Degradation of anthraquinone dye reactive blue 19 using persulfate activated with Fe/Mn modified biochar: Radical/non-radical mechanisms and fixed-bed reactor study

Complexing agent-assisted Cr(VI) removal in a continuous fixed-bed system with nanoscale Fe0/NaA molecular sieve membrane supported on nickel foam

Complexing agents (CAs) can be used for the removal of Cr(VI) via nanoscale Fe0 (nZVI) reduction in cost-effective manner. However, nZVI is prone to aggregation and passivation, and some conventional CAs are toxic and difficult to biodegrade, potentially causing secondary pollution. Therefore, selecting an environmentally friendly CA for assisting in the removal of Cr(VI) via supported nZVI is imperative. Herein, NaA molecular sieve membrane-supported nZVI (nZVI/NaA-NF) was prepared via the secondary growth and liquid-phase reduction method using nickel foam (NF) as the carrier. The physicochemical characteristics of nZVI/NaA-NF before and after reaction were analysed via SEM, EDS, and XPS. A CA-improved nZVI/NaA-NF was used for the effective removal of Cr(VI) in a continuous fixed-bed system. Furthermore, the influences of various experimental factors including the CA type, CA concentration, solution pH, space velocity, and inlet Cr(VI) concentration on Cr(VI) removal were systematically investigated. The results demonstrated that nZVI particles were homogeneously immobilized on the NaA molecular sieve membrane/NF for fresh nZVI/NaA-NF, and tetrasodium iminidisuccinate (IDS-4Na) inhibited the aggregation of Cr(III)/Fe(III) (hydr)oxide precipitates during the reaction. IDS-4Na demonstrated excellent promotive effect on Cr(VI) removal via nZVI/NaA-NF. The breakthrough time for Cr(VI) in the addition of IDS-4Na was considerably longer than that of nZVI/NaA-NF alone. The breakthrough concentration of Cr(VI) only reached 1.1% and 9.9% of the inlet concentration at 220 and 240 min, with an IDS-4Na concentration of 4 mM, a pH of 2.5, and a space velocity of 0.265 min-1. The Bohart-Adams model was appropriate to predict the initial part of Cr(VI) breakthrough curves in the nZVI/NaA-NF fixed bed. The saturated concentration (N0) increased with an increase in inlet Cr(VI) concentration. The Yoon-Nelson model afforded good fitting results for all breakthrough curves of Cr(VI). The k´ value increased with an increase in space velocity, and the τ value decreased.

Chemical inertness conversion of carbon fraction in coal gangue via N-doping for efficient benzo(a)pyrene degradation

Efficient degradation of organic pollutants in complex media via advanced oxidation processes (AOPs) is still critical and challenging. Herein, nitrogen (N)-doped coal gangue (CG) catalysts (N-CG) with economic competitiveness and environmental friendliness were successfully synthesized to activate peroxymonosulfate (PMS), exhibiting ultrafast degradation performance toward benzo(a)pyrene (BaP) with 100.00 % and 93.21 % in contaminated solution and soil under optimized condition, respectively. In addition, 0.4 N-CG possessed excellent reusability toward BaP degradation with over 80.00 % after five cycles. However, BaP removal efficiency was significantly affected by some co-existing anions (HCO3- and SO42-) and humic acid (HA) in solution and soil, as well as inhibited under alkaline conditions, especially pH ≥ 9. According to the characterizations, N-doping could promote the generation of pyridinic N and graphitic N in N-CG via high-temperature calcination, which was conducive to produce hydroxyl radical (•OH), sulfate radical (SO4•-), superoxide radical (•O2-) and single oxygen (1O2). In 0.4 N-CG/PMS system, 1O2 and •O2- were proved to be the predominant reactive oxygen species (ROSs) in BaP degradation, as well as •OH and SO4•- made certain contributions. To sum up, this work provided a promising strategy for synthesis of CG-based catalysts by chemical inertness conversion of carbon fracture via N-doping for PMS activation and opened a novel perspective for environmental remediation of hydrophobic and hydrophilic contaminants pollution.

Application of novel magnetic lignin hydrogels: Activated persulfate degrades pesticide contaminants

Lignin hydrogels have garnered significant attention due to their distinctive three-dimensional structures and potent swelling ability. In this work, a novel magnetic nanocomposite lignin hydrogel (MNLH) was fabricated through organic synthesis and solution immersion reduction. The obtained MNLH was used to activate persulfate(PDS) for pesticide degradation. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure and morphology of MNLH. The influence of factors such as the lignin hydrogel to nano-zero-valent iron (nZVI) and copper oxide (CuO) mass ratio, MNLH dosage, initial pH on the MNLH/PDS/imidacloprid (IMI) system. Remarkably, the MNLH/PDS/IMI system has a removal rate of up to 100%. Quenching and electron paramagnetic resonance (EPR) studies disclosed that the MNLH/PDS system degraded IMI through a combination of free radical and non-free radical pathways, with the latter being dominant. More importantly, in this study, the toxicity and hydrolysis sites of IMI were analyzed using ECOSAR and Gaussian09, respectively, confirming the feasibility of activating persulfate with MNLH. These findings underscore the potential of MNLH as a function material suitable for facilitating the persulfate-activated degradation of organic pollutants.

