Membrane-based nanoconfined heterogeneous catalysis for water purification: A critical review✰

Low-peroxide-consumption fenton-like systems: The future of advanced oxidation processes

Conventional heterogeneous Fenton-like systems employing different peroxides have been developed for water/wastewater remediation. However, a large population of peroxides consumed during various Fenton-like systems with low utilization efficiency and associated secondary contamination have become the bottlenecks for their actual applications. Recent strategies for lowering the peroxide consumptions to develop economic Fenton-like systems are primarily devoted to the effective radical generation and subsequent high-efficiency radical utilization through catalysts/systems engineering, leveraging emerging nonradical oxidation pathways with higher selectivity and longer life of the reactive intermediate, as well as reactor designs for promoting the mass transfer and peroxides decomposition to improve the yield of radicals/nonradicals. However, a comparative review summarizing the mechanisms and pathways of these strategies has not yet been published. In this review, we endeavor to showcase the designated systems achieving the reduction of peroxides while ensuring high catalytic activity from the perspective of the above strategic mechanisms. An in-depth understanding of these aspects will help elucidate the key mechanisms for achieving economic peroxide consumption. Finally, the existing problems of these strategies are put forward, and new ideas and research directions for lowering peroxide consumption are proposed to promote the application of various Fenton-like systems in actual wastewater purification.

Photodegradation of steroid hormone micropollutants with palladium-porphyrin coated porous PTFE of varied morphological and optical properties

In flow-through reactors, the photodegradation rate can be improved by enhancing contact and increasing the photocatalyst loading. Both can be attained with a higher surface-to-volume ratio. While previous studies focused on thin membranes (30 - 130 µm) with small pore sizes of 20 - 650 nm, this work employed poly(tetrafluoroethylene) (PTFE) supports, of which pore sizes are in the order of 10 µm, while the porosities and thicknesses are variable (22.5 - 45.3 % and 0.2 - 3 mm, respectively). These porous materials were anticipated to allow a higher loading of porphyrin photosensitisers and better light penetration for subsequent photodegradation of steroid hormone micropollutants via singlet oxygen (1O2) generation. The reactor surface refers to the surface within the PTFE pores, while the reactor volume is the total void space inside these pores. The surface-to-volume ratios between 105 and 106 m2/m3 are higher than those of typical microreactors (103 to 104 m2/m3). The weighted average light transmittance varied from 38 % with the thinnest and most porous support to 4.8 % with the thickest support. Good light penetration combined with minimal absorption by PTFE enhanced the light utilisation of the porphyrins when coated in the porous supports. Changes in the support porosity of the coated supports minimally affected steroid hormone removal, because the collision frequency in the very large pores remained relatively constant. However, varying the support thickness, porphyrin loading (0.3 - 7.7 μmol/g), and water flux (150 - 3000 L/m2.h), hence the resulting hydraulic residence time, influenced the collision frequency and steroid hormone removal. Results showed that the supports did not outperform membranes most likely because the larger pore size in the former limited contact between the hormones and 1O2. From photostability testing of the pristine supports, perfluoroalkyl substances (PFAS) released from the supports were found at 10 - 300 ng/L concentrations during accelerated ageing. While PFAS formation was detectable, the quantities during water treatment operations would be extremely low. In summary, this study elucidates the capability and limitations of porous supports coated with photosensitisers to remove waterborne micropollutants.

Accelerated arsenic decontamination using graphene oxide-supported metal-organic framework nanoconfined membrane for sustainable performance

Developing highly efficient bimetallic metal-organic frameworks (MOFs) as catalysts for Fenton-like reactions holds significant promise for decontamination processes. Although MOFs with excellent decontamination capabilities are achievable, ensuring their long-term stability, especially in the organoarsenic harmless treatment, remains a formidable challenge. Herein, we proposed a unique nanoconfinement strategy using graphene oxide (GO)-supported Prussian blue analogs (PBA) as catalytic membrane, which modulated the peroxymonosulfate (PMS) activation in p-arsanilic acid (p-ASA) degradation from traditional radical pathways to a synergy of both radical and non-radical pathways. This dual-pathway activation with sulfate radicals (SO4•-) and singlet oxygen (1O2) was a significant advancement, ensuring the exceptionally high reactivity and stability for over 80 h of continuous membrane operation. The PBA@GO membrane achieved a degradation rate constant of 0.79 ms-1, with an increase of four orders of magnitude compared to the nonconfined PBA@GO composites, while ensuring comprehensive arsenic removal ensuring comprehensive arsenic removal and demonstrating remarkably efficient total organic carbon elimination (92.2 % versus 57.6 % in 20 min). The PBA@GO membrane also showed excellent resistance towards inorganic ions, humic acid, and complex water matrices. This facile and universal strategy paves the way for the fabrication of MOFs-based catalytic membranes for optimizing performance in arsenic pollution treatment.

