Gas Separation Applications Research Articles

Metal-organic framework-based porous liquids via surface functionalization engineering for selective gas adsorption

Porous liquids (PLs) combine the distinct porosity of solids with the fluidity of liquids, offering new solutions for carbon capture, membrane separation, and more. This study introduces the development of unique UIO-66-PLs through a meticulous surface functionalization strategy, using surface-modified UIO-66-(OH)2 with the organic oligomer SIT8378.3 (SIT) and polyether amines (PEAs) of various molecular weights (M1000, M2070, and M3085) as the hindering solvents. The resulting UIO-66-PLs exhibit exceptional stability and dispersibility in both aqueous and organic environments. Importantly, benefiting from preserving UIO-66-(OH)2′s porosity in PLs, the affinity of PEAs’ ethylene oxide segments for CO2 via Lewis acid-base interactions, and additional free space within organic chains, UIO-66-PLs revealed enhanced CO2 adsorption capabilities, particularly for CO2 over N2. Encouragingly, CO2 adsorption of UIO-66-PLs was enhanced by 117.54 % (UIO-66-M1000), 106.01 % (UIO-66-M2070), and 22.45 % (UIO-66-M3085) in capacity relative to the respective pure organic outer layer. It is also observed that while surface engineering improves gas adsorption performance, PEAs with a high molecular weight may partially block UIO-66-(OH)2 pores, decreasing gas adsorption capacities. Our research showcases the potential of UIO-66-PLs in gas storage and separation applications, offering a new approach to developing materials functionalized with customized organic molecular weights for advanced CO2 capture technologies.

Tailorable Multi-Modular Pore-Space-Partitioned Vanadium Metal-Organic Frameworks for Gas Separation.

Currently, few porous vanadium metal-organic frameworks (V-MOFs) are known and even fewer are obtainable as single crystals, resulting in limited information on their structures and properties. Here this work demonstrates remarkable promise of V-MOFs by presenting an extensible family of V-MOFs with tailorable pore geometry and properties. The synthesis leverages inter-modular synergy on a tri-modular pore-partitioned platform. New V-MOFs show a broad range of structural features and sorption properties suitable for gas storage and separation applications for C2H2/CO2, C2H6/C2H4, and C3H8/C3H6. The c/a ratio of the hexagonal cell, a measure of pore shape, is tunable from 0.612 to 1.258. Other tunable properties include pore size from 5.0 to 10.9 Å and surface area from 820 to 2964 m2 g-1. With C2H2/CO2 selectivity from 3.3 to 11 and high uptake capacity for C2H2 from 65.2 to 182 cm3 g-1 (298K, 1bar), an efficient separation is confirmed by breakthrough experiments. The near-record high uptake for C2H6 (166.8 cm3 g-1) contributes to the promise for C2H6-selective separation of C2H6/C2H4. The multi-module pore expansion enables transition from C3H6-selective to more desirable C3H8-selective separation with extraordinarily high C3H8 uptake (254.9 cm3 g-1) and high separation potential (1.25mmol g-1) for C3H8/C3H6 (50:50 v/v) mixture.

ZIF-8 Vibrational Spectra: Peak Assignments and Defect Signals.

Zeolitic imidazolate framework (ZIF-8) is a promising material for gas separation applications. It also serves as a prototype for numerous ZIFs, including amorphous ones, with a broader range of possible applications, including sensors, catalysis, and lithography. It consists of zinc coordinated with 2-methylimidazolate (2mIm) and has been synthesized with methods ranging from liquid-phase to solvent-free synthesis, which aim to control its crystal size and shape, film thickness and microstructure, and incorporation into nanocomposites. Depending on the synthesis method and postsynthesis treatments, ZIF-8 materials may deviate from the nominal defect-free ZIF-8 crystal structure due to defects like missing 2mIm, missing zinc, and physically adsorbed 2mIm trapped in the ZIF-8 pores, which may alter its performance and stability. Infrared (IR) spectroscopy has been used to assess the presence of defects in ZIF-8 and related materials. However, conflicting interpretations by various authors persist in the literature. Here, we systematically investigate ZIF-8 vibrational spectra by combining experimental IR spectroscopy and first-principles molecular dynamics simulations, focusing on assigning peaks and elucidating the spectroscopic signals of putative defects present in the ZIF-8 material. We attempt to resolve conflicting assignments from the literature and to provide a comprehensive understanding of the vibrational spectra of ZIF-8 and its defect-induced variations, aiming toward more precise quality control and design of ZIF-8-based materials for emerging applications.

