Gas Adsorption Applications Research Articles

Solvent Free Ambient Pressure CO2 Cycloaddition Catalyzed by Cobalt-Impregnated 2D-Nanofibrous COFs.

Covalent organic frameworks (COFs) constitute an evolving class of permanently porous and ordered materials, and they have recently attracted increased interest due to their intriguing morphological features and numerous applications in gas storage, adsorption, and catalysis. However, their low aqueous stabilities and tedious syntheses generally hamper their use in heterogeneous catalysis. Nonetheless, a capable and water-stable heterogeneous catalytic system for coupling CO2/epoxides to generate industrially important cyclic carbonates is still of great interest. Herein, exceedingly water- and thermally stable 2D-cobalt-impregnated hydrazone-linked fibrous COFs are reported as a catalyst for CO2/epoxide coupling reactions at ambient pressure. The functionalized cobalt (Co)-doped COFs demonstrated excellent catalytic activities with the high TONs (80925) and TOFs (6466 h-1), outperforming reported heterogeneous catalysts for CO2/epoxide coupling at ambient pressure. We found that the Co2+ ions within the COF matrix catalyze CO2 cycloaddition through density functional theory calculations. We also confirmed the excellent structural stability and consistent activity of Co-doped COFs up to ten repeating cycles.

Gas adsorption meets geometric deep learning: points, set and match

Thanks to their unique properties such as ultra high porosity and surface area, metal-organic frameworks (MOFs) are highly regarded materials for gas adsorption applications. However, their combinatorial nature results in a vast chemical space, precluding its exploration with traditional techniques. Recently, machine learning (ML) pipelines have been established as the go-to method for large scale screening by means of predictive models. These are typically built in a descriptor-based manner, meaning that the structure must be first coarse-grained into a 1D fingerprint before it is fed to the ML algorithm. As such, the latter can not fully exploit the 3D structural information, potentially resulting in a model of lower quality. In this work, we propose a descriptor-free framework called “AIdsorb”, which can directly process raw structural information for predicting gas adsorption properties. To accomplish that, the structure is first treated as a point cloud and then passed to a deep learning algorithm suitable for point cloud analysis. As a proof of concept, AIdsorb is applied for predicting CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {CO}_{2}$$\\end{document} uptake in MOFs, outperforming a conventional pipeline that uses geometric descriptors as input. Additionally, to evaluate the transferability of the proposed framework to different host-guest systems, CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {CH}_{4}$$\\end{document} uptake in COFs is examined. Since AIdsorb bases its roots on raw structural information, its applicability extends to all fields of material science.

Gas adsorption and separation applications of MOF materials

Abstract. Low-carbon hydrocarbons (C1-C4) are really important raw materials used in making different kinds of big molecules and stuff in industries. Before, people mostly used super cold cooling and a method where stuff gets soaked up. But these ways need big machines and use a lot of energy. So, scientists are trying to make new ways to separate things that don't use as much energy. One great idea is using how different gases stick to things to separate them. This idea could be a brilliant way to replace the old methods. The most important part of this idea is making things that can stick to the gases. There's this special material called metal-organic frameworks (MOFs) that's a mix of things from nature and chemicals. It has tiny holes and places that can do special things, and it's being studied a lot for separating gases. Traditional porous materials like activated carbon, silica gel, and molecular sieves have been widely used in industries, which has greatly contributed to industrial growth and people's living standards. MOFs have changeable structures and spots that can do special things. By changing the metal bits or the organic parts, we can control the size of the holes in MOFs, the special spots, and how much surface they have. These things make MOFs useful for storing gases, separating stuff by sticking and making reactions happen in fields like chemistry [1-3]. This paper explores the categories of MOF applications.

Double‐Walled Honeycomb‐Like Metal‐Organophosphonium Framework with High H2 Gas Adsorption Capacities

AbstractThis study successfully synthesized a new Metal‐Organic Framework (MOF) named CJLU−L2, which was constructed from phosphorus‐containing ligands and Co(II) ions. The structure revealed through single‐crystal X‐ray diffraction (SCXRD), features a double‐walled honeycomb‐shaped structure with a one‐dimensional channel of ~6.5 Å. According to the PLATON calculation, the pore volume per unit cell of CJLU−L2 was determined to be 6825.0 Å3, constituting 57.5 % of the total crystal volume (11874.9 Å3). The Brunauer‐Emmett‐Teller (BET) surface area of CJLU−L2 was determined to be 954 m2/g by N2 adsorption measurement at 77 K. The phase purity of CJLU−L2 was verified by powder X‐ray diffraction (PXRD) and infrared spectroscopy (IR), while its thermal stability was confirmed by thermogravimetric analysis (TGA). Hydrogen adsorption experiments demonstrate that CJLU−L2 exhibits a high hydrogen adsorption capacity, indicating significant potential for gas adsorption applications.

