Metal-Organic Frameworks and Their Derived Materials: Emerging Catalysts for a Sulfate Radicals-Based Advanced Oxidation Process in Water Purification

Multiporous ZIF-8 carbon/cellulose composite beads: Highly efficient and scalable adsorbents for water treatment

Metal-organic framework (MOF) particles are one of the most promising adsorbents for removing organic contaminants from wastewater. However, powder-type MOF particles face challenges in terms of utilization and recovery. In this study, a novel bead-type adsorbent was prepared using activated carbon based on the zeolitic imidazolate framework-8 (AC-ZIF-8) and a regenerated cellulose hydrogel for dye removal. AC-ZIF-8 particles with a large surface area were obtained by carbonization and chemical activation with KOH. The AC-ZIF-8 powders were efficiently immobilized in hydrophilic cellulose hydrogel beads via cellulose dissolution/regeneration. The prepared AC-ZIF-8/cellulose hydrogel (AC-ZIF-8/CH) composite beads exhibit a large specific surface area of 1412.8 m2/g and an excellent maximum adsorption capacity of 565.13 mg/g for Rhodamine B (RhB). Moreover, the AC-ZIF-8/CH beads were effective over a wide range of pH, temperatures and for different types of dyes. These composite beads also offer economic benefits through desorption of dyes for recycling. The AC-ZIF-8/CH beads can be produced in substantial amounts and used as fillers in a fixed-bed column system, which can purify the continuous inflow of dye solutions. These findings suggest that our simple approach for preparing high-performance adsorbent beads will broaden the application of dye adsorbents, oil-water separation, and catalysts.

From nano- to macroarchitectures: designing and constructing MOF-derived porous materials for persulfate-based advanced oxidation processes

Persulfate-based advanced oxidation processes (PS-AOPs) have gained significant attention as an effective approach for the elimination of emerging organic contaminants (EOCs) in water treatment. Metal-organic frameworks (MOFs) and their derivatives are regarded as promising catalysts for activating peroxydisulfate (PDS) and peroxymonosulfate (PMS) due to their tunable and diverse structure and composition. By the rational nanoarchitectured design of MOF-derived nanomaterials, the excellent performance and customized functions can be achieved. However, the intrinsic fine powder form and agglomeration ability of MOF-derived nanomaterials have limited their practical engineering application. Recently, a great deal of effort has been put into shaping MOFs into macroscopic objects without sacrificing the performance. This review presents recent advances in the design and synthetic strategies of MOF-derived nano- and macroarchitectures for PS-AOPs to degrade EOCs. Firstly, the strategies of preparing MOF-derived diverse nanoarchitectures including hierarchically porous, hollow, yolk-shell, and multi-shell structures are comprehensively summarized. Subsequently, the approaches of manufacturing MOF-based macroarchitectures are introduced in detail. Moreover, the PS-AOP application and mechanisms of MOF-derived nano- and macromaterials as catalysts to eliminate EOCs are discussed. Finally, the prospects and challenges of MOF-derived materials in PS-AOPs are discussed. This work will hopefully guide the design and development of MOF-derived porous materials in SR-AOPs.

Metal-Organic Frameworks Marry Sponge: New Opportunities for Advanced Water Treatment

Metal-organic frameworks (MOFs) have garnered attention across various fields due to their noteworthy features like high specific surface area, substantial porosity, and adjustable performance. In the realm of water treatment, MOFs exhibit great potential for eliminating pollutants such as organics, heavy metals, and oils. Nonetheless, the inherent powder characteristics of MOFs pose challenges in terms of recycling, pipeline blockage, and even secondary pollution in practical applications. Addressing these issues, the incorporation of MOFs into sponges proves to be an effective solution. Strategies like one-pot synthesis, in situ growth, and impregnation are commonly employed for loading MOFs onto sponges. This review comprehensively explores the synthesis strategies of MOFs and sponges, along with their applications in water treatment, aiming to contribute to the ongoing advancement of MOF materials.

Enhancing dye degradation using a novel cobalt metal-organic framework as a peroxymonosulfate activator

Among transition metals, cobalt ions exhibit superior catalytic activity in the peroxymonosulfate (PMS) degradation of pollutants. However, practical application is hindered by their high rate of ion leaching and the propensity for particle reunion issues. In this study, a novel cobalt metal-organic framework catalyst, denoted as CUST-565 ([Co3(BTB)2(BIPY)2]·4.5H2O·DMA), was synthesized via a one-step solvothermal method. The obtained crystal was employed as a catalyst to activate PMS for degrading two pollutants, methyl orange (MO) and rhodamine B (RhB), in wastewater. The catalyst demonstrated efficacy in PMS, achieving 97% degradation of MO and 98% degradation of RhB within 30 min at an initial concentration of 20.0 mg L-1. Additionally, various factors affecting dye degradation, including PMS dosage, catalyst dosage, temperature, initial pH, and coexisting anions, were investigated. Radical quenching experiments confirmed the presence of sulfate radicals (SO4˙-), hydroxyl radicals (HO˙), superoxide radicals (O2˙-), and singlet oxygen (1O2) in the system. After four cycles, CUST-565 retained its ability to catalytically degrade approximately 80% of the pollutants. These observed stability and reusability properties, corroborated by a series of characterization analyses before and after use, suggest that CUST-565 exhibits reliable performance. This work contributes to the development of cobalt-PMS catalysts for efficiently degrading dyes in wastewater.

