Present and future of MOF research in the field of adsorption and molecular separation

Improving gas adsorption modeling for MOFs by local calibration of Hubbard U parameters

While computational screening with density functional theory (DFT) is frequently employed for the screening of metal-organic frameworks (MOFs) for gas separation and storage, commonly applied generalized gradient approximations (GGAs) exhibit self-interaction errors, which hinder the predictions of adsorption energies. We investigate the Hubbard U parameter to augment DFT calculations for full periodic MOFs, targeting a more precise modeling of gas molecule-MOF interactions, specifically for N2, CO2, and O2. We introduce a calibration scheme for the U parameter, which is tailored for each MOF, by leveraging higher-level calculations on the secondary building unit (SBU) of the MOF. When applied to the full periodic MOF, the U parameter calibrated against hybrid HSE06 calculations of SBUs successfully reproduces hybrid-quality calculations of the adsorption energy of the periodic MOF. The mean absolute deviation of adsorption energies reduces from 0.13 eV for a standard GGA treatment to 0.06 eV with the calibrated U, demonstrating the utility of the calibration procedure when applied to the full MOF structure. Furthermore, attempting to use coupled cluster singles and doubles with perturbative triples calculations of isolated SBUs for this calibration procedure shows varying degrees of success in predicting the experimental heat of adsorption. It improves accuracy for N2 adsorption for cases of overbinding, whereas its impact on CO2 is minimal, and ambiguities in spin state assignment hinder consistent improvements of O2 adsorption. Our findings emphasize the limitations of cluster models and advocate the use of full periodic MOF systems with a calibrated U parameter, providing a more comprehensive understanding of gas adsorption in MOFs.

Exclusive Coordination between Melem and Silver(I) Ions: From Irregular Aggregates to Nanofibers to Crystal Cubes

There is growing focus on metal-free molecules and polymers owing to their potential applications in various energy and catalysis-related applications. Melem (2,5,8-triamino-s-heptazine, C6H6N10) has emerged as a metal-free material for solar-to-fuel conversion. However, its reactivity with metal ions or organic molecules has never been reported although it possesses multiple supramolecular interaction sites. In this work, we report on the synthesis of a novel metal-organic coordination framework (melem-Ag) by simply introducing Ag+ into the aqueous suspension of aggregated melem particles. Notably, as the reaction progresses, the melem disappears, and the morphology of the newly formed complex spontaneously evolves from nanofibers to single-crystalline blocks, which possess the same chemical structure, indicating that the morphology evolution is driven by Ostwald ripening. The structure of melem-Ag displays infinite nanocages of triangular pyramids consisting of melem molecules and Ag+, linked via Ag-N coordinate bonding and Ag-Ag argentophilic interactions. It is noteworthy that Ag+ is the only transition-metal cation that reacts with melem suspensions, even in the presence of other transition-metal cations (Co2+, Ni2+, Cu2+, and Zn2+). The coordination of Ag+ to melem results in metal-to-ligand charge transfer (MLCT), resulting in a quenched photoluminescence and enhanced light absorption. Exposing the melem-Ag crystals to UV light for varying time intervals results in the formation of colorful powders, which may be used for Ag-decorated photocatalysts.

Continuous-Flow Catalysis Using Phosphine-Metal Complexes on Porous Polymers: Designing Ligands, Pores, and Reactors

Continuous-flow syntheses using immobilized catalysts can offer efficient chemical processes with easy separation and purification. Porous polymers have gained significant interests for their applications to catalytic systems in the field of organic chemistry. The porous polymers are recognized for their large surface area, high chemical stability, facile modulation of surface chemistry, and cost-effectiveness. It is crucial to immobilize transition-metal catalysts due to their difficult separation and high toxicity. Supported phosphine ligands represent a noteworthy system for the effective immobilization of metal catalysts and modulation of catalytic properties. Researchers have been actively pursuing strategies involving phosphine-metal complexes supported on porous polymers, aiming for high activities, durabilities, selectivities, and applicability to continuous-flow systems. This review provides a concise overview of phosphine-metal complexes supported on porous polymers for continuous-flow catalytic reactions. Polymer catalysts are categorized based on pore sizes, including micro-, meso-, and macroporous polymers. The characteristics of these porous polymers are explored concerning their efficiency in immobilized catalysis and continuous-flow systems.

Exploring microgel adsorption: synthesis, classification, and pollutant removal dynamics

Microgels have gained significant importance for the removal of pollutants owing to their stimulus-responsive behavior, high stability, and reusable capacity. However, despite these advantages, several hurdles need to be overcome to fully maximize their potential as effective adsorbents for eradicating various contaminants from the environment, such as metallic cations, organic compounds, anions, harmful gases, and dyes. Therefore, a critical review on the adsorption of pollutants by microgels is needed. In this regard, this review presents the latest developments in the adsorptive properties of microgels. The synthetic methods, architectural structures, and stimulus-responsive behavior of microgels are explained in detail. In addition, this review explores various factors that directly influence the adsorption of pollutants by microgels, such as pH, feed composition, content of pollutants, content of comonomers, agitation time, temperature, microgel dose, nature of both adsorbates (pollutants) and adsorbents (microgels), nature of the medium, and ionic strength. Various adsorption isotherms are also explored together with the kinetic aspects of the adsorption process to provide a comprehensive understanding.

A porous and photoactive Ti-MOF based on a novel tetranuclear [Ti2Tb2] cluster

A robust and porous titanium metal-organic framework (Ti-MOF; LCU-505) has been solvothermally synthesized based on an unprecedented tetranuclear Ti2(μ3-O)2Tb2(μ2-CH3COO)2(H2O)4(OOC-)8 cluster (abbreviated as [Ti2Tb2]) and tritopic 4,4',4''-s-triazine-2,4,6-triyl-tribenzoic acid ligand (H3TATB). LCU-505 shows remarkable water stability and permanent porosity for N2 and CO2 gas adsorption. Moreover, LCU-505 demonstrates n-type semiconductor behavior and good photocatalytic activity in the degradation of organic dyes.