Synthesis of iron-manganese bimetallic materials supported by activated carbon and application of activated persulfate in the degradation of soil contaminated by crude oil

Heterogeneous catalytic processes based on zero-valent iron (ZVI) have been developed to treat soil and wastewater pollutants. However, the agglomeration of ZVI reduces its ability to activate persulfate (PS). In this study, a new Fe-Mn@AC activated material was prepared to activated PS to treat oil-contaminated soil, and using the microscopic characterization of Fe-Mn@AC materials, the electron transfer mode during the Fe-Mn@AC activation of PS was clarified. Firstly, the petroluem degradation rate was optimized. When the PS addition amount was 8%, Fe-Mn@AC addition amount was 3% and the water to soil ratio was 3:1, the petroluem degradation rate in the soil reached to the maximum of 85.69% after 96 h of reaction. Then it was illustrated that sulfate and hydroxyl radicals played major roles in crude oil degradation, while singlet oxygen contributed slightly. Finally, the indigenous microbial community structures remaining after restoring the Fe-Mn@AC/PS systems were analyzed. The proportion of petroleum degrading bacteria in soil increased by 23% after oxidation by Fe-Mn@AC/PS system. Similarly, the germination rate of wheat seeds revealed that soil toxicity was greatly reduced after applying the Fe-Mn@AC/PS system. After the treatment with Fe-Mn@AC/PS system, the germination rate, root length and bud length of wheat seed were increased by 54.05%, 7.98 mm and 6.84 mm, respectively, compared with the polluted soil group. These results showed that the advanced oxidation system of Fe-Mn@AC activates PS and can be used in crude oil-contaminated soil remediation.

Research progress of persulfate activation technology

Persulfate-based advanced oxidation processes (PS-AOPs) have been widely investigated by academia and industry due to their high efficiency and selectivity for the removal of trace organic pollutants from complex water substrates. PS-AOPs have been extensively studied for the degradation of pesticides, drugs, halogen compounds, dyes, and other pollutants. Utilizing bibliometric statistics, this review presents a comprehensive overview of persulfate-based advanced oxidation technology research over the past decade. The number of published articles about persulfate activation has steadily increased during this time, reflecting extensive international collaboration. Furthermore, this review introduces the most widely employed strategies for persulfate activation reported in the past 10 years, including carbon material activation, photocatalysis, transition metal activation, electrochemical activation, ultrasonic activation, thermal activation, and alkali activation. Next, the potential activation mechanisms and influencing factors, such as persulfate dosage during activation, are discussed. Finally, the application of PS-AOPs in wastewater treatment and in situ groundwater treatment is examined. This review summarizes the previously reported experiences of persulfate-based advanced oxidation technology and presents the current application status of PS-AOPs in organic pollution removal, with the aim of avoiding misunderstandings and providing a solid foundation for future research on the removal of organic pollutants.

Hierarchical Porous Bimetallic FeMn Metal-Organic Framework Gel for Efficient Activation of Peracetic Acid in Antibiotic Degradation

Effective techniques for eliminating antibiotics from water environments are in high demand. The peracetic acid (PAA)-based advanced oxidation process has recently drawn increasing attention for its effective antibiotic degrading capability. However, current applications of PAA-based techniques are limited and tend to have unsatisfactory performance. An additional catalyst for PAA activation could provide a promising solution to improve the performance of PAA. Bulky metal-organic framework gels (MOGs) stand out as ideal catalysts for PAA activation owing to their multiple advantages, including large surface areas, high porosity, and hierarchical pore systems. Herein, a bimetallic hierarchical porous structure, i.e., FeMn13BTC, was synthesized through a facile one-pot synthesis method and employed for PAA activation in ofloxacin (OFX) degradation. The optimized FeMn MOG/PAA system exhibited efficient catalytic performance, characterized by 81.85% OFX degradation achieved within 1 h owing to the specific hierarchical structure and synergistic effect between Fe and Mn ions, which greatly exceeded the performance of the only PAA-catalyzed system. Furthermore, the FeMn MOG/PAA system maintained >80% OFX degradation in natural water. Quenching experiments, electron spin resonance spectra, and model molecular degradation revealed that the primary reactive oxygen species responsible for the catalytic effect was R-O•, especially CH3C(=O)OO•, with minor contributions of •OH and 1O2. Overall, introduction of the MOG catalyst strategy for PAA activation achieved high antibiotic degradation performance, establishing a paradigm for the design of heterogeneous hierarchical systems to broaden the scope of catalyzed water treatment applications.