Confined Space Nanoarchitectonics for Dynamic Functions and Molecular Machines

Nanotechnology has advanced the techniques for elucidating phenomena at the atomic, molecular, and nano-level. As a post nanotechnology concept, nanoarchitectonics has emerged to create functional materials from unit structures. Consider the material function when nanoarchitectonics enables the design of materials whose internal structure is controlled at the nanometer level. Material function is determined by two elements. These are the functional unit that forms the core of the function and the environment (matrix) that surrounds it. This review paper discusses the nanoarchitectonics of confined space, which is a field for controlling functional materials and molecular machines. The first few sections introduce some of the various dynamic functions in confined spaces, considering molecular space, materials space, and biospace. In the latter two sections, examples of research on the behavior of molecular machines, such as molecular motors, in confined spaces are discussed. In particular, surface space and internal nanospace are taken up as typical examples of confined space. What these examples show is that not only the central functional unit, but also the surrounding spatial configuration is necessary for higher functional expression. Nanoarchitectonics will play important roles in the architecture of such a total system.

Nanoleaf-derived carbon materials as a sensitivity coating for solid‑phase microextraction of polycyclic aromatic hydrocarbons

Metal-organic framework-derived carbon materials have shown extensive application in the sensitive extraction of polycyclic aromatic hydrocarbons (PAHs), but more active sites for its adsorption were still a tireless pursuit. In this study, ZIF-nanoleaf-derived carbon (NLCs) was synthesized and developed as a solid-phase microextraction (SPME) fiber (NLCs-F). The extraction performance was compared with ZIF-dodecahedron-derived carbon (DHCs) coated fiber (DHCs-F), which was prepared by only changing the ratio of the reactants. The unique morphology of NLCs provided abundant adsorption active sites for the selected PAHs, while the large average aperture facilitated selective extraction of high molecular weight analytes. Additionally, the high carbon content enhanced the strong enrichment capability for hydrophobic PAHs. Hence, the prepared NLCs-F coupled with GC-MS showed a good correlation coefficient (0.9975) in a wide linear range, low limits of detection (0.3-1.8 ng L-1), satisfactory repeatability, and reproducibility, which made it apply in the enrichment of PAHs in actual tea and coffee samples.

A confined expansion pore-making strategy to transform Zn-MOF to porous carbon nanofiber for water treatment: Insight into formation and degradation mechanism

Electrospinning MOFs nanoparticles derived porous carbon nanofibers with rational structure and design are recently as environmentally friendly and highly efficient catalytic materials for wastewater treatment. However, most of the pore-making strategies are based on precursors structural shrinkage during pyrolysis, which is a challenge to create abundant large pores and open channels. Here, a confined expansion pore-making strategy with active MOF is introduced, where energetic Zn-MOF (Zn2+/triazole) and ZIF-67 (Co2+/dimethylimidazole) are utilized as pore forming additive and precursor of active sites, respectively. The high nitrogen content gives triazole the ability to puff up and realizes N-doped during pyrolysis. Moreover, degradation mechanisms and pathways of pollutants were measured by 3D EEM, LC-MS, quenching experiments, and Fukui function. This pore-making strategy via energetic MOF local contraction and expansion provides a novel method to prepare diversiform function porous carbon materials for environmental remediation.

Nanoarchitectonics of Bimetallic MOF@Lab-Grade Flexible Filter Papers: An Approach Towards Real-Time Water Decontamination and Circular Economy

This study presents a novel approach to decontaminate ferrocyanide-contaminated wastewater. The work effectively demonstrates the use of bimetallic Mo/Zr-UiO-66 as a super-adsorbent for rapid sequestration of Prussian blue, a frequently found iron complex in cyanide-contaminated soils/groundwater. The exceptional performance of Mo/Zr-UiO-66 is attributed to the insertion of secondary metallic sites, which deliver synergistic effects, benefiting the inherent qualities of the framework. Moreover, to extend the industrial applications of metal-organic frameworks (MOFs) in real-world scenarios, an approach is delivered to structure the nanocrystalline powders into MOF-based macrostructures. The work demonstrates an interfacial process to develop continuous MOF nanostructures on ordinary laboratory-grade filter papers. The novelty of the work lies in the development of robust free-standing filtration materials to purify PB dye-contaminated water. Additionally, the work embraces a circular economy concept to address problems related to resource scarcity, excessive waste production, and maintenance of economic benefits. Consequently, the PB dye-loaded adsorbent waste is re-employed for the adsorption of heavy metals (Pb2+ and Cd2+ ). Simultaneously, the study aims to address the problems related to the real-time handling of powdered adsorbents, and the generation of ecologically harmful secondary waste, thereby, progressing toward a more sustainable system.

