Metal-Organic Frameworks for Water Harvesting and Concurrent Carbon Capture: A Review for Hygroscopic Materials

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure-performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal-organic frameworks (MOFs) for their excellent performance in water and CO2 adsorption, and representative role of micro- and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO2 adsorption are reviewed. This review summarizes recent advances in water-harvesting porous materials with special attention on MOFs and expects to direct researchers' attention into the topic of concurrent water harvesting and carbon capture as a future challenge.

Preparation of a Multifunctional and Multipurpose Chitosan/Cyclodextrin/MIL-68(Al) Foam Column and Examining Its Adsorption Properties for Anionic and Cationic Dyes and Sulfonamides

A multifunctional cylindrical hybrid foam column, referred to as the chitosan/cyclodextrin/MIL-68(Al) (CS/CD/MIL-68(Al)) foam column, was prepared for the first time. The prepared foam column could be used for the adsorption/removal of hydrophilic and hydrophobic contaminants by different forms. Here, it was placed in hydrophilic dye solutions to investigate the adsorption behavior of methylene blue and trypan blue. The adsorption process followed the pseudo-second-order kinetic model with R2 ranging from 0.9983 to 0.9998 for methylene blue and from 0.9993 to 1.0000 for trypan blue, and the adsorption process was consistent with the Langmuir isothermal model with R2 greater than 0.96. The RL values for methylene blue and trypan blue were 0.8871 and 0.5366, respectively, which were present between 0 and 1, indicating that the adsorption behaviors of the two dyes onto the CS/CD/MIL-68(Al) foam column were favorable. The maximum adsorption capacities (Qm) of methylene blue and trypan blue were 60.61 and 454.55 mg/g at 298 K, respectively. Also, the CS/CD/MIL-68(Al) foam column was spun into a syringe and used to adsorb trace hydrophobic sulfonamides from water in the form of filtration. The porous structure impeded the need for any external force and equipment, allowing the water sample to pass through the foam column smoothly. The conditions of the CS/CD/MIL-68(Al) foam column were optimized. The adsorption was carried out under the condition of pH = 4, the amount of the adsorbent was two foam columns, and no salt was added. It was found that the removal rate of the CS/CD/MIL-68(Al) foam column for six sulfonamides was 100%, and it could be reused at least five times. Therefore, this CS/CD/MIL-68(Al) foam column had a simple preparation method, offered a flexible and diverse form of use, was nonpolluting, biodegradable, and reusable, and could have a wider application in the field of environmental pollutant removal and adsorption.

Synergistic effect of bimetal in isoreticular Zn-Cu-1,3,5-benzenetricarboxylate on room temperature gaseous sulfides removal

Isoreticular bimetal M-Cu-BTC has considerable potential in improving the sulfides removal performance of Cu-BTC. Herein, three transition metals, namely, Zn²⁺, Ni²⁺ and Co²⁺, were assessed to fabricate M-Cu-BTC, a desirable isoreticular bimetal. Results demonstrated the feasibility of using Zn²⁺ to fabricate an isoreticular bimetallic Zn-Cu-BTC. The Zn²⁺ doping content of Zn-Cu-BTC was varied to investigate its influence on the hydrogen sulfide (H₂S) and methyl sulfide (CH₃SCH₃) removal performance of Cu-BTC. The experimental results indicated that the sulfides removal performance of Zn-Cu-BTC increased and then decreased with increasing Zn doping content. The highest H₂S and CH₃SCH₃ removal capacities of 84.3 and 93.9 mg S/g, respectively, were obtained when the Zn²⁺ doping content was 17%. The hybridisation of Zn and Cu in Zn-Cu-BTC induced a strong interaction between them. This interaction increased the binding energies of H₂S and CH₃SCH₃ towards the Cu and Zn adsorption sites while weakening the bond order between Zn and Cu. The weakened bond order made the Zn-Cu bonds easier to form metal sulfides during desulfurization process, thereby synergistically enhancing sulphide removal.

