Progress and challenges of metal-organic frameworks-based materials for SR-AOPs applications in water treatment

Functional group modulation of Fe-1,3,5-benzenetricarboxylic acid materials: Enhancing peroxymonosulfate activation while preserving synthetic simplicity

This work aims to design peroxymonosulfate (PMS) catalytic materials that exhibit both high catalytic activity and ease of preparation. Fe-1,3,5-benzenetricarboxylic acid (Fe-BTC), known for its environmentally friendly and convenient synthesis, was selected as the template. A series of derived materials were developed under green and mild conditions using a functional group modulation strategy, in which one -COOH group in BTC was substituted with -NO2, -NH2, pyridine nitrogen, or -H. Among these, the amino-modified Fe-BTC (Fe-IPA-NH2), derived via -NH2 substitution, demonstrated a significant improvement in catalytic performance compared to Fe-BTC. Fe-IPA-NH2 effectively activated PMS to degrade 99 % of metronidazole (MNZ) within 60 min. Through comprehensive characterization of the physicochemical properties of the synthesized materials, the influence of functional group modulation on the catalyst's structure-activity relationship was elucidated. The substitution of -COOH with -NH2 enhanced PMS activation by promoting both mass transfer and electron transfer processes. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed the degradation pathways of MNZ, which included hydroxyethyl cleavage, methyl oxidation, N-denitration, and ring-opening reactions. Toxicity assessment indicated that the Fe-IPA-NH2/PMS system holds promise for MNZ detoxification. Electron paramagnetic resonance spectroscopy and quenching experiments identified singlet oxygen (1O2) as the dominant reactive species in the Fe-IPA-NH2/PMS system, and a possible catalytic mechanism was proposed. Additionally, Fe-IPA-NH2 retained the key advantage of Fe-BTC-its facile and eco-friendly synthesis. When Fe-IPA-NH2 was incorporated into a ceramic membrane via an in situ assembly process, the resulting membrane catalytic reactor exhibited effective performance in water treatment. This study offers a compelling strategy for the development of iron-based metal-organic complexes that integrate eco-friendly synthesis, enhanced PMS catalytic activity, and versatile application potential.

Heterogeneous Peroxymonosulfate-Based Advanced Oxidation Mechanisms: New Wine in Old Bottles?

Heterogeneous persulfate-based advanced oxidation processes (PS-AOPs) have been gaining significant attention in water/wastewater treatment; however, the elucidation of mechanisms in PS-AOPs has become increasingly complex as the understanding of potential reactive pathways expands and the rigor of corresponding characterizations intensifies. As such, accurately illustrating system mechanisms with a robust and convincing methodology is crucial, while the influence of substrates must not be overlooked. In this Perspective, established techniques and critical issues are systematically compiled to serve as practical guidelines. Additionally, a newly proposed pathway, the direct oxidation transfer process (DOTP), is discussed in comparison to conventional mineralization processes by reactive oxidative species (ROS) in PS-AOPs. Overall, the investigation of PS-AOP mechanisms across various heterogeneous systems remains contentious and calls for standardization, for which this work aims to serve as a valuable reference.

Bimetallic-nitrogen-carbon aerogel Co/Ni-N-C derived from 2D ordered nanosheet arrays activate PMS-AOPs for effective antibiotic removal: performance, mechanism, and toxicity

In recent years, peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) have garnered increasing attention for their efficacy in eliminating persistent organic pollutants. Metal-nitrogen-carbon (M-N-C) materials are frequently employed as efficient catalysts for the activation of PMS, leading to the effective production of various reactive species. In this study, a novel 3D porous cobalt/nickel bimetallic-nitrogen-carbon aerogel (Co/Ni-N-C) with well-dispersed CoNi-nanosheets that enhance electron transfer and provide a large active surface area was prepared through an in situ growth and a straightforward pyrolysis procedure of 2D cobalt/nickel metal-organic framework (CoNi-MOF) which was contained by a bamboo cellulose aerogel as a precursor. Rapid tetracycline (TC) removal (efficiency of 99.83% and mineralization rate of 69.8%) was achieved via PMS activation, facilitated by a synergistic enhancement effect of well-dispersion CoNi-nanosheet array. The evenly dispersed Co/Ni-N active sites and high Co:Ni ratio (PCo:Ni = 0.21) producing multiple reactive oxygen species (ROS) were essential in accelerating removal of contaminant. The toxicity assessment results of the intermediates further confirmed that the catalytic degradation in the Co/Ni-N-C-800/PMS system reduced the ecological toxicity of TC through dehydroxylation, demethylation, ring-opening, and deamidation. Furthermore, the Co/Ni-N-C-800/PMS system demonstrated exceptional degradation efficiency for various aromatic compounds with diverse substituents and showed good cyclic stability. These findings offer insights into the development of highly effective bimetallic-nitrogen-carbon catalytic materials.