Synthesis Techniques and Biomedical Applications of Cyclodextrin Metal-Organic Frameworks.

Cyclodextrin Metal-Organic Frameworks (CD MOFs) represent an innovative class of materials with remarkable properties and a broad range of applications. This review provides a comprehensive overview of the synthesis techniques, structural characterization, and diverse applications of CD-MOFs. By combining cyclodextrins (CDs) with metal-organic frameworks (MOFs), CD-MOFs are developed with enhanced functionality. The synthesis methods, including various metal sources, coordination modes, and post-synthesis modifications, are discussed alongside advanced structural characterization techniques like X-ray crystallography and spectroscopic methods. The unique characteristics of CD-MOFs, such as high specific surface area, tunable porosity, and customizable chemical structure, make them exceptional candidates for applications in gas adsorption, drug delivery, catalysis, sensing, and environmental remediation. Notably, CD-MOFs show significant promise as nanocarriers in drug delivery systems, offering improved therapeutic outcomes due to their efficient encapsulation and controlled release capabilities. The review highlights recent advancements and underscores the potential impact of CD-MOFs in driving future innovations across various scientific fields.

Fabrication of Spherical Colloidal Supraparticles via Membrane Emulsification.

Colloidal supraparticles are micrometer-scale assemblies of primary particles. These supraparticles have potential application in photonic materials, catalysis, gas adsorption, and drug delivery. Thus, the synthesis of colloidal supraparticles with a narrow size distribution and high yield has become essential. Here, we demonstrate membrane emulsification as a high-throughput approach for fabricating spherical supraparticles with a narrow size distribution and control over particle size and crystallinity. Spherical supraparticles with well-ordered surface structures are synthesized by generating emulsion droplets of an aqueous colloidal dispersion in fluorocarbon oil using a Shirasu porous glass membrane followed by the consolidation of particles through water removal within the emulsion. We systematically investigate process parameters, including the flow rate of the particle dispersion, the particle concentration, and the average pore diameter of the membrane, on the mean size and size distribution of the supraparticles, revealing key factors governing supraparticle properties and production throughput. A comparative evaluation with commonly employed methods highlights the advantage of membrane emulsification, which combines well-defined internal structure and controlled supraparticle sizes with comparably high yields on the order of tens of grams per day. Importantly, in contrast to widely used droplet-based microfluidics, membrane emulsification allows fabrication of supraparticles in nonfluorinated oil. Overall, membrane emulsification offers a simple yet versatile method for fabricating colloidal supraparticles with high quality and yield and may serve as a bridge between existing high-precision techniques, such as droplet-based microfluidics, and high-throughput processes with less control, such as spray-drying.

MOFs with the Stability for Practical Gas Adsorption Applications Require New Design Rules.

Metal-organic frameworks (MOFs) have been widely studied for their ability to capture and store greenhouse gases. However, most computational discovery efforts study hypothetical MOFs without consideration of their stability, limiting the practical application of novel materials. We overcome this limitation by screening hypothetical ultrastable MOFs that have predicted high thermal and activation stability, as judged by machine learning (ML) models trained on experimental measures of stability. We enhance this set by computing the bulk modulus as a measure of mechanical stability and filter 1102 mechanically robust hypothetical MOFs from a database of ultrastable MOFs (USMOF DB). Grand Canonical Monte Carlo simulations are then employed to predict the gas adsorption properties of these hypothetical MOFs, alongside a database of experimental MOFs. We identify privileged building blocks that lead MOFs in USMOF DB to show exceptional working capacities compared to the experimental MOFs. We interpret these differences by training ML models on CO2 and CH4 adsorption in these databases, showing how poor model transferability between data sets indicates that novel design rules can be derived from USMOF DB that would not have been gathered through assessment of structurally characterized MOFs. We identify geometric features and node chemistry that will enable the rational design of MOFs with enhanced gas adsorption properties in synthetically realizable MOFs.

Preparation of Hierarchical Porous Monoliths With High Surface Areas by a Solvent Knitting Strategy.

