Capture and Separation of SO2 Traces in Metal-Organic Frameworks via Pre-Synthetic Pore Environment Tailoring by Methyl Groups

Optimizing the pore environment in biological metal-organic frameworks through the incorporation of hydrogen bond acceptors for inverse ethane/ethylene separation

The development of efficient adsorbents for the selective separation of ethane (C2H6) and ethylene (C2H4) is essential for the cost-effective production of high-purity ethylene. Here, we employ a pore engineering strategy to optimize the pore environment of biological metal-organic frameworks (MOFs) by incorporating hydrogen bond receptors to enhance the inverse separation efficiency of C2H6 and C2H4. Compared to the isomorphic Cu-AD-SA, the methyl-functionalized Cu-AD-MSA and Cu-AD-DMSA not only provide suitable pore confinement but also offer additional binding sites, thus creating an optimal environment for strong interactions with C2H6 (AD = adenine, SA = succinic acid, MSA = 2-methylsuccinic acid, and DMSA = 2,2-dimethylsuccinic acid). Adsorption results show that Cu-AD-DMSA exhibits remarkable C2H6/C2H4 selectivity (up to 2.4) as well as outstanding C2H6 adsorption capacity (3.63 mmol g-1), surpassing most reported C2H6-selective MOFs. Theoretical calculations combined with in situ infrared spectroscopy reveal that the synergetic effect of suitable pore confinement, amino groups, and functional surfaces decorated with multiple methyl binding sites provides strong and multipoint interactions for C2H6. Breakthrough experiments demonstrate that Cu-AD-DMSA exhibits exceptional performance in separating binary C2H6/C2H4 gas mixtures. The high chemical and thermal stability, scalable synthesis, and economic viability of Cu-AD-DMSA illustrate its potential as a candidate for C2H6/C2H4 separation application.

Metal-organic frameworks (MOFs) toward SO2 detection

Developing technology that can precisely monitor specific air pollutants in diverse settings is essential to control emissions and ensure safe exposure limits are not exceeded. Metal-organic frameworks (MOFs) are crystalline organic-inorganic hybrid materials, which are promising candidates for SO2 detection. Their chemically mutable periodic structure confers outstanding surface area, thermal stability, and a well-defined pore distribution. Moreover, MOFs have exhibited extraordinary performance for SO2 capture. Therefore, research has focused on their possible applications for SO2 sequestration due to the selective and robust chemical and physical interactions of SO2 molecules within MOFs. The variable SO2 affinity presented by MOFs enables the adsorption mechanism and preferential adsorption sites to be resolved. However, for MOF-based SO2 detection, selective SO2 capture at shallow partial pressure (0.01-0.1 bar) is required. Thus, capturing SO2 at low concentration is crucial for SO2 detection, where textural properties of MOFs, mainly the pore-limiting diameter, are essential to achieve selective detection. In this review, we discuss the fundamental aspects of SO2 detection in MOFs, providing a step-by-step methodology for SO2 detection in MOFs. We hope this review can provide valuable background around SO2 detection in MOFs and inspire further research within this new and exciting field.

Selective detection of SO2 in NU-1000 via organometallic nickel silylphosphine post-synthetic complex incorporation

The adsorption and detection of SO2 using Zr-based MOF, NU-1000 grafted with an organometallic nickel silylphosphine complex ([NiSi]@NU-1000) via post-synthetic modification are reported. [NiSi]@NU-1000 exhibits high stability under dry and wet SO2, with a high cyclability performance. Moreover, fluorescence experiments postulate [NiSi]@NU-1000 as a promising SO2 detector due to its high SO2 selectivity over CO2 and air, showing an evident quenching effect, especially at low SO2 concentrations (0.1 bar of SO2). Time-resolved photoluminescence experiments suggest that host-guest SO2 interactions are associated with the turn-off effect.

Flue gas desulfurization and SO2 recovery within a flexible hydrogen-bonded organic framework

The removal of SO2 from flue gas remains a challenge. Adsorption-based separation of SO2 using porous materials has been proposed as a more energy-efficient and cost-effective alternative to more traditional methods such as cryogenic distillations. Here we report a flexible hydrogen-bonded organic framework (HOF-NKU-1) that enables the sieving of SO2 through the guest-adaptive response and shape-memory effect of the material. HOF-NKU-1 exhibits a high selectivity of 7,331 for the separation of SO2/CO2 and a high SO2 storage density of 3.27 g cm-3 within the pore space at ambient conditions. The hydrophobic nature of HOF-NKU-1 enables high dynamic SO2 uptake and SO2 recovery, even in conditions of 95% humidity. The SO2/CO2 separation mechanism is studied through combinatorial gas sorption isotherms, breakthrough experiments and single-crystal diffraction studies, paving the way for the development of multifunctional shape-memory porous materials in the future.

Activating the Gate-Opening of a Metal-Organic Framework and Maximizing Its Adsorption Capacity

Metal-organic frameworks (MOFs) are well-known porous materials owing to their useful adsorption properties; however, some MOFs have limited adsorption capabilities, which can significantly undermine their success as porous materials. Therefore, maximizing their porosity is critical for unlocking their full potential and expanding their practical utilization, such as gas storage, separation, and removal. In this study, flexible MOFs with defined defects were synthesized using a ligand-mixing strategy to improve their porosity and maximize their adsorption capacities. Specifically, we employed a combination of two organic linkers, 4,4'-biphenyldicarboxylic acid (H2BPDC) and 1,4-benzenedicarboxylic acid (H2BDC), in various ratios, to fabricate flexible In-MIL-53D hybrids containing controllable defects within the structure due to the incorporation of the short linker (H2BDC) compared to the original linker (H2BPDC). These structural defects in the In-MIL-53D hybrids activated their gate-openings and enhanced gas adsorption capacities for N2 and CO2. Moreover, the gate-opened activated hybrids exhibited excellent adsorption capacity for the harmful chemical warfare agent simulant, 2-chloroethyl ethyl sulfide (CEES). However, excessive incorporation of defects disrupted the framework's integrity, compromising its stability and increasing the risk of collapse. Therefore, achieving an optimal level of defect incorporation is essential to balance structural stability with enhanced functionality. Among the hybrids, the sample with approximately 39% incorporation of the short linker exhibited up to an 11-fold increase in adsorption capacity for CO2 at 1 P/P0. In addition, this hybrid demonstrated up to 5-fold higher CEES adsorption capacity compared to the pristine In-MIL-53D, highlighting its potential for advanced utilization in relevant fields.