Recent trends in wastewater treatment by using metal-organic frameworks (MOFs) and their composites: A critical view-point

Respecting the basic need of clean and safe water on earth for every individual, it is necessary to take auspicious steps for waste-water treatment. Recently, metal-organic frameworks (MOFs) are considered as promising material because of their intrinsic features including the porosity and high surface area. Further, structural tunability of MOFs by following the principles of reticular chemistry, the MOFs can be functionalized for the high adsorption performance as well as adsorptive removal of target materials. However, there are still some major concerns associated with MOFs limiting their commercialization as promising adsorbents for waste-water treatment. The cost, toxicity and regenerability are the major issues to be addressed for MOFs to get insightful results. In this article, we have concise the current strategies to enhance the adsorption capacity of MOFs during the water-treatment for the removal of toxic dyes, pharmaceuticals, and heavy metals. Further, we have also discussed the role of metallic nodes, linkers and associated functional groups for effective removal of toxic water pollutants. In addition to conformist overview, we have critically analyzed the MOFs as adsorbents in terms of toxicity, cost and regenerability. These factors are utmost important to address before commercialization of MOFs as adsorbents for water-treatment. Finally, some future perspectives are discussed to give directions for potential research.

Decontaminating liquid-containing Cs-137 by natural Pumice stone

Radionuclides, emanating as consequential by-products of nuclear operations, are recognized as a potent source of environmentally deleterious contamination. In light of these concerns, the present investigation has employed unmodified natural pumice within a batch process to effectuate the removal of Cs-137 radionuclides from real liquid radioactive wastes (RLRWs). The discernment of optimal adsorption parameters encompassed a pH level of 5, a pumice dosage of 3.33 g/L, a mixing duration of 5 min, a mixing speed of 100 revolutions per minute, all maintained at room temperature. The attainment of a peak removal efficiency of 91.75% for Cs-137 substantiates the efficacy of the chosen conditions. Moreover, the determination of regression coefficients (R2) arising from the application of Freundlich and Langmuir isotherm analyses yielded values of 0.91 and 0.96, respectively, thus validating the appropriateness of both models in depicting the adsorption mechanism. Evidently, the pseudo-second-order kinetic model exhibited a high correlation coefficient of 0.99, attesting to its aptitude in characterizing the adsorption dynamics. A thermodynamic appraisal of the process indicated an endothermic nature, offering insights into the fundamental energetics governing the interaction. Consequently, the adsorption phenomenon unfolded predominantly on monolayer, heterogeneous surfaces, with chemical interactions taking precedence on the active pumice sites.

Metal-organic framework-based high-performance column chip for micro gas chromatography: hybrid function for simultaneous preconcentration and separation of volatile organic compounds

Numerous attempts have been made to replace commercial bulky gas chromatography (GC) systems with compact GC systems for monitoring volatile organic compounds in indoor air. However, recently developed compact GC systems are still too bulky in terms of user convenience, portability, and on-site analysis. Hence, an advanced miniaturization of compact GC systems is needed. Importantly, the small and high-performance gas pretreatment chip devices should be developed for compact GC systems. This paper reports the development of a metal-organic framework (MOF)-coated hybrid micro gas chromatography column chip (hybrid GC chip) capable of preconcentration and separation on harmful volatile organic compounds at low-concentration in one single chip device. The hybrid GC chip, 2 cm × 2 cm in size, was fabricated using a microelectromechanical systems process. The synthesized MOF-5 particles were coated on the inner wall of the fabricated hybrid GC chip and acted as an adsorbent and a stationary phase. The developed hybrid GC chip afforded high preconcentration factors with 1033-1237 and high separation resolutions with 3.8-13.3. The developed column showed good performance as a gas preconcentrator and separation column, and is the first device to perform both roles in one single chip device.

Efficient C2H6/C2H4 adsorption separation by a microporous heterometal-organic framework

Purification of ethylene (C2H4) is an essential and energy-intensive process in the petrochemical industry. Adsorption separation using ethane (C2H6)-selective porous adsorbents is a highly efficient and straightforward method for obtaining polymer-grade C2H4 from a binary C2H6/C2H4 mixture. However, the design and construction of C2H6-selective adsorbents are very challenging tasks. Herein, we demonstrate a microporous heterometal-organic framework, CuIn(ina)4, can preferentially enrich C2H6 than C2H4. Experimental results revealed that CuIn(ina)4 exhibited remarkable separation performance for the C2H6/C2H4 mixture with a high C2H6 loading capacity (3.3 mmol/g), high IAST selectivity (2.3) and separation potential (1578 mmol/L for equimolar C2H6/C2H4 mixture) under ambient conditions. The effectiveness of CuIn(ina)4 for C2H6/C2H4 adsorption separation was confirmed by theoretical calculations and breakthrough experiments.

