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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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Metal‐organic frameworks (MOFs) are promising materials for photocatalytic water splitting reactions, but examples of visible light‐responsive, catalytically active, and stable MOFs are still rare. A detailed investigation is conducted for COK‐47 – a recently described MOF comprising 2D Ti‐O6 secondary building units (SBUs) – toward a photocatalytic hydrogen evolution reaction (HER), showing how overall particle morphology, surface area, and missing ligand defects are central parameters governing the material's ultimate performance. The newly synthesized COK‐47ISO is among the most active MOFs to date, yielding HER‐rates of 8.6 µmol h−1, and an apparent quantum yield (AQY) of 0.5% under visible light illumination. Optoelectronic and photoluminescence investigations, supported by theoretical calculations, enable the unraveling of its electronic structure along with charge transfer and recombination kinetics. A wavelength‐dependent reaction mechanism is proposed involving ligand to metal charge transfer (LMCT) and the main challenges for visible or UV photoexcitation are identified, demonstrating that the unique 2D layered structure aids charge separation and is key to the high performance. This work introduces COK‐47 as a promising alternative to the well‐known MIL‐125 family and offers directions for future studies [ABSTRACT FROM AUTHOR]

The selective removal of one ligand in mixed‐ligand MOFs upon thermolysis provides a powerful strategy to introduce additional mesopores without affecting the overall MOF structure. By varying the initial ligand ratio, MOFs of the MIL‐125‐Ti family with two distinct hierarchical pore architectures are synthesized, resembling either large cavities or branching fractures. The performance of the resulting hierarchically porous MOFs is evaluated toward the adsorptive removal of glyphosate (N‐(phosphonomethyl)glycine) from water, and the adsorption kinetics and mechanism are examined. Due to their strong affinity for phosphoric groups, the numerous Ti–OH groups resulting from the selective ligand removal act as natural anchor points for effective glyphosate uptake. The relationships between contact duration, glyphosate concentration, and adsorbent dosage are investigated, and the impact of these parameters on the effectiveness of glyphosate removal from contaminated water samples is examined. The introduction of additional mesopores has increased the adsorption capacities by nearly 3 times with record values exceeding 440.9 mg g−1, which ranks these MOFs among the best‐reported adsorbents. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) are commended as photocatalysts for H2 evolution and CO2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies. While metal organic frameworks offer highly tunable materials for photocatalytic applications, catalytic site accessibility is a crucial parameter. Here, authors demonstrate selective ligand removal to introduce new active sites and mesopores and to enhance photocatalytic H2 evolution. [ABSTRACT FROM AUTHOR]

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[Display omitted] Metal-organic frameworks (MOFs) hold potential for promoting the redox reaction of sulfur species (RRS) and suppressing the shuttle effect in lithium–sulfur batteries (LSBs). However, except for a limited number of frameworks, most MOFs are found to be inert in accelerating RRS, which is largely related to the fact that their design principles and mechanism of catalysis have not been fully understood. Systematic density functional theory (DFT) calculations and experimental results reveal that the lack of exposed polar catalytic sites restricts MOF's potential in promoting RRS. Herein, based on a series of multivariable MOFs containing ligands with different thermal stability, selective ligand removal and ligand exchange (LE) strategies were applied successively to expose the catalytic metal clusters and introduce extra adsorption sites, rendering inert MOFs into catalytic ones. Such post-modified multivariable MOFs were shown to yield LSBs with remarkably improved specific capacity and cycling stability realizing 7.9 mAh cm−2 of capacity after 100 cycles at high sulfur loading of 8.1 mg·cm−2 under a lean electrolyte condition. The universal strategy proposed in this work will guide the design of catalytic MOFs for RRS and promote the development of advanced catalysts for high-performance LSBs. [ABSTRACT FROM AUTHOR]