A Hydrolytically Stable Metal-Organic Framework for Simultaneous Desulfurization and Dehydration of Wet Flue Gas

Metal-organic frameworks (MOFs) have great prospects as adsorbents for industrial gas purification, but often suffer from issues of water stability and competitive water adsorption. Herein, we present a hydrolytically stable MOF that could selectively capture and recover trace SO2 from flue gas, and exhibits remarkable recyclability in the breakthrough experiments under wet flue-gas conditions, due to its excellent resistance to the corrosion of SO2 and the water-derived capillary forces. More strikingly, its SO2 capture efficiency is barely influenced by the increasing humidity, even if the pore filling with water is reached. Mechanistic studies demonstrate that the delicate pore structure with diverse pore dimensions and chemistry leads to different adsorption kinetics and thermodynamics as well as segregated adsorption domains of SO2 and H2O. Significantly, this non-competitive adsorption mechanism enables simultaneous desulfurization and dehydration by a single adsorbent, opening an avenue toward cost-effective and simplified processing flowcharts for flue gas purification.

UTSA-16(Zn) for SO2 detection: elucidating the fluorescence mechanism

In this study, the potential of the metal-organic framework UTSA-16(Zn) as a fluorescence detector for SO2 is explored. The material was synthesized and characterized by powder X-ray diffraction (PXRD), infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and its fluorescence behavior was analyzed before and after SO2 exposure. A significant decrease in fluorescence intensity was observed and a LOD of 1.79 mM (∼114.6 ppm) was obtained. With the help of time-resolved photoluminescence (TRPL) experiments and X-ray photoelectron (XPS) and ultraviolet-visible (UV-vis) spectroscopy, a static quenching mechanism due to the formation of a non-fluorescent complex in the ground state (GSC) was elucidated.

Host molecules inside metal-organic frameworks: host@MOF and guest@host@MOF (Matrjoschka) materials

The controllable encapsulation of host molecules (such as porphyrin, phthalocyanine, crown ether, calixarene or cucurbituril organic macrocycles, cages, metal-organic polyhedrons and enzymes) into the pores of metal-organic frameworks (MOFs) to form host-in-host (host@MOF) materials has attracted increasing research interest in various fields. These host@MOF materials combine the merits of MOFs as a host matrix and functional host molecules to exhibit synergistic functionalities for the formation of guest@host@MOF materials in sorption and separation, ion capture, catalysis, proton/ion conduction and biosensors. (This guest@host@MOF construction is reminiscent of Russian (Matrjoschka) dolls which are nested dolls of decreasing size placed one inside another.) In this tutorial review, the advantages of MOFs as a host matrix are presented; the encapsulation approaches and general important considerations for the preparation of host@MOF materials are introduced. The state-of-the-art examples of these materials based on different host molecules are shown, and representative applications and general characterization of these materials are discussed. This review will guide researchers attempting to design functional host@MOF and guest@host@MOF materials for various applications.

Novel dual-channel ratiometric fluorescence probe for SO2 detection in food and bioimaging applications based on FRET mechanism

SO2 is commonly used to ensure the safety of food, but englobing of excessive SO2 poses serious risks to human health. Additionally, as fourth gaseous signaling molecule, it plays a critical role in various physiological processes. Therefore, monitoring the concentration of SO2 in food and cells is crucial for correlative research and disease diagnosis. Herein, two ratiometric fluorescence probes (EHDA and EHDB) have been synthesized for detecting sulfite based on fluorescence resonance energy transfer (FRET). Undoubtedly, EHDA as the preferable probe due to its superior discernibility to SO32- than that of EHDB. Moreover, EHDA featured rapid response, high sensitivity, excellent selectivity, and low cytotoxicity in physiological pH. Besides, EHDA could be expanded to establish convenient smartphone SO2 sensing platform through innovatively loading EHDA on polyvinylidene fluoride membrane. Fortunately, EHDA has been utilized for determining SO32- in food samples and imaging the fluctuation of sulfite in living cells and zebrafish.

Chemically Modified HKUST-1(Cu) for Gas Adsorption and Separation: Mixed-Metal and Hierarchical Porosity

The archetypical metal-organic framework (MOF), HKUST-1, has been systematically modified in both its organic and inorganic building blocks to introduce diversity in the metal centers and create defects within the network, achieving a variety of bimetallic hierarchical structures. These modifications changed the affinity of the MOFs for acid gases. The introduction of bimetallic sites mostly affects CO2 adsorption, while the hierarchical structure generates an increase in SO2 uptake capacity, allowing better performance in the separation of binary mixtures of these gases near room temperature. Notably, the synthesized HH-Cu100 material exhibited an exceptionally high IAST SO2/CO2 (10:90) selectivity of 3420 at 298 K, outperforming benchmark MOFs with open metal sites.

Modulator-Directed Counterintuitive Catenation Control for Crafting Highly Porous and Robust Metal-Organic Frameworks with Record High SO2 Uptake Capacity

Sulfur dioxide (SO2) is an important industrial feedstock that can be directly utilized or catalytically transformed to value-added chemicals such as sulfuric acid. The development of regenerable porous sorbents for the highly efficient storage and energy-minimal release of toxic SO2 operating under ambient conditions has attracted growing interest. Herein, we report the topology-guided construction of highly porous acs-type metal-organic frameworks (MOFs) through a counterintuitive modulator-directed catenation control approach. In contrast to the conventional modulator facilitated coordination competition that favors the thermodynamic catenated phase, we show that the elevation of modulator concentration can promote the formation of the noncatenated phase probably through a sublattice dissolution pathway. The assembly of a custom-designed trigonal prismatic triptycene-quinoxaline linker and trinuclear Fe3O cluster affords either the threefold catenated SJTU-219 or noncatenated SJTU-220 with desired acs net. Impressively, the synthetic approach is applicable to various metal ions, including Al3+, V3+, and even Ti4+. The noncatenated SJTU-220 exhibits an extraordinary SO2 sorption capacity of 29.6 mmol g-1 at 298 K and 1 bar, surpassing all reported solid sorbents. The uptake capacity can be further raised to 35.6 mmol g-1 via the replacement of Fe3+ with kinetically more inert Cr3+, resulting in a staggering ∼329-fold volume reduction compared with free ideal SO2 gas. Computational simulations suggest that unique Fe3+···S(SO2) interactions dominate the SO2 seeding process, facilitating the efficient packing of SO2 molecules in the large channels. Besides, the exceptionally low uptake at the low pressure region implies global weak framework-SO2 interactions, which offer great potential for practically implementing an "easy-on/easy-off" SO2 delivery system.