Novel strategies for the formulation and processing of aluminum metal-organic framework-based sensing systems toward environmental monitoring of metal ions

Aluminum is a relatively inexpensive and abundant metal for the mass production of metal-organic frameworks (MOFs). Aluminum-based MOFs (Al-MOFs) have drawn a good deal of research interest due to their unique properties for diverse applications (e.g., excellent chemical and structural stability). This review has been organized to highlight the current progress achieved in the synthesis/functionalization of Al-MOF materials with the special emphasis on their sensing application, especially toward metal ion pollutants in the liquid phase. To learn more about the utility of Al-MOF-based sensing systems, their performances have been evaluated for diverse metallic components in reference to many other types of sensing systems (in terms of the key quality assurance (QA) criteria such as limit of detection (LOD)). Finally, the challenges and outlook for Al-MOF-based sensing systems are discussed to help expand their real-world applications.

Structural Properties of Metal-Organic Frameworks at Elevated Thermal Conditions via a Combined Density Functional Tight Binding Molecular Dynamics (DFTB MD) Approach

The performance of different density functional tight binding (DFTB) methods for the description of six increasingly complex metal-organic framework (MOF) compounds have been assessed. In particular the self-consistent charge density functional tight binding (SCC DFTB) approach utilizing the 3ob and matsci parameter sets have been considered for a set of four Zn-based and two Al-based MOF systems. Moreover, the extended tight binding for geometries, frequencies, and noncovalent interactions (GFN2-xTB) approach has been considered as well. In addition to the application of energy minimizations of the respective unit cells, molecular dynamics (MD) simulations at constant temperature and pressure conditions (298.15 K, 1.013 bar) have been carried out to assess the performance of the different DFTB methods at nonzero thermal conditions. In order to obtain the XRD patterns from the MD simulations, a flexible workflow to obtain time-averaged XRD patterns from (in this study 5000) individual snapshots taken at regular intervals over the simulation trajectory has been applied. In addition, the comparison of pair-distribution functions (PDFs) directly accessible from the simulation data shows very good agreement with experimental reference data obtained via measurements employing synchrotron radiation in case of MOF-5. The comparison of the lattice constants and the associated X-ray diffraction (XRD) patterns with the experimental reference data demonstrate, that the SCC DFTB approach provides a highly efficient and accurate description of the target systems.

Facile fabrication of amino-functionalized MIL-68(Al) metal-organic framework for effective adsorption of arsenate (As(V))

An amino-functionalized MIL-68(Al) metal–organic framework (amino-MIL-68(Al) MOF) was synthesized by solvothermal method and then characterized by FESEM, XRD, FTIR, EDX-mapping, and BET-BJH techniques. In order to predict arsenate (As(V)) removal, a robust quadratic model (R² > 0.99, F-value = 2389.17 and p value < 0.0001) was developed by the central composite design (CCD) method and then the genetic algorithm (GA) was utilized to optimize the system response and four independent variables. The results showed that As(V) adsorption on MOF was affected by solution pH, adsorbent dose, As(V) concentration and reaction time, respectively. Predicted and experimental As(V) removal efficiencies under optimal conditions were 99.45 and 99.87%, respectively. The fitting of experimental data showed that As(V) adsorption on MOF is well described by the nonlinear form of the Langmuir isotherm and pseudo-second-order kinetic. At optimum pH 3, the maximum As(V) adsorption capacity was 74.29 mg/g. Thermodynamic studies in the temperature range of 25 to 50 °C showed that As(V) adsorption is a spontaneous endothermic process. The reusability of MOF in ten adsorption/regeneration cycles was studied and the results showed high reusability of this adsorbent. The highest interventional effect in inhibiting As(V) adsorption was related to phosphate anion. The results of this study showed that amino-MIL-68(Al) can be used as an effective MOF with a high surface area (> 1000 m²/g) and high reusability for As(V)-contaminated water.

Development of Efficient Photocatalyst MIL-68(Ga)_NH2 Metal-Organic Framework for the Removal of Cr(VI) and Cr(VI)/RhB from Wastewater under Visible Light