Co3O4 with the Enhancement of Peroxymonosulfate Adsorption Capacity by Rare Earth Europium-Doping for High-Efficiency Organic Dye Degradation

Cobalt-based metal-organic framework (MOFs)-derived catalysts are acknowledged for their effectiveness in activating peroxymonosulfate (PMS) for the treatment of persistent pollutants. However, the limited adsorption of PMS on the catalyst surface markedly reduces its degradation efficiency. To overcome this limitation, nanoflower-like Eu2O3/Co3O4-0.3 catalysts were successfully fabricated by incorporating europium (Eu) into cobalt-based MOF via the hydrothermal and calcination techniques. The doping of Eu not only enhances the adsorption of more PMS on the catalyst's surface but also serves as an electron transfer mediator to regulate the Co2+/Co3+ redox cycle and promote the generation of oxygen vacancies (OV). The catalyst Eu2O3/Co3O4-0.3 was used to activate PMS for the degradation of rhodamine B (RhB), and it was found that the degradation rate constant (k) of the Eu2O3/Co3O4-0.3/PMS system was approximately 8 times higher than that of the Co3O4/PMS system, achieving complete degradation within 20 min. Furthermore, Eu2O3/Co3O4-0.3 exhibited excellent mineralization capacity, stability, and recyclability. Trapping experiments indicated that singlet oxygen (1O2) is the primary active species, suggesting that this material is applicable in complex aqueous environments. Density Functional Theory (DFT) calculations revealed that the adsorption energy (Eads) of PMS on the Eu2O3 surface is -4.05 eV, which is much greater than that on Co3O4 (Eads = -0.32 eV). This study provides a new method for designing nonhomogeneous catalysts to activate PMS for efficient degradation of pollutants.

New cobalt-based metal-organic frameworks for catalysing sulfite in the degradation of reactive brilliant red

Advanced oxidation processes utilizing metal-organic frameworks (MOFs) to enhance the catalytic degradation efficiency of synthetic dyes in wastewater require a thorough understanding of the activation mechanism. Herein, four new MOFs, named [Co(Hchtc)(bpe)] (1), [Co(Hchtc)(bpy)]·H2O (2), [Co1.5(Hcptc)(bpy)0.5(H2O)2]·2H2O (3) and [Co2(cptc)(bpe)2(H2O)]·H2O (4) (H3chtc = cyclohexane-tricarboxylic acid, H4cptc = cyclopentane-tetracarboxylic acid, bpe = trans-1,2-(bis(4-pyridyl)ethene), bpy = 4,4'-bipyridine), were exploited as catalysts in the degradation of X3B by the activation of sulfites. Complexes 1 and 2, the first MOFs constructed with H3chtc, are similar two-dimensional layered structures composed of double organic linkers and dinuclear units in which the coordination numbers of cobalt ions are five and six, respectively; complex 3 is also a layered framework assembled with six-coordinated trinuclear cobalt units and bpy, whereas complex 4 is a three-dimensional framework including both 5- and 6-coordinated cobalt ions. Interestingly, catalysts 1/SO32- and 4/SO32- demonstrate a superior degradation efficiency on X3B, while 2/SO32- and 3/SO32- exhibit moderate degradation efficacy on X3B. Further investigations suggest that both the adsorption capacity of the dye and the coordination vacancy on the metal ions contribute to the degradation process, with the latter exerting an activation effect of sulfite ions.

Versatile electrospun cobalt-doped carbon films for rapid antibiotic degradation

This study presents a novel approach to water contamination remediation by developing cobalt-doped carbon nanofiber films using electrospun ZIF-67 precursors, aiming to degrade tetracycline hydrochloride (TCH) and other antibiotics. This method uniquely combines the advantages of metal-organic frameworks (MOFs) and electrospinning to enhance catalytic performance, demonstrating significant innovation in environmental catalysis. The research systematically evaluated the impact of various factors on the catalytic activity of carbonized PAN@ZIF-67 films (CPZF), including carbonization temperature, ZIF-67 content, and PMS dosage. Notably, the CPZF catalyst with 11% ZIF-67 content (named as CPZF-11%) achieved an impressive 99.7% degradation of TCH within just 10 min under visible light and PMS activation, highlighting its superior catalytic efficiency. The study revealed that CPZF-11% exhibited excellent stability and recyclability, maintaining near 100% degradation rates even after six cycles. This catalytic performance is attributed to the synergistic effect of photogenerated electrons and PMS activation, leading to the formation of reactive oxygen species (ROS) such as sulfate radicals and singlet oxygen. The research further elucidated the degradation pathways and intermediate products through quenching experiments and electron paramagnetic resonance (EPR) analysis. The findings demonstrate the broad applicability of CPZF/Vis/PMS in various water matrices, including tap water and wastewater, underscoring its potential for real-world applications in wastewater treatment. This innovative integration of MOFs and electrospinning offers a promising strategy for developing efficient, recyclable, and high-performance catalysts for environmental remediation.