Intensive electron transfer of a single-atom Fe-based catalytic ceramic membrane for municipal wastewater treatment: The synergistic effects of nitrogen vacancy defect and ultrathin nanostructure

The integration of membrane separation with heterogeneous advanced oxidation processes is a prospective strategy for the elimination of contaminants during wastewater treatment. Fe-based catalysts and the green oxidant peracetic acid (PAA) are desirable candidates for the development of catalytic membranes because they are environmentally friendly. However, the construction of catalytic ceramic membranes (CMs) modified with efficient Fe-based catalysts that generate increased amounts of high-valent Fe-O species during PAA activation for the degradation of specific pollutants, especially during instantaneous membrane filtration, remains challenging. Herein, a single-atom Fe-based catalytic CM was fabricated and further optimized via the "electron enrichment + electron-transfer enhancement" method, which specifically refers to the simultaneous introduction of nitrogen vacancy (Nv) defects and the construction of ultrathin nanostructures. The CM-UCNv-Fe/PAA system exhibited outstanding bisphenol A (BPA) removal performance, with a first-order rate constant of 0.078 ms-1 (4680 min-1), which was 37 times greater than that of CM-BCN-Fe/PAA system (126 min-1). In addition, the remarkable environmental adaptability, stability and low Fe leakage underscored its practical application potential. Mechanistic investigations revealed that Fe(V)=O was the predominant reactive oxygen species. Multi-scaled characterization and theoretical calculations confirmed that engineered Nv defects facilitated the construction of electron-rich single-atom Fe sites, which had the potential to supply more electrons. Porous ultrathin nanosheets exposed more Fe active sites, and many microinterfaces within the catalytic layers of the CM increased the possibility of contact between the Fe sites and PAA. The synergy of them enabled intensive electron transfer from Fe sites to PAA, which was the driving force for Fe(V)=O conversion during transient membrane filtration. In addition, the efficacy of the catalytic CM in municipal wastewater treatment and membrane fouling control were investigated. This work expands the research on the intensive electron transfer of a single-atom Fe-based catalytic CM for increased Fe(V)=O conversion via Nv defect introduction and ultrathin nanostructure construction.

Nanoconfined catalytic macrostructures for advanced water remediation: From basic understanding to future application strategies

In recent years, nanoconfined catalytic macrostructures applied to advanced oxidation processes (AOPs) have been rapidly developed, effectively solving the problems of traditional heterogeneous AOPs, such as mass transfer limitation, limited diffusion of short-lived reactive oxygen species (ROS), and aggregation/leaching of catalysts. Compared with the traditional heterogeneous AOPs systems, the nanoconfined catalytic macrostructures have unique interactions between the oxidants, catalysts, ROS and micropollutants, which could significantly increase the yield and mass transfer of ROS. At present, there is a lack of comprehensive reviews on the nanoconfined catalytic macrostructures from basic theory to application performances and future development strategies. This study reviewed the preparation routines of various nanoconfined catalytic macrostructures, assessed their structural differences, catalytic properties and nanoconfined catalytic mechanisms via integrated density functional theory (DFT) and molecular dynamics (MD) stimulations. We also proposed the future strategies for nanoconfined catalytic macrostructures in combination with the machine learning, which could provide key information on the feasibility of the technology and future research directions. This review aims to enhance scholarly interest in the application of nanoconfined macrostructures in the AOPs fields, anticipating significant technical feasibilities for scale-up AOPs application of nanoconfinement.

Catalytic membrane with dual-layer structure for ultrafast degradation of emerging contaminants in surface water treatment

The catalytic membrane-based oxidation-filtration process integrates physical separation and chemical oxidation, offering a highly efficient water purification strategy. However, the oxidation-filtration process is limited in practical applications due to the short residence time of milliseconds within the catalytic layer and the interference of coexisting organic pollutants in real water. Herein, a dual-layer membrane containing a top selective layer and a bottom catalytic layer was fabricated using an in situ co-casting method with a double-blade knife. Experimental results demonstrated that the selective layer rejected macromolecular organic pollutants, thereby alleviating their interference with bisphenol A (BPA) degradation. Concurrently, the catalytic layer activated peracetic acid oxidant and achieved a high BPA degradation exceeding 90 % in milliseconds with reactive oxygen species (especially •OH). The finite-element analysis confirmed a high-concentration reaction field occupying the pore cavity of the catalytic layer, enhancing collision probability between reactive oxygen species and BPA, i.e., the nano-confinement effect. Additionally, the dual-layer membrane achieved a long-term stable performance for emerging contaminant degradation in surface water treatment. This work underscores a novel catalytic membrane structure design for high-performance oxidation-filtration processes and elucidates its mechanisms underlying ultrafast degradation.

Tubular nanofiber membranes combined with Z-scheme CuS@Co3S4 heterojunction catalyst for high-efficient removal of polyvinyl alcohol from waste water with high COD

Polyvinyl alcohol (PVA), a typical water-soluble polymer with huge global production, is becoming one of the most ubiquitous pollutants and indeed the villain of the piece contributing high chemical oxygen demand (COD) in wastewater. Membrane technology is an effective method for wastewater purification, in particular, with the combination of peroxymonosulfate (PMS)-assisted advanced oxidation or photocatalytic process, is capable of maintaining high water flux and anti-fouling. Herein, a ZIF-67 derived Z-scheme CuS@Co3S4 heterojunction catalyst immobilized by poly (m-phenylene isophthalamide) (PMIA) tubular nanofiber membrane (CuS@Co3S4/PMIA-TNM) is designed using a polyester braided tube as interior reinforcement. The resultant membrane features with outstanding superhydrophilicity and commendable porosity (82.1 %), leading to a significantly enhanced permeability (water flux > 82.3 L·m-2·h-1). Meanwhile, the membrane shows promising PVA removal efficiency (> 99.9 %) with a high COD removal efficiency (∼ 83.4 %) and enhanced antifouling capacity (flux recovery ratio > 99.7 %) with the assistance of PMS driven by an ultra low-power LED lamp. The universal applicability and environmental adaptability are also verified in various reaction conditions. In terms of ecotoxicological impacts of the PVA wastewater before and after treatment on aquatic organisms, Zebrafish embryonic development dynamically demonstrated that the treated PVA waste water by the developed hybrid membrane is healthy for fish to grow. Our study definitely opens up a new avenue to develop high-performance catalytic membranes for PVA-based wastewater treatment.