Preparation of Mn-doped sludge biochar and its catalytic activity to persulfate for phenol removal

In recent years, the increasing prevalence of phenolic pollutants emitted into the environment has posed severe hazards to ecosystems and living organisms. Consequently, there is an urgent need for a green and efficient method to address environmental pollution. This study utilized waste sludge as a precursor and employed a hydrothermal-calcination co-pyrolysis method to prepare manganese (Mn)-doped biochar composite material (Mn@SBC-HP). The material was used to activate peroxydisulfate (PDS) for the removal of phenol. The study investigated various factors (such as the type and amount of doping metal, pyrolysis temperature, catalyst dosage, PDS dosage, pH value, initial phenol concentration, inorganic anions, and salinity) affecting phenol removal and the mechanisms within the Mn@SBC-HP/PDS system. Results indicated that under optimal conditions, the Mn@SBC-HP/PDS system achieved 100% removal of 100 mg/L phenol within 180 min, with a TOC removal efficiency of 82.7%. Additionally, the phenol removal efficiency of the Mn@SBC-HP/PDS system remained above 90% over a wide pH range (3-9). Free radical quenching experiments and electron spin resonance (ESR) results suggested that hydroxyl radicals (·OH) and sulfate radicals (SO4-) yed a role in the removal of phenol through radical pathways, with singlet oxygen (1O2) being the dominant non-radical pathway. The phenol removal efficiency remained above 90%, demonstrating the excellent adaptability of the Mn@SBC-HP/PDS system under the interference of coexisting inorganic anions or increased salinity. This study proposes an innovative method for the resource utilization of waste, creating metal-biochar composite catalysts for the remediation of water environments. It provides a new approach for the efficiency of organic pollutants in water environments.

Advances in Fe-modified lignocellulosic biochar: Impact of iron species and characteristics on wastewater treatment

Lignocellulosic biomass is an attractive feedstock for biochar production owing to its high abundance and renewability. Various modified biochars have been extensively studied for wastewater treatment to improve the physical and chemical properties of lignocellulosic biochar (L-BC). Particularly, Fe-modified L-BCs have garnered attention owing to the abundance and eco-friendliness of Fe and the outstanding ability to remove various organic and inorganic contaminants via adsorption, oxidation, reduction, and catalytic reactions. Different iron species (e.g., Fe(0), Fe (hydr)oxide, Fe sulfide, and Fe-Metal) are formed during the preparation of Fe-L-BCs, which can completely differentiate the physical and chemical properties of BCs. This review discusses the advances in the synthesis of different Fe-L-BCs, specific changes in the physical and chemical properties of Fe-L-BCs upon Fe addition, and their impacts on wastewater treatment. The results of this review can demonstrate the unique advantages and drawbacks of Fe-L-BCs for the removal of different types of pollutants.

Persulfate enhanced removal of bisphenol A by copper oxide/reduced graphene oxide foam: Influencing factors, mechanism and degradation pathway

The CuO/reduced graphene oxide foam (CuO/RGF) with excellent recyclability was prepared via hydrothermal method followed by freeze drying treatment for bisphenol A (BPA) removal via activating peroxydisulfate (PDS). SEM, XRD, XPS, FT-IR, BET, and TG techniques were used to investigate the structure and property of CuO/RGF. The effect of degradation conditions (pH, PDS amount, Cl-, HCO3-, HA and FA) on BPA removal by CuO/RGF were investigated. The result presented that CuO nanosheet was inserted into the RGF carrier with three-dimensional structure. The degradation rate constant of BPA over CuO/RGF (0.00917 min-1) was 1.24 and 6.46 times higher than those of BPA over CuO (0.00714 min-1) and RGF (0.00142 min-1). More importantly, the pore structure of RGF can successfully limit the release of Cu (II) compared to pure CuO. According to quenching test as well as electron spin resonance (EPR) spectra, BPA degradation was triggered by 1O2, •OH and SO4•-, which was the combination of nonradical (1O2) and radical activation of PDS (•OH and SO4•-). The possible degradation route of BPA was proposed based on intermediates obtained by combining solid phase extraction pretreatment technique with high performance liquid-mass spectrometry. After assessing the viability of MCF-7 cells, we can see that the estrogenic activities of treated solution reduced without producing stronger endocrine disruptors.