Severe environmental pollution is caused by the massive discharge of complex industrial wastewater. The photocatalytic technology has been proved as an effective way to solve the problem, while an efficient photocatalyst is the most critical factor. Herein, a new photocatalyst MIL-68(Ga)_NH₂ was obtained by hydrothermal synthesis and were characterized by PXRD, FTIR, ¹H NMR, and TGA systematically. The result demonstrates that MIL-68(Ga)_NH₂ crystallized in orthorhombic system and Cmcm space group with the unit cell parameters: a = 36.699 Å, b = 21.223 Å, c = 6.75 Å, V = 5257.6 ų, which sheds light on the maintenance of the crystal structure of the prototype material after amino modification. The conversion of Cr(VI) and binary pollutant Cr(VI)/RhB in wastewater under visible light stimulation was characterized by the UV-vis DRS. Complementary experimental results indicate that MIL-68(Ga)_NH₂ exhibits remarkable photocatalytic activity for Cr(VI) and the degradation rate reaches as high as 98.5% when pH = 2 and ethanol as hole-trapping agent under visible light irradiation with good reusability and stability. Owing to the synergistic effect between Cr(VI) and RhB in the binary pollutant system, MIL-68(Ga)_NH₂ exhibits excellent catalytic activity for both the pollutants, the degradation efficiency of Cr(VI) and RhB was up to 95.7% and 94.6% under visible light irradiation for 120 min, respectively. The possible removal mechanism of Cr(VI)/RhB based on MIL-68(Ga)_NH₂ was explored. In addition, Ga-based MOF was applied in the field of photocatalytic treatment of wastewater for the first time, which broadened the application of MOF materials in the field of photocatalysis.

Synthesis, modifications and applications of MILs Metal-organic frameworks for environmental remediation: The cutting-edge review

Ever-increasing anthropogenic activities are radically deteriorating the environment by causing severe pollution. Thus, curtailing the environmental pollution and promotion of sustainable development, are the hot issues confronted by scientists in this modern era. Metal-organic frameworks (MOFs) have been highly recognized as emerging promising materials for environmental remediation due to their versatile structure and extraordinary properties. Among them, MILs (MIL = Matérial Institute of Lavoisier) are the series of MOFs mostly known for their incredible stability, unique tailorable pore structures, and astounding versatile environmental applications. Their exclusive physiochemical properties and multifunctionality make them proficient for a wide range of pollutants removal in the exposure of versatile harsh environments, compared to other MOFs. This piece of research summarizes the state-of-the-art of development of MILs on the broad spectrum, highlighting their specificities, such as synthesis techniques, modifications and applications for environmental remediation. However, MILs wonderful properties and extraordinary applications in multiple fields, their deployment on practical and commercial-scale pollutants remediation is hindered by insufficient scientific research on underlying mechanisms and relationships. Henceforth, this review not only signifies the emerging importance of MILs for environmental applications but also indicates the urgency to maximize the scientific research for exploitation of MOFs on a practical level and promotion of green technologies for environmental remediation.

Interrogating the Behaviour of a Styryl Dye Interacting with a Mesoscopic 2D-MOF and Its Luminescent Vapochromic Sensing

In this contribution, we report on the solid-state-photodynamical properties and further applications of a low dimensional composite material composed by the luminescent trans-4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye interacting with a two-dimensional-metal organic framework (2D-MOF), Al-ITQ-HB. Three different samples with increasing concentration of DCM are synthesized and characterized. The broad UV-visible absorption spectra of the DCM/Al-ITQ-HB composites reflect the presence of different species of DCM molecules (monomers and aggregates). In contrast, the emission spectra are narrower and exhibit a bathochromic shift upon increasing the DCM concentration, in agreeance with the formation of adsorbed aggregates. Time-resolved picosecond (ps)-experiments reveal multi-exponential behaviors of the excited composites, further confirming the heterogeneous nature of the samples. Remarkably, DCM/Al-ITQ-HB fluorescence is sensitive to vapors of electron donor aromatic amine compounds like aniline, methylaniline, and benzylamine due to a H-bonding-induced electron transfer (ET) process from the analyte to the surface-adsorbed DCM. These findings bring new insights on the photobehavior of a well-known dye when interacting with a 2D-MOF and its possible application in sensing aniline derivatives.

Lattice-Guided Construction and Harvest of a Naturally Nonpreferred Metal-Organic Framework

Constructing metal-organic frameworks (MOFs) to have a desired structure from the given components is critical to achieve ideal MOFs with optimal properties. However, thermodynamics and/or kinetics typically impose a restriction on MOF structures. Here, we report the MOF farming concept to produce a naturally nonpreferred structure from the given components. The HKUST-1 template offers ideal places for the efficient seeding and epitaxial growth of Ga-MIL-88B that is a naturally nonpreferred structure however intentionally produced instead of the preferred Ga-MIL-68. The MOF growth on the differently shaped HKUST-1 templates (octahedral, cuboctahedral, and cubic), containing different exposed lattices, proves that a hexagonal lattice with an exposed {111} plane of HKUST-1 selectively directs the perpendicular growth of Ga-MIL-88B, owing to the lattice matching with the {001} plane of Ga-MIL-88B. The grown Ga-MIL-88B is isolated in a pure form, and the refreshed template is reused to grow additional Ga-MIL-88B.