Pilot-scale and large-scale Fenton-like applications with nano-metal catalysts: From catalytic modules to scale-up applications

Recently, great efforts have been made to advance the pilot-scale and engineering-scale applications of Fenton-like processes using various nano-metal catalysts (including nanosized metal-based catalysts, smaller nanocluster catalysts, and single-atom catalysts, etc.). This step is essential to facilitate the practical applications of advanced oxidation processes (AOPs) for these highly active nano-metal catalysts. Before large-scale implementation, these nano-metal catalysts must be converted into the effective catalyst modules (such as catalytic membranes, fluidized beds, or polypropylene sphere suspension systems), as it is not feasible to use suspended powder catalysts for large-scale treatment. Therefore, the pilot-scale and engineering applications of nano-metal catalysts in Fenton-like systems in recent years is exciting. In addition, the combination of life cycle assessment (LCA) and techno-economic analysis (TEA) can provide a useful support tool for engineering scale Fenton-like applications. This paper summarizes the designs and fabrications of various advanced modules based on nano-metal catalysts, analyzes the advantages and disadvantages of these catalytic modules, and further discusses their Fenton-like pilot scale or engineering applications. Concepts of future Fenton-like engineering applications of nano-metal catalysts were also discussed. In addition, current challenges and future expectations in pilot-scale or engineering applications are assessed in conjunction with LCA and TEA. These challenges require further technological advances to enable larger scale engineering applications in the future. The aim of these efforts is to increase the potential of nanoscale AOPs for practical wastewater treatment.

Titanium Carbide (Ti3C2Tx) MXene for Sequestration of Aquatic Pollutants

The rapid expansion of industrialization has resulted in the release of multiple ecological contaminants in gaseous, liquid, and solid forms, which pose significant environmental risks to many different ecosystems. The efficient and cost-effective removal of these environmental pollutants has attracted global attention. This growing concern has prompted the synthesis and optimization of nanomaterials and their application as potential pollutant removal. In this context, MXene is considered an outstanding photocatalytic candidate due to its unique physicochemical and mechanical properties, which include high specific surface area, physiological compatibility, and robust electrodynamics. This review highlights recent advances in shaping titanium carbide (Ti3C2Tx) MXenes, emphasizing the importance of termination groups to boost photoactivity and product selectivity, with a primary focus on engineering aspects. First, a broad overview of Ti3C2Tx MXene is provided, delving into its catalytic properties and the formation of surface termination groups to establish a comprehensive understanding of its fundamental catalytic structure. Subsequently, the effects of engineering the morphology of Ti3C2Tx MXene into different structures, such as two-dimensional (2D) accordion-like forms, monolayers, hierarchies, quantum dots, and nanotubes. Finally, a concise overview of the removal of different environmental pollutants is presented, and the forthcoming challenges, along with their prospective outlooks, are delineated.

Asymmetric defective sites-mediated high-valent cobalt-oxo species in self-suspension aerogel platform for efficient peroxymonosulfate activation

The main pressing problems should be solved for heterogeneous catalysts in activation of peroxymonosulfate (PMS) are sluggish mass transfer kinetics and low intrinsic activity. Here, oxygen vacancies (Vo)-rich of Co3O4 nanosheets were anchored on the superficies of spirulina-based reduced graphene oxide-konjac glucomannan (KGM) aerogel (R-Co3O4-x/SRGA). The porous structure and superhydrophilicity conferred by KGM maximized the diffusion and transport of reactant. More interestingly, R-Co3O4-x/SRGA came true self-suspension rather than conventional self-floating without the aid of external force, maximizing space utilization and facilitating catalysts recovery. Anchored R-Co3O4-x nanosheets acted as "engines" to drive the reaction. Density functional theory (DFT) manifested Vo was capable of breaking the symmetry of the electronic structure of Co3O4. The formation of asymmetric active sites (Vo) was revealed to modulate the d-band center, enhanced affinity for PMS, and promoted evolution of high-valent cobalt-oxo (Co(IV)=O) species. R-Co3O4-x/SRGA achieved complete removal of sulfamethoxazole (SMX) within 12 min. Furthermore, R-Co3O4-x/SRGA demonstrated exceptional stability in the presence of various environmental interference factors and continuous flow device. This insightful work cleverly integrates the macroscopic design of structure, and the microscopic regulation of active sites is expected to open up new opportunities for the development of water treatment.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

A single-atom manganese nanozyme mediated membrane reactor for water decontamination