Constructing Hollow Multishelled Microreactors with a Nanoconfined Microenvironment for Ofloxacin Degradation through Peroxymonosulfate Activation: Evolution of High-Valence Cobalt-Oxo Species

This study constructed hollow multishelled microreactors with a nanoconfined microenvironment for degrading ofloxacin (OFX) through peroxymonosulfate (PMS) activation in Fenton-like advanced oxidation processes (AOPs), resulting in adequate contaminant mineralization. Among the microreactors, a triple-shelled Co-based hollow microsphere (TS-Co/HM) exhibited optimal performance; its OFX degradation rate was 0.598 min-1, which was higher than that of Co3O4 nanoparticles by 8.97-fold. The structural tuning of Co/HM promoted the formation of oxygen vacancies (VO), which then facilitated the evolution of high-valence cobalt-oxo (Co(IV)═O) and shifted the entire t2g orbital of the Co atom upward, promoting catalytic reactions. Co(IV)═O was identified using a phenylmethyl sulfoxide (PMSO) probe and in situ Raman spectroscopy, and theoretical calculations were conducted to identify the lower energy barrier for Co(IV)═O formation on the defect-rich catalyst. Furthermore, the TS-Co/HM catalyst exhibited remarkable stability in inorganic (Cl-, H2PO4-, and NO3-), organic (humic acid), real water samples (tap water, river water, and hospital water), and in a continuous flow system in a microreactor. The nanoconfined microenvironment could enrich reactants in the catalyst cavities, prolong the residence time of molecules, and increase the utilization efficiency of Co(IV)═O. This work describes an activation process involving Co(IV)═O for organic contaminants elimination. Our results may encourage the use of multishelled structures and inform the design of nanoconfined catalysts in AOPs.

Sulfate Radical-Based Degradation of Organic Pollutants: A Review on Application of Metal-Organic Frameworks as Catalysts

The degradation of organic pollutants present in domestic and industrial effluents is a matter of concern because of their high persistence and ecotoxicity. Recently, advanced oxidation processes (AOPs) are being emphasized for organic pollutant removal from effluents, as they have shown higher degradation efficiencies when compared to conventional activated sludge processes. Sulfate radical-based methods are some of the AOPs, mainly carried out using persulfate (PS) and peroxymonosulfate (PMS), which have gained attention due to the ease of sulfate radical generation and the effective degradation of organic molecules. PMS is gaining more popularity because of its high reactivity and ability to generate excess sulfate radicals. PMS has been the major focus; therefore, its mechanism has been explained, and limitations have been elaborated. The involvement of metal-organic frameworks for PMS/PS activation applied to organic pollutant removal and recent advances in the application of biochar and hydrogel-assisted metal-organic frameworks have been discussed.

Photodegradation performance and mechanism of sulfadiazine in Fe(III)-EDDS-activated persulfate system

In order to overcome the shortcomings in the traditional Fenton process, Fe(III)-EDDS-activated persulfate advanced oxidation process under irradiation is carried out as a promising technology. The photodegradation of sulfadiazine (SD) in Fe(III)-EDDS-activated persulfate system was investigated in this paper. The results showed that SD could be effectively degraded in Fe(III)-EDDS/S 2 O 8 2 - /hv system. The effects of Fe(III):EDDS molar ratio, the concentration of Fe(III)-EDDS, and the concentration of S 2 O 8 2 - on SD degradation were explored. At neutral pH, when Fe(III):EDDS = 1:1, Fe(III)-EDDS = 0.1 mM, S 2 O 8 2 -  = 1.5 mM, the best SD degradation was achieved. The experiment of external influence factors showed that the degradation of SD could be obviously inhibited by the presence of C O 3 2 - , S O 4 2 - , whereas the degradation of SD was almost unaffected by the addition ofCl-. The degradation of SD could be slightly inhibited by the presence of humic acid and NO3-. The effect of pH on SD degradation was investigated, and SD could be degraded effectively in the pH range of 3-9. ESR proved that 1O2, ·OH, S O 4 - , and O2- were produced in the process. S O 4 - and ·OH were identified as the main radicals while O2·- also played non-ignorable role. Eleven intermediate products of SD were analysed. The C = N, S-N, and S-C bonds of SD were attacked by radicals firstly, leading to a series of reactions that eventually resulted in the destruction of SD molecules and the formation of small organic molecules.