Modeling and optimization study on degradation of organic contaminants using nZVI activated persulfate based on response surface methodology and artificial neural network: a case study of benzene as the model pollutant

Due to the complicated transport and reactive behavior of organic contamination in groundwater, the development of mathematical models to aid field remediation planning and implementation attracts increasing attentions. In this study, the approach coupling response surface methodology (RSM), artificial neural networks (ANN), and kinetic models was implemented to model the degradation effects of nano-zero-valent iron (nZVI) activated persulfate (PS) systems on benzene, a common organic pollutant in groundwater. The proposed model was applied to optimize the process parameters in order to help predict the effects of multiple factors on benzene degradation rate. Meanwhile, the chemical oxidation kinetics was developed based on batch experiments under the optimized reaction conditions to predict the temporal degradation of benzene. The results indicated that benzene (0.25 mmol) would be theoretically completely oxidized in 1.45 mM PS with the PS/nZVI molar ratio of 4:1 at pH 3.9°C and 21.9 C. The RSM model predicted well the effects of the four factors on benzene degradation rate (R2 = 0.948), and the ANN with a hidden layer structure of [8-8] performed better compared to the RSM (R2 = 0.980). In addition, the involved benzene degradation systems fit well with the Type-2 and Type-3 pseudo-second order (PSO) kinetic models with R2 > 0.999. It suggested that the proposed statistical and kinetic-based modeling approach is promising support for predicting the chemical oxidation performance of organic contaminants in groundwater under the influence of multiple factors.

Silica enhanced activation and stability of Fe/Mn decorated sludge biochar composite for tetracycline degradation

In this study, SiO₂-composited biochar decorated with Fe/Mn was prepared by co-pyrolysis method. The degradation performance of the catalyst was evaluated by activating persulfate (PS) to degrade tetracycline (TC). The effects of pH, initial TC concentration, PS concentration, catalyst dosage and coexisting anions on degradation efficiency and kinetics of TC were investigated. Under optimal conditions (TC = 40 mg L^-1, pH = 6.2, PS = 3.0 mM, catalyst = 0.1 g L^-1), the kinetic reaction rate constant could reach 0.0264 min^-1 in Fe₂Mn₁@BC-0.3SiO₂/PS system, which was 12 times higher than that in the BC/PS system (0.00201 min^-1). The electrochemical, X-ray diffractometer (XRD), Fourier transform infrared spectrum (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis showed that both metal oxides and oxygen-containing functional groups provide more active sites to activate PS. The redox cycle between Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) accelerated the electron transfer and sustained the catalytic activation of PS. Radical quenching experiments and electron spin resonance (ESR) measurements confirmed that surface sulfate radical (SO₄^•-) play a key role in TC degradation. Three possible degradation pathways of TC were proposed based on high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis, the toxicity of TC and its intermediates was analyzed by bioluminescence inhibition test. In addition to the enhanced catalytic performance, the presence of silica also improved the stability of the catalyst, as confirmed by cyclic experiment and metal ion leaching analysis. The Fe₂Mn₁@BC-0.3SiO₂ catalyst, derived from low-cost metals and bio-waste materials, offer an environmentally friendly option to design and implement heterogenous catalyst system for pollutant removal in water.

Applications, impacts, and management of biochar persistent free radicals: A review

Biochar is a promising environmental contaminant remediation agent because of its adsorptive and catalytic properties. However, the environmental effects of persistent free radicals (PFRs) produced by biomass pyrolysis (biochar production) are still poorly understood, though they have received increasing research attention in recent years. Although PFRs both directly and indirectly mediate biochar's removal of environmental pollutants, they also have the potential to cause ecological damage. In order to support and sustain biochar applications, effective strategies are needed to control the negative effects of biochar PFRs. Yet, there has been no systematic evaluation of the environmental behavior, risks, or management techniques of biochar PFRs. Thus, this review: 1) outlines the formation mechanisms and types of biochar PFRs, 2) evaluates their environmental applications and potential risks, 3) summarizes their environmental migration and transformation, and 4) explores effective management strategies for biochar PFRs during both production and application phases. Finally, future research directions are recommended.

Natural siderite derivatives activated peroxydisulfate toward oxidation of organic contaminant: A green soil remediation strategy

Natural siderite (FeCO₃), simulated synthetic siderite and nZVI/FeCO₃ composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil. The key reaction parameters such as catalysts dosage, oxidant concentration and pH, were investigated to evaluate the catalytic performance of different materials in catalytic systems. The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range (3-10). Both the main non-radical of ¹O₂ and free radicals of SO₄^·- and OH^· were evidenced by quenching experiment and electron paramagnetic resonance. The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(III) to Fe(II), but also can directly dechlorinate. Furthermore, the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained. Briefly, this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material.

