Acid-Modulated Synthesis of High Surface Area Amine-Functionalized MIL-101(Cr) Nanoparticles for CO2 Separations

Adsorption and Diffusion of CH4, N2, and Their Mixture in MIL-101(Cr): A Molecular Simulation Study

A comprehensive quantitative grasp of methane (CH4), nitrogen (N2), and their mixture's adsorption and diffusion in MIL-101(Cr) is crucial for wide and important applications, e.g., natural gas upgrading and coal-mine methane capturing. Previous studies often overlook the impact of gas molecular configuration and MIL-101 topology structure on adsorption, lacking quantitative assessment of primary and secondary adsorption sites. Additionally, understanding gas mixture adsorption mechanisms remains a research gap. To bridge this gap and to provide new knowledge, we utilized Monte Carlo and molecular dynamics simulations for computing essential MIL-101 properties, encompassing adsorption isotherms, density profiles, self-diffusion coefficients, radial distribution function (RDF), and CH4/N2 selectivity. Several novel and distinctive findings are revealed by the atomic-level analysis, including (1) the significance of C=C double bond of the benzene ring within MIL-101 for CH4 and N2 adsorption, with Cr and O atoms also exerting notable effects. (2) Density distribution analysis reveals CH4's preference for large and medium cages, while N2 is evenly distributed along pentagonal and triangular window edges and small tetrahedral cages. (3) Calculations of self-diffusion and diffusion activation energies suggest N2's higher mobility within MIL-101 compared to CH4. (4) In the binary mixture, the existence of CH4 can decrease the diffusion coefficient of N2. In summary, this investigation provides valuable microscopic insights into the adsorption and diffusion phenomena occurring in MIL-101, thereby contributing to a comprehensive understanding of its potential for applications, e.g., natural gas upgrading and selective capture of coal-mine methane.

Wide temperature adaptive oxidase-like based on mesoporous manganese based metal-organic framework for detecting total antioxidant capacity

Overcoming the intense variation of enzymatic activity among different temperatures is very critical in catalytic medicine and catalytic biology. Here, Mn-based metal-organic framework-based wide-temperature-adaptive mesoporous artificial enzymes (Mn-TMA-MOF) were designed and synthesized. The oxidase-like Mn-TMA-MOF showed excellent catalytic activity at 0-50 °C and avoided the activity loss and instability due to temperature variation that occurred. The excellent oxidase-like properties of Mn-TMA-MOF with wide temperature adaptativeness are mainly ascribed to the mixed oxidized state (Mn3+/Mn2+) and high substrate affinity (Km = 0.034 mM) of Mn. Moreover, the mesopore-micropores two-level structure of Mn-TMA-MOF provides a large space and surface area for enzyme catalysis. Based on the stability of Mn-TMA-MOF, we developed a colorimetric sensor that can detect total antioxidant capacity in fruits with a limit of detection up to 0.59 μM.

Enhanced degradation of 2,4-dichlorophenol in groundwater by defective iron-based metal-organic frameworks: Role of SO3- and electron transfer

The purposeful formation of crystal defects was regarded as an attractive strategy to enhance the catalytic activity of Fe-MOFs. In this study, the pyrolytic hydrochloric acid-modulated MIL-101-NH2 (P250HMN-2) was fabricated for the first time, and the important role of pyrolysis in the formation of crystal defects was confirmed. PDS was introduced as an enhancer for the P250HMN-2/Na2SO3 system. Without pH adjustment, 99.7 % of 2,4-DCP was removed by the P250HMN-2/Na2SO3/PDS system in 180 min. The catalytic performance of P250HMN-2 improved 2.5-fold than that of MIL-101-NH2. It was found that the high density of Fe-CUSs on P250HMN-2 were the major active sites, which could efficiently react with SO32- to generate ROS through electron transfer. The results of quenching experiments, probe tests, and EPR tests indicated that SO3-, SO4-, 1O2, OH, and SO5- were involved in the 2,4-DCP degradation process, with SO3-, SO4-, and 1O2 playing major roles. Moreover, P250HMN-2 could effectively degrade 2,4-DCP for 148 h in a fixed-bed reactor with excellent stability and reusability, indicating a promising catalyst for practical applications.