Advanced Oxidation Nanoprocessing Boosts Immunogenicity of Whole Tumor Cells

Whole tumor cells expressing a wide array of tumor antigens are considered as a highly promising source of antigens for cancer vaccines. However, simultaneously preserving the antigen diversity, improving immunogenicity, and eliminating the potential tumorigenic risk of whole tumor cells are highly challenging. Inspired by the recent progress in sulfate radical-based environmental technology, herein, an advanced oxidation nanoprocessing (AONP) strategy is developed for boosting the immunogenicity of whole tumor cells. The AONP is based on the activation of peroxymonosulfate by ZIF-67 nanocatalysts to produce SO4 -∙ radicals continuously, leading to sustained oxidative damage to tumor cells and consequently extensive cell death. Importantly, AONP causes immunogenic apoptosis as evidenced by the release of a series of characteristic damage associated molecular patterns and at the same time maintains the integrity of cancer cells, which is critical to preserve the cellular components and thus maximize the diversity of antigens. Finally, the immunogenicity of AONP-treated whole tumor cells is evaluated in a prophylactic vaccination model, demonstrating significantly delayed tumor growth and increased survival rate of live tumor-cell-challenged mice. It is expected that the developed AONP strategy would pave the way to develop effective personalized whole tumor cell vaccines in future.

Enhanced catalytic oxidation of naproxen via activation of peroxymonosulfate by Fe-based metal-organic framework aerogels functionalized with Ag nanoparticles

In this study, Ag₃PO₄ and Fe-based metal-organic frameworks (MOFs)-functionalized three-dimensional (3D) porous gelatin aerogels (Ag/Fe@GMA) were fabricated and used as adsorbents and catalysts for the activation of peroxymonosulfate (PMS) for naproxen (NPX) removal from water. The morphology, crystallinity, surface functional groups, and surface chemical element compositions of the fabricated Ag/Fe@GMA was evaluated using various analytical techniques. Our results showed that as an adsorbent, Ag/Fe@GMA showed a 18.0 % higher NPX adsorption capacity compared with the pristine aerogels. This can be attributed to the well-embedded Ag₃PO₄ and MOFs, indicating a stronger interaction between functionalized aerogels and NPX. After adsorption, 99.9 % of total NPX removal was achieved within 15 min by activating PMS and effectively generating ^•OH and ^•SO₄^- in water. The PMS/Ag/Fe@GMA aerogel system also showed high removal performance for rhodamine B (99.5 %) and tetracycline (93.7 %). Moreover, the Ag/Fe@GMA aerogels showed excellent reusability to achieve 95.7 % NPX removal efficiency after six times of recycling. This study revealed that the Ag/Fe@GMA aerogels had good potential for PMS activation and NPX removal. In particular, as an alternative to powdery materials, 3D shape of Ag/Fe@GMA with excellent reusability facilitates its application in the treatment of water contaminated with organic contaminants.

Construction of Co3O4 anchored on Bi2MoO6 microspheres for highly efficient photocatalytic peroxymonosulfate activation towards degradation of norfloxacin

Dissolved antibiotics have been a research subject due to their widespread presence and potential threats in drinking water treatment. To enhance the photocatalytic activity of Bi₂MoO₆ for the degradation of norfloxacin (NOR), the heterostructured Co₃O₄/Bi₂MoO₆ (CoBM) composites were synthesized by employing ZIF-67-derived Co₃O₄ on Bi₂MoO₆ microspheres. The as-synthesized resultant material 3-CoBM by 300 °C calcination was characterized by XRD, SEM, XPS, transient photocurrent techniques, and EIS. The photocatalytic performance was evaluated by monitoring different concentrations, NOR removal from aqueous solution. Compared with Bi₂MoO₆, 3-CoBM exhibited the better adsorption and elimination capacity of NOR due to the combined effect between peroxymonosulfate activation and photocatalytic reaction. The influences of catalyst dosage, PMS dosage, various interfering ions (Cl^-, NO₃^-, HCO₃^-, and SO₄^2-), pH value, and type of antibiotics for application removal were also invested. By activating PMS under visible-light irradiation, 84.95% of metronidazole (MNZ) can be degraded within 40 min, and NOR and tetracycline (TC) can be completely degraded using 3-CoBM. Degradation mechanism was elucidated by quenching tests in combination with EPR measurement, and the degree of activity of the active groups from strong to weak is h⁺, SO₄^-•, and •OH, respectively. The degradation products and conceivable degradation pathways of NOR were speculated by LC-MS. In combination of excellent peroxymonosulfate activation and highly enhanced photocatalytic performance, this newly Co₃O₄/Bi₂MoO₆ catalyst might be a promising candidate for degrading emerging antibiotic contamination in wastewater.