A high-throughput screening of metal-organic framework based membranes for biogas upgrading

Applications of biomethane as a source of renewable energy and transport fuel rely heavily on successful implementation of purification methods capable of removing undesirable impurities from biogas and increasing its calorific content. Metal-organic frameworks (MOFs) are competitive candidates for biogas upgrading due to a versatile range of attractive physical and chemical properties which can be utilised in membrane materials. In this work, we present a high-throughput computational screening methodology for efficient identification of MOF structures with promising gas separation performance. The proposed screening strategy is based on initial structural analysis and predictions of the single-component permeation of CO₂, CH₄ and H₂S from adsorption and diffusion calculations at infinite dilution. The identified top performing candidates are subject to further analysis of their gas separation performance at the operating conditions of 10 bar and 298 K, using grand canonical Monte Carlo and equilibrium molecular dynamics simulations on equimolar CO₂/CH₄ and H₂S/CH₄ mixtures. The Henry constant for the adsorption of H₂O was also calculated to determine the hydrophobicity of MOF structures, as the presence of H₂O often leads to membrane instability and performance limitations. For the considered gas mixtures, the top MOF candidates exhibit superior separation capabilities over polymer-, zeolite-, and mixed matrix-based membranes as indicated by the predicted values of selectivity and permeability. The proposed screening protocol offers a powerful tool for the rational design of novel MOFs for biogas upgrading.

Effect of axial molecules and linker length on CO2 adsorption and selectivity of CAU-8: a combined DFT and GCMC simulation study

Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) calculations are performed to study the structures and carbon dioxide (CO₂) adsorption properties of the newly designed metal–organic framework based on the CAU-8 (CAU stands for Christian-Albrechts Universität) prototype. In the new MOFs, the 4,4′-benzophenonedicarboxylic acid (H₂BPDC) linker of CAU-8 is substituted by 4,4′-oxalylbis(azanediyl)dibenzoic acid (H₂ODA) and 4,4′-teraphthaloylbis(azanediyl)dibenzoic acid (H₂TDA) containing amide groups (–CO–NH- motif). Furthermore, MgO₆ octahedral chains where dimethyl sulfoxide (DMSO) decorating the axial position bridged two Mg²⁺ ions are considered. The formation energies indicate that modified CAU-8 is thermodynamically stable. The reaction mechanisms between the metal clusters and the linkers to form the materials are also proposed. GCMC calculations show that CO₂ adsorptions and selectivities of Al-based MOFs are better than those of Mg-based MOFs, which is due to DMSO. Amide groups made CO₂ molecules more intensively distributed besides organic linkers. CO₂ uptakes and selectivities of MOFs containing H₂TDA linkers are better in comparison with those of MOFs containing H₂BPDC linkers or H₂ODA linkers.

Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) calculations are performed to study the structures and CO₂ adsorption properties of the newly designed metal–organic framework based on the CAU-8 prototype.

Application of an MOF-based dispersive micro solid phase extraction method followed by dispersive liquid–liquid microextraction for plasticizers’ detection and determination

In this research, MIL-68 (Al) was synthesized and used for the extraction of some plasticizers from various samples stored in plastic bottles.

Dialing in Catalytic Sites on Metal Organic Framework Nodes: MIL-53(Al) and MIL-68(Al) Probed with Methanol Dehydration Catalysis

Many metal organic frameworks (MOFs) incorporate metal oxide clusters as nodes. Node sites where linkers are missing can be catalytic sites. We now show how to dial in the number and occupancy of such sites in MIL-53 and MIL-68, which incorporate aluminum-oxide-like nodes. The methods involve modulators used in synthesis and postsynthesis reactions to control the modulator-derived groups on these sites. We illustrate the methods using formic acid as a modulator, giving formate ligands on the sites, and these can be removed to leave μ₂-OH groups and open Lewis acid sites. Methanol dehydration was used as a catalytic reaction to probe these sites, with infrared spectra giving evidence of methoxide ligands as reaction intermediates. Control of node surface chemistry opens the door for placement of a variety of ligands on a wide range of metal oxide cluster nodes for dialing in reactivity and catalytic properties of a potentially immense class of structurally well-defined materials.