Facile fabrication of shape-controllable and reusable nanoporous catalytic aerogels based on Co-MOF and agarose for efficient decomposition of organic pollutants in water

Sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs) have been studied to date by utilizing metal-organic frameworks as efficient catalysts to generate sulfate radicals by peroxymonosulfate (PMS) activation in water purification. It is important to select high-performance and reliable catalysts for efficient water remediation, and separation and recovery of catalysts are essential in the practical application of MOFs. Herein, we adapted thermally curable, shape-controllable, and cost-effective agarose (AG) as a smart matrix and ZIF-67, as a powerful catalyst to prepare nanoarchitectured aerogel (Z67@AG). This nanoporous aerogel composite can efficiently generate sulfate radicals and hydroxyl radicals by activating PMS in the nanopores. Z67@AG aerogel could be easily fabricated in various molds to make desired shapes. This approach enables its utilization for different filtering systems and demonstrates cost-effective and stable performance by mass production and reusability. In the SR-AOP, aerogel exhibited excellent catalytic decomposition performances of 95 % and 88 % efficiencies within 8 and 10 min for dye and levofloxacin, respectively. It is believed that the proposed highly catalytic nanoporous aerogel nanocomposite having cost-effectiveness, excellent catalytic activity, facile fabrication of desired shapes, and an excellent porous structure can be extended to the synthesis of various nanocomposites and emerging applications.

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.

Enhanced water stability and catalytic activity of Fe-based metal-organic frameworks with co-ligands for 2,4-dichlorophenol degradation

Fe-based metal-organic frameworks (MOFs) have good photocatalytic performance, environmental friendliness, low cost, and abundance. However, their applications are limited by low water stability, particularly in the presence of light irradiation and oxidizing agents. In this study, we present a MIL-53(Fe)-based MOF using 1,4-naphthalene dicarboxylic (1,4-NDC) and 1,4-benzenedicarboxylic (H2BDC) acid co-ligands, denoted MIL-53(Fe)-Nx, where Nx represents the ratio of 1,4-NDC. This MOF exhibits high water stability and good photocatalytic activity because of the hydrophobicity of naphthalene. The removal and mineralization rates for 100 mg/L 2,4-dichlorophenol reached 100% and 22%, respectively, within 60 min. After three cycles of use, the Fe leached into the solution from the catalysts was significantly lower than the maximum permissible limit indicated in the European Union standard. Of note, 1,4-NDC can be used to make a rigid MOF, thereby improving the crystallinity, porosity, and hydrophobicity of the resultant materials. It also significantly reduced the bandgap energy and improved the charge separation efficiency of the catalysts. This study provides a route to enhance the water stability of Fe-based MOFs via a mixed-ligand strategy to expand their applications in pollutant control.

Advances and challenges in the removal of organic pollutants via sulfate radical-based advanced oxidation processes by Fe-based metal-organic frameworks: A review

Organic contaminants, notorious for their complexity and resistance to degradation, are prevalent in aquatic environments, posing severe threats to ecosystems. Sulfate radical-based advanced oxidation processes (SR-AOPs), known for their stability and high effectiveness, have become a common choice for treating organic wastewater. Metal-organic framework materials (MOFs) have garnered substantial attention due to their facile chemical manipulation, unique structural configurations, and other favorable properties. Therefore, this article critically reviews recent advances in research involving the utilization of Fe-based MOFs (Fe-MOFs) and their derivatives in SR-AOPs. Specifically, it highlights the manipulation of influencing factors within the system to enhance the degradation of organic pollutants. The mechanisms and applications underlying the degradation of organic pollutants in the SR-AOPs system are also elucidated.

Enhancement of Peroxydisulfate Activation for Complete Degradation of Refractory Tetracycline by 3D Self-Supported MoS2/MXene Nanocomplex

Antibiotic abuse, particularly the excessive use of tetracycline (TC), a drug with significant environmental risk, has gravely harmed natural water bodies and even posed danger to human health. In this study, a three-dimensional self-supported MoS2/MXene nanohybrid with an expanded layer spacing was synthesized via a facile one-step hydrothermal method and used to activate peroxydisulfate (PDS) for the complete degradation of TC. The results showed that a stronger •OH signal was detected in the aqueous solution containing MoS2/MXene, demonstrating a superior PDS activation effect compared to MoS2 or Ti3C2TX MXene alone. Under the conditions of a catalyst dosage of 0.4 g/L, a PDS concentration of 0.4 mM, and pH = 5.0, the MoS2/MXene/PDS system was able to fully eliminate TC within one hour, which was probably due to the presence of several reactive oxygen species (ROS) (•OH, SO4•-, and O2•-) in the system. The high TC degradation efficiency could be maintained under the influence of various interfering ions and after five cycles, indicating that MoS2/MXene has good anti-interference and reusability performance. Furthermore, the possible degradation pathways were proposed by combining liquid chromatography-mass spectrometry (LC-MS) data and other findings, and the mechanism of the MoS2/MXene/PDS system on the degradation process of TC was elucidated by deducing the possible mechanism of ROS generation in the reaction process. All of these findings suggest that the MoS2/MXene composite catalyst has strong antibiotic removal capabilities with a wide range of application prospects.