Single-atom nanozymes possess high catalytic activity and selectivity, and are emerging as advanced heterogeneous catalysts for environmental applications. Herein, we present the innovative synthesis and characterization of a single-atom manganese-doped carbon nitride (SA-Mn-CN) nanozyme, integrated into a polyvinylidene fluoride (PVDF) membrane for advanced water treatment applications. The SA-Mn-CN nanozyme demonstrates high peroxidase-like activity, efficiently catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and generating reactive oxygen species (ROS) for effective antibacterial action. Notably, the SA-Mn-CN/PVDF membrane showcases enhanced water permeability, superior antifouling properties, and ultra-fast degradation kinetics of organic pollutants. Mechanistic studies reveal that the nanozyme selectively generates Mn(IV)-oxo species via peroxymonosulfate (PMS) activation, crucial for the efficient oxidation processes. Our integrated membrane system effectively removes (within 1 min, > 92 % removal) a variety of organic micropollutants in continuous-flow operations, demonstrating excellent stability and minimal manganese leaching. Compared to conventional advanced oxidation process (AOPs)/membrane system, the SA-Mn-CN/PVDF/PMS system holds the advantages of high catalytic activity and selectivity for generation of reactive species, wide working pH range (pH3-11) and excellent stability and reusability under the backwashing conditions. The developed device-scale AOPs/membrane system was proven to be effective in bacterial inactivation and pollutants degradation, verifying the vast application potential of the SA-Mn-CN/PVDF membrane for practical water decontamination. This work pioneers the development of enzyme-mimicking nanozyme membranes, offering a sustainable and high-performance solution for wastewater treatment, and sets a new benchmark for the design of nanozyme-based catalytic membranes in environmental applications.

A Nanoconfined FeCo2O4-Embedded Ceramic Membrane Regulates Electron Transfer in Peroxymonosulfate Activation to Selectively Generate Singlet Oxygen for Water Decontamination

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs), as a promising technology for water decontamination, are constrained by low reaction kinetics due to limited reaction selectivity and mass transfer. Herein, we designed a nanoconfined FeCo2O4-embedded ceramic membrane (FeCo2O4-CM) under flow-through pattern for PMS activation. Confining PMS and FeCo2O4 within nanochannels (3.0-4.7 nm) enhanced adsorption interactions (-7.84 eV vs -2.20 eV), thus boosting mass transfer. Nanoconfinement effect regulated electron transfer pathways from PMS to FeCo2O4-CM by modulating the active site transformation to ≡Co(III) in nanoconfined FeCo2O4-CM, enabling selectively generating 1O2. The primary role of 1O2 in the nanoconfined system was confirmed by kinetic solvent isotope experiments and indicative anthracene endoperoxide (DPAO2). The system enabled 100% removal of atrazine (ATZ) within a hydraulic retention time of 2.124 ms, demonstrating a rate constant over 5 orders of magnitude higher than the nonconfined system (3.50 × 103 s-1 vs 0.42 min-1). It also exhibited strong resilience to pH variations (3.3-9.0) and coexisting substances, demonstrating excellent stability indicated by consistent 100% ATZ removal for 14 days. This study sheds light on regulating electron transfer pathways to selectively generate 1O2 through the nanoconfinement effect, boosting the practical application of PMS-based AOPs in environmental remediation and potentially applying them to various other AOPs.

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Singlet oxygen dominant-activation by hollow structural cobalt-based MOF/peroxymonosulfate system for micropollutant removal

Despite the keen interest in potentially using the metal-organic framework (MOF) in advanced oxidation processes (AOPs), their application for environmental abatement and the corresponding degradation mechanisms have remained largely elusive. This study explores the use of cobalt-based MOF (CoMOF) for peroxymonosulfate (PMS) activation to remove tetracycline (TC) from water resources. Under optimal conditions, the given catalytic system could achieve a TC removal of 83.3%. Radical quenching tests and EPR analysis revealed that SO4•-, HO•, •O2-, and 1O2 could participate in the catalytic degradation, but the discernible removal mechanism was mainly ascribed to the nonradical pathway induced by 1O2. At only 5 mg/L of CoMOF, the performance of the catalytic system was superior to that of PMS alone for different types of micropollutants. The CoMOF/PMS system could also reliably deal with typical anions in water, such as Cl-, SO42-, HCO3-, and PO43-. The MOF catalyst could last for four cycles with a minor decrease in reactivity of ∼30%. However, the removal performance decreased markedly when aromatic natural organic matter (NOM) were present in the water bodies, and the effectiveness was lower in alkaline or acidic environments. Our work offers insights into the catalytic degradation of CoMOF/PMS applied in contaminated water remediation and serves as a baseline for fabricating an efficient MOF with enhanced catalytic performance and stability.

Tempospatially Confined Catalytic Membranes for Advanced Water Remediation

The application of homogeneous catalysts in water remediation is limited by their excessive chemical and energy input, weak regenerability, and potential leaching. Heterogeneous catalytic membranes (CMs) offer a new approach to facilitate efficient, selective, and continuous pollutant degradation. Thus, integrating membranes and continuous filtration with heterogeneous advanced oxidation processes (AOPs) can promote thermodynamic and kinetic mass transfers in spatially confined intrapores and facilitate diffusion-reaction processes. Despite the remarkable advantages of heterogeneous CMs, their engineering application is practically restricted due to the fuzzy design criteria for specific applications. Herein, the recent advances in CMs for advanced water remediation are critically reviewed and the design flow for tempospatially confined CMs is proposed. Further, state-of-the-art CM materials and their catalytic mechanisms are reviewed, after which the tempospatial confinement mechanisms comprising the nanoconfinement effect, interface effect, and kinetic mass transfer are emphasized, thus clarifying their roles in the construction and performance optimization of CMs. Additionally, the fabrication methods for CMs based on their catalysts and pore sizes are summarized and an overview of their application and performance evaluations is presented. Finally, future directions for CMs in materials research and water treatment, are presented.