Two amino-functionalized metal-organic frameworks with different topologies for C2H2/C2H4 separation

The rational design of metal-organic framework adsorbents is crucial for target gas separation. Herein, we report two three-dimensional MOFs with different topologies by regulating metal ions with amino-functionalized V-type ligands. Adsorption isotherms and Grand Canonical Monte Carlo simulation reveal that UPC-122 with channel-cavity structure has the potential to separate C2H2/C2H4 at room temperature with a separation ratio of 2.35 (50/50).

Microwave-Assisted Ultrafast Synthesis of Bimetallic Nickel-Cobalt Metal-Organic Frameworks for Application in the Oxygen Evolution Reaction

Herein, a series of monometallic Ni-, Co- and Zn-MOFs and bimetallic NiCo-, NiZn- and CoZn-MOFs of formula M2(BDC)2DABCO and (M,M')2(BDC)2DABCO, respectively, (M, M'=metal) with the same pillar and layer linkers 1,4-diazabicyclo[2.2.2]octane (DABCO) and benzene-1,4-dicarboxylate (BDC) were prepared through a fast microwave-assisted thermal conversion synthesis method (MW) within only 12 min. In the bimetallic MOFs the ratio M:M' was 4 : 1. The mono- and bimetallic MOFs were selected to systematically explore the catalytic-activity of their derived metal oxide/hydroxides for the oxygen evolution reaction (OER). Among all tested bimetallic MOF-derived catalysts, the NiCoMOF exhibits superior catalytic activity for the OER with the lowest overpotentials of 301 mV and Tafel slopes of 42 mV dec-1 on a rotating disk glassy carbon electrode (RD-GCE) in 1 mol L-1 KOH electrolyte at a current density of 10 mA cm-2. In addition, NiCoMOF was insitu grown in just 25 min by the MW synthesis on the surface of nickel foam (NF) with, for example, a mass loading of 16.6 mgMOF/gNF, where overpotentials of 313 and 328 mV at current densities of 50 and 300 mA cm-2, respectively, were delivered and superior long-term stability for practical OER application. The low Tafel slope of 27 mV dec-1, as well as a low reaction resistance from electrochemical impedance spectroscopy (EIS) measurement (Rfar=2 Ω), confirm the excellent OER performance of this NiCoMOF/NF composite. During the electrocatalytic processes or even before upon KOH pre-treatment, the MOFs are transformed to the mixed-metal hydroxide phase α-/β-M(OH)2 which presents the active species in the reactions (turnover frequency TOF=0.252 s-1 at an overpotential of 320 mV). Compared to the TOF from β-M(OH)2 (0.002 s-1), our study demonstrates that a bimetallic MOF improves the electrocatalytic performance of the derived catalyst by giving an intimate and uniform mixture of the involved metals at the nanoscale.

Simultaneous capture of trace benzene and SO2 in a robust Ni(II)-pyrazolate framework

Benzene and SO2, coexisting as hazardous air pollutants in some cases, such as in coke oven emissions, have led to detrimental health and environmental effects. Physisorbents offer promise in capturing benzene and SO2, while their performance compromises at low concentration. Particularly, the simultaneous capture of trace benzene and SO2 under humid conditions is attractive but challenging. Here, we address this issue by constructing a robust pyrazolate metal-organic framework (MOF) sorbent featuring rich accessible Ni(II) sites with low affinity to water and good stability. This material achieves a high benzene uptake of 5.08 mmol g-1 at 10 Pa, surpassing previous benchmarks. More importantly, it exhibits an adsorption capacity of ~0.51 mmol g-1 for 10 ppm benzene and ~1.21 mmol g-1 for 250 ppm SO2 under 30% relative humidity. This work demonstrates that a pioneering MOF enables simultaneous capture of trace benzene and SO2, highlighting the potential of physisorbents for industrial effluent remediation, even in the presence of moisture.

Effect of the Number of Methyl Groups in DMOF on N2O Adsorption and N2O/N2 Separation

Nitrous oxide (N2O), as the third largest greenhouse gas in the world, also has great applications in industry, so the purification of N2O from N2 in industrial tail gas is a crucial process for achieving environmental protection and giving full play to its economic value. Based on the polarity difference of N2O and N2, N2O adsorption was researched on DMOF series materials with different polarities and methyl numbers of the ligand. N2O adsorption at 0.1 bar is enhanced, attributed to an increase of the methyl group densities at the benzenedicarboxylate linker. Grand canonical Monte Carlo simulations demonstrate the key role of methyl groups within the pore surface in the preferential N2O affinity. Methyl groups preferentially bind to N2O and thus enhanced low (partial) pressure N2O adsorption and N2O/N2 separation. The result shows that DMOF-TM has the highest N2O adsorption capacity (19.6 cm3/g) and N2O/N2 selectivity (23.2) at 0.1 bar. Breakthrough experiments show that, with an increase of the methyl number, the coadsorption time and retention time also increase, and DMOF-TM has the best N2O/N2 separation performance.

Deep learning and big data mining for Metal-Organic frameworks with high performance for simultaneous desulfurization and carbon capture

Carbon capture and desulfurization of flue gases are crucial for the achievement of carbon neutrality and sustainable development. In this work, the "one-step" adsorption technology with high-performance metal-organic frameworks (MOFs) was proposed to simultaneously capture the SO2 and CO2. Four machine learning algorithms were used to predict the performance indicators (NCO2+SO2, SCO2+SO2/N2, and TSN) of MOFs, with Multi-Layer Perceptron Regression (MLPR) showing better performance (R2 = 0.93). To address sparse data of MOF chemical descriptors, we introduced the Deep Factorization Machines (DeepFM) model, outperforming MLPR with a higher R2 of 0.95. Then, sensitivity analysis was employed to find that the adsorption heat and porosity were the key factors for SO2 and CO2 capture performance of MOF, while the influence of open alkali metal sites also stood out. Furthermore, we established a kinetic model to batch simulate the breakthrough curves of TOP 1000 MOFs to investigate their dynamic adsorption separation performance for SO2/CO2/N2. The TOP 20 MOFs screened by the dynamic performance highly overlap with those screened by the static performance, with 76 % containing open alkali metal sites. This integrated approach of computational screening, machine learning, and dynamic analysis significantly advances the development of efficient MOF adsorbents for flue gas treatment.