Hierarchical porous hypercrosslinked monoliths (PolyHIPE-HCP) with ultrahigh specific surface areas are prepared via a solvent knitting strategy. Compared to previous work, the solvent knitting strategy is carried out in a relatively low air-controlled atmosphere with gradient heating starting from low temperature while using DCM (Dichloromethane) as both a solvent and a cross-linker, allowing for a slow and controlled cross-linking process, thereby achieving a BET surface area ranging from 514 to 728m2g-1. Scanning electron microscopy (SEM) shows that the knitting process does not affect the presence of macroporous structure in the PolyHIPE. With the introduction of mesopores and micropores, these hierarchical porous monoliths exhibit significant potential for applications in gas adsorption and water treatment. Hence, a universal, simple and low-cost method to synthesize polymeric monoliths with hierarchically porous structure and higher surface area is proposed, which has fascinating prospects in industrialization.

Optimizing the prediction of adsorption in metal–organic frameworks leveraging Q‐learning

AbstractThe application of machine learning (ML) techniques in materials science has revolutionized the pace and scope of materials research and design. In the case of metal–organic frameworks (MOFs), a promising class of materials due to their tunable properties and versatile applications in gas adsorption and separation, ML has helped survey the vast material space. This study explores the integration of reinforcement learning (RL), specifically Q‐learning, within an active learning (AL) context, combined with Gaussian processes (GPs) for predictive modeling of adsorption in MOFs. We demonstrate the effectiveness of the RL‐driven framework in guiding the selection of training data points and optimizing predictive model performance for methane and carbon dioxide adsorption, using two different reward metrics. Our results highlight the integration of RL as an AL method for adsorption predictions in MFs, and how it compares to a previously implemented AL scheme.

Bioorganic activated carbon from cashew nut shells for H2 adsorption and H2/CO2, H2/CH4, CO2/CH4, H2/CO2/CH4 selectivity in industrial applications

This research explores the production of activated carbon (AC) from cashew nut shells using a potassium hydroxide (KOH) activation method, with a focus on its application in high-pressure gas adsorption. Among the synthesized samples, AC850 demonstrated the highest efficiency, displaying a specific surface area of 1972 m2/g and total and micropore volumes of 0.847 cm3/g and 0.724 cm3/g, respectively. The bioorganic activated carbon exhibited significant sorption capabilities for H2, with uptake values of 13.34 mmol/g (2.69 wt%) at 10 bar and 25 °C, and a H2/CH4 selectivity range between 43.4 and 2.6. Calculations were also conducted for selectivity in a mixture of three gases (H2, CO2, and CH4) in industrial settings. Advanced characterization methods such as N2/CO2 adsorption isotherms, FT-IR, Raman spectroscopy, SEM, and TGA were employed to analyze the structural and chemical properties of the produced AC, including its functional groups and molecular structure. The research underscores the potential of utilizing agricultural waste, particularly cashew nut shells, to develop efficient materials for H2 storage and purification. The high-pressure adsorption capability and eco-friendly nature of the manufactured activated carbon make it suitable for both environmental and industrial applications.

Theoretical study on the luminescence mechanism of AIEgens based HOFs adsorbing small molecules

The diversity and reversibility of non-covalent interactions give hydrogen-bonded organic frameworks (HOFs) excellent gas adsorption and separation performance. Here we designed and synthesized HOFs based on aggregation-induced emission luminogens (AIEgens) to visualize the adsorption process of HOFs. We focused on the SQ system and its solvated SQ frameworks by different solvent conditions, employing the thermal vibration correlation function rate formalism coupled hybrid quantum mechanics/molecular mechanics protocol, to elucidate the relation between crystal structure and luminescent properties, as well as the specific adsorption ability of porous SQ HOF crystals on acetylene gas. It is found that compare to SQ crystal, the SQ symmetry in cocrystals are improved, and SQ-DCM cocrystal has the best symmetry. The absorption spectra of five SQ-based crystals are close to each other, and their emission spectra blueshifted from 540 nm of SQ, to 509 nm, 508 nm, 507 nm of SQ-EA, SQ-ACN, SQ-DCM, and then to 495 nm of SQ-TOL, consistent with experimental results. The kic of solvated cocrystals are about 1∼2 orders of magnitude smaller than that of non-solvated crystal SQ, resulting in significantly higher Φexp of solvated cocrystals than that of un-solvated one. DCM with small volume and C2v point group is more suitable for SQ crystal channel, indicating that small free region and shape matching are the key factors affecting the reversibility of crystallization of porous frames during solvent transport. Finally, the volume of the adsorbed gas C2H2 which is close to DCM, is more easily adsorbed by SQ framework. Our study offers theoretical insights into the design of porous crystals for gas adsorption and separation applications.