Dual redox cycles of Mn(Ⅱ)/Mn(III) and Mn(III)/Mn(IV) on porous Mn/N co-doped biochar surfaces for promoting peroxymonosulfate activation and ciprofloxacin degradation

Mn and N co-doped biochar (Mn-N-TS) was prepared as an effective catalyst to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. As opposed to Mn-TS and N-TS, Mn-N-TS had more active sites containing N and Mn, as well as a greater specific surface area (923.733 m² g^-1). The Mn-N-TS exhibited excellent PMS activation ability. In the Mn-N-TS/PMS system, the CIP removal efficiency was 91.9% in 120 min. Mn and N co-doping could accelerate electron transfer between CIP and PMS molecules. Simultaneously, defect sites, graphitic N, pyridinic N, C═O groups, and Mn(II)/Mn(III)/Mn(IV) redox cycles acted as active sites to activate PMS and generate free radicals (OH, SO₄^- and ¹O₂). Furthermore, the Mn-N-TS/PMS system could effectively degrade CIP in a wide pH range, background substances, and actual water. Finally, a probable mechanism of PMS activation by Mn-N-TS was proposed. In conclusion, this work gave a novel direction for the rational design of Mn and N co-doped biochar.

Application of biochar activated persulfate in the treatment of typical azo pigment wastewater

With the increase of the azo pigment wastewater, it is necessary to seek an efficient and sustainable treatment method to address issues of damaging water ecosystems and human health. In this work, organic representing azo dye Acid Orange 7 (AO7), heavy metal representing hexavalent chromium (Cr(VI)), and inorganic representing ammonia nitrogen (NH₄⁺-N) were selected to roughly simulate the azo pigment wastewater. The simultaneous decontamination of multi-target pollutants by 700 °C pyrolyzed peanut shell biochar (BC) with persulfate (PDS) was evaluated. The results showed that AO7, Cr(VI) and NH₄⁺-N could finally reach 100%, 85% and 30% removal ratios separately in the BC/PDS/mixed pollutants system under certain basic conditions. Functional groups (hydroxyl groups (C-OH) and carboxylic ester/lactone groups (O-C=O)) were found by XPS as competing sites for adsorption and activation and were gradually consumed as the reaction proceeded. Combining a series of experiments results and EPR analysis, it was found that AO7 removal worked best and it relied on both the radical pathway (including SO₄^•-, •OH, O₂^-•, but not ¹O₂) and adsorption. Cr(VI) was mainly adsorbed and reduced by BC surface to form Cr(OH)₃ and Cr₂O₃, and the remaining part could be reduced by O₂^-•, followed by •OH. NH₄⁺-N was removed primarily by the radical same as AO7. Meanwhile, the three target pollutants have a co-competitive mechanism. Specifically, they competed for radicals and adsorption sites simultaneously, while the presence of AO7 and NH₄⁺-N would consume the generated oxidizing radicals and further promote the removal of Cr(VI). The fixed-bed reactor simulated the continuous treatment of wastewater. Various anions (chloride (Cl^-), nitrate (NO₃^-), carbonate (CO₃^2-), and hydrogen phosphate (HPO₄^2-)) interfered differently with the pollutant removal. These findings demonstrate a new dimension of BC potential for decontamination of azo pigment wastewater.

Enhanced degradation of DDT using a novel iron-assisted hydrochar catalyst combined with peroxymonosulfate: Experiment and mechanism analysis

Poplar wood (PW) hydrochar modified by iron (Fe@HC) was prepared greenly by one-step hydrothermal method. The adsorption and degradation performance of DDT was investigated in a heterogeneous advanced oxidation system (Fe@HC/PMS) formed by Fe@HC collaborated with peroxymonosulfate (PMS). The effects of Fe@HC dosage, PMS dosage and DDT initial concentration were quantitatively analyzed. The results showed that DDT removal efficiency can reach to 88.62% in 240 min under optimal conditions (4 g/L Fe@HC, 10 mM PMS, 0.5 mg/L DDT, 5.5 pH₀) in Fe@HC/PMS system. Furthermore, Fe@HC/PMS system exhibited high degradation rate and TOC removal efficiency for the removal of various organic contaminants. The influence mechanisms of Fe@HC/PMS system on DDT adsorption and degradation were proposed based on electron paramagnetic resonance (EPR) testing analysis and radical quenching experiments. Based on the mechanism analysis, the influence of Fe@HC/PMS on DDT removal efficiency can be concluded in the order: Active substance indirect degradation (60.95%) > Fe@HC direct degradation (10.13%) > Fe@HC adsorption (17.54%). Among active substance indirect degradation, SO₄^•-, ^•OH, O₂^•- and ¹O₂ occupied 27.56%, 15.74%, 5.33% and 12.32%, respectively. Moreover, DDT degradation intermediates were detected by a gas chromatography-mass spectrometer (GC-MS) to predict DDT degradation pathways. This study provided a green progress for the reuse of biomass resources and a new way for the enhanced degradation of DDT.