Fine-tuning porosity of In-MOFs with ncb topology based on reticular chemistry for one-step purification C2H4 from ternary C2H6/C2H4/C2H2 mixtures

One-step purification of C2H4 from ternary C2H6/C2H4/C2H2 mixtures by single adsorbent is of great industrial significance, but few adsorbents can achieve this purpose. Herein, four isoreticular In-MOFs, In-BDC-AINA, In-ATC-INA, In-Fum-INA, and In-Fum-AINA (H2BDC, H2ATC, H2Fum, HINA, and HAINA are 1,4-benzenedicarboxylic acid, 2-amino-terephthalic acid, fumaric acid, isonicotinic acid and 3-amino-isonicotinic acid, respectively), were designed and synthesized by the guidance of reticular chemistry, using the known In-BDC-INA as the platform, through amino modification and ligand shortening approaches. In-ATC-INA and In-BDC-AINA were aminations of H2BDC and HINA, respectively. In-Fum-INA is replacing H2BDC to shorter H2Fum. In-Fum-AINA is obtained by further amination of In-Fum-INA. Due to the molar ratio of isoniacic and dicarboxylic ligands in this series structure is 2/1, they exhibit different site numbers, site distributions, pore sizes and pore volumes after regulation. These frameworks without open metal sites provided the ability of C2H6/C2H4 inversion adsorption. The amino modification and ligand shortening approaches successfully improved the selectivity of C2H2/C2H4, and the equimolar C2H2/C2H4 selectivities of In-ATC-INA (1.82) and In-Fum-INA (2.81) were higher than that of In-BDC-INA (1.73) calculated by IAST method. The breakthrough results show that In-BDC-INA, In-ATC-INA and In-Fum-INA can achieve one-step separation of the ternary C2 mixtures and the C2H4 yields are 0.08, 0.13 and 0.09 mmol/g, respectively, demonstrating that the two approaches have successfully improved the gas separation performance. In addition, these materials possess exceptional thermal and chemical stability, the low-cost ligand used in In-Fum-INA synthesis further enhances its potential application for industrial gas separation.

Electrochemical engineering of ZIF-7 electrode using ion beam technology for better supercapacitor performance

In the study, ZIF-7 material was exposed to 500 keV copper (Cu++) ions at dosages of 1 × 1014, 1 × 1015, and 5 × 1014 ions/cm2. The ZIF-7 unirradiated reveals a polycrystalline with an intense peak at 16.231° with a crystal plane of (012). The intensity of the peak in the XRD pattern broadens as the radiation of copper ions increases. In the ZIF-7 FTIR, the CC stretching vibration of the benzene ring is visible at 1469 cm−1, and the hydroxy phenyl benzimidazole (bIm) ligand's CH bending vibration is visible at 740 cm−1. Irradiated ZIF-7 reveals CH bending at 758, 759, and 754 cm−1 from the bIm ligand and CC stretching at 1456, 1460, and 1457 cm−1. The CV plots showed redox peaks, demonstrating faradaic processes. The ZIF-7's unirradiated estimated specific capacitances at scan rates of 50, 40, 30, 20, and 10 mV/s are 156, 195, 260, 390, and 781 F/g. The estimated specific capacitance of the irradiated ZIF-7 material with copper ions of 1 × 1014 ions/cm2 is 185, 308, 462, and 925 F/g. The estimated specific capacitance for ZIF-7 with copper ions of 1 × 1015 and 5 × 1014 ions/cm2 are 187, 234, 468, 937, and 1200 F/g, and 300, 375, 500, 750, and 1200 F/g respectively. The unirradiated (ZIF-7) shows bandgap energy of 3.53 eV which is suitable for applications in gas separation, catalysis, and optoelectronics. The irradiated sample with 1 × 1014 ions/cm2, 1 × 1015 ions/cm2 and 5 × 1014 ions/cm2 revealed bandgap energy of 2.52 to 2.87 eV which is suitable energy storage application.

