Crystalline Nanoporous Materials Research Articles

Recent Advances of Metal-Organic Framework for Heavy Metal Ions Adsorption.

Heavy metal ion wastewater is a pressing and inescapable issue that is closely related to human health and ecological security due to its toxicity, carcinogenicity, and the unmanageable property of this type of wastewater. Metal-Organic Frameworks (MOFs) are a class of crystalline nanoporous materials with flexible designability and controllability, showing great potential in the field of adsorption and purification of heavy metals in wastewater. In this Perspective, we first discuss the harm of different heavy metal ions and briefly expound virtues of MOFs for pollutant adsorption. Then, we mainly summarize the recent advances in the construction of different metal-based MOFs (Zr-based, Zn-based, Co-based, Al-based, etc.) and their research progress in heavy metal ions adsorption. Furthermore, various types of MOF additives can often be effectively applied for heavy metal ion adsorption by functional modification or with other materials composition. Additionally, several commonly used adsorption kinetics and isotherm models are also detailed to help an in-depth understanding of the adsorption mechanism. Finally, the challenges and opportunities of MOFs for heavy metal ion adsorption are additionally discussed, and this review may provide new insight for other potential water purification applications.

Monte Carlo Simulations of Water Pollutant Adsorption at Parts-per-Billion Concentration: A Study on 1,4-Dioxane.

1,4-dioxane, an emerging water pollutant with high production volumes, is a probable human carcinogen. The inadequacy of conventional treatment processes demonstrates the need for an effective remediation strategy. Crystalline nanoporous materials are cost-effective adsorbents due to their high capacity and selective separation in mixtures. This study explores the potential of all-silica zeolites for the separation of 1,4-dioxane from water. These zeolites are highly hydrophobic and can preferentially adsorb nonpolar molecules from mixtures. We investigated six zeolite frameworks (BEA, EUO, FER, IFR, MFI, and MOR) using Monte Carlo simulations in the Gibbs ensemble. The simulations indicate high selectivity by FER and EUO, especially at low pressures, which we attribute to pore sizes and shapes with a greater affinity to 1,4-dioxane. We also demonstrate a Monte Carlo simulation workflow using gauge cells to model the adsorption of an aqueous solution of 1,4-dioxane at a 0.35 ppb concentration. We quantify 1,4-dioxane and water coadsorption and observe selectivities ranging from 1.1 × 105 in MOR to 8.7 × 106 in FER. We also demonstrate that 1,4-dioxane is in the infinite dilution regime in the aqueous phase at this concentration. This simulation technique can be extended to model other emerging water contaminants such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), chlorofluorocarbons, and others, which are also found in extremely low concentrations.

Nanoporous Crystalline Materials for the Recognition and Applications of Nucleic Acids.

Nucleic acid plays a crucial role in countless biological processes. Hence, there is great interest in its detection and analysis in various fields from chemistry, biology, to medicine. Nanoporous crystalline materials exhibit enormous potential as an effective platform for nucleic acid recognition and application. These materials have highly ordered and uniform pore structures, as well as adjustable surface chemistry and pore size, making them good carriers for nucleic acid extraction, detection, and delivery. In this review, the latest developments in nanoporous crystalline materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular organic frameworks (SOFs) for nucleic acid recognition and applications are discussed. Different strategies for functionalizing these materials are explored to specifically identify nucleic acid targets. Their applications in selective separation and detection of nucleic acids are highlighted. They can also be used as DNA/RNA sensors, gene delivery agents, host DNAzymes, and in DNA-based computing. Other applications include catalysis, data storage, and biomimetics. The development of novel nanoporous crystalline materials with enhanced biocompatibility has opened up new avenues in the fields of nucleic acid analysis and therapy, paving the way for the development of sensitive, selective, and cost-effective diagnostic and therapeutic tools with widespread applications.