Degradation of 2, 4-dichlorophenol by peroxymonosulfate catalyzed by ZnO/ZnMn2 O4

In this study, a highly efficient peroxymonosulfate (PMS) activator, ZnO/ZnMn2 O4 , was synthesized using a simple one-step hydrothermal method. The resulting bimetallic oxide catalyst demonstrated a homogenous and high-purity composition, showcasing synergistic catalytic activity in activating PMS for degrading 2, 4-dichlorophenol (2, 4-DCP) in aqueous solution. This catalytic performance surpassed that of individual ZnO, Mn2 O3 , and ZnMn2 O4 metal materials. Under the optimized conditions, the removal efficiency of 2, 4-DCP reached approximately 86% within 60 min, and the catalytic ability remained almost constant even after four cycles of recycling. The developed degradation system proved effective in degrading other azo-dye pollutants. Certain inorganic anions such as HPO4 - , HCO3 - , and NO3 - significantly inhibited the degradation of 2, 4-DCP, while Cl- and SO4 2- did not exhibit such interference. Results from electrochemical experiments indicated that the electron transfer ability of ZnO/ZnMn2 O4 surpassed that of individual metals, and electron transfer occurred between ZnO/ZnMn2 O4 and the oxidant. The primary active radicals responsible for degrading 2, 4-DCP were identified as SO4 •- , OH• and O2 •- , generated through the oxidation and reduction of PMS catalyzed by Zn (II) and Mn (III). Furthermore, X-ray photoelectron spectroscopy (XPS) analysis of the fresh and used catalysts revealed that the exceptional electron transfer ability of ZnO facilitated the valence transfer of Mn (III) and the transfer of electrons to the catalyst's oxygen surface, thus enhancing the catalytic efficiency. The analysis of radicals and intermediates indicates that the two main pathways for degrading 2, 4-DCP involve hydroxylation and radical attack on its aromatic ring. PRACTITIONER POINTS: A bimetallic ZnO/ZnMn2 O4 catalyst was synthesized and characterized. ZnO/ZnMn2 O4 can synergistically activate PMS to degrade 2, 4-DCP compared with single metal oxide. Three primary active radicals, O2 •- , • OH, and SO4 •- , were generated to promote the degradation. ZnO promoted electron transfer among the three species of Mn to facilitate oxidizing pollutants. Hydroxylation and radical attack on the aromatic ring of 2, 4-DCP are the two degradation pathways.

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.

Mechanisms of interaction between metal-organic framework-based material and persulfate in degradation of organic contaminants (OCs): Activation, reactive oxygen generation, conversion, and oxidation

Metal-organic frameworks (MOFs)-based materials have been of great public interest in persulfate (PS)-based catalytic oxidation for wastewater purification, because of their excellent performance and selectiveness in organic contaminants (OCs) removal in complex water environments. The formation, fountainhead and reaction mechanism of reactive oxygen species (ROSs) in PS-based catalytic oxidation are crucial for understanding the principles of PS activation and the degradation mechanism of OCs. In the paper, we presented the quantitative structure-activity relationship (QSAR) of MOFs-based materials for PS activation, including the relationship of structure and removal efficiency, active sites and ROSs as well as OCs. In various MOFs-based materials, there are many factors will affect their performances. We discussed how various surface modification projects affected the characteristics of MOFs-based materials used in PS activation. Moreover, we revealed the process of ROSs generation by active sites and the oxidation of OCs by ROSs from the micro level. At the end of this review, we putted forward an outlook on the development trends and faced challenges of MOFs for PS-based catalytic oxidation. Generally, this review aims to clarify the formation mechanisms of ROSs via the active sites on the MOFs and the reaction mechanism between ROSs and OCs, which is helpful for reader to better understand the QSAR in various MOFs/PS systems.

Wastewater treatment using nanodiamond and related materials

Nanodiamonds (NDs) are zero-dimensional (0D) carbon-based nanoparticles with SP3/SP2-hybridized carbon atoms that have shown great potential in wastewater treatment areas due to their high surface area, chemical stability, and unique adsorption properties. They can efficiently remove a wide range of pollutants from water, including heavy metals, organic compounds, and dyes via various mechanisms such as electrostatic interactions, π-π stacking, and ion exchange. NDs can be functionalized following different surface chemistries, enabling tailored surface properties and enhanced pollutant adsorption capabilities. This review covers recent research on the application of nanodiamonds in wastewater treatment domain with a major emphasis on adsorption, photocatalytic degradation, and membrane separation, highlighting their promising performances, challenges, and future directions.

Co-based MOF heterogeneous catalyst for the efficient degradation of organic dye via peroxymonosulfate activation

In this study, a new cobalt-based metal-organic framework (JLNU-500), [Co2(OH)(PBA)(AIP)]·3DMA·0.75H2O (4-(pyridin-4-yl) benzoic acid (HPBA), 5-aminoisophthalic acid (H2AIP) and N,N-dimethylacetamide (DMA)), was fabricated using a solvothermal method. JLNU-500 has 3D network architecture with 1D nanopore channels. The prepared JLNU-500 can activate peroxymonosulfate (PMS) for Rhodamine B (RhB) dye decolorization. Interestingly, catalyst JLNU-500 exhibited high efficiency for PMS activation, and nearly 100% (above 99.8%) removal of RhB with a high concentration (50.0 mg L-1, 100 mL) was achieved within 6 min. The reaction rate constant of the JLNU-500/PMS system was 1.02 min-1 calculated based on the pseudo-first-order kinetics, which is higher than that of the other reported catalysts. Furthermore, the factors, which could influence PMS activation were also investigated, such as PMS dosage, catalyst dosage, pollutant RhB concentration, reaction temperature and solution pH. More importantly, the radical trapping experiments ferreted out that sulfate (SO4˙-) and hydroxyl (˙OH) radicals were the dominating oxidants in the removal of RhB. Moreover, the possible degradation mechanism was elucidated. This study provides new prospects for fabricating new MOFs that can potentially be employed for high-efficiency catalytic oxidation as heterogeneous catalysts.