Oxygen doping of cobalt-single-atom coordination enhances peroxymonosulfate activation and high-valent cobalt-oxo species formation

The high-valent cobalt-oxo species (Co(IV)=O) is being increasingly investigated for water purification because of its high redox potential, long half-life, and antiinterference properties. However, generation of Co(IV)=O is inefficient and unsustainable. Here, a cobalt-single-atom catalyst with N/O dual coordination was synthesized by O-doping engineering. The O-doped catalyst (Co-OCN) greatly activated peroxymonosulfate (PMS) and achieved a pollutant degradation kinetic constant of 73.12 min-1 g-2, which was 4.9 times higher than that of Co-CN (catalyst without O-doping) and higher than those of most reported single-atom catalytic PMS systems. Co-OCN/PMS realized Co(IV)=O dominant oxidation of pollutants by increasing the steady-state concentration of Co(IV)=O (1.03 × 10-10 M) by 5.9 times compared with Co-CN/PMS. A competitive kinetics calculation showed that the oxidation contribution of Co(IV)=O to micropollutant degradation was 97.5% during the Co-OCN/PMS process. Density functional theory calculations showed that O-doping influenced the charge density (increased the Bader charge transfer from 0.68 to 0.85 e), optimized the electron distribution of the Co center (increased the d-band center from -1.14 to -1.06 eV), enhanced the PMS adsorption energy from -2.46 to -3.03 eV, and lowered the energy barrier for generation of the key reaction intermediate (*O*H2O) during Co(IV)=O formation from 1.12 to 0.98 eV. The Co-OCN catalyst was fabricated on carbon felt for a flow-through device, which achieved continuous and efficient removal of micropollutants (degradation efficiency of >85% after 36 h operation). This study provides a new protocol for PMS activation and pollutant elimination through single-atom catalyst heteroatom-doping and high-valent metal-oxo formation during water purification.

Guest Molecule Insertion-Optimized d-Band Center Position in MoS2 with Improved Sulfite Activation Ability Inspired by Sulfite Oxidase

As a prospective member in the family of advanced oxidation processes (AOPs), heterogeneous sulfite activation shows low cost and high safety for poisonous organic pollutants' degradation. To obtain an efficient sulfite activator, sulfite oxidase (SuO_x), a molybdenum-based enzyme that can prompt oxidation and activation of sulfite, inspired us greatly. Based on the structure of SuO_x, MoS₂/BPE (BPE = 1, 2-bis-(4-pyridyl)-ethylene) is synthesized successfully. In MoS₂/BPE, the BPE molecule is inserted between the MoS₂ layers as a pillar and the N atom links with Mo⁴⁺ directly. MoS₂/BPE shows excellent SuO_x mimic activity. Theoretical calculation implies that BPE insertion optimizes the d-band center position of MoS₂/BPE, which regulates the interaction between MoS₂ and *SO₄^2-. This prompts ^•SO₄^- generation and organic pollutants' degradation. At pH 7.0, its tetracycline degradation efficiency achieved is 93.9% in 30 min. Furthermore, its sulfite activation ability also endows MoS₂/BPE with excellent antibiofouling performance because ^•SO₄^- can kill the microorganisms in water effectively. This work develops a new sulfite activator based on SuO_x. The connection between structure and SuO_x mimic activity and sulfite activation ability is clarified in detail.

Rational regulation of peroxymonosulfate activation over porous Co3O4 with carbon coating to boost utilization efficiency of peroxymonosulfate and achieve rapid removal of pollutants

It is of great significance to regulate rationally the activation mechanism of persulfate for promoting the development of sulfate radical-based advanced oxidation processes in wastewater treatment. Herein, carbon coated porous Co₃O₄ with hollow structure was synthesized. Notably, the formation of porous hollow structure improved specific surface area of Co₃O₄ and offered more redox couples of Co²⁺/Co³⁺, thereby reducing electron transfer resistance. Thus, the generation of reactive oxygen species and the role of high-valent transition metal complexes (namely Co₃O₄Co⁴⁺) were improved. The formation of carbon layer on the Co₃O₄ surface can avoid the release of Co ion during reaction process. Benefiting from the role of carbon layer in electron transport, catalyst-mediated the direct electron transfer from pollutant to PMS was boosted. Radical and nonradical pathways worked in coordination each other and realized the rapid removal of various organic pollutants in the presence of a little PMS. In short, current work revealed that modulating rationally the microstructure of catalyst was an efficient strategy for achieving controllable regulation of PMS activation process. More significantly, whether the direct electron transfer process can occur or not depended on both catalyst structure and electronic density of pollutants.

Improvement of peroxymonosulfate utilization efficiency for sulfamethazine degradation by photo-electron activating peroxymonosulfate: Performance and mechanism

Enhancing the utilization efficiency of oxidant is of great importance for advanced oxidation processes (AOPs). Herein, nitrogen-doped titania dioxide/carbon (NTC7) catalyst was fabricated via pyrolyzing NH₂-MIL-125 under nitrogen atmosphere at 700 °C. Excitation of NTC7 under visible light can successfully achieve efficient activation of peroxymonosulfate (PMS) (NTC7 + PMS + Vis). Degradation performance and PMS activation mechanism were systematically investigated using sulfamethazine (SMT) as the target pollutant. It was found that the photo-generated electrons excited from NTC7 under visible light played the dominant role in enhancing the productive consumption of PMS. Its utilization increased by 66 % (Δ[PMS]/Δ[SMT] = 7.0) in NTC7 + PMS + Vis process and the degradation rate was 2.14 times higher than that of NTC7 + PMS process. The ketonic CO groups and structural defects were responsible for the generation of ¹O₂ in dark activation while radicals (•OH, O₂^•-) were more inclined to be continuously produced in NTC7 + PMS + Vis process. The involved degradation pathways, intermediates, and toxicity assessment have been studied in detail. This work provides an effective approach to enhance the utilization efficiency of oxidant for pollutant degradation by AOPs.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