MIL-101 (Cr) hybrid nanoporous carbon derived MOF as a nano-adsorbent for dye removal using RSM-CCD

Metal-organic frameworks (MOFs) are a promising class of nanoporous crystalline materials with potential applications in gas storage, catalysis, biomedical, adsorption, and clean energy. The massive parts of commercial dyes are interring to our environment and are considered danger for humans and animals. In this research work, nanohybrids based on MOFs have been studied as a suitable nanoadsorbent for the adsorption of cationic dyes such as methylene blue (MB). In this article, a nanopore carbon (NPC) was prepared from Zn-MOF. The Zn-MOF NPC with MI-101 NPs has been used to prepare Zn-MOF NPC@MIL nanohybrid by the hydrothermal method. Various XRD, FT-IR, SEM, EDX, TEM, TGA, and BET techniques have been used to characterize the nano adsorbent. Four essential variables effective in adsorption, loading percentage of NPs, initial concentration of MB, contact time and pH, were optimized by Central Composite Response Surface Method (RSM-CCD). The removal percentage (Re%) of MB is equal to 95.7% was obtained under the following conditions: The loading value of 25Wt.%, the MB initial concentration of 50 mg. L-1, contact time 30 min and pH 8. Also, the experimental data were investigated with famous kinetic models and isotherms, and it was observed that MB removal by nanohybrid is correlated with pseudo-second-order kinetic model and Langmuir isotherm.

MOFs as Versatile Catalysts: Synthesis Strategies and Applications in Value-Added Compound Production.

Catalysts played a crucial role in advancing modern human civilization, from ancient times to the industrial revolution. Due to high cost and limited availability of traditional catalysts, there is a need to develop cost-effective, high-activity, and nonprecious metal-based electrocatalysts. Metal-organic frameworks (MOFs) have emerged as an ideal candidate for heterogeneous catalysis due to their physicochemical properties, hybrid inorganic/organic structures, uncoordinated metal sites, and accessible organic sections. MOFs are high nanoporous crystalline materials that can be used as catalysts to facilitate polymerization reactions. Their chemical and structural diversity make them effective for various reactions compared to traditional catalysts. MOFs have been applied in gas storage and separation, ion-exchange, drug delivery, luminescence, sensing, nanofilters, water purification, and catalysis. The review focuses on MOF-enabled heterogeneous catalysis for value-added compound production, including alcohol oxidation, olefin oligomerization, and polymerization reactions. MOFs offer tunable porosity, high spatial density, and single-crystal XRD control over catalyst properties. In this review, MOFs were focused on reactions of CO2 fixation, CO2 reduction, and photoelectrochemical water splitting. Overall, MOFs have great potential as versatile catalysts for diverse applications in the future.

Quantifying molecular surface barriers and intracrystalline diffusion in nanoporous materials by zero‐length column

AbstractThe zero‐length column (ZLC) method has been frequently used to measure the effective diffusivity of guest molecules in nanoporous crystalline materials. Recent studies unveiled that the mass transport of guest molecules could originate from either intracrystalline diffusion and/or surface barriers. Directly quantifying the intracrystalline diffusivity and surface permeability of guest molecules. therefore, is essential for understanding the mass transfer and thus optimizing the design of nanoporous crystalline materials. In this work, we extended the ZLC method, based on a derived theoretical expression of the desorption rate, to decouple the surface barriers and intracrystalline diffusion from effective diffusion of guest molecules in nanoporous materials. The diffusivities of ethane, propane and n‐pentane in SAPO‐34 and Beta zeolites have been experimentally measured to verify the effectiveness of this method.

Structure-Property Relationship of Piezoelectric Properties in Zeolitic Imidazolate Frameworks: A Computational Study.

Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials with very high structural tunability. They possess a very low dielectric permittivity εr due to their porosity and hence are favorable for piezoelectric energy harvesting. Even though they have huge potential as piezoelectric materials, a detailed analysis and structure-property relationship of the piezoelectric properties in MOFs are lacking so far. This work focuses on a class of cubic non-centrosymmetric MOFs, namely, zeolitic imidazolate frameworks (ZIFs) to rationalize how the variation of different building blocks of the structure, that is, metal node and linker substituents affect the piezoelectric constants. The piezoelectric tensor for the ZIFs is computed from ab initio theoretical methods. From the calculations, we analyze the different contributions to the final piezoelectric constant d14, namely, the clamped ion (e140) and the internal strain (e14int) contributions and the mechanical properties. For the studied ZIFs, even though e14 (e140 + e14int) is similar for all ZIFs, the resultant piezoelectric coefficient d14 calculated from piezoelectric constant e14 and elastic compliance constant s44 varies significantly among the different structures. It is the largest for CdIF-1 (Cd2+ and -CH3 linker substituent). This is mainly due to the higher elasticity or flexibility of the framework. Interestingly, the magnitude of d14 for CdIF-1 is higher than II-VI inorganic piezoelectrics and of a similar magnitude as the quintessential piezoelectric polymer polyvinylidene fluoride.