A stable Zr(IV)-MOF for efficient removal of trace SO2 from flue gas in dry and humid conditions

Obtaining suitable adsorbents for selective separation of SO2 from flue gas still remains an important issue. A stable Zr(IV)-MOF (Zr-PTBA) can be conveniently synthesized through the self-assembly of a tetracarboxylic acid ligand (H4L = 4,4',4'',4'''-(1,4-phenylenebis(azanetriyl))tetrabenzoic acid) and ZrCl4 in the presence of trace water. It exhibits a three-dimensional porous structure. The BET surface area is 1112.72 m2/g and the average pore size distribution focus on 5.9, 8.0 and 9.3 Å. Interestingly, Zr-PTBA shows selective adsorption of SO2. The maximum uptake reaches 223.21 cm3/g at ambient condition. While it exhibits lower adsorption uptake of CO2 (30.50 cm3/g) and hardly adsorbs O2 (2.57 cm3/g) and N2 (1.31 cm3/g). Higher IAST selectivities of SO2/CO2 (21.9), SO2/N2 (912.7), SO2/O2 (2269.9) and SO2/CH4 (85.0) have been obtained, which reveal its' excellent gas separation performance. Breakthrough experiment further confirms its application for flue gas deep desulfurization both in dry and humid conditions. Furthermore, the gas adsorption results and mechanisms have also been studied by theoretical calculations.

SO2 capture and detection with carbon microfibers (CMFs) synthesised from polyacrylonitrile

SO2 emissions not only affect local air quality but can also contribute to other environmental issues. Developing low-cost and robust adsorbents with high uptake and selectivity is needed to reduce SO2 emissions. Here, we show the SO2 adsorption-desorption capacity of carbon microfibers (CMFs) at 298 K. CMFs showed a reversible SO2 uptake capacity (5 mmol g-1), cyclability over ten adsorption cycles with fast kinetics and good selectivity towards SO2/CO2 at low-pressure values. Additionally, CMFs' photoluminescence response to SO2 and CO2 was evaluated.

Linker-Guided Growth of Single-Crystal Covalent Organic Frameworks

The core features of covalent organic frameworks (COFs) are crystallinity and porosity. However, the synthesis of single-crystal COFs with monomers of diverse reactivity and adjustment of their pore structures remain challenging. Here, we show that linkers that can react with a node to form single-crystal COFs can guide other linkers that form either COFs or amorphous polymers with the node to gain single-crystal COFs with mixed components, which are homogeneous on the unit cell scale with controlled ratios. With the linker-guided crystal growth method, we created nine types of single-crystal COFs with up to nine different components, which are more complex than any known crystal. The structure of the crystal adapted approximately to that of the main component, and its pore volume could be expanded up to 8.8%. Different components lead to complex and diverse pore structures and offer the possibilities to gain positive synergies, as exemplified by a bicomponent COF with 2200 and 733% SO2 uptake capacity of that of the two pure-component counterparts at 298 K and 0.002 bar. The selectivity for separation of SO2/CO2 ranges from 1230 to 4247 for flue gas based on ideal adsorbed solution theory, recording porous crystals. The bicomponent COF also exhibits a 1300% retention time of its pure-component counterparts for SO2 in a dynamic column breakthrough experiment for deep desulfurization.

Microporous Fluorinated MOF with Multiple Adsorption Sites for Efficient Recovery of C2H6 and C3H8 from Natural Gas

Purifying C2H6/C3H8 from a ternary natural gas mixture through adsorption separation is an important but challenging process in the petrochemical industry. To address this challenge, the industry is exploring effective strategies for designing high-performance adsorbents. In this study, we present two metal-organic frameworks (MOFs), DMOF-TF and DMOF-(CF3)2, which have fluorinated pores obtained by substituting linker ligands in the host material. This pore engineering strategy not only provides suitable pore confinement but also enhances the adsorption capacities for C2H6/C3H8 by providing additional binding sites. Theoretical calculations and transient breakthrough experiments show that the introduction of F atoms not only improves the efficiency of natural gas separation but also provides multiple adsorption sites for C2H6/C3H8-framework interactions.

Effective Strategy toward Obtaining Reliable Breakthrough Curves of Solid Adsorbents

Metal-organic frameworks (MOFs) have demonstrated their versatility in a wide range of applications, including chemical separation, gas capture, and storage. In industrial adsorption processes, MOFs are integral to the creation of selective gas adsorption fixed beds. In this context, the assessment of their separation performance under relevant conditions often relies on breakthrough experiments. One aspect frequently overlooked in these experiments is the shaping of MOF powders, which can significantly impact the accuracy of breakthrough results. In this study, we present an approach for immobilizing MOF particles on the surface of glass beads (GBs) utilizing trimethylolpropane triglycidyl ether (TMPTGE) as a binder, leading to the creation of MOF@GB materials. We successfully synthesized five targeted MOF composites, namely, SIFSIX-3-Ni@GB, CALF-20@GB, UiO-66@GB, HKUST-1@GB, and MOF-808@GB, each possessing distinct pore sizes and structural topologies. Characterization studies employing powder X-ray diffraction and adsorption isotherm analyses demonstrated that MOFs@GB retained their crystallinity and 73-90% of the Brunauer-Emmett-Teller area of their parent MOFs. Dynamic breakthrough experiments revealed that, in comparison to their parent MOFs, MOF@GB configurations enhanced the accuracy of breakthrough measurements by mitigating pressure buildup and minimizing reductions in the gas flow rate. This work underscores the significance of meticulous experimental design, specifically in shaping MOF powders, to optimize the efficacy of breakthrough experiments. Our proposed strategy aims to provide a versatile platform for MOF powder processing, thereby facilitating more reliable breakthrough experiments.

SO2 Capture at Low Pressure in a Prototypical MIL-53 Aluminum MOF Family: The Influence of Pore Expansion

Not only is excellent performance in SO2 capture by porous materials (uptake above 17 mmol g-1) relevant, but also finding a correlation between the architecture changes into a family and their SO2 adsorption is very useful. In this contribution, we studied the SO2 adsorption behavior (at very low pressure) of an Al(III)-MOF family that shares the pore architecture of MIL-53. The results indicate an inversely proportional trend for the SO2 capture and pore expansion, since by increasing the length of the channel pore, the SO2 uptake gradually decreases. In addition, this trend is clearly observed in the heat of adsorption, which describes the interaction between the SO2 molecule and the μ-OH functional group. These finding are supported by experimental analysis and computational studies.