Computational Simulations of Metal-Organic Frameworks to Enhance Adsorption Applications.

Metal-organic frameworks (MOFs), renowned for their exceptional porosity and crystalline structure, stand at the forefront of gas adsorption and separation applications. Shortly after their discovery through experimental synthesis, computational simulations quickly become an important method in broadening the use of MOFs by offering deep insights into their structural, functional, and performance properties. This review specifically addresses the pivotal role of molecular simulations in enlarging the molecular understanding of MOFs and enhancing their applications, particularly for gas adsorption. After reviewing the historical development and implementation of molecular simulation methods in the field of MOFs, high-throughput computational screening (HTCS) studies used to unlock the potential of MOFs in CO2 capture, CH4 storage, H2 storage, and water harvesting are visited and recent advancements in these adsorption applications are highlighted. The transformative impact of integrating artificial intelligence with HTCS on the prediction of MOFs' performance and directing the experimental efforts on promising materials is addressed. An outlook on current opportunities and challenges in the field to accelerate the adsorption applications of MOFs is finally provided.

The Effects of Halogen (Cl, Br) Decorating on the Gas Adsorption Behaviors of the Pristine Black Phosphorene: A First-Principles Study

As a novel two-dimensional (2D) material, black phosphorene (BP) finds wide applications in gas adsorption and detection devices due to its distinctive optical, thermoelectric, and surface properties. However, numerous studies have demonstrated that BP exhibits strong selectivity towards gas adsorption and displays significant affinity towards gas molecules containing the element N, thereby greatly impeding its utilization in gas detection. To partially compensate for this deficiency, this study investigates the impact of halogen atom decoration on the adsorption behavior of BP towards CO2, H2O, and O2 molecules. Furthermore, a comparison is made between the variations in gas adsorption energy with and without decorated halogen atoms. The results showed that the adsorbates of CO2, H2O, and O2 molecules and halogen atoms (Cl, Br) adsorbed at the top (T) site of BP was much stronger than those at the bridge (B) and the hollow (H) sites of the P-P bond of BP, owing to their low adsorption energies. After the t position of BP is modified by the halogen (Cl, Br) atom, the optimal adsorption of CO2 changes from −0.85 eV to −1.70 eV (Cl) and −1.64 eV (Br), and the optimal adsorption of H2O changes from −0.72 eV to −1.48 eV (Cl) and −1.23 eV (Br), respectively. The adsorption properties were significantly enhanced. That is to say, the gas adsorption properties of BP have been largely improved by halogen Cl (Br) atoms decorating.

Cashew nut shell biomass: A source for high-performance CO2/CH4 adsorption in activated carbon

This study embarks on the synthesis of activated carbon (AC) from cashew nut shells using a potassium carbonate (K2CO3) activation process, with a specific focus on its practical application in high-pressure gas adsorption. Among the synthesized samples, MCAK85 emerged as the most efficient, demonstrating a specific surface area of 1693 m2/g and total and micropore volumes of 0.839 cm3/g and 0.641 cm3/g, respectively. Importantly, this bioorganic activated carbon exhibited high sorption capacities for CO2 and CH4, with uptake values of 11.0 mmol/g and 5.5 mmol/g at 10 bar at 25°C, and a CO2/CH4 selectivity range between 9.1 and 1.8. A comprehensive range of characterization techniques were employed to analyze the structural and chemical properties of the synthesized AC, providing valuable insights into the functional groups and molecular structure. The morphology of the AC was examined using SEM, while the point of zero charge was determined to understand the surface charge characteristics. Additionally, TGA was utilized to assess the thermal stability and composition of the AC. This study underscores the potential of utilizing agricultural waste, specifically cashew nut shells, in the creation of effective materials for gas storage and purification applications. The high-pressure adsorption capacity of the produced AC, coupled with its sustainable and eco-friendly nature, underscores its suitability for environmental and industrial applications, particularly in areas focusing on greenhouse gas capture and air purification, thereby inspiring further research and development in this field.