Reclamation of real textile wastewater by sequential advanced oxidation and adsorption processes using corn-cob based materials

Wastewater management has become crucial for sustaining biological life in the near future. One of the key aspects is integration of treatment processes aiming reuse of treated water for many purposes instead of water discharge. This study focused on combining two different methods, photo-Fenton-like oxidation, and adsorption, for treatment of real textile wastewater to improve water quality to be reused for irrigation. The real textile wastewater was collected from a local plant and subjected to photo-Fenton-like oxidation and adsorption as hybrid process. The operational parameters were optimized for each step by assessing the water quality according to the domestic regulations for irrigation water. The photo-Fenton-like oxidation itself was not successful to achieve the targeted water quality for reuse whereas adsorption as an additional step made the treated water reusable in terms of organic content. But the treated water still contained a certain amount of salinity due to extreme salt usage in textile processing. It was concluded that the treated water at the end of hybrid process could be used for salinity resistant plants such as sugar beet, barley, and cotton which demonstrates a promising contribution to the circular economy for biomass.

Peroxymonocarbonate activation via Co nanoparticles confined in metal-organic frameworks for efficient antibiotic degradation in different actual water matrices

Traditional advanced oxidation processes suffer from low availability of ultrashort lifetime radicals and declining stability of catalysts. Co nanoparticles in hollow bimetallic metal-organic frameworks (Co@MOFs) were synthesized via a solvothermal method. Nanoconfinement and peroxymonocarbonate (PMC) degradation system endows Co@MOFs with high catalytic activity and stability even in the actual water matrices. The nanocomposites exhibited 100-200 nm polyhedron structure with irregular nanocavity between the 20 nm shell and multicores. Co nanoparticles were completely encapsulated by the FeIII-MOF-5 shell according to the X-ray diffraction and photoelectron spectra. Both 0.8 nm micropores and 3.6 nm mesopores were proven to be present. The yolk-shell Co@MOFs exhibited higher catalytic performance than that of Co nanoparticles, hollow FeIII-MOF-5 and its core-shell counterpart toward PMC activation during sulfamethoxazole degradation. The catalytic activities of Co@MOFs for the activation of unsymmetrical peroxides (PMC and peroxymonosulfate) were much higher than those for the symmetrical peroxides (H2O2 and persulfate) and the heterogeneous catalysis was dominant in the Co@MOFs activated H2O2 and PMC systems. The MOF stability was the highest and metal leakages were the least in the activated PMC system among the four peroxides because of mild reaction conditions and the alkalescent solution (pH = 8.3-8.4). Furthermore, the high removal efficiencies (>94%) and degradation rates could be maintained in the different actual water matrices due to the confinement effects. The contributions of carbonate and hydroxyl radicals were primary for sulfamethoxazole degradation, and superoxide anion and singlet oxygen also played essential roles according to scavenging experiments and time-series spin-trapping electron spin resonance spectra. Six degradation pathways were proposed according to 26 intermediate identification and the pharmacophores of more than 80% intermediates were destroyed, which would benefit subsequent biological treatment. Successful combination of nanoconfinement and PMC might provide a new effective solution for pollution remediation.

Functional MOF-Based Materials for Environmental and Biomedical Applications: A Critical Review

Over the last ten years, there has been a growing interest in metal-organic frameworks (MOFs), which are a unique category of porous materials that combine organic and inorganic components. MOFs have garnered significant attention due to their highly favorable characteristics, such as environmentally friendly nature, enhanced surface area and pore volume, hierarchical arrangements, and adjustable properties, as well as their versatile applications in fields such as chemical engineering, materials science, and the environmental and biomedical sectors. This article centers on examining the advancements in using MOFs for environmental remediation purposes. Additionally, it discusses the latest developments in employing MOFs as potential tools for disease diagnosis and drug delivery across various ailments, including cancer, diabetes, neurological disorders, and ocular diseases. Firstly, a concise overview of MOF evolution and the synthetic techniques employed for creating MOFs are provided, presenting their advantages and limitations. Subsequently, the challenges, potential avenues, and perspectives for future advancements in the utilization of MOFs in the respective application domains are addressed. Lastly, a comprehensive comparison of the materials presently employed in these applications is conducted.