A novel high activity MnXFe3-XO4 spinel catalyst for selective catalytic reduction of NO using NH3 prepared by a short process from natural minerals for low-temperature sintering flue gas: Effect of X value on catalytic mechanism

The process of smelting and purifying the catalyst precursor salt from minerals is extremely complex, which directly leads to high catalyst costs and serious secondary pollution. In order to achieve energy saving and emission reduction in the catalyst preparation process, in-situ synthesis of catalyst materials from natural minerals is a new research direction. In this study, we firstly explored the optimal X value of MnXFe3-XO4 for the NH3 selective catalytic reduction of NO (NH3-SCR) reaction, i.e., the Mn, Fe ratio, and then prepared a novel highly active mineral-based pure phase MnXFe3-XO4 spinel NH3-SCR catalyst by natural ferromanganese ore fines with iron-red fines (Fe2O3) allotment through in situ solid-phase synthesis and magnetic separation methods according to this ratio. The results show that the X value of 1.5 (Mn1.5Fe1.5O4) is the best for NH3-SCR reaction. Mn1.5Fe1.5O4 nano-particles (201 nm) has nearly 100 % NO conversion (with 5 % H2O(g)) at 125-300 °C. The combination of characterizations and density functional theory (DFT) calculation shows that the catalytic process of Eley-Rideal (E-R) dehydrogenation is enhanced at both the active site Mn site and Fe site, which is a key factor in the acceleration of the NH3-SCR reaction with increasing X value at the MnXFe3-XO4 surface.

Modulator-Dependent Dynamics Synergistically Enabled Record SO2 Uptake in Zr(IV) Metal-Organic Frameworks Based on Pyrene-Cored Molecular Quadripod Ligand

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal-organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g-1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in isostructural Zr-TPA variants synthesized with different capping modulators (formate, acetate, benzoate, and trifluoroacetate, abbreviated as FA, HAc, BA, and TFA, respectively) through computational analyses. These analyses revealed unexpected SO2-induced modulator-node dynamics, resulting in transient chemisorption that enhanced synergistic SO2 sorption. Additionally, we conducted a proof-of-concept experiment demonstrating that the captured SO2 in Zr-TPA-FA can be converted in situ into a valuable pharmaceutical intermediate known as aryl N-aminosulfonamide, with a high yield and excellent recyclability. This highlights the potential of robust Zr-MOFs for storing SO2 in catalytic applications. In summary, this work contributes significantly to the development of efficient SO2 solid sorbents and advances our understanding of the molecular mechanisms underlying SO2 sorption in Zr-MOF materials.

Smart crystalline framework materials with a triazole carboxylic acid ligand: fluorescence sensing and catalytic reduction of PNP

Triazole polycarboxylic acid ligands are widely employed in the construction of MOFs due to their strong coordination ability and flexible coordination modes. In this work, three novel complexes (Pb(MCTCA)(H2O) (1), Co(HMCTCA)2(H2O)2 (2) and Cu(HMCTCA)2(H2O)2 (3)) based on the H2MCTCA ligand (5-methyl-1-(4-carboxyl)-1H-1,2,3-triazole-4-carboxylic acid) were successfully synthesized under hydrothermal conditions, respectively. X-ray single crystal structure analysis shows that complex 1 is a 3D network structure, where the central metal Pb(II) is six coordinated to form deformed triangular prism geometry. The complexes 2 and 3 are both 2D layer supramolecular structures connected through intermolecular hydrogen, where the central metals (Co/Cu) are six coordinated to form octahedral configuration geometry. Based on functional properties, it is found that complex 1 exhibits excellent detection ability for small-molecule drugs (azithromycin, colchicine and balsalazide disodium) and actinide cations (Th4+ and UO22+) within a lower concentration range without interference from other components. In particular, the detection limits of three small-molecule drugs are all lower than 0.30 μM. In addition, complexes 2 and 3 exhibited excellent catalytic reduction performance toward p-nitrophenol (PNP), with a reduction efficiency exceeding 98%. These experimental results evidence that complexes 1-3 have potential application prospects in fluorescence sensing and catalytic reduction.

Fabrication of Pillar-Cage Fluorinated Anion Pillared Metal-Organic Frameworks via a Pillar Embedding Strategy and Efficient Separation of SO2 through Multi-Site Trapping

Flue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade-off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion-pillared metal-organic frameworks (APMOFs) with a pillar-cage structure is fabricated through pillar-embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5 ]2- and [TaOF5 ]2- anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2 /CO2 and SO2 /N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2 /CO2 gas mixtures and their cyclic stability. SO2 -loaded single-crystal X-ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple-site host-guest and guest-guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas-purification processes.

Surface engineering on a microporous metal-organic framework to boost ethane/ethylene separation under humid conditions

Recently, examples of metal-organic frameworks (MOFs) have been identified displaying ethane (C2H6) over ethylene (C2H4) adsorption selectivity. However, it remains a challenge to construct MOFs with both large C2H6 adsorption capacity and high C2H6/C2H4 adsorption selectivity, especially under humid conditions. Herein, we reported two isoreticular MOF-5 analogues (JNU-6 and JNU-6-CH3) and their potential applications in one-step separation of C2H4 from C2H6/C2H4 mixtures. The introduction of CH3 groups not only reduces the pore size from 5.4 Å in JNU-6 to 4.1 Å in JNU-6-CH3 but also renders an increased electron density on the pyrazolate N atoms of the organic linker. JNU-6-CH3 retains its framework integrity even after being immersed in water for six months. More importantly, it exhibits large C2H6 adsorption capacity (4.63 mmol g-1) and high C2H6/C2H4 adsorption selectivity (1.67) due to the optimized pore size and surface function. Breakthrough experiments on JNU-6-CH3 demonstrate that C2H4 can be directly separated from C2H6/C2H4 (50/50, v/v) mixtures, affording benchmark productivity of 22.06 and 18.71 L kg-1 of high-purity C2H4 (≥99.95%) under dry and humid conditions, respectively.

Halogen-modified metal-organic frameworks for efficient separation of alkane from natural gas

As a rich green energy source, natural gas is widely used in many fields such as the chemical industry, automobile energy, and daily life. However, it is very challenging to separate and recover C2H6 and C3H8 from natural gas. Metal-organic frameworks (MOFs) as an emerging type of multi-pore porous materials show huge potential in gas adsorption separation. Herein, we report pillar-layered MOFs, Ni (BDC)(DABCO)0.5 (DMOF-X), modified by halogen atoms (F, Cl, Br), and investigate their CH4/C2H6/C3H8 separation performance. The experimental results show that DMOF-Cl exhibited a extremely high adsorption capacity for C3H8 and C2H6. Under the conditions of 298 K and 100 kPa, the adsorption capacities for C3H8 and C2H6 on DMOF-Cl are as high as 6.23 and 4.94 mmol g-1, which are superior to the values for most of the porous materials that have been reported. In addition, DMOF-Cl also shows high C3H8/CH4 (5: 85, V/V) and C2H6/CH4 (10: 85, V/V) separation selectivities, with values of 130.9 and 12.5, respectively. Finally, DMOF-Cl also demonstrated great potential as an adsorbent for separating C3H8/C2H6/CH4.