Highly Defective Zirconium-Based Metal-Organic Frameworks for the Efficient Adsorption and Detection of Sugar Phosphates in the Biological Sample

Enrichment and quantification of sugar phosphates (SPx) in biological samples were of great significance in biological medicine. In this work, a series of zirconium-based metal-organic frameworks (MOFs) with different degrees of defects, namely, HP-UiO-66-NH2-X, were synthesized using acetic acid as a modulator and were utilized as high-capacity adsorbents for the adsorption of SPx in biological samples. The results indicated that the addition of acetic acid altered the morphology of HP-UiO-66-NH2-X, with corresponding changes in pore size (3.99-9.28 nm) and specific surface area (894.44-1142.50 m2·g-1). HP-UiO-66-NH2-10 showed the outstanding performance by achieving complete adsorption of all four SPx using only 80 μg of the adsorbent. The excellent adsorption efficiency of HP-UiO-66-NH2-10 was also obtained with a wide pH range and short adsorption time (10 min). Adsorption experiments demonstrated that the adsorption process involved chemical adsorption and multilayer adsorption. By utilizing X-ray photoelectron spectroscopy and density functional theory to explain the adsorption mechanism, it was found that various interactions (including coordination, hydrogen bonding, and electrostatic interactions) collectively contributed to the exceptional adsorption capability of HP-UiO-66-NH2-10. Those results indicated that the defect strategy not only increased the specific surface area and pore size, providing additional adsorption sites, but also reduced the adsorption energy between HP-UiO-66-NH2-10 and SPx. Moreover, HP-UiO-66-NH2-10 showed a low limit of detection (0.001-0.01 ng·mL-1), high precision (<13.77%), and accuracy (80.10-111.83%) in serum, liver, and cells, good stability, high selectivity (SPx/glucose, 1:100 molar ratio), and high adsorption capacity (292 mg·g-1 for SPx). The practical detection of SPx from human serum was also verified, prefiguring the great potentials of defective zirconium-based MOFs for the enrichment and detection of SPx in the biological medicine.

Properties and release behavior of sodium alginate-based nanocomposite active films: Effects of particle size of IRMOF-3

Nanoparticles are used as fillers to improve the properties of biopolymers, and their particle size is an important parameter. This work aims to investigate the effect of particle size of isoreticular metal-organic framework-3 (IRMOF-3) on the mechanical, physical, and release properties of sodium alginate (SA)-based composite active film. In our study, IRMOF-3 with six different particle sizes was synthesized by introducing additives. IRMOF-3 loading with carvacrol (IRMOF-3/CA nanoparticles) was incorporated into the SA matrix to prepare the composite film. The characterization and testing results of films showed that the particle size of nanoparticles affected the physical morphology and chemical structure of the film. Especially smaller nanoparticles uniformly dispersed into the SA matrix more easily, forming a denser and more stable spatial network structure with SA, which could more significantly improve the tensile strength, water vapor barrier, and hydrophobic properties of the film (P < 0.05). In addition, the CA release rate from the active film could be significantly reduced by about 33.90 % even when the smallest particle size of the IRMOF-3/CA nanoparticles was added. Therefore, when IRMOF-3/CA is used as the nano-filler to develop SA-based active film, its particle size has a potential influence on the properties of the film.

Metal-organic frameworks (MOFs) for energy production and gaseous fuel and electrochemical energy storage applications