Degradation of lomefloxacin by MoS2/MIL-53(Fe, Cu) catalyst in heterogeneous electro-Fenton process

A novel heterogeneous catalyst named MoS₂/MIL-53(Fe, Cu) (MMFC) was prepared by hydrothermal method and applied in a heterogeneous electro-Fenton (hetero-EF) system for lomefloxacin (LOM) degradation in this work. Under the optimal conditions of current density 3 mA/cm², catalyst dosage 0.100 g/L, and initial pH 6, 93.5% LOM (2 mg/L) removal efficiency was achieved in the MMFC hetero-EF system within 60 min, indicating an obvious improvement compared with the MIL-53(Fe, Cu) hetero-EF system. The good catalytic activity was attributed to more effective active sites of the catalyst and the conversion of Fe(II)/Fe(III) and Cu(I)/Cu(II) promoted by Mo(IV) in MoS₂, which could be inferred by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) characterizations. The reusability and stability of MMFC were explored based on five cyclic experiments, and the average degradation efficiency reached 73.9%. Furthermore, the hetero-EF system could achieve the total removal of moxifloxacin and tetracycline within 6 min and 40 min, respectively. Quenching experiments revealed that the hydroxyl radicals (·OH) were the main reactive radicals while superoxide radicals (·O₂^-) and singlet oxygen (¹O₂) played a certain part in LOM degradation. Finally, the possible mechanism of the hetero-EF process and LOM degradation pathways were proposed, including substitution, elimination, and cleavage of ring structures. Accounting for good catalytic performance, low preparation cost, and satisfactory versatility, the MMFC exhibited good potential to work as a hetero-EF catalyst for wastewater treatment.

Preparation of VCo-MOF@MXene composite catalyst and study on its removal of ciprofloxacin by catalytically activating peroxymonosulfate: Construction of ternary system and superoxide radical pathway

The synergistic effect between transition metal active centers and the generation of multiple removal pathways has a significant impact on the catalytic activation efficiency of peroxymonosulfate. In this work, a kind of composite catalyst was prepared by growing VCo-metal-organic frameworks (VCo-MOF) in-situ on the surface of Ti3C2Tx by a solvothermal method. The morphology and structure are characterized by Transmission Electron Microscope (TEM), Energy Dispersion Spectrum (EDS), Atomic Force Microscope (AFM), etc. Response surface methodology was used to optimize the experimental conditions. Only 5 mg catalyst can be used to effectively activate PMS and remove 96.14 % ciprofloxacin (CIP, 20 mg/L) within 30 min. The removal effect of catalyst on CIP in different actual water environment was explored. In addition, the fluorescence spectrum test also verified the effective removal of ciprofloxacin. V-Co-Ti ternary system provides a wealth of active sites for CIP removal. Cyclic voltammetry (CV) and lear sweep voltammetry (LSV) tests showed the existence of the electron transfer pathway. The results of density functional theory (DFT) calculation show that VCo-MOF@Ti3C2Tx has excellent adsorption and activation ability for PMS. At the same time, the hydrophilicity of the catalyst makes PMS more inclined to react with water molecules, which promotes the formation of a unique superoxide radical path.

Generation of red light with intense photoluminescence assisted by Forster resonance energy transfer from Znq2 and DCM thin films

In this work, a novel experimental investigation of photoluminescence properties of Znq₂ thin films co-doped with different concentrations of DCM were performed. The thin films were successfully deposited on glass substrates with different compositions, under high vacuum, by using the vacuum evaporation technique. For all compositions, the photoluminescence was measured at room temperature and also at low temperature in a wide range from 77 to 300 K with a step of 25 K in a high vacuum. The lifetime of the sample studied in real time was also measured using the decay time technique. The results obtained confirm that the doping influences the intensity of the DCM photoluminescence and also shows a complete energy transfer occurred from Znq₂ to DCM which may have shifted the photoluminescence peak from Znq₂ to the orange wavelength region which is related to DCM. The lifetime of the sample studied in real time was about 4.47 ns for Znq₂ and while all the other samples showed two decay time components. As a result, the doping influences the optical properties of Znq₂ and makes it a potential candidate for optoelectronic applications.