Mixed-matrix membranes based on semi-oxidation MXene modified g-C3N4 nanosheet for enhanced CO2 separation

While mixed matrix membranes (MMMs) containing two-dimensional (2D) layered materials (such as, GO, g-C3N4 and MXene, etc.) have revealed potential application prospects for gas separation applications, it still faces a serious challenge to enhance the performance of CO2 separation. Owing to the structural defects of g-C3N4 nanosheets produced during the exfoliation process, which has greatly reduced the gas selectivity. Herein, we describe the construction of g-C3N4-MXene/Pebax MMM composed by MXene modified the structural defects in g-C3N4 nanosheets to surmount the low gas selectivity of g-C3N4 membrane. However, the stacking of nanosheets on each other hinder the gas transport channels. The TiO2 nanoparticles derived in-situ from MXene semi-oxidation can support an intermediate layer between g-C3N4 nanosheet and MXene nanosheet to expand the gas transport channels. Eventually, a novel g-C3N4-TiO2@MXene/Pebax MMM was obtained that exhibited maximum CO2 permeability of 1673.69 Barrer in separation of CO2/CH4, CO2/N2 selectivity of 45.13, and CO2/CH4 selectivity of 47.76, exceeding the bond 2008 limit on Robeson. What's more, the MMM within 100 h (1 bar and 298 K) are measured to have outstanding separation performance. Overall, this concept offers a novel strategy to enhance CO2 separation by MXene modified defects in g-C3N4 nanosheets.

Enhanced gas separation performance for H2 purification using MIL-68(ln)-nh2/PES mixed-matrix membranes

The growing demand for sustainable and efficient gas separation technologies has prompted the exploration of advanced materials to enhance the gas permeability and selectivity. Polyethersulfone (PES) membranes are widely used in gas separation, gas upgrading, and clean energy production owing to their environmental friendliness and low cost. However, their gas permeability and selectivity can be further improved for commercial application. This study explored the incorporation of 10 wt % of MIL-68(ln)-NH2 into PES membranes using a phase-inversion approach to enhance gas permeability and selectivity. The morphological, structural, and thermal properties of the resulting MOF/PES membrane were characterized using SEM, AFM, BET, XRD, FTIR, and TGA-DTG. Gas permeation experiments were conducted using different gases (CO2, N2, CH4, and H2) under different heating conditions (20–60 °C) to evaluate the gas permeability and selectivity of the MOF/PES membrane. The results showed that the incorporation of MOF into the mixed matrix membrane (MMMs) led to a 9% increase in porosity, 87% reduction in roughness, and 32% decrease in pore size compared to neat PES membranes. Significant changes in the morphology, crystallinity, and thermal stability were observed, with notable improvements of up to 22%. Moreover, the MOF/PES membrane exhibited high gas permeability (CO2 = 124656, N2 = 83650, CH4 = 159298, and H2 = 427075 Barrer) and selectivity (H2/N2 = 5.7, H2/CO2 = 4, CH4/N2 = 2, and CH4/CO2 = 1.7) for flammable gases. The optimal gas separation performance was observed at 20 °C and 60 °C for H2/N2 and H2/CO2 separation, respectively. These findings demonstrate the potential of MOF-based PES membranes for gas separation applications, particularly in H2 purification.

Pd(OAc)2/P–COF: A phosphine-based COF supported palladium-salt heterogeneous catalyst for Suzuki-Miyaura coupling reactions at ambient conditions

A new type of phosphine covalent organic frameworks (P-COFs) has garnered interest because of their high specific surface area and good thermal stability. These microporous materials have potential applications in gas storage, separation, heterogeneous catalysis, and other fields. Here, we present a heterogeneous catalyst consisting of a phosphine-based COF supported by palladium salt (Pd(OAc)2/P-COF) for Suzuki-Miyaura coupling reactions. The electron-rich heteroatoms (P, N) can securely anchor the active component (Pd) within the walls of P–COF. This catalyst exhibits excellent catalytic activity and cyclic stability. The coupling yield of phenylboronic acid and chlorobenzene with low activity reaches 100 % at room temperature for 3 h. After five cycles, the coupling yield of bromobenzene and phenylboronic acid remains above 93 %.

