Network‐Nanostructured ZIF‐8 to Enable Percolation for Enhanced Gas Transport

Abstract

Membrane-based separations offer energy-efficient solutions for various applications, but commercial polymer membranes show limited performance and stability. Mixed-matrix membranes (MMMs), incorporating nanoporous inorganic materials in polymer matrices, have been of great interest to circumvent these polymer-specific issues. However, reaching the percolation threshold is crucial to leverage high-performing inorganic phases fully, yet the traditional sphere-like nanofillers require high loadings that easily result in agglomerations and non-selective defects. Here, a branch-shaped zeolitic imidazole framework-8 (ZIF-8) nanoparticle is synthesized where its unique morphology automatically interconnects, readily forming percolated networks within the polymer matrix at loadings as low as 20 wt.%. Because of the high surface-area-to-volume ratios of branched ZIF-8 (BZ), strong polymer-particle interactions suppress polymer chain dynamics and the rotation of the ZIF-8 ligand. This interphase confinement results in enhanced membrane stability and a smaller diffusion cut-off than traditional ZIF-8. With pre-connected diffusion pathways and confined ZIF pores, BZ MMMs significantly outperformed MMMs with sphere-like ZIF-8 for H 2 -based separations. Overall, the findings provide a novel approach to enhance filler effects in MMMs even at low loadings without any alignment, which can enable the development of advanced membranes in fields where percolation is desired, including separations, sensors, conductors, and batteries.

Removing Perfluoro Pollutants PFOA and PFOS by Two-Pronged Design of a Ni8-Pyrazolate Porous Framework

“…In spite of the insignificant adsorption of activated Ni L1 for N 2 (Figure S8), the activated samples of Ni L1 , Ni L1 -CCH, and Ni L1 -F all display typical type-I CO 2 adsorption isotherms at 195 K (Figure ), with BET surface areas of 185, 490, and 309 m 2 /g respectively, suggesting sustained porosity throughout the in situ deprotection as well as post-synthetic modification steps. The hysteresis between the adsorption/desorption curves suggests smaller pores blocking gas departure from the larger pore in the desorption cycle (aka the percolation effect). − The linker deficiency gives rise to larger pores, which are connected to small pores/apertures caused by the bulky side arms of Ni L1 and Ni L1 -F (cf. the less bulky side arms of Ni L1 -CCH and its correspondingly lesser hysteresis).…”

Conceptual and Practical Aspects of Metal–Organic Frameworks for Solid–Gas Reactions

“…The most challenging estimation, the effective diffusivity constant, can be determined using one of several experimental techniques, of which we will highlight a few. (1) Diffusion kinetics may be quantified using gas sorption gravimetric methods. , Assuming that the adsorbent particle has a spherical shape, at low time values t , the transient fraction uptake relates to the effective diffusivity constant as Q t Q t = ∞ = 6 R π D e t , where Q t is the quantity of sorbate adsorbed per mass of adsorbent at time t , Q t =∞ is the quantity of sorbate adsorbed per mass of adsorbent at equilibrium, R is the radius of the particle, and D e is the effective diffusivity constant. This equation generally holds well for transient fraction uptake values of Q t Q t = ∞ ≤ 0.6 .…”

“…(1) Diffusion kinetics may be quantified using gas sorption gravimetric methods. 33,34 Assuming that the adsorbent particle has a spherical shape, at low time values t, the transient fraction uptake relates to the effective diffusivity constant as…”

Hollow Heteropoly Acid-Functionalized ZIF Composite Membrane for Proton Exchange Membrane Fuel Cells

“…Metal–organic frameworks (MOFs), which are formed by bridging metal ions (or clusters) and organic ligands, have a well-defined crystalline structure, a high Brunauer–Emmett–Teller (BET) surface area, an adjustable pore aperture, tunable external morphology, chemical functionalization availability, and high chemical/thermal stability. − Functional MOFs have been incorporated into sulfonated polymer matrixes to enhance proton transfer through organic ligand functionalization (e.g., −SO 3 H or −NH 2 ) and efficiently manage water to prevent polymer chain swelling. , MOFs have also been used to immobilize HPAs with well-defined porous structures in order to use their strong acidity for catalytic applications. , In particular, HPAs can be simply functionalized into MOF nanoparticles using an imidazole intermediate, resulting in a high solid proton conductor that maintains the high BET surface area and water-insoluble properties of the MOF. , Synthesizing zeolitic imidazolate framework-67 (ZIF-67) requires a low-cost and facile method compared to other complicated MOF series. In addition, the ZIF-67 nanoparticles have been used for chemical functionalization to develop a core–shell nanostructure .…”