The design and development of porphyrinic POM-based MOFs (POMMOFs) represents an advanced approach to building materials that seamlessly integrate the collective strengths of POMs, porphyrins, and MOFs into a single framework. POMMOFs thus showcase their ability to combine predictable redox chemistry and biomimetic functions with the exceptional porosity of the resulting matrix. This review outlines the synthesis techniques and diverse catalytic applications of these materials, paving the path for further exploration and advancement of POMMOFs. [Display omitted] • This article demonstrates the incorporation of POMs, either encapsulated within the cavity or embedded within the structural framework of porphyrinic MOFs. • The possibility of integration of multiple metalloporphyrin linkers within POM-based MOFs is highlighted. • A detailed discussion of the innovative synthetic approaches utilized in crafting POM-based porphyrinic MOFs, along with their various applications in heterogeneous catalysis, is provided. • Despite being fabricated infrequently up to now, the impact of existing POMMOFs on shaping the future design of such materials is highlighted. The ever-increasing appearance of inorganic–organic hybrid materials incorporating organic metalloporphyrins (MPs) and inorganic polyoxometalates (POMs) – separately, two groups of effective molecular catalysts – which combine to form the ground-breaking class of metal–organic frameworks (MOFs), has allowed this class to participate in numerous kinds of chemical reactions and mimic the activity of heterogeneous bio-, photo- and electrocatalysts. Recent results have shown that the integration of POMs and MPs in a porous structure not only maintains the characteristic functionalities of both components, but can also generate novel and unparalleled features including augmented stabilities, remarkable selectivity, improvable porosity, and novel and more favorable topologies. Furthermore, the immobilization of these component species (POMs and MPs) within a unified framework can prevent their catalytic deactivation, which mostly arises from suicidal self-oxidation of porphyrin moieties. It has also been established that the introduction of POMs – owing to their broad range of size, structure, and highly negative charge distribution throughout the cluster – can further expand their structural diversity and greatly influence the stability and catalytic performance of porous porphyrinic MOFs. What is more, the incorporation of POMs inside the pores or their use as secondary building units (SBUs) within the framework can give rise to an increase in their original reusability, perpetuity, and adsorption ability. Moreover, their incorporation can also boost the transfer of electrons (e.g., photoexcited charge carriers) through the network. Therefore, POM-based porphyrinic MOFs (porphyrinic POMMOFs) are materials that can simultaneously take advantage of the combined uniqueness of the individual traits of POMs, porphyrins and MOFs, which display rich redox photochemistry, biomimetic ability, and porosity, respectively. This review aims to represent the latest progress in porous porphyrinic POMMOFs, encompassing their categorization, fabrication and exploitation in the catalysis field. To the best of our knowledge, hitherto no specific attempt has been made to cover this topic, and our review would be the first systematic scrutiny of these porous materials. Last but not least, the POMs that have been templated to synthesize porphyrinic POMMOFs are still mostly limited to a few types of POMs. Moreover, the porphyrin linkers which were used to create such MOFs have also been confined to only a few kinds. Thus, we suggest that other POMs ((iso-) heteropolyoxometalates) and porphyrin-based linkers could be explored, with an eye to creating new state-of-the-art porphyrinic POMMOFs. In the short term, it is anticipated that this review will encourage scientists to substantially extend the frontiers of knowledge about these systems, not only in the area of catalysis, but also in such versatile and underexplored domains as magnetism, gas sorption, sensing, biomedicine, and electrochemical and photocatalytic utilizations. For these reasons, we strongly believe that this comprehensive review will not only provide a better overview of the subject, but also open up promising directions of research and stimulate scientific interest and enthusiastic curiosity. It will also pave the way to generating important new ideas for the future of the synthesis and applications of these invaluable types of MOFs. [ABSTRACT FROM AUTHOR]

• We unravelled the impact of ligand composition on photocatalytic hydrogen evolution over Ti-based MOFs. • MIL-125-Ti outperforms NH2-containing counterparts by up to 38 times in methanol • Photoluminescence spectroscopy shows effective hole scavenging by methanol in MIL-125-Ti. • Triethanolamine leads to corrosion of the MOFs within the first few hours through partial ligand exchange. • We propose three mechanisms for photocatalytic hydrogen evolution for both single-ligand and mixed-ligand MOFs. We synthesized a series of isostructural MIL-125-Ti with various terephthalic: amino-terephthalic acid ratios and evaluated their photostability and performance for photocatalytic hydrogen evolution in aqueous solutions with different hole scavengers. We demonstrate that the commonly used triethanolamine corroded the MOFs under photocatalytic conditions, in contrast to methanol. The combination of MIL-125-Ti and methanol outperformed the photocatalytic activity of NH 2 -MIL-125-Ti by 45 times under broad UV irradiation. Photoluminescence spectroscopy under simulated photocatalytic conditions and in solid-state as well as time-resolved emission studies reveal that the holes residing in the metal-oxo cluster can be effectively scavenged by methanol, leading to high HER activity, while the holes residing in the NH 2 -groups in the ligand favour charge recombination and are thus detrimental to the photocatalytic performance. The mixed-ligand MOFs follow a dual-excitation pathway, introducing new states and transitions. These results are expected to advance our understanding of MOF-based photocatalysis. [ABSTRACT FROM AUTHOR]