A Short Review of Advances in MOF Glass Membranes for Gas Adsorption and Separation.

The phenomenon of melting in metal-organic frameworks (MOFs) has recently garnered attention. Crystalline MOF materials can be transformed into an amorphous glassy state through melt-quenching treatment. The resulting MOF glass structure eliminates grain boundaries and retains short-range order while exhibiting long-range disorder. Based on these properties, it emerges as a promising candidate for high-performance separation membranes. MOF glass membranes exhibit permanent and accessible porosity, allowing for selective adsorption of different gas species. This review summarizes the melting mechanism of MOFs and explores the impact of ligands and metal ions on glassy MOFs. Additionally, it presents an analysis of the diverse classes of MOF glass composites, outlining their structures and properties, which are conducive to gas adsorption and separation. The absence of inter-crystalline defects in the structures, coupled with their distinctive mechanical properties, renders them highly promising for industrial gas separation applications. Furthermore, this review provides a summary of recent research on MOF glass composite membranes for gas adsorption and separation. It also addresses the challenges associated with membrane production and suggests future research directions.

Gas-Triggered Gate-Opening in a Flexible Three-Dimensional Covalent Organic Framework.

The development of novel soft porous crystals (SPCs) that can be transformed from nonporous to porous crystals is significant because of their promising applications in gas storage and separation. Herein, we systematically investigated for the first time the gas-triggered gate-opening behavior of three-dimensional covalent organic frameworks (3D COFs) with flexible building blocks. FCOF-5, a 3D COF containing C-O single bonds in the backbone, exhibits a unique "S-shaped" isotherm for various gases, such as CO2, C2, and C3 hydrocarbons. According to in situ characterization, FCOF-5 undergoes a pressure-induced closed-to-open structural transition due to the rotation of flexible C-O single bonds in the framework. Furthermore, the gated hysteretic sorption property of FCOF-5 can enable its use as an absorbent for the efficient removal of C3H4 from C3H4/C3H6 mixtures. Therefore, 3D COFs synthesized from flexible building blocks represent a new type of SPC with gate-opening characteristics. This study will strongly inspire us to design other 3D COF-based SPCs for interesting applications in the future.

Efficient Selective Carbon Dioxide Separation via Task-Specific Ionic Liquids Incorporated in ZIF-8.

Owing to the rapid increase in anthropogenic emission of carbon dioxide (CO2) in the atmosphere, which has resulted in a number of global climate challenges, a decrease in CO2 emissions is urgently needed in the current scenario. This study focuses on the development and characterization of composites for carbon dioxide (CO2) separation. The composites consist of two task-specific ionic liquids (TSILs), namely, tetramethylgunidinium imidazole [TMGHIM] and tetramethylgunidinium phenol [TMGHPhO], impregnated in ZIF-8. The performance of CO2 separation, including sorption capacity and selectivity, was evaluated for pristine ZIF-8 and composites of TMGHIM@ZIF-8 and TMGHPhO@ZIF-8. To demonstrate the thermal stability of the material, thermogravimetric analysis (TGA) was performed. Additionally, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to showcase the crystal structures and morphology. Fourier transform infrared spectroscopy (FTIR) and BET were also utilized to confirm the successful incorporation of TSILs into ZIF-8. The composite synthesized with TMGHIM@ZIF-8 demonstrated superior CO2 sorption performance as compared with TMGHPhO@ZIF-8. This is attributed to its strong attraction toward CO2, resulting in a higher CO2/CH4 selectivity of 110 while pristine MOFs showed 12 that is 9 times higher than that of the pristine ZIF-8. These TSILs@ZIF-8 composites have significant potential in designing sorbent materials for efficient acid gas separation applications.

On the Diffusion of Ionic Liquids in ILs@ZIF-8 Composite Materials: A Density Functional Theory Study.