Feasible bottom-up development of conjugated microporous polymers (CMPs) for boosting the deep removal of sulfur dioxide

A pain-point for material development is that computer-screened structures are usually difficult to realize in experiments. Herein, considering that linkages are crucial for building functional nanoporous polymers with diverse functionalities, we develop an efficient approach for constructing target-specific conjugated microporous polymers (CMPs) based on screening feasible polymerization pathways. Taking the deep removal of SO2 from a SO2/CO2 mixture as the specific target, we precisely screen the linkages and fabricate different CMPs by manipulating the porosity and hydrophobicity. Based on the optimized Buchwald-Hartwig amination, the obtained CMPs can achieve SO2/CO2 selectivity as high as 113 and a moderate Qst of 30 kJ mol-1 for feasible regeneration. Furthermore, the potential of CMPs for practical SO2/CO2 separation is demonstrated through continued breakthrough tests. The SO2 binding sites are consistent with the screening results and proved by in situ Fourier transform infrared spectroscopy and grand canonical Monte Carlo simulation, providing solid feasibility for synthesis realizability for future boosts of task-specific CMPs.

Molecular adsorption and self-diffusion of NO2, SO2, and their binary mixture in MIL-47(V) material

The loading dependence of self-diffusion coefficients (Ds) of NO2, SO2, and their equimolar binary mixture in MIL-47(V) have been investigated by using classical molecular dynamics (MD) simulations. The Ds of NO2 are found to be two orders of magnitude greater than SO2 at low loadings and temperatures, and its Ds decreases monotonically with loading. The Ds of SO2 exhibit two diffusion patterns, indicating the specific interaction between the gas molecules and the MIL-47(V) lattice. The maximum activation energy (Ea) in the pure component and in the mixture for SO2 are 16.43 and 18.35 kJ mol-1, and for NO2 are 2.69 and 1.89 kJ mol-1, respectively. It is shown that SO2 requires more amount of energy than NO2 to increase the diffusion rate. The radial distribution functions (RDFs) of gas-gas and gas-lattice indicate that the Oh of MIL-47(V) are preferential adsorption site for both NO2 and SO2 molecules. However, the presence of the hydrogen bonding (HB) interaction between the O of SO2 and the H of MIL-47(V) and also their binding angle (θ(OHC)) of 120° with the linkers of lattice indicate a stronger binding interaction between the SO2 and the MIL-47(V), but it does not occur with NO2. The jump-diffusion of SO2 between adsorption sites within the lattice has been confirmed by the 2D density distribution plots. Moreover, the extraordinarily high Sdiff for NO2/SO2 of 623.4 shows that NO2 can diffuse through the MIL-47(V) significantly faster than SO2, especially at low loading and temperature.

Surfactant-assisted mesopores in hierarchical metal-organic frameworks for the immobilization of model protein Cyt c

A hierarchical metal-organic framework, H-mMOF-1 (representing hierarchical medi-MOF-1), was successfully synthesized by the coassembly of MOF starting reagents and a triblock copolymer surfactant F127. The obtained H-mMOF-1 retained its microporous structure but also exhibited mesopores with a size range from 3 to 10 nm. The mesopores were able to accommodate protein Cyt c with a loading capacity of 160 mg g^-1. The surfactant-assisted synthesis of hierarchical MOFs provides promising applications for enzyme immobilization.

Structural Compromise Between Conflicted Spatial-Arrangements of Two Linkers in Metal-Organic Frameworks

The structural control of metal-organic frameworks (MOFs) is essential for the development of superlative MOFs because the structural features of MOFs and their components play a critical role in determining their properties, and ultimately, their applications. The best components to endow the desired properties for MOFs are available via the appropriate choice from many existing chemicals or synthesizing new ones. However, to date, considerably less information exists regarding fine-tuning the MOF structures. Herein, a strategy for tuning MOF structures by merging two MOF structures into a single MOF, is demonstrated. Depending on the incorporated amounts and relative contributions of the two coexisting organic linkers, benzene-1,4-dicarboxylate (BDC^2- ) and naphthalene-1,4-dicarboxylate (NDC^2- ), which have conflicting spatial-arrangement preferences within an MOF structure, MOFs are rationally designed to have a Kagomé or rhombic lattice. In particular, MOFs with rhombic lattices are constructed to have specific lattice angles by compromising the optimal structural arrangements between the two mixed linkers. The relative contributions of the two linkers during MOF construction determine the final MOF structures, and the competitive influence between BDC^2- and NDC^2- is effectively regulated to produce specific MOF structures with controlled lattices.

Synthesis of Ketjenblack Decorated Pillared Ni(Fe) Metal-Organic Frameworks as Precursor Electrocatalysts for Enhancing the Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni2(BDC)2DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)2DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L-1). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm-2 and a Tafel slope of 32 mV dec-1, which is comparable with commercial RuO2, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm-2. The low Tafel slope of 25 mV dec-1 as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm-2, respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm-2. More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)2, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N2 sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity.

Construction of Fluorinated Propane-Trap in Metal-Organic Frameworks for Record Polymer-Grade Propylene Production under High Humidity Conditions

Propane/propene (C₃ H₈ /C₃ H₆ ) separation is essential in the petrochemical industry but challenging because of their similar physical and chemical properties. Adsorptive separation with C₃ H₈ -selective porous materials can energy-efficiently produce high-purity C₃ H₆ , which is highly promising for replacing conventional cryogenic distillation but suffers from unsatisfactory performance. Herein, through the precise incorporation of fluorinated functional groups into the confined pore space, a new fluorinated metal-organic framework (FDMOF-2) featuring the unique and strong C₃ H₈ -trap is successfully constructed. FDMOF-2 exhibits an unprecedented C₃ H₈ capture capacity of 140 cm³ cm^-3 and excellent C₃ H₈ /C₃ H₆ (1:1, v/v) selectivity up to 2.18 (298 K and 1 bar), thus setting new benchmarks for all reported porous materials. Single-crystal X-ray diffraction studies reveal that the tailored pore confinement in FDMOF-2 provides stronger and multiple attractive interactions with C₃ H₈ , enabling excellent binding affinities. Breakthrough experiments demonstrate that C₃ H₈ can be directly extracted from various C₃ H₈ /C₃ H₆ mixtures with FDMOF-2, affording an outstanding C₃ H₆ production (501 mmol L^-1 ) with over 99.99% purity. Benefiting from the robust framework and hydrophobic ligands, the separation performance of FDMOF-2 can be well maintained even under 70% relative humidity conditions.