Thermally Conductive Self-Healing Nanoporous Materials Based on Hydrogen-Bonded Organic Frameworks.

Hydrogen-bonded organic frameworks (HOFs) are a class of nanoporous crystalline materials formed by the assembly of organic building blocks that are held together by a network of hydrogen-bonding interactions. Herein, we show that the dynamic and responsive nature of these hydrogen-bonding interactions endows HOFs with a host of unique physical properties that combine ultraflexibility, high thermal conductivities, and the ability to "self-heal". Our systematic atomistic simulations reveal that their unique mechanical properties arise from the ability of the hydrogen-bond arrays to absorb and dissipate energy during deformation. Moreover, we also show that these materials demonstrate relatively high thermal conductivities for porous crystals with low mass densities due to their extended periodic framework structure that is comprised of light atoms. Our results reveal that HOFs mark a new regime of material design combining multifunctional properties that make them ideal candidates for gas storage and separation, flexible electronics, and thermal switching applications.

Quasicontinuous Cooperative Adsorption Mechanism in Crystalline Nanoporous Materials.

The hase behavior of confined fluids adsorbed in nanopores differs significantly from their bulk counterparts and depends on the chemical and structural properties of the confining structures. In general, phase transitions in nanoconfined fluids are reflected in stepwise adsorption isotherms with a pronounced hysteresis. Here, we show experimental evidence and an in silico interpretation of the reversible stepwise adsorption isotherm which is observed when methane is adsorbed in the rigid, crystalline metal–organic framework IRMOF-1 (MOF-5). In a very narrow range of pressures, the adsorbed fluid undergoes a structural and highly cooperative reconstruction and transition between low-density and high-density nanophases, as a result of the competition between the fluid–framework and fluid–fluid interactions. This mechanism evolves with temperature: below 110 K, a reversible stepwise isotherm is observed, which is a result of the bimodal distribution of the coexisting nanophases. This temperature may be considered as a critical temperature of methane confined to nanopores of IRMOF-1. Above 110 K, as the entropy contribution increases, the isotherm shape transforms to a common continuous S-shaped form that is characteristic to a gradual densification of the adsorbed phase as the pressure increases.

ZIF-Based Metal-Organic Frameworks for Cantilever Gas Sensors

Among the different gas sensing platforms, cantilever-based sensors have attracted considerable interest in recent years thanks to their ultra-sensitivity and high-speed response. The gas sensing mechanism in a dynamic cantilever sensor is based on its resonance frequency shift upon adsorption of a gas molecule on the sensor. In order to sensitize the surface of a cantilever, a sensitive receptor material with large surface area is required. Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials composed of metal ions coordinated to organic linkers. MOFs are promising for gas sensing applications as they have large surface area, rich porosity with adjustable pore size and excellent selective adsorption capability for various gasses.[1] Zeolite imidazole frameworks (ZIFs) are a class of MOFs where metals with tetrahedral coordination (i.e. Zn, Co, Fe, Cu) are the central node and the ligands are imidazolate-based organic molecules.In this work, we developed a ZIF-based thin film for dynamic cantilever gas-sensing applications. We employed a novel atmospheric pressure spatial atomic layer deposition (AP-SALD)[2][3] technique to deposit a ZnO sacrificial layer on the silicon cantilevers. This technique allows the deposition of high-quality films at atmospheric pressure, faster than conventional ALD. The ZnO layer was then converted to a particular ZIF film with desired porosity and size, through a MOF-CVD process.[4] A gas-sensing bench setup was developed for the cantilever actuation and read-out. We present the chemical and morphological properties of the ZIF, as well as the frequency response of the sensor to various gases. The device showed reliable sensitivity to humidity, CO2 and several VOCs.