A comparative study on Fe(III)/H2O2 and Fe(III)/S2O82- systems modified by catechin for the degradation of atenolol

The processes of Fe(III) activated persulfate (PS) and H₂O₂ modified by catechin (CAT) had been shown to be effective in degrading contaminants. In this study, the performance, mechanism, degradation pathways and products toxicity of PS (Fe(III)/PS/CAT) and H₂O₂ (Fe(III)/H₂O₂/CAT) systems were compared using atenolol (ATL) as a model contaminant. 91.0% of ATL degradation was reached after 60 min in H₂O₂ system which was much higher than that in PS system (52.4%) under the same experimental condition. CAT could react directly with H₂O₂ to produce small amounts of HO^• and the degradation efficiency of ATL was proportional to CAT concentration in H₂O₂ system. However, the optimal CAT concentration was 5 μM in PS system. The performance of H₂O₂ system was more susceptible to pH than that of PS system. Quenching experiments were conducted indicating that SO₄^•- and HO^• were produced in PS system while HO^• and O₂^•- accounted for ATL degradation in H₂O₂ system. Seven pathways with nine byproducts and eight pathways with twelve byproducts were put forward in PS and H₂O₂ systems respectively. Toxicity experiments showed that the inhibition rates of luminescent bacteria were both decreased about 25% after 60 min reaction in two systems. Although the software simulation result showed few intermediate products of both systems were More toxic than ATL, but the amounts of them were 1-2 orders of magnitude lower than ATL. Moreover, the mineralization rates were 16.4% and 19.0% in PS and H₂O₂ systems respectively.

A Review on Photocatalysis Used For Wastewater Treatment: Dye Degradation

Water pollution is a global issue as a consequence of rapid industrialization and urbanization. Organic compounds which are generated from various industries produce problematic pollutants in water. Recently, metal oxide (TiO2, SnO2, CeO2, ZrO2, WO3, and ZnO)-based semiconductors have been explored as excellent photocatalysts in order to degrade organic pollutants in wastewater. However, their photocatalytic performance is limited due to their high band gap (UV range) and recombination time of photogenerated electron-hole pairs. Strategies for improving the performance of these metal oxides in the fields of photocatalysis are discussed. To improve their photocatalytic activity, researchers have investigated the concept of doping, formation of nanocomposites and core-shell nanostructures of metal oxides. Rare-earth doped metal oxides have the advantage of interacting with functional groups quickly because of the 4f empty orbitals. More precisely, in this review, in-depth procedures for synthesizing rare earth doped metal oxides and nonocomposites, their efficiency towards organic pollutants degradation and sources have been discussed. The major goal of this review article is to propose high-performing, cost-effective combined tactics with prospective benefits for future industrial applications solutions.

Controllable synthesis of copper-organic frameworks via ligand adjustment for enhanced photo-Fenton-like catalysis

The efficient heterogeneous photo-Fenton-like catalysts based on two secondary ligand-induced Cu(II) metal-organic frameworks (Cu-MOF-1 and Cu-MOF-2) were constructed for the first time and investigated for the degradation of multiple antibiotics. Herein, two novel Cu-MOFs were prepared using mixed ligands by a facile hydrothermal method. The one-dimensional (1D) nanotube-like structure could be obtained by using V-shaped, long and rigid 4,4'-bis(3-pyridylformamide)diphenylether (3-padpe) ligand in Cu-MOF-1, while polynuclear Cu cluster could be prepared more easily by using short and small isonicotinic acid (HIA) ligand in Cu-MOF-2. Their photocatalytic performances were measured by degradation of multiple antibiotics in Fenton-like system. Comparatively, Cu-MOF-2 exhibited superior photo-Fenton-like performance under visible light irradiation. The outstanding catalytic performance of Cu-MOF-2 was ascribed to the tetranuclear Cu cluster configuration and excellent ability of photoinduced charge transfer and hole separation thus improved the photo-Fenton activity. In addition, Cu-MOF-2 showed high photo-Fenton activity in wide pH working range 3-10 and maintained wonderful stability after five cyclic experiments. The degradation intermediates and pathways were deeply studied. The main active species h⁺, O₂^- and OH worked together in photo-Fenton-like system and possible degradation mechanism was proposed. This study provided a new approach to design the Cu-based MOFs Fenton-like catalysts.

The Collision between g-C3 N4 and QDs in the Fields of Energy and Environment: Synergistic Effects for Efficient Photocatalysis

Recently, graphitic carbon nitride (g-C₃ N₄ ) has attracted increasing interest due to its visible light absorption, suitable energy band structure, and excellent stability. However, low specific surface area, finite visible light response range (<460 nm), and rapid photogenerated electron-hole (e^- -h⁺ ) pairs recombination of the pristine g-C₃ N₄ limit its practical applications. The small size of quantum dots (QDs) endows the properties of abundant active sites, wide absorption spectrum, and adjustable bandgap, but inevitable aggregation. Studies have confirmed that the integration of g-C₃ N₄ and QDs not only overcomes these limitations of individual component, but also successfully inherits each advantage. Encouraged by these advantages, the synthetic strategies and the fundamental of QDs/g-C₃ N₄ composites are briefly elaborated in this review. Particularly, the synergistic effects of QDs/g-C₃ N₄ composites are analyzed comprehensively, including the enhancement of the photocatalytic performance and the avoidance of aggregation. Then, the photocatalytic applications of QDs/g-C₃ N₄ composites in the fields of environment and energy are described and further combined with DFT calculation to further reveal the reaction mechanisms. Moreover, the stability and reusability of QDs/g-C₃ N₄ composites are analyzed. Finally, the future development of these composites and the solution of existing problems are prospected.