Synthesis and Characterization of Ru-MOFs on Microelectrode for Trace Mercury Detection

Mercury ions (Hg2+) pollution in the water environment can cause serious harm to human health. Trace Hg2+ detection is of vital importance for environmental monitoring. Herein, we report a novel design of Ru-MOFs modified gold microelectrode for Hg2+ determination. Ru-MOFs are synthesized directly by the cathodic method on gold microelectrode, with the covered area accurately controlled. Cathodic synthesized Ru-MOFs show good conductivity and are suitable to be used as the electrode surface material directly. The synergy of the pre-deposition process and the adsorption process of Ru-MOFs can effectively improves the performance of the sensor. The results show good linearity (R2 = 0.996) from 0.1 ppb to 5 ppb, with a high sensitivity of 0.583 μA ppb-1 mm-2. The limit of detection is found to be 0.08 ppb and the test process is within 6 min. Most importantly, the senor has a good anti-interference ability and the recoveries are satisfactory. This miniature electrochemical sensor has the potential for on-site detection of trace mercury in the field.

Hydrogen Sulfide (H2S) Removal via MOFs

The removal of the environmentally toxic and corrosive hydrogen sulfide (H₂S) from gas streams with varying overall pressure and H₂S concentration is a long-standing challenge faced by the oil and gas industries. The present work focuses on H₂S capture using a relatively new type of material, namely metal-organic frameworks (MOFs), in an effort to shed light on their potential as adsorbents in the field of gas storage and separation. MOFs hold great promise as they make possible the design of structures from organic and inorganic units, but also as they have provided an answer to a long-term challenging objective, i.e., how to design extended structures of materials. Moreover, in designing MOFs, one may functionalize the organic units and thus, in essence, create pores with different functionalities, and also to expand the pores in order to increase pore openings. The work presented herein provides a detailed discussion, by thoroughly combining the existing literature on new developments in MOFs for H₂S removal, and tries to provide insight into new areas for further research.

Removal of Hydrogen Sulfide From Various Industrial Gases: A Review of The Most Promising Adsorbing Materials

The separation of hydrogen sulfide (H2S) from gas streams has significant economic and environmental repercussions for the oil and gas industries. The present work reviews H2S separation via nonreactive and reactive adsorption from various industrial gases, focusing on the most commonly used materials i.e., natural or synthetic zeolites, activated carbons, and metal oxides. In respect to cation-exchanged zeolites, attention should also be paid to parameters such as structural and performance regenerability, low adsorption temperatures, and thermal conductivities, in order to create more efficient materials in terms of H2S adsorption. Although in the literature it is reported that activated carbons can generally achieve higher adsorption capacities than zeolites and metal oxides, they exhibit poor regeneration potential. Future work should mainly focus on finding the optimum temperature, solvent concentration, and regeneration time in order to increase regeneration efficiency. Metal oxides have also been extensively used as adsorbents for hydrogen sulfide capture. Among these materials, ZnO and Cu–Zn–O have been studied the most, as they seem to offer improved H2S adsorption capacities. However, there is a clear lack of understanding in relation to the basic sulfidation mechanisms. The elucidation of these reaction mechanisms will be a toilsome but necessary undertaking in order to design materials with high regenerative capacity and structural reversibility.

Amino-Functionalized β-Cyclodextrin to Construct Green Metal-Organic Framework Materials for CO2 Capture

The adsorption of CO₂ by conventional liquid alkanolamine adsorbents does not meet the requirements for green-friendly development in industrial applications. In this work, we constructed NH₂-β-CD-MOF for the first time through the amino-functionalization of the lowest-priced, readily available, and biocompatible β-CD. Subsequently, the samples were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, elemental analysis, and N₂ adsorption/desorption. The CO₂ adsorption capacity of NH₂-β-CD-MOF was found to be 12.3 cm³/g, which is 10 times that of β-CD-MOF. In addition, NH₂-β-CD-MOF has outstanding selective adsorption of CO₂/N₂ (947.52) compared with the reported materials. The adsorption mechanism of CO₂ was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Furthermore, we have found that NH₂-β-CD-MOF has better water stability relative to β-CD-MOF and γ-CD-MOF, and it can be recycled by an ultrasonic method.

In situ Raman and FTIR spectroscopic study on the formation of the isomers MIL-68(Al) and MIL-53(Al)

The paper describes a method to induce the formation of MIL-68(Al) rather than MIL-53(Al) using a formic acid modulated synthesis approach.