Exploring the Influence of Inter- and Intra-crystal Diversity of Surface Barriers in Zeolites on Mass Transport by Using Super-Resolution Microimaging of Time-Resolved Guest Profiles.

The applications of nanoporous crystalline materials are closely related to the mass transfer of guest molecules. However, the fundamental knowledge of mass transfer, and in particular the surface barriers controlled by the permeation of guest molecules through the external surfaces of materials, is still incomplete. The diversity of surface permeability at the single-crystal level, caused by the varying origins of surface transport resistance, hinders the rational materials design and needs better understanding. Herein, we probe the molecular transport in single zeolite crystals with fluorescent 4-(4-diethylaminostyryl-1-methylpyridinium iodide) (DAMPI) using super-resolution structured illumination microscopy (SIM). It showed that both the inter- and intra-crystal diversity of surface barriers could be monitored by detecting the diffusion behaviors on the center and surface planes in single crystals. This adds a new perspective for studying the origins of the surface barriers as well as the molecular transport mechanisms in nanoporous materials.

Exploring the Influence of Inter‐ and Intra‐crystal Diversity of Surface Barriers in Zeolites on Mass Transport by Using Super‐Resolution Microimaging of Time‐Resolved Guest Profiles

AbstractThe applications of nanoporous crystalline materials are closely related to the mass transfer of guest molecules. However, the fundamental knowledge of mass transfer, and in particular the surface barriers controlled by the permeation of guest molecules through the external surfaces of materials, is still incomplete. The diversity of surface permeability at the single‐crystal level, caused by the varying origins of surface transport resistance, hinders the rational materials design and needs better understanding. Herein, we probe the molecular transport in single zeolite crystals with fluorescent 4‐(4‐diethylaminostyryl‐1‐methylpyridinium iodide) (DAMPI) using super‐resolution structured illumination microscopy (SIM). It showed that both the inter‐ and intra‐crystal diversity of surface barriers could be monitored by detecting the diffusion behaviors on the center and surface planes in single crystals. This adds a new perspective for studying the origins of the surface barriers as well as the molecular transport mechanisms in nanoporous materials.

Metal-organic Framework Materials Coupled to Optical Fibers for Chemical Sensing: A Review.

Metal-organic frameworks (MOFs), a newer class of crystalline nanoporous materials, have been in the limelight owing to their exceptional tunability for structures and physicochemical properties, and have found successful applications in gas storage, gas separation, and catalysis. The mesmerizing properties of MOFs, especially the extensive and tunable porosity and chemical selectivity, also make them an excellent candidate class as chemo-sensory materials. Moreover, MOF-based sensors have attracted considerable attention in the past decade. Recent literature reviews focused on the progress of MOF-based electronic sensors and luminescent MOF sensors, while sensors exploiting the dielectric properties (refractive index) of MOFs were also demonstrated and discussed very recently. The motivation of this report is to provide, for the first time, a general review on such MOF sensors with a particular focus on miniature optical fiber (OF) based MOF sensors and to demonstrate the promising potential of MOFs as dielectric coatings on OF for highly sensitive chemical sensing. The fundamental principle of OF-MOF sensors relies on the tunability of the refractive index of a MOF, which is dependent on the amount and type of adsorbed guest molecules in the MOF pores. MOF sensors based on different optical sensing principles are reviewed; challenges and perspectives on further research into the field of OF-MOF sensors are also discussed.

Structure and dynamics of water confined in cylindrical nanopores with varying hydrophobicity.

We report a detailed study of the main structural and dynamical features of water confined in model Lennard–Jones nanopores with tunable hydrophobicity and finite length ( Å). The generic model of cylindrical confinement used is able to reproduce the wetting features of a large class of technologically and biologically relevant systems spanning from crystalline nanoporous materials, to mesoporous silica and ion channels. The aim of this work is to discuss the influence of parameters such as wall hydrophobicity, temperature, and pore size on the structural and dynamical features of confined water. Our simulation campaign confirmed the existence of a core domain in which water displays bulk-like structural features even in extreme ( Å) confinement, while dynamical properties were shown to depend non-trivially on the size and hydrophobicity of the pores.This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

Quantifying Impact of Intrinsic Flexibility on Molecular Adsorption in Zeolites

The majority of molecular simulations of adsorption in crystalline nanoporous materials such as zeolites and metal–organic frameworks (MOFs) are performed using a rigid framework. This assumption i...

