ZIF-8 membranes supported on silicalite-seeded substrates for propylene/propane separation

Asymmetric Pore Windows in Pillar-Layered Metal-Organic Framework Membranes for H2/CO2 Separation

In this study, a novel ultramicroporous pillar-layered Ni-LAP-NH2 [Ni2(l-asp)2(Pz-NH2)] (l-asp = l-aspartic acid, Pz-NH2 = aminopyrazine) membranes on porous α-Al2O3 tubes with high performance and good thermal stability was first fabricated using isostructural Ni-LAP[Ni2(l-asp)2(Pz)] (Pz = pyrazine) crystals as seeds. Utilizing the principle of reticular chemistry, here, we introduced the active amino side group into the Ni-LAP frameworks by replacing the pillar-layered ligand Pz with Pz -NH2 while maintaining the original Ni-LAP small pore size, and the amino side group induced a "steric hindrance" effect and the physical adsorption affinity, which synergistically delayed CO2 penetration. It was found that the preferential (111) orientation Ni-LAP-NH2 membrane (Z10) exhibited a high H2/CO2 separation performance with a separation factor of 41.7 and H2 permeance of 9.08 × 10-8 mol·m-2·s-1·Pa-1 under optimal conditions. These MOF materials demonstrated potential for industrial H2 purification due to their tunable pore structure and remarkable stability. Moreover, this strategy offers an effective approach to tailoring pillar-layered MOF membranes with targeted molecular sieving ability.

Bimetallic NiCo@C with a Hollow Sea Urchin Structure Enables Li-S Batteries to Hasten the Reaction Kinetics and Effectively Inhibit the Shuttling of Polysulfides

The "shuttle effect" and several issues related to it are seen as "obstacles" to the study and development of lithium-sulfur batteries (LSBs). This work aims at finding how to fully expose bimetallic sites and quicken the battery reaction kinetics. Here, a bimetallic NiCo-MOF and its derivative NiCo@C with a hollow sea urchin structure are produced. The obtained NiCo@C possesses a micromesoporous structure and fully disclosed bimetallic active sites because of its distinctive structure. The experimental findings demonstrate that fully exposed bimetallic active sites take on chemical adsorbents and collaborate with micromesopores as physical constraints to effectively suppress the "shuttle effect". Furthermore, the hollow sea urchin structure of NiCo@C enables a highly conductive grid, which provides channels to facilitate the movement of solvated Li+. Thanks to these advantages, the NiCo@C-based sulfur cathode offers a high initial discharge specific capacity of 924.41 mAh g-1 at 0.1 C and sustains 390.35 mAh g-1 discharge specific capacity after 100 cycles. The quick transfer of solvated lithium ions (DLi+ = 1.81 × 10-8 cm2 s-1) enables the battery to still contribute a discharge specific capacity of 367.54 mAh g-1 at 1 C. This work provides a new understanding for the structural design of positive electrodes in LSBs.

Engineering Oxygen Vacancies of Co-Mn-Ni-Fe-Al High-Entropy Spinel Oxides by Adjusting Co Content for Enhanced Catalytic Combustion of Propane

Transition metal-based oxides with similar oxidation activities for catalytic hydrocarbon combustion have attracted much attention. In this study, a new class of metal high-entropy oxides (CoxMnNiFeAl)3O4 (x = 1, 2, 3, 4, 5) with a porous structure was fabricated through a simple and inexpensive NaCl template-assisted sol-gel approach, which was employed for the catalytic oxidation of propane. The results indicated that the content of cobalt has a great impact on its activity, and the (Co4MnNiFeAl)3O4 catalyst exhibited the best catalytic activity. At the high space velocity of 60 000 mL·g-1·h-1, the optimized one with high-temperature treatment can still achieve 90% propane conversion at 309 °C, which is 68 and 178 °C lower than those of the (CoMnNiFeAl)3O4 catalyst and pure cobalt oxide, respectively. Meanwhile, it has the lowest apparent activation energy (46.6 KJ·mol-1) and the fastest reaction rate (26.976 × 10-6 mol·gcat-1·s-1 at 290 °C). The improved performance of the (Co4MnNiFeAl)3O4 catalyst could be attributed to the enhancement of low-temperature reducibility, the increased number of reactive surface oxygen species, and the cocktail effect of the high-entropy oxides. This work provides new insights into the preparation of efficient light alkane degradation catalysts and a realistic approach for the large-scale application of high-entropy oxides in the field of oxidation catalysts.

Fabrication of Polycrystalline Zeolitic Imidazolate Framework Membranes by a Vapor-Phase Seeding Method

The reliable fabrication of polycrystalline zeolitic imidazolate framework (ZIF) membranes continues to pose challenges for their industrial applications. Here, we present a vapor-phase seeding approach that integrates atomic layer deposition (ALD) with ligand vapor treatment to synthesize ZIF membranes with high propylene/propane separation performance. This method began with depositing a ZnO coating onto the support surface via ALD. The support underwent treatment with 2-methylimidazole vapor to transform ZnO to ZIF-8, forming the seed layer. Subsequent secondary growth was employed at near-room temperature, allowing the seeds to grow into a continuous membrane. ZIF-8 membranes made on macroporous ceramic support by this method consistently demonstrated propylene permeances above 1 × 10-8 mol Pa-1 m-2 s-1 and a propylene/propane separation factor exceeding 50. Moreover, we demonstrated the effectiveness of the vapor-phase seeding method in producing the ZIF-67 membrane.