Cell Wall Binding Strategies Based on Cu3SbS3 Nanoparticles for Selective Bacterial Elimination and Promotion of Infected Wound Healing

Utilizing nanomaterials as an alternative to antibiotics, with a focus on maintaining high biosafety, has emerged as a promising strategy to combat antibiotic resistance. Nevertheless, the challenge lies in the indiscriminate attack of nanomaterials on both bacterial and mammalian cells, which limits their practicality. Herein, Cu3SbS3 nanoparticles (NPs) capable of generating reactive oxygen species (ROS) are discovered to selectively adsorb and eliminate bacteria without causing obvious harm to mammalian cells, thanks to the interaction between O of N-acetylmuramic acid in bacterial cell walls and Cu of the NPs. Coupled with the short diffusion distance of ROS in the surrounding medium, a selective antibacterial effect is achieved. Additionally, the antibacterial mechanism is then identified: Cu3SbS3 NPs catalyze the generation of O2•-, which has subsequently been conversed by superoxide dismutase to H2O2. The latter is secondary catalyzed by the NPs to form •OH and 1O2, initiating an in situ attack on bacteria. This process depletes bacterial glutathione in conjunction with the disruption of the antioxidant defense system of bacteria. Notably, Cu3SbS3 NPs are demonstrated to efficiently impede biofilm formation; thus, a healing of MRSA-infected wounds was promoted. The bacterial cell wall-binding nanoantibacterial agents can be widely expanded through diversified design.

Reactive layered hydroxide membrane for advanced water treatment: Micropollutant degradation and antifouling potential

The effective removal of micropollutants by water treatment technologies remains a significant challenge. Herein, we develop a CoFe layered double hydroxide (CoFeLDH) catalytic membrane for peroxymonosulfate (PMS) activation to achieve efficient micropollutant removal with improved mass transfer rate and reaction kinetics. This study found that the CoFeLDH membrane/PMS system achieved an impressive above 98% degradation of the probe chemical ranitidine at 0.1 mM of PMS including five more micropollutants (Sulfamethoxazole, Ciprofloxacin, Carbamazepine, Acetaminophen and Bisphenol A) at satisfactory level (above 80%). Moreover, significant improvements in water flux and antifouling properties were observed, marking the membrane as a specific advancement in the removal of membrane fouling in water purification technology. The membrane demonstrated consistent degradation efficiency for several micropollutants and across a range of pH (4-9) as well as different anionic environments, thereby showing it suitability for scale-up application. The key role of reactive species such as SO4•-, and O2• - radicals in the degradation process was elucidated. This is followed by the confirmation of the occurrence of redox cycling between Co and Fe, and the presence of CoOH+ that promotes PMS activation. Over the ten cycles, the membrane could be operated with a flux recovery of up to 99.8% and maintained efficient performance over 24 h continuous operation. Finally, the efficiency in degrading micropollutants, coupled with reduced metal leaching, makes the CoFeLDH membrane as a promising technology for application in water treatment.

High-performance, stable CoNi LDH@Ni foam composite membrane with innovative peroxymonosulfate activation for 2,4-dichlorophenol destruction

In this study, the cobalt-nickel layered double hydroxides (CoNi LDH) were synthesized with a variety of Co/Ni mass ratio, as CoxNiy LDHs. In comparison, Co1Ni3 LDH presented the best peroxymonosulfate (PMS) activation efficiency for 2,4-dichlorophenol removal. Meanwhile, CoNi LDH@Nickel foam (CoNi LDH@NF) composite membrane was constructed for enhancing the stability of catalytic performance. Herein, CoNi LDH@NF-PMS system exerted high degradation efficiency of 99.22% within 90 min for 2,4-DCP when [PMS]0 = 0.4 g/L, Co1Ni3 LDH@NF = 2 cm × 2 cm (0.2 g/L), reaction temperature = 298 K. For the surface morphology and structure of the catalyst, it was demonstrated that the CoNi LDH@NF composite membrane possessed abundant cavity structure, good specific surface area and sufficient active sites. Importantly, ·OH, SO4·- and 1O2 played the primary role in the CoNi LDH@NF-PMS system for 2,4-DCP decomposition, which revealed the PMS activation mechanism in CoNi LDH@NF-PMS system. Hence, this study eliminated the stability and adaptability of CoNi LDH@NF composite membrane, proposing a new theoretical basis of PMS heterogeneous catalysts selection.

Sustainable conversion of polyethylene plastic bottles into terephthalic acid, synthesis of coated MIL-101 metal-organic framework and catalytic degradation of pollutant dyes