Recently, composite materials consisting of ionic liquids (ILs) and metal-organic frameworks (MOFs) have attracted a great deal of attention due to their fantastic properties. Many theoretical studies have been performed on their special structures and gas separation applications. Yet, the mechanism for the diffusion of ILs inside MOF channels still remains unclear. Here, the DFT calculations (e.g., rigid and relaxed potential energy surface, PES, scan) together with frontier orbital analysis, natural charge analysis, and energy decomposition analysis were performed to investigate the diffusion behavior of a typical IL, [C4mim][PF6], into the ZIF-8 SOD cage. The PES profiles indicate that it is quite difficult for the cation [C4min]+ to diffuse into the cage of ZIF-8 through the pristine pores because of the large imidazole steric hindrance, which results in a large energy barrier of ca. 40 kcal·mol-1 at the least. Interestingly, the PES reveals that a successful diffusion could be obtained by thermal contributions, which enlarge the pore size through swing effects at higher temperatures. For example, both [C4mim]+ and [PF6]- could easily diffuse through the channel of the ZIF-8 SOD cage when the pore size was increased to 6.9 Å. Subsequently, electronic structure analyses reveal that the main interactions between [PF6]- or [C4mim]+ and ZIF-8 are the steric repulsion interactions. Finally, the effects of the amounts of [C4mim][PF6] on the ZIF-8 structures were investigated, and the results show that two pairs of [C4mim][PF6] per SOD cage are the most stable in terms of the interaction between energies and structural changes. With these findings, we propose that the high-temperature technique could be employed during the synthesis of IL@MOF membranes, to enrich their family members and their industrial applications.

Tuning the assembly of MgNiO2 nanoparticles-infused polysulfone membranes for efficient gas separation: The selectivity-permeability conundrum

The persistent surge in global energy demand, coupled with escalating environmental apprehensions, has underscored the imperative for adept and sustainable gas separation technologies. Mixed matrix membranes (MMMs) have surfaced as a promising avenue to confront these multifaceted challenges, synergistically harnessing the strengths of conventional polymeric membranes and nanoparticle reinforcements. In this work, MMMs have been tailored for gas separation applications by incorporating MgNiO2 nanoparticles as an additive into the polysulfone (PSf) matrix as they provide additional space (in the form of nanoscale voids) for gas diffusion, facilitating faster gas transport, promoting selective permeation of specific gases, and enhancing membrane stability, in addition to their versatility, ease of preparation, cost-effectiveness and high activity. The crystalline nature of MgNiO2 nanoparticles, as characterized by finely tuned grain sizes, has been validated by powder X-ray diffraction (XRD) analysis. Gas permeation experiments on the developed MMMs encompassing a diverse range of pure gases and gas mixtures have been performed. Among the different MMMs investigated, PSM1 with a composition of 100 mg MgNiO2 nanoparticles has yielded substantial enhancements in permeability and selectivity. The PSM1 membrane exhibits remarkable permeance of 56.9 for H2, 16.3 for CH4, and 15 GPU for CO2, having ideal selectivity ratios of 3.5 and 3.8 for H2/CH4 and H2/CO2, respectively. Finally, this work provides new directions for improving the trade of relationship between the selectivity and permeability of gas mixtures under relevant process conditions.

Application of Graphene-Based Derived Rice Husk Waste for Membrane Gas Separation Technologies: A Comprehensive Review

This study intends to comprehensively evaluate the application of graphene-based nanofillers obtained from rice husk waste in the field of membrane gas separation technologies. Graphene, owing to its distinctive structural characteristics, has emerged as a highly promising filler material for membrane fabrication in gas separation applications. This comprehensive review provides an in-depth evaluation of the diverse synthesis methods employed and the resulting properties of graphene obtained from rice husk waste materials, with an inclusive chemical mechanism of graphene formation from rice husk waste. Furthermore, this study reveals the inherent capabilities of graphene in enhancing the performance of membranes while also examining the influence of nanofillers on solubility selectivity. In conclusion, it is imperative to underline the need for additional research and development activities aimed at expanding the efficiency and scalability of the membrane fabrication process through the utilization of graphene nanofillers derived from rice husk waste.

Tunable Gas Admission via a "Molecular Trapdoor" Mechanism in a Flexible Cationic Metal-Organic Framework Featuring 1D Channels.

