Mechanical Control of the Kinetic Propylene/Propane Separation by Zeolitic Imidazolate Framework‐8

3D MOF Nanoarchitecture Membrane via Ultrafast Laser Nanoforging

Metal-organic framework (MOF) crystals are useful in a vast area of applications because of their unique chemical and physical properties. Manufacturing of an integrated MOF membrane with 3D nanoarchitectures on the surface is especially important for their applications. However, as MOF crystals usually exist as powdery crystals, fabrication of their large area, monolithic, and high-resolution patterns is challenging. Here, it is found that isolated MOF nanocrystals could be directly converted to a monolithic MOF film with designed 3D nanoarchitectures/patterns via an ultrafast laser induced nanoforging without binders. During the nanosecond laser shock, the voids among MOF nanocrystals are eliminated due to the surface amorphization effect, which allows the fusing of the MOF nanocrystals on the grain boundaries, leading to the formation of a dense film while preserving the nature of the pristine MOF. The high strain rate by laser enhances formability of MOFs and overcomes their brittleness to generate arbitrary 3D nanoarchitectures with feature sizes down to 100 nm and high productivity up to 80 cm² min^-1 . These 3D MOF nanoarchitectures also exhibit boosted mechanical strength up to 100% compared with their powdery particles. This method is facile and low-cost and could potentially be used in various fields, such as devices, separation, and biochemical applications.

Separation and Purification of Hydrocarbons with Porous Materials

This Minireview focuses on the developments of the adsorptive separation of methane/nitrogen, ethene/ethane, propene/propane mixtures as well as on the separation of C8 aromatics (i.e. xylene isomers) with a wide variety of materials, including carbonaceous materials, zeolites, metal-organic frameworks, and porous organic frameworks. Some recent important developments for these adsorptive separations are also highlighted. The advantages and disadvantages of each material category are discussed and guidelines for the design of improved materials are proposed. Furthermore, challenges and future developments of each material type and separation processes are discussed.

Pressure-Responsive Two-Dimensional Metal-Organic Framework Composite Membranes for CO2 Separation

The regulation of permeance and selectivity in membrane systems may allow effective relief of conventional energy-intensive separations. Here, pressure-responsive ultrathin membranes (≈100 nm) fabricated by compositing flexible two-dimensional metal-organic framework nanosheets (MONs) with graphene oxide nanosheets for CO₂ separation are reported. By controlling the gas permeation direction to leverage the pressure-responsive phase transition of the MONs, CO₂ -induced gate opening and closing behaviors are observed in the resultant membranes, which are accompanied with the sharp increase of CO₂ permeance (from 173.8 to 1144 gas permeation units) as well as CO₂ /N₂ and CO₂ /CH₄ selectivities (from 4.1 to 22.8 and from 4 to 19.6, respectively). The flexible behaviors and separation mechanism are further elucidated by molecular dynamics simulations. This work establishes the relevance of structural transformation-based framework dynamics chemistry in smart membrane systems.

Connecting theory and simulation with experiment for the study of diffusion in nanoporous solids

Nanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems.

Tuning the Adsorption Selectivity of ZIF-8 by Amorphization

Amorphous metal-organic frameworks (a_m MOFs) with a partially collapsed structure are a new category of porous hybrid materials. Here, solid-state amorphization of ZIF-8 was achieved by mechanical compression at 0.75 GPa. The compression-induced amorphous ZIF-8 (a_m ZIF-8) had a collapsed structure, but retained partial porosity. Benefiting from the deformed channel, the resultant a_m ZIF-8 exhibited preferable adsorption of C₃ H₆ , resulting in higher thermodynamic adsorption selectivity of C₃ H₆ /C₃ H₈ (6.72) than the crystalline counterparts (1.06). Further, a_m ZIF-8 achieved complete separation of an equimolar C₃ H₆ /C₃ H₈ mixture with the first breakthrough of C₃ H₈ . a_m ZIF-8 also displayed an enhancement in CO₂ /N₂ and CO₂ /CH₄ adsorption selectivities. More importantly, a self-standing a_m ZIF-8 membrane with boundary-free microstructure was constructed for the first time, and exhibited separation potential for H₂ /CH₄ , CO₂ /N₂ , CO₂ /CH₄ , and C₃ H₆ /C₃ H₈ with ideal selectivities of 14.79, 12.83, 16.23, and 2.67, respectively.

Energy-efficient separation alternatives: metal–organic frameworks and membranes for hydrocarbon separation

The diversity of metal–organic frameworks enables the design of highly efficient adsorbents and membranes towards hydrocarbon separations for energy consumption mitigation.