Three-step nucleation of metal–organic framework nanocrystals

Metal-organic frameworks (MOFs) are crystalline nanoporous materials with great potential for a wide range of industrial applications. Understanding the nucleation and early growth stages of these materials from a solution is critical for their design and synthesis. Despite their importance, the pathways through which MOFs nucleate are largely unknown. Using a combination of in situ liquid-phase and cryogenic transmission electron microscopy, we show that zeolitic imidazolate framework-8 MOF nanocrystals nucleate from precursor solution via three distinct steps: 1) liquid-liquid phase separation into solute-rich and solute-poor regions, followed by 2) direct condensation of the solute-rich region into an amorphous aggregate and 3) crystallization of the aggregate into a MOF. The three-step pathway for MOF nucleation shown here cannot be accounted for by conventional nucleation models and provides direct evidence for the nonclassical nucleation pathways in open-framework materials, suggesting that a solute-rich phase is a common precursor for crystallization from a solution.

Breaking two-dimensional polymeric crystals

Covalent organic frameworks (COFs) are an emerging class of polymeric crystalline nanoporous materials with a broad range of applications. In this issue of <i>Matter</i>, Fang et al. demonstrate that two-dimensional COFs exhibit extraordinary mechanical properties including high strength, high modulus and flaw insensitivity at low mass and high surface densities.

A concurrent high strength and ductility of 3D gyroidal nanoporous metallic glasses

By using molecular dynamics simulations, we investigate the tensile response of nanoporous (NP) Cu50Zr50 metallic glasses (MGs) with 3D gyroidal structure. Similar to nanoporous crystalline metals, NP–MGs fail by the plastic necking of ligaments, but shear bandings (SBs) prevail in those thick–ligament specimens. Particularly, with ligament diameter decreasing to 2.34 nm, SBs are hardly observed due to the limit of translation from shear transformation zones, resulting in superior strength and ductility of NP–MGs. The critical ligament size to suppress the formation of SBs is much smaller than those calculated value in MGs. The observations reveal a design strategy that a concurrent high strength and ductility of MGs could be obtained by designing 3D nanoporous structure with supra–nano size. The scaling laws for Young's modulus and strength as functions of relative density and ligament diameters are addressed, consistent with those in nanoporous crystalline materials.

Control of Surface Barriers in Mass Transfer to Modulate Methanol‐to‐Olefins Reaction over SAPO‐34 Zeolites

AbstractMass transfer of guest molecules has a significant impact on the applications of nanoporous crystalline materials and particularly shape‐selective catalysis over zeolites. Control of mass transfer to alter reaction over zeolites, however, remains an open challenge. Recent studies show that, in addition to intracrystalline diffusion, surface barriers represent another transport mechanism that may dominate the overall mass transport rate in zeolites. We demonstrate that the methanol‐to‐olefins (MTO) reaction can be modulated by regulating surface permeability in SAPO‐34 zeolites with improved chemical liquid deposition and acid etching. Our results explicitly show that the reduction of surface barriers can prolong catalyst lifetime and promote light olefins selectivity, which opens a potential avenue for improving reaction performance by controlling the mass transport of guest molecules in zeolite catalysis.

Control of Surface Barriers in Mass Transfer to Modulate Methanol-to-Olefins Reaction over SAPO-34 Zeolites.

Mass transfer of guest molecules has a significant impact on the applications of nanoporous crystalline materials and particularly shape-selective catalysis over zeolites. Control of mass transfer to alter reaction over zeolites, however, remains an open challenge. Recent studies show that, in addition to intracrystalline diffusion, surface barriers represent another transport mechanism that may dominate the overall mass transport rate in zeolites. We demonstrate that the methanol-to-olefins (MTO) reaction can be modulated by regulating surface permeability in SAPO-34 zeolites with improved chemical liquid deposition and acid etching. Our results explicitly show that the reduction of surface barriers can prolong catalyst lifetime and promote light olefins selectivity, which opens a potential avenue for improving reaction performance by controlling the mass transport of guest molecules in zeolite catalysis.