Identifying pathways to metal-organic framework collapse during solvent activation with molecular simulations

Metal-organic framework (MOF) materials are a vast family of nanoporous solids with potential applications ranging from drug delivery to environmental remediation. Application of MOFs in these scenarios is hindered, however, by difficulties in MOF 'activation' after initial synthesis - removal of the synthesis solvent from the pores to make the pore space accessible - often leading to framework collapse if improperly performed. While experimental studies have correlated collapse to specific solvent properties and conditions, the mechanism of activation-collapse is currently unknown. Developing this understanding would enable researchers to create better activation protocols for MOFs, accelerating discovery and process intensification. To achieve this goal, we simulated solvent removal using grand-canonical Monte Carlo and free energy perturbation methods. By framing activation as a fluid desorption problem, we investigated activation processes in the isoreticular metal organic framework (IRMOF) family of MOFs for different solvents. We identified two pathways for solvent activation - the solvent either desorbs uniformly from each individual pore or forms coexisting phases during desorption. These mesophases in turn lead to large capillary stresses within the framework, corroborating experimental hypotheses for the cause of activation-collapse. Finally, we found that the activation energy of solvent removal increased with pore size and connectivity due to the increased stability of solvent mesophases, matching experimental findings. Using these simulations, it is possible to screen MOF activation procedures, enabling rapid identification of ideal solvents and conditions and thus enabling faster development of MOFs for practical applications.

One-pot synthesis of bimetallic Fe-Cu metal-organic frameworks composite for the elimination of organic pollutants via peroxymonosulphate activation

A series of bimetallic of FeCu metal-organic frameworks (MOFs) have been synthesised using a solvothermal process by varying the ratio between the two metals. Further, the bimetallic MOF catalysts were characterised by X-ray powder diffraction, scanning electron microscopy, and infrared spectroscopy techniques. Their catalytic properties for activation of peroxymonosulphate (PMS) have been tested by the removal of a model dye, rhodamine B. As a result, NH2-Fe2.4Cu1-MOF demonstrated the highest degradation, the effect of the ratio NH2-Fe2.4Cu1-MOF/PMS has been studied, and the main reactive species have been assessed. The application of these MOFs in powder form is difficult to handle in successive batch or flow systems. Thus, this study assessed the feasibility of growing NH2-Fe2,4Cu1-MOF on polyacrylonitrile (PAN) spheres using the one-pot solvothermal synthesis method. The optimisation of the catalytic activity of the synthesised composite (NH2-Fe2.4Cu1-MOF@PAN) has been evaluated by response surface methodology using a central composite face-centred experimental design matrix and selecting as independent variables: time, PMS concentration, and catalyst dosage. Based on the results, the optimisation of the operational conditions has been validated. At 2.5 mM PMS, 90 min, and 1.19 g·L-1 of catalyst dosage, maximum degradation (80.92%) has been achieved, which doubles the removal values obtained in previous studies with other MOFs. In addition, under these conditions, the catalyst has been proven to maintain its activity and stability for several cycles without activity loss.

Dual-mode transfer response based on electrochemical and fluorescence signals for the detection of amyloid-beta oligomers (AβO)

An aptamer sensor has been developed utilizing a dual-mode and stimuli-responsive strategy for quantitative detection of AβO (amyloid-beta oligomers) through simultaneous electrochemical and fluorescence detection. To achieve this, we employed UIO-66-NH2 as a carrier container to load MB (Methylene Blue), and Fe3O4 MNPs (iron oxide magnetic nanoparticles) with aptamer (ssDNA-Fe3O4 MNPs) fixed on their surface for biological gating. The ssDNA-Fe3O4 MNPs were immobilized onto the surface of UIO-66-NH2 through hydrogen bonding between the aptamer and the -NH2 group on the surface of UIO-66-NH2, thereby encapsulating MB and forming ssDNA-Fe3O4@MB@UIO-66-NH2. During the detection of AβO, the aptamer selectively reacted with AβO to form the AβO-ssDNA-Fe3O4 complex, leading to its detachment from the surface of UIO-66-NH2. This detachment facilitated the release of MB, enabling its electrochemical detection. Simultaneously, the AβO-ssDNA-Fe3O4 complex was efficiently collected and separated using a magnet after leaving the container's surface. Furthermore, the addition of NaOH facilitated the disconnection of biotin modifications at the 3' end of the aptamer from the avidin modifications on the Fe3O4 MNPs. Consequently, the aptamer detached from the surface of Fe3O4 MNPs, resulting in the restoration of fluorescence intensity of FAM (fluorescein-5'-carboxamidite) modified at its 5' end for fluorescence detection. The dual-mode sensor exhibited significantly enhanced differential pulse voltammetry signals and fluorescence intensity compared to those in the absence of AβO. The sensor demonstrated a wide detection range of 10 fM to 10 μM, with a detection limit of 3.4 fM. It displayed excellent performance in detecting actual samples and holds promising prospects for early diagnosis of Alzheimer's disease.

Recent advances in the chemistry and applications of fluorinated metal-organic frameworks (F-MOFs)

Metal-organic frameworks are a class of porous crystalline materials based on the ordered connection of metal centers or metal clusters by organic linkers with comprehensive functionalities. The interest in these materials is rapidly moving towards their application in industry and real life. In this context, cheap and sustainable synthetic strategies of MOFs with tailored structures and functions are nowadays a topic widely studied from different points of view. In this review, fluorinated MOFs (F-MOFs) and their applications are investigated. The principal aim is to provide an overview of the structural features and the main application of MOFs containing fluorine atoms both as anionic units or as coordinating elements of more complex inorganic units and, therefore, directly linked to the structural metals or as part of fluorinated linkers used in the synthesis of MOFs. Herein we present a review of F-MOFs reported in the recent literature compared to benchmark compounds published over the last 10 years. The compounds are discussed in terms of their structure and properties according to the aforementioned classification, with an insight into the different chemical nature of the bonds. The application fields of F-MOFs, especially in sustainability related issues, such as harmful gas sorption and separation, will also be discussed. F-MOFs are compounds containing fluorine atoms in their framework and they can be based on: (a) fluorinated metallic or semi-metallic anionic clusters or: (b) fluorinated organic linkers or (c) eventually containing both the building blocks. The nature of a covalent C-F bond in terms of length, charge separation and dipole moment sensibly differs from that of a partly ionic M-F (M = metal) one so that the two classes of materials (points a and b) have different properties and they find various application fields. The study shows how the insertion of polar M-F and C-F bonds in the MOF structure may confer several advantages in terms of interaction with gaseous molecules and the compounds can find application in gas sorption and separation. In addition, hydrophobicity tends to increase compared to non-fluorinated analogues, resulting in an overall improvement in moisture stability.