A multifunctional cobalt-organic framework for proton conduction and selective sensing of Fe3+ ions

Developing multifunctional metal-organic frameworks (MOFs) is a new research trend. MOFs have shown remarkable performances in both proton conduction and fluorescence sensing, but the MOFs integrating the two performances are scarce. Herein, a Co-MOF, [Co₆(oba)₄(Hatz)(atz)(H₂O)₂(μ₃-OH)₂(μ₂-OH)]·H₂O (1, H₂oba = 4,4-oxybis(benzoic acid), Hatz = 5-amino-1H tetrazole), has been assembled by Co²⁺ ions with H₂oba and Hatz ligands, providing a unique example of multifunctional MOFs with both proton conduction and fluorescence sensing performances. The framework of 1 displays a pillar-layer structure built by the oba ligand as a pillar and a layer composed of Co-clusters and atz linkers. Because large-scale single crystals of 1 were successfully synthesized, the proton conduction ability of 1 was investigated using single crystal samples. 1 exhibits highly anisotropic conduction with conductivity values of 1.1 × 10^-3 S cm^-1 along the [001] direction and 9.1 × 10^-6 S cm^-1 along the [010] direction at 55 °C and 95% RH, respectively. Meanwhile, the fluorescence sensing of 1 towards metal ions was studied in aqueous solutions. Attractively, 1 may sensitively and selectively detect Fe³⁺ ions in the presence of other interfering ions by fluorescence quenching.

A Novel Aluminum-Based Metal-Organic Framework with Uniform Micropores for Trace BTEX Adsorption

Metal-organic frameworks (MOFs) are potential porous adsorbents for benzene, toluene, ethylbenzene and xylene (BTEX). A novel MOF, using low toxic aluminum (Al) as the metal, named as ZJU-620(Al), with uniform micropore size of 8.37±0.73 Å and specific surface area of 1347 m²  g^-1 , was synthesized. It is constructed by one-dimensional rod-shaped AlO₆ clusters, formate ligands and 4,4',4''-(2,4,6-trimethylbenzene-1,3,5-triyl) tribenzoic ligands. ZJU-620(Al) exhibits excellent chemical-thermal stability and adsorption for trace BTEX, e.g., benzene adsorption of 3.80 mmol g^-1 at P/P₀ =0.01 and 298 K, which is the largest one reported. Using Grand Canonical Monte Carlo simulations and Single-crystal X-ray diffraction analyses, it was observed that the excellent adsorption could be attributed to the high affinity of BTEX molecules in ZJU-620(Al) micropores because the kinetic diameters of BTEX are close up to the pore size of ZJU-620(Al).

Fine-Tuned Ultra-Microporous Metal-Organic Framework in Mixed-Matrix Membrane: Pore-Tailoring Optimization for C2 H2 /C2 H4 Separation

Effective separation of ethyne from ethyne/ethylene (C₂ H₂ /C₂ H₄ ) mixtures is a challenging and crucial industrial process. Herein, an ultra-microporous metal-organic framework (MOF) platform, Cd(dicarboxylate)₂ (ditriazole), with triangular channels is proposed for high-efficiency separation of C₂ H₂ from C₂ H₄ . The targeted structures are constructed via a mixed-ligand strategy by selecting different-sized ligands, allowing for tunable pore sizes and volumes. The pore properties can be further optimized by additional modification via pore environment tailoring. This concept leads to the successful synthesis of three ultra-microporous Cd-MOFs (JLU-MOF87-89). As intended, C₂ H₂ uptake and C₂ H₂ /C₂ H₄ selectivity gradually increase with progressively optimizing the pore structure by adjusting ligand length and substituents. JLU-MOF89, functionalized with methyl groups, features the most optimal pore chemistry and shows selective recognition of C₂ H₂ over C₂ H₄ , owing to the framework-C₂ H₂ host-guest interactions. Furthermore, JLU-MOFs are fabricated into mixed-matrix membranes for C₂ H₂ /C₂ H₄ separation. C₂ H₂ permeability and C₂ H₂ /C₂ H₄ permselectivity are substantially enhanced by ≥400% and ≥200%, respectively, after hybridization of JLU-MOF88 and JLU-MOF89 with a polyimide polymer (6FDA-ODA). These membranes can work efficiently and are stable under different conditions, demonstrating their potential in actual ethyne separation.

Porous Covalent Organic Framework Based Hydrogen-Bond Nanotrap for the Precise Recognition and Separation of Gold

Utilizing weak interactions to effectively recover and separate precious metals in solution is of great importance but the practice remains a challenge. Herein, we report a novel strategy to achieve precise recognition and separation of gold by regulating the hydrogen-bond (H-bond) nanotrap within the pore of covalent organic frameworks (COFs). It is found that both COF-HNU25 and COF-HNU26 can efficiently capture Au^III with fast kinetics, high selectivity, and uptake capacity. In particular, the COF-HNU25 with the high density of H-bond nanotraps exhibits an excellent gold uptake capacity of 1725 mg g^-1 , which is significantly higher than that (219 mg g^-1 ) of its isostructural COF (COF-42) without H-bond nanostrap in the pores. Importantly, the uptake capacity is strongly correlated to the number of H-bonds between phenolic OH in the COF and [AuCl₄ ]^- in water, and multiple H-bond interactions are the key driving force for the excellent gold recovery and reusability of the adsorbent.

Ratio Fluorescent Detecting of Tryptophan and Its Metabolite 5-Hydroxyindole-3-acetic Acid Relevant with Depression via Tb(III) Modified HOFs Hybrids: Further Designing Recyclable Molecular Logic Gate Connected by Back Propagation Neural Network

Exploring intelligent fluorescent materials with high reliability and precision to diagnose diseases is significant but remains a great challenge. Herein, based on coordination post-synthetic modification, a Tb³⁺ functionalized ME-PA (Tb@1) is prepared, which can emit brilliant green fluorescence through ligand-to-mental charge transfer-assisted energy transfer (LMCT-ET) process from ME-PA to Tb³⁺ ions. Tb@1 can simultaneously distinguish Tryptophan (Try) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA), two effective indicators for depression, in ratio and colorimetric mode. And this sensor behaves the advantages of high efficiency and sensitivity, as well as excellent reusability and anti-interference. The PET process from ME to Try and 5-HIAA, and the competitive absorption between analytes and Tb@1 may be relevant to sensing mechanism. In realistic serum or urine environment, the detection limits of Tb@1 for Try and 5-HIAA are 0.0183 and 0.0149 mg L^-1 respectively. Moreover, in conjunction with back propagation neural network (BPNN), two dual-output molecular logic gates that can be calculated circularly are further designed, which realizes intelligent control of the electronic component to identify the existence of two biomarkers and judge their concentrations from fluorescence images. This work offers a novel approach to modulate logic circuits based on ML-assisted HOF fluorescent sensor, with promising application for a precise and pictorial depression diagnosis.

Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure

In this study, the ability of the highly scalable metal-organic framework (MOF) CALF-20 to adsorb polar and non-polar gases at low pressure was investigated using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results from the simulated adsorption isotherms revealed that the highest loading was achieved for SO2 and Cl2, while the lowest loading was found for F2 molecules. The analysis of interaction energies indicated that SO2 molecules were able to form the strongest adsorbent-adsorbate interactions and had a tight molecular packing due to their polarity and angular structure. Additionally, Cl2 gas was found to be highly adsorbed due to its large van der Waals surface and strong chemical affinity in CALF-20 pores. MD simulations showed that SO2 and Cl2 had the lowest mobility inside CALF-20 pores. The values of the Henry coefficient and isosteric heat of adsorption confirmed that CALF-20 could selectively adsorb SO2 and Cl2. Based on the results, it was concluded that CALF-20 is a suitable adsorbent for SO2 and Cl2 but not for F2. This research emphasizes the importance of molecular size, geometry, and polarity in determining the suitability of a porous material as an adsorbent for specific adsorbates.

Stimulus-Responsive Lanthanide MOF Materials Encapsulated with Viologen Derivatives: Characterization, Photophysical Properties and Sensing on Nitrophenols

Viologens (1,1'-disubstituted 4,4'-bipyridyls) possessing electron-deficient properties and redox activity are a class of suitable chromophores to assemble metal-organic hybrid photochromic materials. Thus, viologen-functionalized metal-organic frameworks (MOFs) have attracted much attention for their photochromic properties; however, the syntheses of lanthanide-viologen hybrid crystalline photochromic materials still face many challenges. For example, the structures and properties of the final products are difficult to predict and are limited by molecular configurations. In this work, host-guest composite-material Ln-NH₂ BDC-pbpy MOFs were constructed by encapsulating viologen derivative pbpyCl₂ . The pbpy²⁺ moieties are uniformly embed by their π-π conjugation in the pores of the 3D structure by electrostatic interactions. Due to the encapsulation of the chromophore pbpy²⁺ moieties, Ln-NH₂ BDC-pbpy MOFs have reversible photochromic properties: they can change color after irradiation and can return to the original color after being protected from light or heating. Interestingly, the fluorescence intensity decreases with illumination time and recovers in the dark. As a result, Ln-NH₂ BDC-pbpy MOFs show both photochromic and photomodulated fluorescence. Based on the outstanding fluorescence performance of the Ln-NH₂ BDC-pbpy MOFs, they also show a wonderful effect for detecting nitrophenols, especially TNP.

Porous functional metal–organic frameworks (MOFs) constructed from different N-heterocyclic carboxylic ligands for gas adsorption/separation

This review mainly summarizes the recent progress of MOFs composed of N-heterocyclic carboxylate ligands in gas sorption/separation. This work may help to understand the relationship between the structures of MOFs and gas sorption/separation.

High-Symmetry Co/Ni Triazine Polycarboxylate Diverse Frameworks Constructed by Mx(COO)y Building Blocks: Characterization and Catalytic Performance Evaluation of p-Nitrophenol

Three new triazine compounds [Co_1.5(H₃TDPAT)(H₂O)₃]·6H₂O (1), [Co₂(TCPT)(μ₂-H₂O)₂]·OH (2), and [Ni₃(TCPT)]·3OH (3) were designed and synthesized via the reaction of the symmetrical triazine ligand connected by C-N-C and C-O-C bonds with triazine poly(carboxylic acid)s ligands as the side arms: H₆TDPAT (H₆TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) and H₃TCPT (H₃TCPT = 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine) as well as the corresponding metal salts under the solvothermal condition. Three triazine polycarboxylate frameworks were characterized by elemental analysis, infrared spectroscopy, ultraviolet spectroscopy, thermogravimetric analysis, X-ray powder diffraction, and solid fluorescent spectra in detail. The structural analysis results showed that the three-dimensional porous cage framework of compound 1 was constructed by three different polyhedral cages connected with [Co(COO)₄(H₂O)₂] building blocks. One of the compounds, 2, is formed by twin propeller Co₂(μ₂-H₂O)(COO)₃ building blocks connecting two-dimensional layers and the intermolecular π-π interactions involved the triazine rings between the layers. While the structure of compound 3 is similar to that of 2, assembly is by Ni(COO)₃ building blocks and adjacent layers of the face-to-face π-π interaction between the triazine rings. In order to explore functional properties, the catalytic reduction of p-nitrophenol (PNP) of compounds 1-3 was investigated. They exhibit excellent catalytic activity of more than 95% for reduction of PNP with a dose of 2.5 mg of the compounds.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Creating High-Number Defect Sites through a Bimetal Approach in Metal-Organic Frameworks for Boosting Trace SO2 Removal

Herein, we represent a bimetallic approach to enhance the defect number, leading to eight defect sites per node in a metal-organic framework, showing both a higher SO₂ adsorption capacity and higher SO₂/CO₂ selectivity. The results can be further strongly supported by density functional theory calculations.

Surface, Interface and Structure Optimization of Metal-Organic Frameworks: Towards Efficient Resourceful Conversion of Industrial Waste Gases

Industrial waste gas emissions from fossil fuel over-exploitation have aroused great attention in modern society. Recently, metal-organic frameworks (MOFs) have been developed in the capture and catalytic conversion of industrial exhaust gases such as SO₂ , H₂ S, NO_x , CO₂ , CO, etc. Based on these resourceful conversion applications, in this review, we summarize the crucial role of the surface, interface, and structure optimization of MOFs for performance enhancement. The main points include (1) adsorption enhancement of target molecules by surface functional modification, (2) promotion of catalytic reaction kinetics through enhanced coupling in interfaces, and (3) adaptive matching of guest molecules by structural and pore size modulation. We expect that this review will provide valuable references and illumination for the design and development of MOF and related materials with excellent exhaust gas treatment performance.