Insights into the correlation between different adsorption/oxidation/catalytic performance and physiochemical characteristics of Fe-Mn oxide-based composites

Fe-Mn oxide-based composites have been widely used in the solidification of heavy metals or the removal of organic pollutants, which can not only show excellent adsorption/oxidation performance, but also show catalytic activity for common oxidants. At present, the correlation between adsorption/oxidation/catalytic performance and physicochemical characteristics of these composites, and the underlying mechanisms are still unclear. Therefore, the main purpose of this review is to disclose the internal relationship between the physicochemical properties of Fe-Mn oxide-based composites and the pollutant removal performance. From the perspective of crystal phase, the basic units of Fe-Mn oxide composites are divided into Fe-Mn binary oxide (FMBO) and spinel MnFe₂O₄, and the two species were discussed separately in most chapters. The selected physicochemical properties mainly include the type of Fe-Mn oxide composites, surface-to-volume ratio, pore volume, pH_pzc, crystal type, surface functional groups. Because the physicochemical properties that determine how effective Fe-Mn oxide material is at removing contaminants may differ as it performs different functions, we discussed the above problems under different application scenarios (adsorption, oxidation, and advanced oxidation process). Additionally, internal factor (Fe/Mn mole ratio) and external factors (pH_ini, co-ions and ionic strength) were analyzed, and several common synthetic strategies of these composites were presented.

A sustainable reuse strategy of converting waste activated sludge into biochar for contaminants removal from water: Modifications, applications and perspectives

Conversion of sewage sludge to biochar for contaminants removal from water achieves the dual purpose of solid waste reuse and pollution elimination, in line with the concept of circular economy and carbon neutrality. However, the current understanding of sludge-derived biochar (SDB) for wastewater treatment is still limited, with a lack of summary regarding the effect of modification on the mechanism of SDB adsorption/catalytic removal aqueous contaminants. To advance knowledge in this aspect, this paper systematically reviews the recent studies on the use of (modified) SDB as adsorbents and in persulfate-based advanced oxidation processes (PS-AOPs) as catalysts for the contaminants removal from water over the past five years. Unmodified SDB not only exhibits stronger cation exchange and surface precipitation for heavy metals due to its nitrogen/mineral-rich properties, but also can provide abundant catalytic active sites for PS. An emphatic summary of how certain adsorption removal mechanisms of SDB or its catalytic performance in PS-AOPs can be enhanced by targeted regulation/modification such as increasing the specific surface area, functional groups, graphitization degree, N-doping or transition metal loading is presented. The interference of inorganic ions/natural organic matter is one of the unavoidable challenges that SDB is used for adsorption/catalytic removal of contaminants in real wastewater. Finally, this paper presents the future perspectives of SDB in the field of wastewater treatment. This review can contribute forefront knowledge and new ideas for advancing sludge treatment toward sustainable green circular economy.

Surface Modification of Biochar for Dye Removal from Wastewater

Nowadays, biochar is being studied to a great degree because of its potential for carbon sequestration, soil improvement, climate change mitigation, catalysis, wastewater treatment, energy storage, and waste management. The present review emphasizes on the utilization of biochar and biochar-based nanocomposites to play a key role in decontaminating dyes from wastewater. Numerous trials are underway to synthesize functionalized, surface engineered biochar-based nanocomposites that can sufficiently remove dye-contaminated wastewater. The removal of dyes from wastewater via natural and modified biochar follows numerous mechanisms such as precipitation, surface complexation, ion exchange, cation–π interactions, and electrostatic attraction. Further, biochar production and modification promote good adsorption capacity for dye removal owing to the properties tailored from the production stage and linked with specific adsorption mechanisms such as hydrophobic and electrostatic interactions. Meanwhile, a framework for artificial neural networking and machine learning to model the dye removal efficiency of biochar from wastewater is proposed even though such studies are still in their infancy stage. The present review article recommends that smart technologies for modelling and forecasting the potential of such modification of biochar should be included for their proper applications.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Adsorption Characteristics and Mechanisms of Fe-Mn Oxide Modified Biochar for Pb(II) in Wastewater