Advanced BIFs with Co, B, N, and S for Electrocatalytic Oxygen Reduction and Oxygen Evolution Reactions

In this work, a new alkaline-stable boron imidazolate framework (BIF-90) was rationally designed and successfully synthesized by solvothermal reaction. Due to its potential electrocatalytic active sites (Co, B, N, and S) and chemical stabilities, BIF-90 was explored as a bifunctional electrocatalyst toward electrochemical oxygen reactions, namely, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). This work will open new avenues toward the design of stable, cheap, and more active BIFs as bifunctional catalysts.

Effective adsorptive removal of sulfamethoxazole (SMX) from aqueous solution by ZIF-8 derived adsorbent ZC-0.5

Efficient removal of antibiotics from the aquatic environment is urgently needed due to their obstinate accumulation and non-biodegradability. In this study, a mesoporous carbon material (ZC-0.5) was successfully synthesized for the adsorption of sulfamethoxazole (SMX), one of the major antibiotics for the treatment of human and animal infections. ZIF-8 as the precursor of ZC-0.5, specifically, using cetyl trimethyl ammonium bromide (CTAB) and sodium laurate (SL) as dual templates and carbonizing at 800 ℃. This novel adsorbent exhibited a high proportion of mesopore (75.64%) and a large specific surface area (1459.73 m²·g^-1). The adsorption experiment examined the reusability of ZC-0.5 and that it could retain superior maximum adsorption capacities (167.45 mg∙L^-1) after five cycles of adsorption and desorption. The adsorption process satisfied the pseudo-second-order kinetic (PSO) and mixed first- and second-order kinetic (MOE). It also satisfied the Freundlich and Sips isotherm models. Moreover, thermodynamic calculation indicated the adsorption process was spontaneous, endothermal, and entropy-increasing. Furthermore, plausible adsorption mechanisms were explained through van der Waals force, electrostatic interaction, hydrophobic force, π-π interaction, and hydrogen bond. This work offers a new efficient adsorbent for antibiotic elimination.

Synthesis of an IRMOF-1@SiO2 Core-Shell and Amino-Functionalization with APTES for the Adsorption of Urea and Creatinine Using a Fixed-Bed Column Study

Kidney dysfunction is a clinical disease that disables the kidneys to remove the waste products and uremic toxins from the circulation and may lead to fatal kidney failure. Hemodialysis is advantageous in this circumstance since it prevents the accumulation of waste products in the body and facilitates the removal of uremic toxins. However, hemodialysis cannot entirely remove some uremic toxins, such as urea and creatinine. In this paper, a high-performance fixed-bed column for urea and creatinine removal was offered. As a result, a MOF layer was built on SiO₂, which was then amino-functionalized using APTES. Numerous assays were used to characterize the final adsorbent. The adsorption of urea and creatinine was evaluated in batch and continuous conditions. Thus, it was demonstrated that the adsorption behavior of A(0.2)-IRMOF-1@SiO₂ followed the Langmuir isotherm, and it exhibited the maximum adsorption capacity. The batch experiment determined that urea and creatinine had an adsorption capacity of 1325.73 and 625.00 mg·g^-1, respectively. The adsorption capacity was increased, which was due to the presence of amino groups (APTES) on the MOF surface. The continuous operation was evaluated using the A(0.2)-IRMOF-1@SiO₂ fixed-bed column. Thomas and Nelson's models were examined to achieve a better understanding of the adsorption behaviors. The A(0.2)-IRMOF-1@SiO₂ fixed-bed column successfully removed 92.57% of urea and 80.47% of creatinine. The separation factor for urea in comparison to creatinine was 2.40 in the A(0.2)-IRMOF-1@SiO₂ fixed-bed column.

Recent advances in Metal Organic Framework (MOF)-based hierarchical composites for water treatment by adsorptional photocatalysis: A review

Architecting a desirable and highly efficient nanocomposite for applications like adsorption, catalysis, etc. has always been a challenge. Metal Organic Framework (MOF)-based hierarchical composite has perceived popularity as an advanced adsorbent and catalyst. Hierarchically structured MOF material can be modulated to allow the surface interaction (external or internal) of MOF with the molecules of interest. They are well endowed with tunable functionality, high porosity, and increased surface area epitomizing mass transfer and mechanical stability of the fabricated nanostructure. Additionally, the anticipated optimization of nanocomposite can only be acquired by a thorough understanding of the synthesis techniques. This review starts with a brief introduction to MOF and the requirement for advanced nanocomposites after the setback faced by conventional MOF structures. Further, we discussed the background of MOF-based hierarchical composites followed by synthetic techniques including chemical and thermal treatment. It is important to rationally validate the successful nanocomposite fabrication by characterization techniques, an overview of challenges, and future perspectives associated with MOF-based hierarchically structured nanocomposite.

Post-Synthetic Surface Modification of Metal-Organic Frameworks and Their Potential Applications

Metal-organic frameworks (MOFs) are porous hybrid materials with countless potential applications. Most of these rely on their porous structure, tunable composition, and the possibility of incorporating and expanding their functions. Although functionalization of the inner surface of MOF crystals has received considerable attention in recent years, methods to functionalize selectively the outer crystal surface of MOFs are developed to a lesser extent, despite their importance. This article summarizes different types of post-synthetic modifications and possible applications of modified materials such as: catalysis, adsorption, drug delivery, mixed matrix membranes, and stabilization of porous liquids.

