystallization-deposition, and pyrolysis methods, aiming at exploring the feasibility of MOFs-based anode/peroxymonosulfate (PMS) mediated PHE elimination, revealing the in-depth mechanisms, simultaneously overcoming the intrinsic drawbacks of MOFs. The FBTT-4 (doping content of 30 %) efficiently degraded PHE by 90.01 % and 74.5 % within 10 min at 350 μg/L and 3 mg/L, respectively, mediated by the ^·OH compared to the SO₄^·-, ¹O₂, and O₂^·-. Post-optimized range of anodic potential enabled (i) anodic oxidation, (ii) activation of water and PMS molecules to produce active species, (iii) capture of electrons in reactants to reduce Fe³⁺/Ti⁴⁺ to Fe²⁺/Ti³⁺, maintaining the proportion of Fe/Ti with low valence and thus stable PMS activation capacity, and (iv) regulation of the Fe/Ti d-band center to modulate the anode adsorption capacity. The further increment in anodic potential could promote "dark photocatalysis" with a Z-scheme-like mechanism. Thus, it is proposed that the development of macroscopic MOFs-based anode, especially those with small band gaps, represents vast potentials in electrocatalytic contamination elimination. Simultaneously, the MOFs-based anode is expected to fully exploit their catalytic capacities and solve their intrinsic defects as well.

Manganese removal and product characteristics of a marine manganese-oxidizing bacterium Bacillus sp. FF-1

Biogenic manganese oxides (BioMnO_x) have been found all over the world, and most of them were formed by Mn(II)-oxidizing bacteria (MnOB). In this study, a MnOB designated as FF-1 was isolated from marine surface sediments in the Bohai Sea, China. This strain was identified as Bacillus sp. and can tolerate more than 5% salinity. It can grow in the presence of 0-7 mM Mn(II) and pH range from 5.0 to 7.0. When the initial Mn(II) was 5 mM, the percentage of Mn(II) oxidation reached the highest value of 16% after 10 days of incubation. The initial pH (5.0 to 7.0) affected the percentage of Mn(II) oxidation, but the ability of the strain FF-1 to self-regulate pH resulted in the final pH being almost 7.6. The removal of Mn(II) by the strain FF-1 involves extracellular and intracellular adsorption as well as Mn(II) oxidation. Intracellular Mn adsorption contributed a small part to the total Mn removal, and extracellular adsorption was dominant in the initial stage of Mn removal. The solid products after Mn removal were a mixture of MnO_x and MnCO₃. The layered MnO_x formed in the extracellular space could be easily collected and used for adsorption and oxidation of pollutants.