Achieving high gas selectivity is challenging when dealing with gas pairs of similar size and physiochemical properties. The "molecular trapdoor" mechanism discovered in zeolites holds promise for highly selective gas adsorption separation but faces limitations like constrained pore volume and slow adsorption kinetics. To address these challenges, for the first time, a flexible metal-organic framework (MOF) featuring 1D channels and functioning as a "molecular trapdoor" material is intoduced. Extra-framework anions act as "gate-keeping" groups at the narrowest points of channels, permitting gas admissions via gate opening induced by thermal/pressure stimuli and guest interactions. Different guest molecules induce varied energy barriers for anion movement, enabling gas separation based on distinct threshold temperatures for gas admission. The flexible framework of Pytpy MOFs, featuring swelling structure with rotatable pyridine rings, facilitates faster gas adsorption than zeolite. Analyzing anion properties of Pytpy MOFs reveals a guiding principle for selecting anions to tailor threshold gas admission. This study not only overcomes the kinetic limitations related to gas admission in the "molecular trapdoor" zeolites but also underscores the potential of developing MOFs as molecular trapdoor adsorbents, providing valuable insights for designing ionic MOFs tailored to diverse gas separation applications.

A semi-rigid co-poly(imide) derived from an isomeric mixture of monomers. Assessing gas transport properties in self-standing polymer membrane

Chemical structure and morphology of polymers are directly related with the membrane separation performance. Poly(imide)s (PIs) are the most widely used polymers in the preparation of membranes for gas separation applications; thus, research on the structural design of polymers is of great interest to develop new membranes. In the present work, we reported the synthesis, characterization, and measurement of the gas transport properties of a new co-poly(imide)s (PI-D2a-D2b-6FDA) prepared from a mixture of isomeric diamines. The co-poly(imide) synthetic route involved several steps, starting by a bromination reaction, followed by a double nucleophilic aromatic substitution giving an isomeric mixture of precursors, which suffered a Suzuki-Miyaura C–C cross-coupling reaction followed by the reduction of nitro groups to give two new isomeric diamines. Finally, diamines simultaneously reacted with the dianhydride 6FDA to obtain PI-D2a-D2b-6FDA. The co-poly(imide) had a Mn of 47.7 kDa and a Mw of 74.0 kDa with a PDI of 1.6. The sample exhibited a 10% weight loss at 540 °C, Tg of 280 °C, BET surface area of 110 m2 g−1, and wide-angle X-ray diffraction (WAXD) interchain d-spacing at 9.5 Å and 6.3 Å. Tensile strength, elongation at break and Young's modulus were 109.6 MPa, 6.66% and 2.18 GPa, respectively. co-Poly(imide) was soluble in various polar aprotic organic solvents such as DMSO, NMP, DMF, DMAc, THF, and chloroform, forming a self-standing dense film whose gas transport properties were measured. Pure gas permeability coefficients for H2, CO2, O2, N2, and CH4, were 47.28, 24.04, 4.35, 1.02, and 0.76 (Barrer), respectively, which follows a decreasing order by the increasing kinetic diameters of the respective gases. Ideal gas selectivities H2/N2, O2/N2, CO2/CH4, and CO2/N2 were 46.4, 4.3, 31.6, and 23.6, respectively. These gas transport properties were compared with the commercial polymer Matrimid®, showing higher gas permeability coefficients than Matrimid®.

Modulated synthesis of stoichiometric and sub-stoichiometric two-dimensional covalent organic frameworks for enhanced ethylene purification

Controlled synthesis of two-dimensional covalent organic frameworks (2D COFs), including stoichiometric and sub-stoichiometric variations, is a topic of growing interest due to its potential in gas separation applications. In this study, we successfully synthesized three distinct 2D COFs by carefully adjusting solvent compositions and monomer ratios during the synthesis of [4 + 4] type COFs. These included a stoichiometric [4 + 4] type COF and two sub-stoichiometric [4 + 2] type COFs, featuring unreacted amino or formyl groups. The resulting COFs exhibit different gas adsorption and separation properties. Specifically, sub-stoichiometric COF-DA with residual amino groups shows comparable adsorption capacity for C2H2, C2H4, and CO2 to stoichiometric COF-DAPy. In contrast, sub-stoichiometric COF-Py with residual formyl groups displays enhanced adsorption selectivity for C2H2/C2H4 and C2H2/CO2 separation, with the C2H2/C2H4 selectivity being the highest among reported COFs, attributed to increased pore polarity resulting from the presence of formyl groups. This study not only offers an additional example of sub-stoichiometric COF synthesis but also advocates for further exploration of sub-stoichiometric COF materials, particularly in the field of gas adsorption and separation.