A robust and porous titanium metal-organic framework for gas adsorption, CO2 capture and conversion

A robust and porous titanium metal-organic framework (Ti-MOF; LCU-402) has been hydrothermally synthesized through combining a tetranuclear Ti2Ca2(μ3-O)2(μ2-H2O)1.3(H2O)4(O2C-)8 cluster and a tritopic 1,3,5-benzene(tris)benzoic (BTB) ligand. LCU-402 shows remarkable stability and permanent porosity for CO2, CH4, C2H2, C2H4, and C2H6 gas adsorption. Moreover, LCU-402 as a heterogeneous catalyst can smoothly convert CO2 under a simulated flue atmosphere into organic carbonate molecules by cycloaddition reactions of CO2 and epoxides, indicating that LCU-402 might be a promising catalyst candidate in practical applications. We are confident that the identification of a persistent titanium-oxo building unit would accelerate the development of new porous Ti-MOF materials.

Porous Materials for Water Purification

Water pollution is a growing threat to humanity due to the pervasiveness of contaminants in water bodies. Significant efforts have been made to separate these hazardous components to purify polluted water through various methods. However, conventional remediation methods suffer from limitations such as low uptake capacity or selectivity, and current water quality standards cannot be met. Recently, advanced porous materials (APMs) have shown promise in improved segregation of contaminants compared to traditional porous materials in uptake capacity and selectivity. These materials feature merits of high surface area and versatile functionality, rendering them ideal platforms for the design of novel adsorbents. This Review summarizes the development and employment of APMs in a variety of water treatments accompanied by assessments of task-specific adsorption performance. Finally, we discuss our perspectives on future opportunities for APMs in water purification.

Amide Functionalized Mesoporous MOF LOCOM-1 as a Stable Highly Active Basic Catalyst for Knoevenagel Condensation Reaction

Acyl-amide is extensively used as functional group and is a superior contender for the design of MOFs with the guest accessible functional organic sites. A novel acyl-amide-containing tetracarboxylate ligand, bis(3,5-dicarboxy-pheny1)terephthalamide, has been successfully synthesized. The H₄L linker has some fascinating attributes as follows: (i) four carboxylate moieties as the coordination sites confirm affluent coordination approaches to figure a diversity of structure; (ii) two acyl-amide groups as the guest interaction sites can engender guest molecules integrated into the MOF networks through H-bonding interfaces and have a possibility to act as functional organic sites for the condensation reaction. A mesoporous MOF ([Cu₂(L)(H₂O)₃]·4DMF·6H₂O) has been prepared in order to produce the amide FOS within the MOF, which will work as guest accessible sites. The prepared MOF was characterized by CHN analysis, PXRD, FTIR spectroscopy, and SEM analysis. The MOF showed superior catalytic activity for Knoevenagel condensation. The catalytic system endures a broad variety of the functional groups and presents high to modest yields of aldehydes containing electron withdrawing groups (4-chloro, 4-fluoro, 4-nitro), offering a yield > 98 in less reaction time as compared to aldehydes with electron donationg groups (4-methyl). The amide decorated MOF (LOCOM-1-) as a heterogeneous catalyst can be simply recovered by centrifugation and recycled again without a flagrant loss of its catalytic efficiency.

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.

Size-dependent acute toxicity and oxidative damage caused by cobalt-based framework (ZIF-67) to Photobacterium phosphoreum

Metal-organic frameworks (MOFs) are emerging nanomaterials with widespread applications for their superior properties. However, the potential health and environmental risks of MOFs still need further understanding. In this work, we investigated the toxicity of a typical cobalt-based MOF (ZIF-67) with varied primary particle sizes (100, 200, 400, 700 and 1200 nm) to Photobacterium Phosphoreum T3 strain, a kind of luminescent bacteria. The luminescence inhibition rate of all ZIF-67 nanoparticles (NPs) reached 40 % and higher at the concentration of 5 mg/L, exhibiting strong toxicity. Combined cellular assays and gene expression analysis confirmed that the general bioactivity inhibition and oxidative damage were induced mainly by ZIF-67 NPs, rather than Co²⁺ released from the ZIF-67 NPs. Additionally, the toxicity of ZIF-67 NPs demonstrated an evident size-dependent effect. For ZIF-67 smaller than 400 nm, the toxicity increased with the particle size decreased, while the trend was not significant when the particle size was larger than 400 nm. A potential explanation for this phenomenon is the smaller NPs (100 and 200 nm) may enter the cytoplasm, accumulating in the cytoplasm and causing more severe toxicity. Furthermore, Co²⁺ released from the ZIF-67 NPs was not the primary contributor to the toxic effect of ZIF-67 NPs which was verified by the toxicity results and the variation of toxicity-related indicators. These findings provided insight into the better design and safer use of MOFs, and it also implied the potential environmental risk of the MOF's cannot be ignored, especially for the bioapplication.