Preparation and Lithium-Ion Separation Property of ZIF-8 Membrane with Excellent Flexibility

Metal-organic framework (MOF) membranes exhibit immense potential for separation applications due to their regular pore channels and scalable pore sizes. However, structuring a flexible and high-quality MOF membrane remains a challenge due to its brittleness, which severely restricts its practical application. This paper presents a simple and effective method in which continuous, uniform, defect-free ZIF-8 film layers of tunable thickness are constructed on the surface of inert microporous polypropylene membranes (MPPM). To provide heterogeneous nucleation sites for ZIF-8 growth, an extensive amount of hydroxyl and amine groups were introduced on the MPPM surface using the dopamine-assisted co-deposition technique. Subsequently, ZIF-8 crystals were grown in-situ on the MPPM surface using the solvothermal method. The resultant ZIF-8/MPPM exhibited a lithium-ion permeation flux of 0.151 mol m^-2 h^-1 and a high selectivity of Li⁺/Na⁺ = 1.93, Li⁺/Mg²⁺ = 11.50. Notably, ZIF-8/MPPM has good flexibility, and the lithium-ion permeation flux and selectivity remain unchanged at a bending curvature of 348 m^-1. These excellent mechanical characteristics are crucial for the practical applications of MOF membranes.

XRD and Spectroscopic Investigations of ZIF-Microchannel Glass Plates Composites

In this study, new composite materials comprising zeolitic imidazolate framework (ZIF) structures and microchannel glass (MCG) plates were fabricated using the hydrothermal method and their morphological and spectral properties were investigated using XRD, SEM, FTIR, and Raman spectroscopy. XRD studies of powder samples revealed the presence of an additional phase for a ZIF-8 sample, whereas ZIF-67 samples, which were prepared through two different chemical routes, showed no additional phases. A detailed analysis of the FTIR and micro-Raman spectra of the composite samples revealed the formation of stable ZIF structures inside the macropores of the MCG substrate. The hydrophilic nature of the MCG substrate and its interaction with the ZIF structure resulted in the formation of stable ZIF-MCG composites. We believe that these composite materials may find a wide range of important applications in the field of sensors, molecular sieving.

Synthesis of ZIF-8 tubular membrane via solvent evaporation seeding coupled with microwave assisted heating method for separation of small molecule gases

In this work, we systematically study the performance of tubular ZIF-8 membranes in the separation of small molecules including H₂, CO₂, N₂ and CH_4. The tubular ZIF-8 membranes were synthesized on α-alumina support via novel dual approach known as solvent evaporation seeding coupled with microwave assisted growth. The durations for the growth of the seed layer through solvent evaporation and membrane layer via microwave heating were varied. The crystallinity and morphology of the resultant membranes were evaluated by using XRD, SEM and IFM analyses. The performance of the resultant tubular ZIF-8 membranes was assessed for small molecule gases permeation at various pressures and temperatures. Highest flux ranging from 0.02 to 0.61 mol/m²s were obtained for gases CO₂, CH₄, N₂, and H₂ at feed pressure of 10 bar, whereas highest ideal selectivity of 12.4, 9.3 and 6.9 were obtained for H₂/CH_4, CO₂/CH₄, N₂/CH₄, respectively, at feed pressure of 10 bar and temperature of 30 °C. This work reveals that the tubular ZIF-8 membrane can be synthesized via a feasible and reproducible solvent evaporation seeding coupled with microwave assisted growth method, which can be further explored for the upscaling of the ZIF-8 tubular membrane in pilot scale for gas separation application.

Metal organic frameworks (MOFs) as multifunctional nanoplatform for anticorrosion surfaces and coatings

Corrosion of metallic materials is a long-standing problem in many engineering fields. Various organic coatings have been widely applied in anticorrosion of metallic materials over the past decades. However, the protective performance of many organic coatings is limited due to the undesirable local failure of the coatings caused by micro-pores and cracks in the coating matrix. Recently, metal organic frameworks (MOFs)-based surfaces and coatings (MOFBSCs) have exhibited great potential in constructing protective materials on metallic substrates with efficient and durable anticorrosion performance. The tailorable porous structure, flexible composition, numerous active sites, and controllable release properties of MOFs make them an ideal platform for developing various protective functionalities, such as self-healing property, superhydrophobicity, and physical barrier against corrosion media. MOFs-based anticorrosion surfaces and coatings can be divided into two categories: the composite surfaces/coatings using MOFs-based passive/active nanofillers and the surfaces/coatings using MOFs as functional substrate support. In this work, the state-of-the-art fabrication strategies of the MOFBSCs are systematically reviewed. The anticorrosion mechanisms of MOFBSCs and functions of the MOFs in the coating matrix are discussed accordingly. Additionally, we highlight both traditional and emerging electrochemical techniques for probing protective performances and mechanisms of MOFBSCs. The remaining challenging issues and perspectives are also discussed.

Interactions of Ag Particles Stabilized by 7,7,8,8-Tetracyanoquinodimethane with Olefin Molecules in Poly(ether-block-amide)

In this study, to use a stabilized carrier, silver nanoparticles (AgNPs) were used as carriers and electron acceptors were added to activate the surface of AgNPs as olefin carriers. In addition, poly(ether-block-amide) (PEBAX), consisting of polyamide (hard segments) and polyether (soft segments), was investigated for the correlation of the between-segments ratio related to the stability of AgNPs and separation performance. As a result, contrary to the expectation that high permeance would be observed in PEBAX-1657/AgNPs/7,7,8,8-tetracyanoquinodimethane (TCNQ) membrane, which had a higher ratio of polyether soft segment, the PEBAX-5513/AgNPs/TCNQ membrane, which had a relatively high proportion of polyamide, showed a higher permeance without difference in selectivity. These unexpected data were attributable to the fact that the relatively abundant amount of PA groups in PEBAX-5513 was able to stabilize and positively polarize the surface of AgNPs, resulting in the stabilized and high performance of olefin separation.