Application of Nanocatalysts in Advanced Oxidation Processes for Wastewater Purification: Challenges and Future Prospects

The increase in population demands for industrialization and urbanization which led to the introduction of novel hazardous chemicals in our environment. The most significant parts of these harmful substances found in water bodies remain in the background, causing a health risk to humans and animals. It is critical to remove these toxic chemicals from the wastewater to keep a cleaner and greener environment. Hence, wastewater treatment is a challenging area these days to manage liquid wastes effectively. Therefore, scientists are in search of novel technologies to treat and recycle wastewater, and nanotechnology is one of them, thanks to the potential of nanoparticles to effectively clean wastewater while also being ecologically benign. However, there is relatively little information about nanocatalysts’ applicability, efficacy, and challenges for future applications in wastewater purification. This review paper is designed to summarize the recent studies on applying various types of nanocatalysts for wastewater purification. This review paper highlights innovative work utilizing nanocatalysts for wastewater applications and identifies issues and challenges to overcome for the practical implementation of nanocatalysts for wastewater treatment.

Rational Regulation of Co-N-C Coordination for High-Efficiency Generation of 1O2 toward Nearly 100% Selective Degradation of Organic Pollutants

Single oxygen-based advanced oxidation processes (¹O₂-AOPs) exhibit great prospects in selective degradation of organic pollutants. However, efficient production of ¹O₂ via tailored design of catalysts to achieve selective oxidation of contaminants remains challenging. Herein, we develop a simple strategy to regulate the components and coordination of Co-N-C catalysts at the atomic level by adjusting the Zn/Co ratio of bimetallic zeolitic imidazolate frameworks (Zn_xCo₁-ZIFs). Zn₄Co₁-C demonstrates 98% selective removal of phenol in the mixed phenol/benzoic acid (phenol/BA) solutions. Density functional theory calculations and experiments reveal that more active CoN₄ sites are generated in Zn₄Co₁-C, which are beneficial to peroxymonosulfate activation to generate ¹O₂. Furthermore, the correlation between the origin of selectivity and well-defined catalysts is systematically investigated by the electron paramagnetic resonance test and quenching experiments. This work may provide novel insights into selective removal of target pollutants in a complicated water matrix.

Oxygen-Independent Sulfate Radical for Stimuli-Responsive Tumor Nanotherapy

Variant modalities are quested and merged into the tumor nanotherapy by leveraging the excitation from external or intratumoral incentives. However, the ubiquitous hypoxia and the insufficient content of hydrogen peroxide (H₂ O₂ ) in tumor microenvironments inevitably hinder the effective production of reactive oxygen species (ROS). To radically extricate from the shackles, peroxymonosulfate (PMS: HSO₅^- )-loaded hollow mesoporous copper sulfide (CuS) nanoparticles (NPs) are prepared as the distinct ROS donors for sulfate radical (•SO₄^- )-mediated and stimuli-responsive tumor nanotherapy in an oxygen-independent manner. In this therapeutic modality, the second near-infrared laser irradiation, together with the released copper ions as well as the heat produced by CuS after illumination, work together to activate PMS thus triply ensuring the copious production of •SO₄^- . Different from conventional ROS, the emergence of •SO₄^- , possessing a longer half-life and more rapid reaction, is independent of the oxygen (O₂ ) and H₂ O₂ content within the tumor. In addition, this engineered nanosystem also exerts the function of photoacoustic imaging and skin restoration on the corresponding animal models. This study reveals the enormous potential of sulfate radical in oncotherapy and broadens pave for exploring the application of multifunctional and stimuli-responsive nanosystems in biomedicine.

High yield M-BTC type MOFs as precursors to prepare N-doped carbon as peroxymonosulfate activator for removing sulfamethazine: The formation mechanism of surface-bound SO4•- on Co-Nx site

M-BTCs (M = Fe, Co and Mn)/melamine were used to prepare N-doped carbon materials, and their performances as activator of peroxymonosulfate (PMS) for sulfamethazine (SMZ) removal were compared. M-BTC type metal-organic frameworks (MOFs) were synthesized under room temperature, with their yield about 7.5 times of ZIF-67 which is the most used MOFs to prepare N-doped carbon materials as the catalyst of persulfate-based advanced oxidation processes. Co-BTC/melamine derived N-doped carbon materials (Co-BTC/5MNC) performed the best, even better than that of ZIF-67 derived N-doped carbon materials. Initial pH (3-9), 0-10 mM inorganic anions (Cl^-, NO₃^-, HCO₃^- and H₂PO₄^2-) and humic acid (5 and 10 mg/L) had no obvious inhibition on SMZ removal with Co-BTC/5MNC as catalyst. The results of both X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicated that N-coordinated cobalt single atom site (Co-N_x) was the possible active site of Co-BTC/5MNC. Importantly, surface-bound SO₄^•- was identified as the dominant reactive oxygen species for SMZ removal. The SO₄^•- generated through the charge transfer between PMS and catalyst, and was tightly adsorbed on Co-N_x site.