A Critical Review of the Removal of Radionuclides from Wastewater Employing Activated Carbon as an Adsorbent

Radionuclide-contaminated water is carcinogenic and poses numerous severe health risks and environmental dangers. The activated carbon (AC)-based adsorption technique has great potential for treating radionuclide-contaminated water due to its simple design, high efficiency, wide pH range, quickness, low cost and environmental friendliness. This critical review first provides a brief overview of the concerned radionuclides with their associated health hazards as well as different removal techniques and their efficacy of removing them. Following this overview, this study summarizes the surface characteristics and adsorption capabilities of AC derived from different biomass precursors. It compares the adsorption performance of AC to other adsorbents, such as zeolite, graphene, carbon nano-tubes and metal-organic frameworks. Furthermore, this study highlights the different factors that influence the physical characteristics of AC and adsorption capacity, including contact time, solution pH, initial concentration of radionuclides, the initial dosage of the adsorbent, and adsorption temperature. The theoretical models of adsorption isotherm and kinetics, along with their fitting parameter values for AC/radionuclide pairs, are also reviewed. Finally, the modification procedures of pristine AC, factors determining AC characteristics and the impact of modifying agents on the adsorption ability of AC are elucidated in this study; therefore, further research and development can be promoted for designing a highly efficient and practical adsorption-based radionuclide removal system.

N-Heterocyclic Carbene Silver Complex Modified Polyacrylonitrile Fiber/MIL-101(Cr) Composite as Efficient Chiral Catalyst for Three-Component Coupling Reaction

Complex asymmetric synthesis can be realized by the chiral induction of amino acids in nature. It is of great significance to design a new biomimetic catalytic system for asymmetric synthesis. In this context, we report the preparation and characterization of the composite of polyacrylonitrile fiber (PANF) and metal-organic framework to catalyze the chiral synthesis of propargylamines. A confined microenvironment is established with N-heterocyclic carbene (NHC) silver complex-supported PANF and D-proline-encapsulated MIL-101(Cr). This novel supported catalyst demonstrated high activity in addition to excellent stereoselectivity in the three-component reaction between alkynes, aldehydes, and amines (A3). The regeneration can be realized by adsorption of D-proline again when the stereoselectivity decreases after recycle uses. By regulating the confined microenvironment on the composite, the activity and selectivity of the catalytic system are improved with turnover numbers of up to 2800 and 98% ee. The biomimetic catalytic system to A3 coupling reaction is systematically studied, and the synergistic catalytic mechanism between NHC-Ag and D-proline in the confined microenvironment is revealed.

Facile Fabrication of α-Alumina Hollow Fiber-Supported ZIF-8 Membrane Module and Impurity Effects on Propylene Separation Performance

The separation of C₃ olefin and paraffin, which is essential for the production of propylene, can be facilitated by the ZIF-8 membrane. However, the commercial application of the membrane has not yet been achieved because the fabrication process does not meet industrial regulatory criteria. In this work, we provide a straightforward and cost-effective membrane fabrication technique that permits the rapid synthesis of ZIF-8 hollow fiber membranes. The scalability of the technology was confirmed by the incorporation of three ZIF-8 hollow fiber membranes into a single module using an introduced fiber mounting methodology. The molecular sieving characteristics of the ZIF-8 membrane module on a binary combination of C3 olefin and paraffin (C₃H₆/C₃H₈ selectivity of 110 and a C₃H₆ permeance of 13 GPU) were examined at atmospheric conditions. In addition, the high-pressure performance of these membranes was demonstrated at a 5 bar of equimolar binary feed pressure with a C₃H₆/C₃H₈ selectivity of 55 and a C₃H₆ permeance of 9 GPU due to propylene adsorption site saturation. To further accurately portray the separation performance of the membrane on an actual industrial feed, the effect of impurities (ethylene, ethane, butylene, i-butane, and n-butane), which can be found in C3 splitters, was investigated and a considerable decrement (~15%) in the propylene permeance upon an interaction with C4 hydrocarbons was confirmed. Finally, the long-term stability of the ZIF-8 membrane was confirmed by continuous operation for almost a month without any loss of its initial performance (C₃H₆/C₃H₈ separation factor of 110 and a C₃H₆ permeance of 13 GPU). From an industrial point of view, this straightforward technique could offer a number of merits such as a short synthesis time, minimal chemical requirements, and excellent reproductivity.

A facile synthesis of CeO2 from the GO@Ce-MOF precursor and its efficient performance in the oxygen evolution reaction

Electrochemical water splitting has enticed fascinating consideration as a key conduit for the advancement of renewable energy systems. Fabricating adequate electrocatalysts for water splitting is fervently preferred to curtail their overpotentials and hasten practical utilizations. In this work, a series of Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF were synthesized and used as high-proficient electrocatalysts for the oxygen evolution reaction. The physicochemical characteristics of the prepared samples were measured by diverse analytical techniques including SEM, HRTEM, FTIR, BET, XPS, XRD, and EDX. All materials underwent cyclic voltammetry tests and were evaluated by electrochemical impedance spectroscopy and oxygen evolution reaction. Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF have remarkable properties such as enhanced specific surface area, improved catalytic performance, and outstanding permanency in the alkaline solution (KOH). These factors upsurge ECSA and intensify the OER performance of the prepared materials. More exposed surface active-sites present in calcinated GO@Ce-MOF could be the logic for superior electrocatalytic activity. Chronoamperometry of the catalyst for 15°h divulges long-term stability of Ce-MOF during OER. Impedance measurements indicate higher conductivity of synthesized catalysts, facilitating the charge transfer reaction during electrochemical water splitting. This study will open up a new itinerary for conspiring highly ordered MOF-based surface active resources for distinct electrochemical energy applications.

Enzyme-immobilized metal-organic frameworks: From preparation to application

As a class of widely used biocatalysts, enzymes possess advantages including high catalytic efficiency, strong specificity and mild reaction condition. However, most free enzymes have high requirements on the reaction environment and are easy to deactivate. Immobilization of enzymes on nanomaterial-based substrates is a good way to solve this problem. Metal-organic framework (MOFs), with ultra-high specific surface area and adjustable porosity, can provide a large space to carry enzymes. And the tightly surrounded protective layer of MOFs can stabilize the enzyme structure to a great extent. In addition, the unique porous network structure enables selective mass transfer of substrates and facilitates catalytic processes. Therefore, these enzyme-immobilized MOFs have been widely used in various research fields, such as molecule/biomolecule sensing and imaging, disease treatment, energy and environment protection. In this review, the preparation strategies and applications of enzymes-immobilized MOFs are illustrated and the prospects and current challenges are discussed.