Expandable Layered Hybrid Materials Based on Individual 1D Metalorganic Nanoribbons

Different metalorganic lamellar hybrid materials based on associated nanoribbons were synthesized by the use of alkyl-benzyl monocarboxylate spacers, containing alkyl tails with variable lengths, which acted like structural growing inhibitors. These molecular agents were perpendicularly located and coordinated to aluminium nodes in the interlayer space, controlling the separation between individual structure sub-units. The hybrid materials were studied by X-ray diffraction (XRD), chemical and thermogravimetrical analysis (TGA), nuclear magnetic resonance (NMR) and infrared spectroscopy (IR), and field emission scanning electron microscopy (FESEM)/transmission electron microscopy (TEM), showing their physicochemical properties. The specific capacity of the metalorganic materials to be exfoliated through post-synthesis treatments, using several solvents due to the presence of 1D structure sub-units and a marked hydrophobic nature, was also evidenced.

Outstanding reversible H2S capture by an Al(iii)-based MOF

The MOF-type MIL-53(Al)-TDC was demonstrated to be an optimal adsorbent for H2S capture combining an unprecedented uptake at room temperature, excellent cyclability and low-temperature regeneration.

Contrastive removal of oxytetracycline and chlortetracycline from aqueous solution on Al-MOF/GO granules

The presence of tetracycline antibiotics (TCS) in the water and wastewater has raised growing concern due to its potential environmental impacts; thus, their removal is of high importance. In this study, a novel aluminum-based MOF/graphite oxide (Al-MOF/GO) granule was prepared as an adsorbent for the removal of TCS including oxytetracycline (OTC) and chlortetracycline (CTC). The adsorbent was characterized via XRD, FTIR, BET, SEM, and XPS methods. The granules exhibited similar crystal structure and some new mesopores appearing compared to the parent Al-MOF/GO powder. In addition, the adsorption behavior of OTC and CTC on samples was explored as a function of initial concentration, contact time, pH, and ionic strength by means of batch experiments. The adsorption capacity reached to 224.60 and 240.13 mg·L^-1 for OTC and CTC, at C₀ = 60 mg·L^-1 as well as ambient temperature respectively. Moreover, the adsorption process of OTC and CTC on Al-MOF/GO samples can be better delineated by pseudo-second-order kinetics and Freundlich isotherm models. Besides, the adsorption mechanism over Al-MOF/GO granules was proposed, which could be ascribed to π-π interaction, cation-π bonding, and hydrogen bond. Finally, the great water stability, separation performance, and regeneration efficiency of these novel granules indicated their potential application in the OTC and CTC removals from aqueous solution.

Nanosheets of MIL-53(Al) applied in membranes with improved CO2/N2 and CO2/CH4 selectivities

Nanosheets obtained from MOF MIL-53(Al) applied in mixed matrix membranes with improved CO₂/N₂ and CO₂/CH₄ selectivities.

Retraction: Insight into the reversible structural crystalline-state transformation from MIL-53(Al) to MIL-68(Al)

Retraction of ‘Insight into the reversible structural crystalline-state transformation from MIL-53(Al) to MIL-68(Al)’ by Adelaida Perea-Cachero et al., CrystEngComm, 2018, 20, 402–406.

Removal of tetracycline from aqueous solution by MOF/graphite oxide pellets: Preparation, characteristic, adsorption performance and mechanism

Tetracycline (TC) as a typical antibiotic has been used extensively and detected in soil, surface water, ground water and drinking water, which results in toxic effect and bacterial resistance. In this study, aluminum-based metal organic framework/graphite oxide (MIL-68(Al)/GO) pellets were prepared through the addition of sodium alginate (SA), a natural crosslinking agent, and applied as a novel adsorbent for aqueous TC removal. The adsorption materials were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption analysis and X-ray photoelectron spectroscopy (XPS). Results demonstrated that the pellets maintained similar chemical structure with parent MIL-68(Al)/GO powder. It is noted that the surface area and total volume of the pellets decreased obviously due to the disappearance of micropores. Besides, the efficiency of MIL-68(Al)/GO pellets for TC removal was evaluated by adsorption properties compared with parent powder, including key influential parameters, and adsorption isotherms, kinetics and mechanisms. It is found that the adsorption process was conformed to pseudo-first-order kinetics model and more suitably described through Langmuir isotherm model, with 228 mg g^-1 of the maximum adsorption capacity. Moreover, these pellets which were separated easily and quickly presented high adsorption capacity and good stability in a wide pH range. The adsorption mechanism of the pellets may be ascribed to the complex interactions of hydrogen bonding, π-π stacking as well as Al-N covalent bonding. Overall, the MIL-68(Al)/GO pellets might be a promising adsorbent and show great potential for the removal of aqueous TC.