Persistent environmental colored compounds, resistant to biodegradation, accumulate and harm eco-systems. Developing effective methods to break down these pollutants is crucial. This study introduces Ag-MIL-101 (Ag-MIL-101) as a composite and reusable catalyst that efficiently degrades specific colored organic pollutants (COPs) like Methylene blue (MB), 4-Nitrophenol (4-NP), and 4-Nitroaniline (4-NA) using sodium borohydride at room temperature. The MIL-101 was synthesized using Terephthalic acid (TPA) derived from the degradation of Polyethylene Terephthalate (PET) plastic waste, with the assistance of zinc chloride. To further investigation, the kinetics of degradation reaction was studied under optimized conditions in the presence of Ag-MIL-101 as catalyst. Our results demonstrated the remarkable efficiency of the degradation process, with over 93% degradation achieved within just 8 min. The catalyst was characterized using FTIR, XRD, FESEM, and TEM. In this study, the average particle size of Ag-MIL-101 was determined using SEM and XRD analysis. These methods allow us to accurately and precisely determine the particle size. We determined the reaction rate constants for the degradation of each COP using a pseudo first-order kinetic equation, with values of 0.585, 0.597 and 0.302 min-1 for MB, 4-NP, and 4-NA, respectively. We also evaluated the recyclability of the catalyst and found that it could be reused for up to three cycles with only a slight decrease in efficiency (10-15%). Overall, our findings highlight the promising application of Ag-MIL-101 as an effective catalyst for the degradation of COPs, emphasizing the importance of optimizing reaction conditions to achieve enhanced efficiency.

A two dimensional Co(OH)2 catalytic gravity-driven membrane for water purification: a green and facile fabrication strategy and excellent water decontamination performance

Cobalt-based materials are reported to be the most efficient catalysts in sulfate radical advanced oxidation processes (SR-AOPs). A green and facile method was developed in this work to prepare uniform Co(OH)2 hexagonal nanosheets, which was void of any organic solvents via mere ambient temperature stirring. The obtained nanosheets were assembled into a catalytic gravity-driven membrane, through which the removal efficiency of a typical pharmaceutical contaminant, ranitidine (RNTD), could reach ∼100% within 20 min. Meanwhile, the catalytic membrane also demonstrated effective removal performance towards various pollutants. In order to augment the long-term stability of catalytic membranes, Co(OH)2/rGO composites were fabricated using the same strategy, and a Co(OH)2/rGO catalytic membrane was prepared correspondingly. The Co(OH)2/rGO membrane could maintain a ∼100% removal of RNTD over a constant reaction period lasting for up to 165 hours, which was approximately 11 times that of the sole Co(OH)2 membrane (15 h). Analysis of element chemical states, metal ion concentration in filtrates, and quenching experiments suggested that the combination with rGO could promote the electron transfer to accelerate the Co(II) regeneration, restrain the cobalt dissolution to alleviate the active site loss, and contribute to the production of 1O2via synergistic effects of oxygen-containing groups in rGO. Toxicity assessment was performed on RNTD and its degradation intermediates to confirm the reduction in ecotoxicity of the treated feed. Overall, this work not only offered guidance for the application of nanosheets in AOP membranes, but also had implications for the environmentally-friendly preparation protocol to obtain functional metal hydroxides.

Chalcopyrite functionalized ceramic membrane for micropollutants removal and membrane fouling control via peroxymonosulfate activation: The synergy of nanoconfinement effect and interface interaction

This work developed a novel chalcopyrite (CuFeS2) incorporated catalytic ceramic membrane (CFSCM), and comprehensively evaluated the oxidation-filtration efficiency and mechanism of CFSCM/peroxymonosulfate (PMS) for organics removal and membrane fouling mitigation. Results showed that PMS activation was more efficient in the confined membrane pore structure. The CFSCM50/PMS filtration achieved almost complete removal of 4-Hydroxybenzoic acid (4-HBA) under the following conditions: pH = 6.0, CPMS = 0.5 mM, and C4-HBA = 10 mg/L. Meanwhile, the membrane showed good stability after multiple uses. During the reaction, SO4•- and •OH were generated in the CFSCM50/PMS system, and SO4•- was considered to be the dominant reactive species for pollutant removal. The roles of copper, iron, and sulfur species, as well as the possible catalytic mechanism were also clarified. Besides, the CFSCM50/PMS catalytic filtration exhibited excellent antifouling properties against NOM with reduced reversible and irreversible fouling resistances. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis showed an increased in repulsive energy at the membrane-foulant interface in the CFSCM50/PMS system. Membrane fouling model analysis indicated that standard blocking was the dominant fouling pattern for CFSCM50/PMS filtration. Overall, this work demonstrates an efficient catalytic filtration process for foulants removal and outlines the synergy of catalytic oxidation and interface interaction.

Progress in layered double hydroxides (LDHs): Synthesis and application in adsorption, catalysis and photoreduction

Layered double hydroxides (LDHs), also known as anionic clays, have attracted significant attention in energy and environmental applications due to their exceptional physicochemical properties. These materials possess a unique structure with surface hydroxyl groups, tunable properties, and high stability, making them highly desirable. In this review, the synthesis and functionalization of LDHs have been explored including co-precipitation and hydrothermal methods. Furthermore, extensive research on LDH application in toxic pollutant removal has shown that modifying or functionalizing LDHs using materials such as activated carbon, polymers, and inorganics is crucial for achieving efficient pollutant adsorption, improved cyclic performance, as well as effective catalytic oxidation of organics and photoreduction. This study offers a comprehensive overview of the progress made in the field of LDHs and LDH-based composites for water and wastewater treatment. It critically discusses and explains both direct and indirect synthesis and modification techniques, highlighting their advantages and disadvantages. Additionally, this review critically discusses and explains the potential of LDH-based composites as absorbents. Importantly, it focuses on the capability of LDH and LDH-based composites in heterogeneous catalysis, including the Fenton reaction, Fenton-like reactions, photocatalysis, and photoreduction, for the removal of organic dyes, organic micropollutants, and heavy metals. The mechanisms involved in pollutant removal, such as adsorption, electrostatic interaction, complexation, and degradation, are thoroughly explained. Finally, this study outlines future research directions in the field.