Simultaneous Estimation of Gas Adsorption Equilibria and Kinetics of Individual Shaped Adsorbents

Shaped adsorbents (e.g., pellets, extrudates) are typically employed in several gas separation and sensing applications. The performance of these adsorbents is dictated by two key factors, their adsorption equilibrium capacity and kinetics. Often, adsorption equilibrium and textural properties are reported for materials. Adsorption kinetics are seldom presented due to the challenges associated with measuring them. The overarching goal of this work is to develop an approach to characterize the adsorption properties of individual shaped adsorbents with less than 100 mg of material. To this aim, we have developed an experimental dynamic sorption setup and complemented it with mathematical models, to describe the mass transport in the system. We embed these models into a derivative-free optimizer to predict model parameters for adsorption equilibrium and kinetics. We evaluate and independently validate the performance of our approach on three adsorbents that exhibit differences in their chemistry, synthesis, formulation, and textural properties. Further, we test the robustness of our mathematical framework using a digital twin. We show that the framework can rapidly (i.e., in a few hours) and quantitatively characterize adsorption properties at a milligram scale, making it suitable for the screening of novel porous materials.

Carboxymethyl Cellulose/Zn-Organic Framework Down-Regulates Proliferation and Up-Regulates Apoptosis and DNA Damage in Colon and Lung Cancer Cell Lines

A solvothermal technique was used to prepare a Zn–benzenetricarboxylic acid (Zn@BTC) organic framework covered with a carboxymethyl cellulose (CMC/Zn@BTC). Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), and Brunauer, Emmett, and Teller (BET) surface area were applied to characterize CMC/Zn@BTC. Moreover, the anticancer, anti-migrative, anti-invasive, and anti-proliferative action of CMC/Zn@BTC nanoparticles were assessed on cancer cell lines. Apoptotic markers and DNA damage were assessed to explore the cellular and biological changes induced by CMC/Zn@BTC nanoparticles. The microscopic observation revealed that CMC controls the surface morphology and surface characteristics of the Zn@BTC. The obtained BET data revealed that the Zn@BTC nanocomposite surface area lowers from 1061 m²/g to 740 m²/g, and the pore volume decreases from 0.50 cm³/g to 0.37 cm³/g when CMC is applied to Zn@BTC nanocomposites. The cellular growth of DLD1 and A549 was suppressed by CMC/Zn@BTC, with IC50 values of 19.1 and 23.1 μg/mL, respectively. P53 expression was upregulated, and Bcl-2 expression was downregulated by CMC/Zn@BTC, which promoted the apoptotic process. Furthermore, CMC/Zn@BTC caused DNA damage in both cancer cell lines with diverse impact, 66 percent (A549) and 20 percent (DLD1) compared to cisplatin’s 52 percent reduction. CMC/Zn@BTC has anti-invasive properties and significantly reduced cellular migration. Moreover, CMC/Zn@BTC aims key proteins associated with metastasis, proliferation and programmed cellular death.

Facile solvothermal synthesis of a MIL-47(V) metal-organic framework for a high-performance Epoxy/MOF coating with improved anticorrosion properties

The vanadium-based metal–organic framework MIL-47 distinguishes itself among other MOFs for its distinctive structure and unique properties (e.g., flexible structure, high thermal stability, and high surface area). The synthesis of MIL-47 has been reported from various metal precursors, including vanadium(iii) chloride (VCl₃) as a rich source of metal ions. Attempts have been made to include other starting materials, a step forward towards large-scale production. Synthesis from various solid materials is encouraged, seeking an economic and greener approach. In this study, vanadium pentoxide (V₂O₅), a readily abundant low-cost and thermodynamically stable metal source, was used to synthesize the MIL-47(V) framework via a facile solvothermal route. This precursor provides a controllable rate of metal ion production depending on the applied reaction conditions. In our method, the synthesis took place at a low temperature and reaction time (180 °C for 20 h, instead of 220 °C for 72 h), yielding MIL-47 microrods. Moreover, among its unique properties, the metal centers of MIL-47 oxidize under the influence of thermal or chemical treatments, preserving the framework structure. This unusual character is not commonly witnessed in comparable MOF structures. This property can be leveraged in anti-corrosion applications, whereby a redox reaction would sacrifice the framework components, protecting the metal in contact. However, the chemical stability of MIL-47 is doubted against a corrosive medium. Thus, an epoxy coating with 10 wt% MOF loading was incorporated in our investigation to extend the aluminum alloy (AA2024) surface protection for prolonged exposure duration. The uniformity of distribution of the prepared MOF within the epoxy matrix was confirmed using SEM/EDX. Electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion performance of the coated samples. The results showed that the inclusion of V-MOF offers extended corrosion prevention, over 60 days, for the AA2024 alloy against artificial seawater. The neat epoxy coating could not prevent the corrosion of AA2024 over two weeks of immersion, whereby pitting corrosion was clearly observed. The V-MOF could induce a series of redox reactions leading to the precipitation of vanadium on the cathodic sites of metal surfaces.

The well-known MIL-47(V) metal–organic framework was synthesized solvothermally with high quality using V₂O₅ as a precursor. Applying the MOF particles in an epoxy coating resulted in an improved anticorrosion protective barrier for the AA2024 substrate against a chloride-rich environment.

Metal-hydrogen-pi-bonded organic frameworks

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.