Visible light-mediated supramolecular framework for tunable CO2 adsorption

In the pursuit of creating azobenzene-functionalized photo-responsive supramolecular frameworks (PSMFs) activated by the visible spectrum, an endeavor traditionally relied on ultraviolet activation, we report the successful fabrication of a visible light-mediated metal–organic cage-based PSMF, designated as NUT-104. This achievement was realized by the hierarchical self-assembly process of Zr-metal–organic cages featuring ortho-fluoroazobenzene functional terephthalic acid and tri-nuclear Zr-clusters. NUT-104 displays permanent porosity coupled with reversible responsiveness to visible light. This remarkable behavior emerges as a consequence of the σ-electron-withdrawing effect induced by the presence of fluorine substituents. Visible light-regulated CO2 adsorption capacity can be achieved and the change value can reach 61 %, while the change for CH4 and N2 is only 7 % and 3 %, respectively. In response to irradiation at wavelengths of 520 and 420 nm, respectively, the azobenzene moieties within the NUT-104 structure exhibit a remarkable capacity for visible light-controlled reversible conformational changes. Grand Canonical Monte Carlo simulations unveiled that the dynamic reorganization of the NUT-104 proficiently governs the accessibility of CO2 adsorption sites positioned within the interstitial regions of proximate cages. The advent of NUT-104, underpinned by its visible light responsiveness and versatile tunability, paves the way for avenues of exploration in controlled gas separation and storage applications.

ZeoSyn: A Comprehensive Zeolite Synthesis Dataset Enabling Machine-Learning Rationalization of Hydrothermal Parameters.

Zeolites, nanoporous aluminosilicates with well-defined porous structures, are versatile materials with applications in catalysis, gas separation, and ion exchange. Hydrothermal synthesis is widely used for zeolite production, offering control over composition, crystallinity, and pore size. However, the intricate interplay of synthesis parameters necessitates a comprehensive understanding of synthesis-structure relationships to optimize the synthesis process. Hitherto, public zeolite synthesis databases only contain a subset of parameters and are small in scale, comprising up to a few thousand synthesis routes. We present ZeoSyn, a dataset of 23,961 zeolite hydrothermal synthesis routes, encompassing 233 zeolite topologies and 921 organic structure-directing agents (OSDAs). Each synthesis route comprises comprehensive synthesis parameters: 1) gel composition, 2) reaction conditions, 3) OSDAs, and 4) zeolite products. Using ZeoSyn, we develop a machine learning classifier to predict the resultant zeolite given a synthesis route with >70% accuracy. We employ SHapley Additive exPlanations (SHAP) to uncover key synthesis parameters for >200 zeolite frameworks. We introduce an aggregation approach to extend SHAP to all building units. We demonstrate applications of this approach to phase-selective and intergrowth synthesis. This comprehensive analysis illuminates the synthesis parameters pivotal in driving zeolite crystallization, offering the potential to guide the synthesis of desired zeolites. The dataset is available at https://github.com/eltonpan/zeosyn_dataset.

Predicting Spin-Dependent Phonon Band Structures of HKUST-1 Using Density Functional Theory and Machine-Learned Interatomic Potentials.

The present study focuses on the spin-dependent vibrational properties of HKUST-1, a metal-organic framework with potential applications in gas storage and separation. Employing density functional theory (DFT), we explore the consequences of spin couplings in the copper paddle wheels (as the secondary building units of HKUST-1) on the material's vibrational properties. By systematically screening the impact of the spin state on the phonon bands and densities of states in the various frequency regions, we identify asymmetric -COO- stretching vibrations as being most affected by different types of magnetic couplings. Notably, we also show that the DFT-derived insights can be quantitatively reproduced employing suitably parametrized, state-of-the-art machine-learned classical potentials with root-mean-square deviations from the DFT results between 3 cm-1 and 7 cm-1. This demonstrates the potential of machine-learned classical force fields for predicting the spin-dependent properties of complex materials, even when explicitly considering spins only for the generation of the reference data used in the force-field parametrization process.