This study prepared iron-manganese oxide-modified biochar (FM-BC) by impregnating rice straw biochar (BC) with a mixed solution of ferric nitrate and potassium permanganate. The effects of pH, FM-BC dosage, interference of coexisting ions, adsorption time, incipient Pb(II) concentration, and temperature on the adsorption of Pb(II) by FM-BC were investigated. Moreover, the Pb(II) adsorption mechanism of FM-BC was analyzed using a series of characterization techniques. The results showed that the Fe-Mn oxide composite modification significantly promoted the physical and chemical functions of the biochar surface and the adsorption capacity of Pb(II). The specific surface area of FM-BC was 18.20 times larger than that of BC, and the maximum Pb(II) adsorption capacity reached 165.88 mg/g. Adsorption kinetic tests showed that the adsorption of Pb(II) by FM-BC was based on the pseudo-second-order kinetic model, which indicated that the adsorption process was mainly governed by chemical adsorption. The isothermal adsorption of Pb(II) by FM-BC conformed to the Langmuir model, indicating that the adsorption process was spontaneous and endothermic. Characterization analyses (Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy) showed that the adsorption mechanism of Pb(II) by FM-BC was mainly via electrostatic adsorption, chemical precipitation, complexation, ion exchange, and the transformation of Mn₂O₃ into MnO₂. Therefore, FM-BC is a promising adsorbent for Pb(II) removal from wastewater.

Recent advances in biochar technology for textile dyes wastewater remediation: A review

With the continuous rise of industrialization and agriculture, the concentration of organic contaminants such as dyes in the ecosystem has increased in subsequent years, causing major environmental contamination. Adsorption has been revealed to be a reliable and cost-effective way of eliminating organic pollutants. Biochar technology has the potential of converting trash into treasure when utilized for environmental remediation since it has numerous benefits such as the availability of diverse types of raw materials, low cost, and reusability. The potential of biochar as an adsorbent, support for catalysis, and a composite catalyst for dye degradation and mineralization is summarized in this research. It discusses its current research status in the adsorption and degradation of various dyes, incorporates the pertinent adsorption variables, encapsulates its regeneration techniques, investigates its engineering applications, and finally analyses limitations and discusses future development prospects.

A novel chitosan-urea encapsulated material for persulfate slow-release to degrade organic pollutants

A novel eco-friendly material (CS-U@PS) for persulfate slow-release to effectively degrade organic pollutants (methyl orange and pyrene) was synthesized using chitosan and urea as the encapsulated framework materials via an emulsion cross-linking method for the first time. The obtained CS-U@PS exhibits spherical shapes with a uniform size of approximately 2-3 µm according to the particle-size distribution and SEM image results. The slow-release mechanism was proposed through a kinetics model study and the Ritger-Peppas model fit well (r² = 0.9699) to indicate that the slow-release process is non-Fickian diffusion. The influences of urea and PS dosages and oxidative conditions on methyl orange degradation were studied, and all the results suggested that urea played an important role in PS slow-release and can also catalyze the activation of PS by iron to further produce radicals and improve the removal efficiency of pollutants. A pyrene removal rate of 90.53% was achieved in aqueous solutions and an above 80% removal rate was obtained in weakly acidic or neutral soil environments by CS-U@PS activated by Fe²⁺ with citric acid as the chelating agent. Therefore, the fabricated slow-release oxidation materials exhibit application potential for the remediation of organic polluted groundwater and soil.

Oxidative degradation of tetracycline using peroxymonosulfate activated by cobalt-doped pomelo peel carbon composite

Tetracycline (TC) is a typical ecotoxic antibiotic, which easily causes bacterial resistance. Therefore, it is necessary to remove TC from the water environment. In recent years, advanced oxidation processes (AOPs) rely on the use of highly reactive oxidizing sulfate radical which is turning into an increasingly popular as a tool of the removal of TC. In this study, cobalt-doped pomelo peel carbon composite (Co-PPCC) was prepared by the impregnation coprecipitation method to activate peroxymonosulfate (PMS) to remove TC. SEM, BET, XRD, FTIR, XPS, TGA, and other analytical techniques indicated that a carbon composite catalyst with excellent performance has been successfully prepared. TC was removed by the synergistic effect of adsorption and catalytic degradation processes. The adsorption capacity was limited (only approximately 20% within 60 min) and tending to saturation, which indicated that the removal of TC in the Co-PPCC/PMS system was mainly due to oxidative degradation. The influence of the Co-PPCC and PMS dosage, initial TC concentration, initial pH values, and coexisting anions on the removal efficiency of TC was investigated. When the Co-PPCC catalyst dosage was 1 g/L, PMS concentration was 2 g/L, and pH value was 11, the removal efficiency of TC with a concentration of 50 mg/L reached 99% within 60 min. Free radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that the free radical and non-radical degradation processes exist in the Co-PPCC/PMS/TC system. The main degradation products and the possible transformation pathways of TC were explored by LC-MS. In addition, after four cycles of Co-PPCC tests, the removal efficiency of TC can reach 64%. This study provides a new method to reuse abandoned pomelo peels and synthesize an economical and environmentally friendly catalyst for activating peroxymonosulfate to remove TC antibiotics in water.