Metal phosphonates as heterogeneous catalysts for highly efficient chemical fixation of CO2 under mild conditions

Two new compounds with novel structures were prepared, one of which displays excellent catalytic activity to transform CO2 gas to cyclic carbonates under mild conditions and free of solvent.

A multifunctional fluorescent Cd-MOF probe: its synthesis, structure, and sensing properties

A Cd-MOF with a one-dimensional cavity can be used as a multifunctional fluorescent probe to effectively recognize CrO42− and Cr2O72− ions, Fe3+ ions and TNP molecules.

Microfluidic synthesis of optically responsive materials for nano- and biophotonics

Recently, nanomaterials demonstrating optical response under illumination, the so-called optically responsive nanoparticles (NPs), have found their broad application as optical switchers, gas adsorbents, data storage devices, and optical and biological sensors. Unique optical properties of such nanomaterials are strongly related to their chemical composition, geometrical parameters and morphology. Microfluidic approaches for NPs' synthesis allow overcoming the known critical stages in conventional synthesis of NPs due to a high rate of heat/mass transfer and precise regulation of synthesis conditions, which results in reproducible synthesis outcomes with the desired physico-chemical properties. Here, we review the recent advances in microfluidic approach for synthesis of optically responsive nanomaterials (plasmonic, photoluminescent, shape-changeable NPs), highlighting the general background of microfluidics, common considerations in the design of microfluidic chips (MFCs), and theoretical models of the NPs' formation mechanisms. Comparative analysis of microfluidic synthesis with conventional synthesis methods is provided further, along with the recent applications of optically responsive NPs in nano- and biophotonics.

Smart chemistry of enzyme immobilization using various support matrices - A review

The surface chemistry, pendent functional entities, and ease in tunability of various materials play a central role in properly coordinating with enzymes for immobilization purposes. Due to the interplay between the new wave of support matrices and enzymes, the development of robust biocatalytic constructs via protein engineering expands the practical scope and tunable catalysis functions. The concept of stabilization via functional entities manipulation, the surface that comprises functional groups, such as thiol, aldehyde, carboxylic, amine, and epoxy have been the important driving force for immobilizing purposes. Enzyme immobilization using multi-functional supports has become a powerful norm and presents noteworthy characteristics, such as selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness. There is a plethora of literature on traditional immobilization approaches, e.g., intramolecular chemical (covalent) attachment, adsorption, encapsulation, entrapment, and cross-linking. However, the existing literature is lacking state-of-the-art smart chemistry of immobilization. This review is a focused attempt to cover the literature gap of surface functional entities that interplay between support materials at large and enzyme of interest, in particular, to tailor robust biocatalysts to fulfill the growing and contemporary needs of several industrial sectors.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Material Screening for Gas Sensing Using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations

To detect multiple gases in a mixture, one must employ an electronic nose or sensor array, composed of several materials, as a single material cannot resolve all the gases in a mixture accurately. Given the many candidate materials, choosing the right combination of materials to be used in an array is a challenging task. In a sensor whose sensing mechanism depends on a change in mass upon gas adsorption, both the equilibrium and kinetic characteristics of the gas-material system dictate the performance of the array. The overarching goal of this work is twofold. First, we aim to highlight the impact of thermodynamic characteristics of gas-material combination on array performance and to develop a graphical approach to rapidly screen materials. Second, we aim to highlight the need to incorporate the gas sorption kinetic characteristics to provide an accurate picture of the performance of a sensor array. To address these goals, we have developed a computational test bench that incorporates a sensor model and a gas composition estimator. To provide a generic study, we have chosen, as candidate materials, hypothetical materials that exhibit equilibrium characteristics similar to those of metal-organic frameworks. Our computational studies led to key learnings, namely, (1) exploit the shape of the sensor response as a function of gas composition for material screening purposes for gravimetric arrays; (2) incorporate both equilibrium and kinetics for gas composition estimation in a dynamic system; and (3) engineer the array by accounting for the kinetics of the materials, the feed gas flow rate, and the size of the device.

Gas adsorption and separation in metal-organic frameworks by PC-SAFT based density functional theory

In this work, we examine the theoretical performance of perturbed-chain statistical associating fluid theory based density functional theory (DFT) in predicting gas adsorption and separation in metal-organic frameworks by using simulation and experimental data as the benchmark. Adsorption isotherms of methane and ethane in pure gas and mixtures and selectivities for ethane/methane mixtures are calculated. The predicted isotherms by DFT are in excellent agreement with simulation and experimental data for pure methane and ethane, whereas for the mixture, DFT is in semi-quantitative accordance with simulation results. For fast and high-throughput screening of material purpose, three algorithms including Picard iteration with line search, Anderson mixing, and Picard-Anderson-hybrid algorithm are proposed to calculate the three dimensional density distribution of confined gases. The advantages and limitations of the three algorithms under various conditions are discussed.

Capture of Toxic Oxoanions from Water Using Metal-Organic Frameworks

The effective capture of common water contaminants using metal-organic frameworks (MOFs) presents a remedy for current environmental concerns arising from the pollution of water sources. The crystalline porous nature of MOFs, their high internal surface area, and exceptional tunability make them suitable candidates for sequestration and removal of pollutants. However, the efficiency of capture depends largely on the nature of the interactions between the anions and the MOF. In this work, to elucidate the host-guest interactions involved in the capture of such pollutants, we explore three characteristically different MOFs: ZIF-8, iMOF-2c, and MOF-74. We demonstrate by ab initio electronic structure calculations the importance of exploiting qualitatively different binding modes for strong host-guest interactions available in the selected MOFs. Our simulations reveal the relative performance of neutral and cationic adsorbents while underscoring the importance of employing MOFs containing open metal sites for the efficient uptake of anions.