Stable Metal-Organic Frameworks: Design, Synthesis, and Applications

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal-carboxylate frameworks and low-valency metal-azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Brønsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.

Exploring the Photodynamics of a New 2D-MOF Composite: Nile Red@Al-ITQ-HB

In this work, we unravel the photodynamics of Nile Red (NR) interacting with Al-ITQ-HB nanostructure, a new layer-type metal-organic framework (MOF) with potential catalytic and photonic applications. Steady-state spectroscopy reveals the presence of NR monomers and aggregates when interacting with the MOF structure. Time-resolved experiments provide emission lifetimes of the interacting monomers, H- and J-type aggregates. We observed contributions from two monomer populations having different environments. One monomer species emits from the local-excited state and another from a photoproduced charge-separated state resulting from an ultrafast intramolecular charge transfer (ICT). Femtosecond fluorescence experiments reveal that the ICT process occurs in ∼1 ps. Fluorescence microscopy on single crystals and agglomerates of the composites shows a homogenous distribution of the dye lifetimes within the material. This study shows that the photobehavior of NR in Al-ITQ-HB MOF is dictated by its location within the material. The reported findings using a well-known polarity probe and a new two-dimensional MOF provide information on the microenvironment of this material, which may help for designing smart MOFs with potential applications in photonics and nanocatalysis.

Growth-modulating agents for the synthesis of Al-MOF-type materials based on assembled 1D structural subdomains

Specific long-alkyl aromatic mono-carboxylate linkers, combined with metallic nodes, favors the formation of 1D metalorganic nanoribbon-type structural sub-units which are assembled to generate novel organized Al-MOF-type solids.

Comment on “Insight into the reversible structural crystalline-state transformation from MIL-53(Al) to MIL-68(Al)” by A. Perea-Cachero, E. Romero, C. Téllez and J. Coronas, CrystEngComm, 2018, 20, 402

The inadvertently published phase transformation from MIL-53 to MIL-68 is merely a deformation of the MIL-53 structure upon DMF adsorption.

Adsorption behavior of methyl orange onto an aluminum-based metal organic framework, MIL-68(Al)

MIL-68(Al), a powdered aluminum-based metal organic framework (MOF), was synthesized and used to explore its adsorption behavior toward methyl orange (MO). The adsorption isotherm, thermodynamics, kinetics, and some key operating factors as well as changes in the material's structure were investigated. The adsorption isotherm conformed to the Langmuir isotherm model and the maximum equilibrium adsorption capacity was 341.30 mg g^-1. Thermodynamic data demonstrated that the adsorption process was spontaneous, endothermic and showed positive entropy. For kinetics, the process of MO adsorption onto MIL-68(Al) was more suitably described by a pseudo-second-order model. Electrostatic and hydrogen-bonding interactions contributed to dye adsorption, with electrostatic interactions considered to be the principal binding force between adsorbent and adsorbate. Furthermore, MIL-68(Al) maintained a stable structure after adsorption. From these results, MIL-68(Al) was suggested here to be a stable MOF adsorbent for removing MO from aqueous solution.

Single-Layered Hybrid Materials Based on 1D Associated Metalorganic Nanoribbons for Controlled Release of Pheromones

A new family of stable layered organic-inorganic materials has been prepared, in one-step solvothermal process. They are based on an ordered nickel cluster-type nanoribbons separated from each other by specific alkyl (heptyl- or dodecyl-) arylic mono-carboxylate moieties acting as molecular spacers, perpendicular to the 1D inorganic chains. These organic spacers contain hydrocarbon tails with different length which control the separation level between inorganic 1D sub-units, inhibiting the 3D growth of conventional DUT-8-type metal-organic frameworks (MOFs). The lamellar nature of the materials formed was studied and confirmed by different characterization techniques, showing the structural location of individual organic and inorganic building units. They have been successfully used as a long-lasting biodegradable and water-proof materials for controlled release of chemicals, such as pheromones for sustainable treatment of insect plagues.