Coagulation/co-catalytic membrane integrated system for fouling-resistant and efficient water purification

Low-pressure catalytic membranes allow efficient rejection of particulates and simultaneously removing organics pollutant in water, but the accumulation of dissolved organic matters (DOM) on membrane surface, which cover the catalytic sites and cause membrane fouling, challenges their stable operation in practical wastewater treatment. Here we propose a ferric salt-based coagulation/co-catalytic membrane integrated system that can effectively mitigate the detrimental effects of DOM. Ferric salt (Fe3+) serving both as a DOM coagulant to lower the membrane fouling and as a co-catalyst with the membrane-embedded MoS2 nanosheets to drive perxymonosulfate (PMS) activation and pollutant degradation. The membrane functionalized with 2H-phased MoS2 nanosheets showed improved hydrophilicity and fouling resistance relative to the blank polysulfone membrane. Attributed to the DOM coagulation and co-catalytic generation of surface-bound radicals for decontamination at membrane surface, the catalytic membrane/PMS/ Fe3+ system showed much less membrane fouling and 2.6 times higher pollutant degradation rate in wastewater treatment than the catalytic membrane alone. Our work imply a great potential of coagulation/co-catalytic membrane integrated system for water purification application.

Nanoconfined catalytic membrane assembled by nitrogen-doped carbon encapsulating Fe-based nanoparticles for rapid removal of 2,4-dichlorophenol in wastewater by peroxymonosulfate activation

Surface-dependent non-radical oxidation of carbon materials-based persulfate systems show a better application prospect in the removal of pollutants in complex wastewater. However, their potential is severely limited by the restricted liquid-to-solid mass transfer efficiency of conventional suspension systems. In this paper, a nitrogen-doped carbon encapsulating iron-based nanoparticles (Fe@NC) was prepared, and loaded onto a polyvinylidene fluoride (PVDF) membrane to construct a novel catalytic membrane Fe@NC/PVDF. The Fe@NC/PVDF/PMS system could achieve 99.74% of 2,4-dicholophenol (2,4-DCP) removal within a retention time of 0.867 s, the kinetic constant is 840 times higher than that of Fe@NC/PMS system, and 2-5 orders of magnitude higher than that of various reported advanced oxidation processes systems. The system exhibits strong anti-interference to various water matrices, long-time operational stability at high flux (306 L·m-2·h-1), universality to pollutants that do not contain strong electron-withdrawing groups and mitigation of membrane fouling. Mechanism studies indicate that the electron transfer pathway dominates the 2,4-DCP removal, and singlet oxygen (1O2) plays an auxiliary role. The higher mass transfer efficiency of the filtration mode releases the full potential of the non-radical pathway. This paper provides theoretical and technical support for the development and efficient utilization of carbon-based materials with excellent persulfate catalytic properties.

Structure Evolution of Iron (Hydr)oxides under Nanoconfinement and Its Implication for Water Treatment

In the development of nanoenabled technologies for large-scale water treatment, immobilizing nanosized functional materials into the confined space of suitable substrates is one of the most effective strategies. However, the intrinsic effects of nanoconfinement on the decontamination performance of nanomaterials, particularly in terms of structural modulation, are rarely unveiled. Herein, we investigate the structure evolution and decontamination performance of iron (hydr)oxide nanoparticles, a widely used material for water treatment, when confined in track-etched (TE) membranes with channel sizes varying from 200 to 20 nm. Nanoconfinement drives phase transformation from ferrihydrite to goethite, rather than to hematite occurring in bulk systems, and the increase in the nanoconfinement degree from 200 to 20 nm leads to a significant drop in the fraction of the goethite phase within the aged products (from 41% to 0%). The nanoconfinement configuration is believed to greatly slow down the phase transformation kinetics, thereby preserving the specific adsorption of ferrihydrite toward As(V) even after 20-day aging at 343 K. This study unravels the structure evolution of confined iron hydroxide nanoparticles and provides new insights into the temporospatial effects of nanoconfinement on improving the water decontamination performance.

Overcoming the permeability-selectivity challenge in water purification using two-dimensional cobalt-functionalized vermiculite membrane

Clean water and sanitation are major global challenges highlighted by the UN Sustainable Development Goals. Water treatment using energy-efficient membrane technologies is one of the most promising solutions. Despite decades of research, the membrane permeability-selectivity trade-off remains the major challenge for synthetic membranes. To overcome this challenge, here we develop a two-dimensional cobalt-functionalized vermiculite membrane (Co@VMT), which innovatively combines the properties of membrane filtration and nanoconfinement catalysis. The Co@VMT membrane demonstrates a high water permeance of 122.4 L·m-2·h-1·bar-1, which is two orders of magnitude higher than that of the VMT membrane (1.1 L·m-2·h-1·bar-1). Moreover, the Co@VMT membrane is applied as a nanofluidic advanced oxidation process platform to activate peroxymonosulfate (PMS) for degradation of several organic pollutants (dyes, pharmaceuticals, and phenols) and shows excellent degradation performance (~100%) and stability (for over 107 h) even in real-world water matrices. Importantly, safe and non-toxic effluent water quality is ensured by the Co@VMT membrane/PMS system without brine, which is totally different from the molecular sieving-based VMT membrane with the concentrated pollutants remaining in the brine. This work can serve as a generic design blueprint for the development of diverse nanofluidic catalytic membranes to overcome the persistent membrane permeability-selectivity issue in water purification.

Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139-228 L·m-2·h-1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.

Iron-Cobalt magnetic porous carbon beads activated peroxymonosulfate for enhanced degradation and Microbial inactivation

Magnetic carbon-based catalysts are promising materials for advanced oxidation processes, offering both high catalytic activity and environmental friendliness, and hold great potential in environmental remediation. In this work, Fe and Co zeolite imidazole frameworks (ZIFs) derived micron-sized magnetic porous carbon beads (MPCBs) were prepared by phase inversion and following the carbonization procedure, and the morphological and structural characteristics of the MPCBs were confirmed. The presence of pores and channels in the MPCBs provides a specific microenvironment for the for the catalysis of the core. Bisphenol A (BPA) was selected for the targeted pollutant, and the catalytic experiments confirmed that the effective catalytic activity of MPCBs in the presence of peroxymonosulfate (PMS), which could almost completely degrade BPA in 20 min with a reaction rate of 0.368 min-1. Furthermore, the MPCBs were used to effectively bacterial inactivation. Intermediate products of the BPA degradation process were validated and the toxicological studies showed a gradual decrease in toxicity, indicating effective reduction of potential hazards. The macroscopic preparation methods we developed for MPCBs that is promising for industrial applications and has the potential to cope with complex environmental remediation.

B-doping mediated formation of oxygen vacancies in Bi2Sn2O7 quantum dots with a unique electronic structure for efficient and stable photoelectrocatalytic sulfamethazine degradation

This study devised a straightforward one-step approach that enabled simultaneous boron (B) doping and oxygen vacancies (OVs) production on Bi₂Sn₂O₇ (BSO) (B-BSO-OV) quantum dots (QDs), optimizing the electrical structure of the photoelectrodes. Under light-emitting diode (LED) illumination and a low potential of 1.15 V, B-BSO-OV demonstrated effective and stable photoelectrocatalytic (PEC) degradation of sulfamethazine (SMT), achieving the first-order kinetic rate constant of 0.158 min^-1. The surface electronic structure, the different factors influencing the PEC degradation of SMT, and the degradation mechanism were studied. Experimental studies have shown that B-BSO-OV exhibits strong visible light trapping ability, high electron transport ability, and superior PEC performance. DFT calculations show that the presence of OVs on BSO successfully reduces the band gap, controls the electrical structure, and accelerates charge transfer. This work sheds light on the synergistic effects of the electronic structure of B-doping and OVs in heterobimetallic oxide BSO under the PEC process and offers a promising approach for the design of photoelectrodes.

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as electrochemical sensors for the efficient detection of pharmaceutical residues

Pharmaceutical residues are the undecomposed remains from drugs used in the medical and food industries. Due to their potential adverse effects on human health and natural ecosystems, they are of increasing worldwide concern. The acute detection of pharmaceutical residues can give a rapid examination of their quantity and then prevent them from further contamination. Herein, this study summarizes and discusses the most recent porous covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) for the electrochemical detection of various pharmaceutical residues. The review first introduces a brief overview of drug toxicity and its effects on living organisms. Subsequently, different porous materials and drug detection techniques are discussed with materials' properties and applications. Then the development of COFs and MOFs has been addressed with their structural properties and sensing applications. Further, the stability, reusability, and sustainability of MOFs/COFs are reviewed and discussed. Besides, COFs and MOFs' detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles are analyzed and discussed. Lastly, this review summarized and discussed the MOF@COF composite as sensors, the fabrication strategies to enhance detection potential, and the current challenges in this area.

3D variable Co species carbon foam enhanced reactive oxygen species generation and ensured long-term stability for water purification

Cobalt (Co) and oxides are the most common catalysts for activating peroxymonosulfate (PMS). However, practical applications of Co-based PMS-advanced oxidation processes are difficult to realize the degradation of the targeted pollutants due to poor yield of reactive oxygen species (ROS) and inaccessible active sites. Here, we designed 3D oxygen vacancy-rich (V_o-rich) variable Co species@carbon foam (Co_xO_y@CF) via coupling solvent-free and pyrolysis strategies for degrading tetracycline by PMS activation. The kinetic rate of optimized (Co@CoO) Co_xO_y@CF-1.0 (1.0 presented the molar ratio of Co²⁺ and 2-methylimidazole) enhanced by an order of magnitude compared to that of ZIFs derivatives (ZIFs-500) (0.073 vs 0.155 min^-1) due to the special structure. The flow-through unit maintained over 90% removal within 12 h, which was far better than that of ZIFs-500/PMS system. We used electrochemical analysis, quenching experiment, in-situ FTIR and Raman spectra to further investigate the possible mechanism of the 3D Co_xO_y@CF-1.0/PMS system. 3D Co_xO_y@CF-1.0 stimulated the production of the metastable catalyst-PMS* complex obtained O₂^- as intermediates accompanied by the redox cycling of Co²⁺/Co³⁺, which created the dominant ROS (more ¹O₂) in the presence of V_o, which was completely different for ZIFs-500/PMS with coordinated and dominant radical and non-radical pathways. This study could large-scale generate variable cobalt-based catalysts for enhanced ROS generation, leading the new insight for boosting practical applications.