Magnetic MgFe2O4/biochar derived from pomelo peel as a persulfate activator for levofloxacin degradation: Effects and mechanistic consideration

Biochar (BC) has been demonstrated the potential to activate persulfate (PS), but the limited catalytic efficiencies hindered their further application. Herein, an innovative magnetic MgFe₂O₄/BC (MMB) derived from pomelo peel was prepared for persulfate-based advanced oxidation process (PS-AOPs). Benefitting from the extraordinary properties, levofloxacin (LFX) was efficiently removed in the MMB/PS system. MMB700 exhibited the best catalytic activity, 87.87% of LFX was removed in the MMB700/PS system. In addition, it could maintain 67.90% of LFX degradation efficiency after 3 times of reuse. Quenching experiments, electron spin resonance (ESR) detection, and electrochemical test results indicated that both non-radical pathway and direct electron-transfer pathway advanced LFX degradation. LFX was oxidized by O₂^·- and ¹O₂, O₂^·- acted as the dominant active species. PS activation was induced by the active sites of MMB700. This work not only developed a promising magnetic biochar PS catalyst for antibiotics elimination, but also facilitated insights PS activation mechanisms.

Efficacy and cytotoxicity of engineered ferromanganese-bearing sludge-derived biochar for percarbonate-induced phthalate ester degradation

Phthalate esters (PAEs) are a group of ubiquitous organic environmental contaminants. Engineered ferromanganese-bearing sludge-derived biochar (SDB), synthesized using one-step pyrolysis in the temperature range between 300 and 900 °C, was used to enable Fenton-like processes that decontaminated PAE-laden sediments. SDB was thoroughly characterized using scanning electron microscopyenergy-dispersive spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface area, thermogravimetric analysis, Raman spectroscopy, Fourier-transform infrared spectroscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis. The maximum PAE degradation was remarkable at 90% in 12 h at pH 6.0 in the presence of 1.7 g L^-1 of SDB 900. The highly-effective PAE degradation was mainly attributed to the synergism between FeO_x and MnO_x, which strengthened the activation of percarbonate (PC) via electron transfer, hydroxy addition, and hydrogen abstraction through radical (HO•) and nonradical (¹O₂) oxidation mechanisms, thereby facilitating PAE catalytic degradation over SDB in real sediments, which clearly proved the efficacy of ferromanganese-bearing SDB and PC for the remediation of contaminated sediments. The cytotoxicity exhibited by human skin keratinocyte cells exposure to high SDB concentration (100-400 µg mL^-1) for 24-48 h was low indicating insignificant cellular toxicity and oxidative damages. This study provides a new strategy for freshwater sludge treatment and reutilization, which enables a water-cycle-based circular economy and waste-to-resource recycling.

The photocatalytic performance and mechanism of magnetically retrievable Z-scheme Cr2O3–Fe3O4/C hetero-nanostructure polyhedra

Magnetically retrievable Cr2O3–Fe3O4/C hetero-nanostructure polyhedra have been fabricated. The formation of Z-scheme Cr2O3–Fe3O4/C obviously improves the visible light absorption and promotes the separation of photogenerated charge carriers.

Insights into enhanced peroxydisulfate activation with S doped Fe@C catalyst for the rapid degradation of organic pollutants

In this study, the S modified iron-based catalyst (S-Fe@C) for activating peroxydisulfate (PDS) was fabricated by heating the S-MIL-101 (Fe) precursor at 800 °C. The resulted S-Fe@C composite mainly consisted of carbon, Fe⁰, FeS, FeS₂, and Fe₃O₄, and showed strong magnetism. Compared with Fe@C obtained from MIL-101 (Fe), the S-Fe@C exhibited much higher performance (1.5 times larger) on PDS activation and the S-Fe@C/PDS could rapidly degrade various organic pollutants in 5 min under the attack of the species of SO₄^-·, ¹O₂, electro-transfer and Fe(IV). The S element in enhancing the PDS activation mainly involved two mechanisms. Firstly, the doped S could speed up the electron transfer efficiency, resulting in a promotion on PDS decomposition; secondly, the S^2- S₂^2- or S⁰ could achieve the circulation of Fe²⁺ and Fe³⁺, leading to the formation of non-radicals Fe(IV) and ¹O₂.

Al-Doped magnetite encapsulated in mesoporous carbon: a long-lasting Fenton catalyst for CWPO of phenol in a fixed-bed reactor under mild conditions

Al substituted magnetite was identified as a promising heterogeneous Fenton catalyst for CWPO of 200 ppm phenol in a continuous system under mild conditions (pH 5, 40 °C, 0.1 ml min−1, 1.2S H2O2) for 500 h with 80% TOC conversion, 1 ppm Fe leaching.