Activation of peroxymonosulfate by Co-Mg-Fe layered doubled hydroxide for efficient degradation of Rhodamine B

Reactive species serve as a key to remediate the contamination of refractory organic contaminants in advanced oxidation processes. In this study, a novel heterogeneous catalyst, CoMgFe-LDH layered doubled hydroxide (CoMgFe-LDH), was prepared for an efficient activation of peroxymonosulfate (PMS) to oxidize Rhodamine B (RhB). The characterization results showed that CoMgFe-LDH had a good crystallographic structure. Correspondingly, the CoMgFe-LDH/PMS process exhibited good capacity to remove RhB, which was equivalent to degradation performance as homogeneous Co(II)/PMS process. The RhB oxidation in the CoMgFe-LDH/PMS process was well described with pseudo-first-order kinetic model. Additionally, the oxidation process presented an excellent stability, and only 0.9% leaching rate was detected after six sequential reaction cycles at pH 5.0. The effects of initial pH, CoMgFe-LDH dosage, PMS concentration, RhB concentration, and inorganic anions on the RhB degradation were discussed in detail. Quenching experiments showed that sulfate radicals (SO₄^•-) acted as the dominant reactive species. Further, the removal of RhB from simulated wastewater was explored. The removal efficiency of RhB (90 μM) could reach 94.3% with 0.8 g/L of catalyst and 1.2 mM of PMS addition at pH 5.0, which indicated the CoMgFe-LDH/PMS process was also effective in degrading RhB in wastewater.

Boosting catalytic activity of SrCoO2.52 perovskite by Mn atom implantation for advanced peroxymonosulfate activation

Material-enhanced heterogeneous peroxymonosulfate (PMS) activation for degradation of antibiotic in water has attracted intensive attention. However, one challenge is the electron transfer efficiency from the material to PMS for reactive oxygen species (ROS) production. Considering that the B-sites of perovskite oxides are closely associated with the catalytic performance, partial substitution of the B-sites of perovskite oxides can enhance the redox cycle of metals. Consequently, adjusting the ratio of each element at the B site can introduce oxygen vacancies on the surface of perovskite. Herein, a method was developed in which manganese (Mn) partially substitutes B-sites to modify surface properties of SrCoO_2.52 perovskite oxides, resulting in the enhancement of catalytic activity. In degradation kinetics studies using SrCoMnO_3-δ-0.5/PMS (SrCoMnO_3-δ-0.5 denotes that the molar substitution of Mn at the B site of SrCoO_2.52 perovskite oxide is 0.5) reaction system and sulfamethoxazole (SMX) as the target pollutant, it was found that the reaction rate constant (k_obs) is 0.287 min^-1 which is 2.4 times that of SrCoO_2.52/PMS system. Experimental and theoretical analyses revealed that Mn-O covalent bonding governs the intrinsic catalytic activity of SrCoMnO_3-δ-0.5 perovskite oxides. The Mn sites exhibits stronger adsorption energy with PMS than the Co sites, facilitating the breaking of O-O bond. Simultaneously, oxygen vacancies and surface adsorbed oxygen species have a synergistic effect for PMS adsorption. This work can provide a potential route in developing advanced catalysts based on manipulation of the B-sites of perovskite oxides for PMS activation.

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.

A newly-designed free-standing NiCo2O4 nanosheet array as effective mediator to activate peroxymonosulfate for rapid degradation of emerging organic pollutant with high concentration

Nowadays effective treatment of high concentration organic wastewater is still a formidable task facing human beings. Herein, for the first time, a well-defined ZIF-67-derived NiCo₂O₄ nanosheet array was successfully prepared by a feasible method. In comparison with ordinary NiCo₂O₄ nanosphere, the formation of nanosheet structure could offer more opportunities to exposure internal active sites of NiCo₂O₄, thereby resulting in smaller interface resistance and higher charge transfer efficiency. As expected, ZIF-67-derived NiCo₂O₄ nanosheet array displayed great performance in peroxymonosulfate (PMS) activation. More importantly, recyclable redox couples of Co³⁺/Co²⁺ and Ni³⁺/Ni²⁺ endowed the stable catalytic activity of NiCo₂O₄ nanosheet. Interestingly, developed NiCo₂O₄-1/PMS oxidation system could achieve the effective degradation of antibiotics with high concentration in a short time. Both radical and nonradical pathways were involved into PMS activation, wherein SO₄^-, OH, O₂^- and ¹O₂ were major reactive oxygen species. The formation paths of reactive oxygen species and effects of inorganic anions were also investigated. Electrochemical analyses revealed that NiCo₂O₄-1 with nanosheet structure mediated the electron transfer between PMS and tetracycline (TC), which played a vital role in TC degradation. Furthermore, developed NiCo₂O₄-1/PMS oxidation system displayed great removal ability towards TC in actual water samples, and degradation products were low toxicity or no toxicity. In short, current work not only developed an effective oxidation system for completing the rapid degradation of antibiotic with high concentration, but also shared some novel insights into the activation mechanism of SR-AOPs.