Activation of 2D/3D zeolitic-imidazole frameworks affecting crystal properties and adsorption performance

The zeolitic-imidazole frameworks (ZIFs) have become popular due to their uniformly structured cavities and portals of framework dimensions, which make them suitable for numerous applications. In order to access pores and functional surfaces, thermal activation is significantly post-treatment on the synthesis of ZIFs for their applications. This study explores the impact of different thermal activation conditions on two- to three-dimensional ZIFs, which significantly affect their structure, morphology, and properties. Their transform structure is evidenced by integrated X-ray diffraction technique, Thermogravimetric analysis, Scanning electron microscope, and Fourier transform infrared spectroscopy. Moreover, the performance of greenhouse gas adsorption (CO2 and CH4) applications is affected by the transformation through the thermal activation of materials. Therefore, understanding the activated conditions that impact material synthesis is crucial to maximizing the potential applications of ZIFs in various fields. The 2D ZIF-L has more exposed external surfaces and open structures, which makes it more reactive towards adsorptive reactants, unlike the 3D ZIFs. The 3D ZIFs have a robust structure and a higher porosity framework that can withstand challenging application conditions. Thus, it's essential to ensure appropriate activation conditions to maintain the functional properties of ZIFs, which are crucial for their optimal performance in various applications.

Hypercrosslinked polymers with hierarchical pores synthesized using biphenyl crosslinker for carbon dioxide capture

Microporous hypercrosslinked polymers have an upright capacity to develop into prime materials in energy and environmental applications in the near future. The chemical tunability, structural robustness and high surface area are some of the critical factors that lead to their application in the gas adsorption area. Three novel hypercrosslinked porous polymers viz. PABMC, PFBMC and PPzBMC were synthesized via the Friedel-Crafts alkylation process using 4,4′-bis(chloromethyl)biphenyl as the external cross-linker and anhydrous FeCl3 as the catalyst. The polymers obtained are found to be microporous with very high surface areas of 983 m2/g, 1002 m2/g, and 1265 m2/g, respectively, for PABMC, PFBMC and PPzBMC. The polymers PABMC, PFBMC and PPzBMC exhibited appreciable carbon dioxide uptake of 10.18 wt%, 12.02 wt% and 14.18 wt%, respectively, at 273 K. The results reveal a practical approach to synthesizing low-cost heteroatom-rich hypercrosslinked organic polymers with hierarchical pores for gas adsorption and storage applications.

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants.

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Zeolite/Polymer Composites Prepared by Photopolymerization: Effect of Compensation Cations on Opacity and Gas Adsorption Applications.

The fabrication of structured zeolite adsorbents through photopolymerization-based 3D printing which offers a solution to the limitations of conventional shaping techniques has been demonstrated but many parameters still need to be optimized. In this study, we studied the influence of zeolite compensation cations on the photopolymerization and the composite's properties. Modified zeolites (LTA 4 A and FAU 13X exchanged with K+ , Li+ , Sr2+ , Ca2+ or Mg2+ ) were incorporated in PEGDA with BDMK as photoinitiator, and the formulation was cured under mild conditions (LED@405 nm, room temperature, under air). Our results indicate that the nature of zeolite compensation cations affects the colorimetric properties of polymer/zeolite composites: a better translucency parameter results in higher depth of cure. After calcination at 650 °C and complete removal of PEGDA, pure zeolitic monoliths were tested for adsorption of gas molecules of interest (carbon dioxide, dichlorobenzene and water). Structured 4 A and 13X monoliths obtained by 3D printing exhibit comparable adsorption capacity to commercial beads prepared from the same zeolites. This study enhances our understanding of the photopolymerization process involved in the production of polymer/zeolite composites. These composites are used in the fabrication of zeolitic objects through 3D printing, offering potential solutions to various environmental and dental challenges.

Metal-organic cages for gas adsorption and separation.

The unique high surface area and tunable cavity size endow metal-organic cages (MOCs) with superior performance and broad application in gas adsorption and separation. Over the past three decades, for instance, numerous MOCs have been widely explored in adsorbing diverse types of gas including energy gases, greenhouse gases, toxic gases, noble gases, etc. To gain a better understanding of the structure-performance relationships, great endeavors have been devoted to ligand design, metal node regulation, active metal site construction, cavity size adjustment, and function-oriented ligand modification, thus opening up routes toward rationally designed MOCs with enhanced capabilities. Focusing on the unveiled structure-performance relationships of MOCs towards target gas molecules, this review consists of two parts, gas adsorption and gas separation, which are discussed separately. Each part discusses the cage assembly process, gas adsorption strategies, host-guest chemistry, and adsorption properties. Finally, we briefly overviewed the challenges and future directions in the rational development of MOC-based sorbents for application in challenging gas adsorption and separation, including the development of high adsorption capacity MOCs oriented by adsorbability and the development of highly selective adsorption MOCs oriented by separation performance.

Metalation of metal-organic frameworks: fundamentals and applications.

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.