The increasing energy demands in society and industrial sectors have inspired the search for alternative energy sources that are renewable and sustainable, also driving the development of clean energy storage and delivery systems. Various solid-state materials (e.g., oxides, sulphides, polymer and conductive nanomaterials, activated carbon and their composites) have been developed for energy production (water splitting-H2 production), gaseous fuel (H2 and CH4) storage and electrochemical energy storage (batteries and supercapacitors) applications. Nevertheless, the low surface area, pore volume and conductivity, and poor physical and chemical stability of the reported materials have resulted in higher requirements and challenges in the development of energy production and energy storage technologies. Thus, to overcome these issues, the development of metal-organic frameworks (MOFs) has attracted significant attention. MOFs are a class of porous materials with extremely high porosity and surface area, structural diversity, multifunctionality, and chemical and structural stability, and thus they can be used in a wide range of applications. In the present review, we precisely discuss the interesting properties of MOFs and the various methodologies for their synthesis, and also the future dependence on the valorization of solid waste for the recovery of metals and organic ligands for the synthesis of new classes of MOFs. Subsequently, the utilization of these interesting characteristics for energy production (water splitting), storage of gaseous fuels (H2 and CH4), and electrochemical storage (batteries and supercapacitors) applications are described. However, although MOFs are efficient materials with versatile uses, they still have many challenges, limiting their practical applications. Therefore, finally, we highlight the challenges associated with MOFs and show the way forward in overcoming them for the development of these highly porous materials with large-scale practical utility.

Engineering the Polymer-MOF Interface in Microporous Composites to Address Complex Mixture Separations

Poor interfacial compatibility remains a pressing challenge in the fabrication of high-performance polymer-MOF composites. In response, introducing compatible chemistries such as a carboxylic acid moiety has emerged as a compelling strategy to increase polymer-MOF interactions. In this work, we leveraged compatible functionalities in UiO-66-NH2 and a carboxylic acid-functionalized PIM-1 to fabricate mixed-matrix membranes (MMMs) with improved separation performance compared to PIM-1-based MMMs in industrially relevant conditions. Under pure-gas conditions, PIM-COOH-based MMMs retained selectivity with increasing MOF loading and showed increased permeability due to increased diffusion. The composites were further investigated under industrially relevant conditions, including CO2/N2, CO2/CH4, and H2S/CO2/CH4 mixtures, to elucidate the effects of competitive sorption and plasticization. Incorporation of UiO-66-NH2 in PIM-COOH and PIM-1 mitigated the effects of CO2- and H2S-induced plasticization typically observed in linear polymers. In CO2-based binary mixed-gas tests, all samples showed similar performance as that in pure-gas tests, with minimal competitive sorption contributions associated with the amine functional groups of the MOF. In ternary mixed-gas tests, improved plasticization resistance and interfacial compatibility resulted in PIM-COOH-based MMMs having the highest H2S/CH4 and CO2/CH4 selectivity combinations among the films tested in this study. These findings demonstrate that selecting MOFs and polymers with compatible functional groups is a useful strategy in developing high-performing microporous MMMs that require stability under complex and industrially relevant conditions.

MIL-101-NH2(Fe)-Coated Nylon Microfibers for Immobilized Photocatalysts in RhB and Cr(VI) Removal

MIL-101-NH₂(Fe) is one of the effective photocatalytic metal-organic frameworks (MOFs) working under visible light. However, its powder-type form inhibits reusability in practical applications. In this study, we immobilized MIL-101-NH₂(Fe) on a polymeric microfiber mesh to improve reusability while minimizing the loss of catalytic performance. To overcome the lack of surface functionality of the nylon fibers, an atomic layer deposition Al₂O₃ layer and NH₂-BDC linker were introduced to facilitate uniform coating of the MOF on the fiber surface. The reactions of the metal precursor to the nylon substrate and NH₂-BDC ligand of the MOF allow chemical bonding from the core to the shell of the entire hybrid catalytic materials. The resulting fiber-immobilized MOFs (Nylon@Al₂O₃@MOF) demonstrated high photocatalytic performance in the removal of RhB and Cr(VI) as representatives of organic dyes and heavy metals, respectively, while retaining over 85% of its efficiency after five cycles.

Advances in Metal-Organic Frameworks MIL-101(Cr)

MIL-101(Cr) is one of the most well-studied chromium-based metal-organic frameworks, which consists of metal chromium ion and terephthalic acid ligand. It has an ultra-high specific surface area, large pore size, good thermal/chemical/water stability, and contains unsaturated Lewis acid sites in its structure. Due to the physicochemical properties and structural characteristics, MIL-101(Cr) has a wide range of applications in aqueous phase adsorption, gas storage and separation, and catalysis. In this review, the latest synthesis of MIL-101(Cr) and its research progress in adsorption and catalysis are reviewed.

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.