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

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

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

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

Strategies for improving the catalytic activity of metal-organic frameworks and derivatives in SR-AOPs: Facing emerging environmental pollutants

As persulfate activator, Metal organic frameworks (MOFs) and derivatives are widely concerned in degradation of emerging environmental pollutants by advanced oxygen technology dominated by sulfate radical () (SR-AOPs). However, the poor stability and low catalytic efficiency limit the performance of MOFs, requiring multiple strategies to further enhance their catalytic activity. The aim of this paper is to improve the catalytic activity of MOFs and their derivatives by physical and chemical enhancement strategies. Physical enhancement strategies mainly refer to the activation strategies including thermal activation, microwave activation and photoactivation. However, the physical enhancement strategies need energy consumption and require high stability of MOFs. As a substitute, chemical enhancement strategies are more widely used and represented by optimization, modification, composites and derivatives. In addition, the identification of reactive oxygen species, active site and electron distribution are important for distinguishing radical and non-radical pathways. Finally, as a new wastewater treatment technology exploration of unknown areas in SR-AOPs could better promote the technology development.

Analysis of the degradation of m-cresol with Fe/AC in catalytic wet peroxide oxidation enhanced by swirl flow

Catalytic wet peroxide oxidation (CWPO) enhanced by swirl flow (SF-CWPO) was developed for the first time to explore the degradation of m-cresol in 3%iron/activated carbon catalysed Fenton reaction. Under the conditions of catalyst dosage of 0.6 g/L, H₂O₂ dosage of 1.5 mL/L, pH = 6 and reaction time of 20 min, the degradation rate of m-cresol and total organic carbon in 100 mg/L m-cresol solution reaches 81.5% and 82%, respectively. The reaction speed in the SF-CWPO system with an independently designed cyclone reactor was two times faster than the traditional CWPO systems. In addition, via liquid chromatography-mass spectrometry analysis of the degradation product, the possible degradation pathway for m-cresol was proposed. The proposed SF-CWPO can potentially be an efficient and economical method to treat organic pollutants in wastewaters.

N-TiO2-Coated SiC Foam for the Treatment of Dyeing Wastewater under Blue Light LED Irradiation

TiO2 is widely used for the photocatalytic degradation of organic pollutants in wastewater, but the practical applications of the photocatalyst are limited due to its poor visible light absorption and low recovery rate. In this study, high production of nitrogen-doped TiO2 was achieved by a hydrolysis precipitation method; the obtained N-TiO2 had a small crystallite size and good dispersibility. The effect of calcining temperature on the photocatalytic performance of N-TiO2 was evaluated through the degradation of methylene blue (MB) in a blue light LED irradiation cylinder, it was found the N-TiO2 calcined at 400 °C showed the best photocatalytic activity. Then the N-TiO2 was immobilized on SiC ceramic foam by dip-coating with PVA as the binder. The prepared N-TiO2/SiC foam showed excellent photocatalytic activity under blue light LED irradiation; as high as 96.3% of MB was degraded at optimum conditions. After five cycles of MB photodegradation, the photocatalytic activity of N-TiO2/SiC foam only changed slightly, which makes it a promising photocatalytic material for wastewater treatment.

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.

Degradation of oxytetracycline by magnetic MOFs heterojunction photocatalyst with persulfate: high stability and wide range

Photocatalysis with persulfate (PS) is an effective method for the degradation of degrading organic pollutants. In this study, Fe₃O₄/MIL-101(Fe), a magnetic heterojunction photocatalyst, was produced using a hydrothermal method. The material coupled with PS exhibited excellent removal efficiency for oxytetracycline (OTC) (87.1%, 1 h). And it has a wide range of applications, with good removal efficiency for OTC concentrations of 30 to 70 mg/L and pH values of 3 to 9. •SO₄^- and •OH played a major role in the OTC removal reaction and there was an Fe(III)/Fe(II) cycle during the reaction. With excellent stability and recoverability, the OTC removal efficiency decreased by only 4.29% after four cycles, and the Fe leaching did not exceed 0.035 mg/L per cycle. This study provides significant insights into the removal of organic pollutants from water bodies.

Enhanced catalytic peroxymonosulfate activation for sulfonamide antibiotics degradation over the supported CoSx-CuSx derived from ZIF-L(Co) immobilized on copper foam

The CoS_x-CuS_x was firmly immobilized on copper foam (CF) substrate to fabricate supported CoS_x-CuS_x/CF using ZIF-L(Co)/CF as a self-sacrificing template, in which CF substrate played an important role in improving the adhesion between CF and target catalyst as well as the interfacial interaction between CoS_x and CuS_x. The CoS_x-CuS_x/CF performed well in catalytic peroxymonosulfate (PMS) activation, which can accomplish 97.0% sulfamethoxazole (SMX) degradation within 10 min due to the special structure and Co²⁺ regeneration promoted by S^2- and Cu⁺. The influences of pH, PMS dosage, catalyst dosage, co-existing anions and natural organic matter (NOM) on SMX removal were studied in detail. CoS_x-CuS_x/CF presented excellent catalytic activity and reusability, which might be fascinating candidate for real wastewater treatment. The possible pathway of SMX degradation was proposed, and the toxicity of the intermediates during the degradation process were evaluated. It is noteworthy that long-term continuous degradation of sulfonamide antibiotics was achieved using a self-developed continuous-flow fixed-bed reactor. This work demonstrated that CF as a substrate to fabricate supported catalysts derived from MOF had great potential in actual wastewater remediation.