Derivatives of metal-organic frameworks for heterogeneous Fenton-like processes: From preparation to performance and mechanisms in wastewater purification - A mini review

Organic pollution is an ever-growing issue in aquatic environment, Fenton-like processes have gained widespread acceptance due to their high oxidative potential and environmental compatibility. Derivatives of metal-organic frameworks (MOFs) are emerging heterogeneous Fenton-like catalysts, which have advantages of large surface area, diversity of structures, and abundant active sites. This work focuses on the recent advances in MOFs derivatives including metal compounds and metal incorporated carbons for Fenton-like processes. First, preparation strategies, structures and compositions are introduced. And then, the removal of organic pollutant in Fenton, electro-Fenton, and photo-Fenton process catalyzed by MOFs derivative is summarized, respectively. The contents particularly devote efforts to build connections among preparation, structures, compositions, and performance. Furthermore, the mechanisms of improving performance are discussed in detail. Finally, the perspectives of MOFs derivatives toward Fenton-like applications are proposed.

Facile preparation of nanocellulose/Zn-MOF-based catalytic filter for water purification by oxidation process

Sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs) have recently attracted much attention due to their potential in degrading organic pollutants. Metal-organic frameworks (MOFs) have been reported as effective materials to generate SO₄^•-. However, it is challenging to separate and recover the dispersed MOF particles from the reaction solution when MOFs are used alone. We used cellulose nanofibers (CNFs) as a porous filter template to immobilize Zn-based MOF, zeolitic imidazolate framework-8 (ZIF-8), and obtained a catalytic composite membrane having peroxymonosulfate (PMS) activating function to produce SO₄^•-. The CNF was effective in holding ZIF-8 nanoparticle and making a durable porous filter. The activated PMS-produced ^•OH and SO₄^•- radicals from ZIF-8 play an important role in the catalytic reaction. More than 90% of methylene blue and rhodamine B was degraded by ZIF-8/CNFs composite membrane in the PMS environment within 60 min. The ZIF-8/CNFs catalytic filters can be used several times without performance reduction for organic dye degradation. The results show that ZIF-8/CNFs catalytic membrane can be separated from organic pollution system quickly and used for the efficient separation and recovery of MOF particle-based catalytic materials. Therefore, this study provides a new perspective for fabricating the MOFs particles-immobilized catalytic filter by biomass nanocellulose-based materials for water purification. This method can be used for facile fabrication of the cellulose-based porous functional filter and open diverse applications.

Activation of peroxymonosulfate by ZIFs derived Fe/Cu encapsulated N-doped carbon for bisphenol A degradation: The role of N doping

Bisphenol A (BPA) is a typical kind of endocrine disruption chemical, which has a negative effect on human health, and thus it is necessary to remove BPA from water. Herein, activation of peroxymonosulfate (PMS) by Fe, Cu-Coordinated ZIF-Derived Carbon Framework bifunctional catalyst (Fe/Cu@NC-x) fabricated via hydrothermal-calcination method for BPA removal. The physicochemical properties of Fe/Cu@NC-x were studied by X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy, Raman Spectroscopy, Brunauer-Emmett Teller, and X-ray photoelectron spectroscopy. The effects of the Fe/Cu@NC-900 dosage and PMS concentration, initial pH, and co-existing anions on BPA degradation were evaluated. Under optimized factors (pH unadjusted, Fe/Cu@NC-900 = 0.2 g/L, and PMS = 0.75 g/L), the degradation efficiency of BPA can reach 98% after 30 min. In addition, the BPA degradation efficiency was different extents restrain by inorganic anions (SO₄^2- > Cl^- > HCO₃^- > NO₃^-). Furthermore, the free radicals (SO₄^-·, ·OH, and O₂^-·) and non-radical (¹O₂) contribute to rapid BPA degradation in Fe/Cu@NC-900/PMS system. This study presents a novel material with significant performance for the removal of organic pollutants.

Macroscopic MOF Architectures: Effective Strategies for Practical Application in Water Treatment

Metal-organic frameworks (MOFs) have potential applications in removing pollutants such as heavy metals, oils, and toxins from water. However, due to the intrinsic fragility of MOFs and their fine powder form, there are still technical barriers to their practical application such as blockage of pipes, difficulty in recovery, and potential environmental toxicity. Therefore, attention has focused on approaches to convert nanocrystalline MOFs into macroscopic materials to overcome these limitations. Recently, strategies for shaping MOFs into beads (0D), nanofibers (1D), membranes (2D), and gels/sponges (3D) with macrostructures are developed including direct mixing, in situ growth, or deposition of MOFs with polymers, cotton, foams or other porous substrates. In this review, successful strategies for the fabrication of macroscopic materials from MOFs and their applications in removing pollutants from water including adsorption, separation, and advanced oxidation processes, are discussed. The relationship between the macroscopic performance and the microstructure of materials, and how the range of 0D to 3D macroscopic materials can be used for water treatment are also outlined.

Heterogeneous activation of peroxymonosulfate by stable Co-MOF for the efficient degradation of organic dye pollutants

A new Co-MOF with splendid stability can act as an excellent heterogeneous catalyst to activate peroxymonosulfate, exhibiting highly efficient organic dye degradation in aquatic environments.