Structure-performance relationship of silane-grafted MIL-100(In) membranes for liquid organic hydrogen carrier separation

Eight silane coupling agents are grafted onto MIL-100(In) membranes for TOL/MCH pervaporation. • Cyclohexyl-configured silane with amine group enables superior TOL/MCH recognition. • Configurational effects maximize binding energy difference, boosting separation factor by 175%. • Two-stage process achieves flux of 402 g·m −2 ·h −1 and separation factor of 8.1. Hydrogen is recognized as a promising green energy carrier, yet its large-scale transportation remains a critical challenge. Toluene/methylcyclohexane (TOL/MCH) serves as a safe and cost-effective liquid organic hydrogen carrier (LOHC), but practical deployment is constrained by inefficient post-dehydrogenation separation. Membrane-based separation offers a potential solution; however, most existing membranes lack sufficient molecular discrimination capability for these two analogues. In this work, MIL-100(In), a metal-organic framework with intrinsic adsorption selectivity toward TOL and MCH, was selected as the membrane substrate. A series of silane coupling agents with and without amino functionality and varying molecular configurations were grafted onto the membrane surface. Remarkably, the three-dimensional saturated cyclohexyl configuration outperforms the planar phenyl group in molecular discrimination among the amino-bearing silanes, overturning the conventional preference for aromatic functionalities. As a result, the separation factor of the MIL-100(In) membrane is enhanced by 175% upon surface modification. Complementary molecular simulations reveal that the spatial configuration of the grafted silane governs the recognition behavior toward aromatic and cycloalkane molecules, as corroborated by binding energy analysis and the minimum intermolecular contact distances obtained from energy-minimized conformations. These findings provide a mechanistic basis for tailoring membrane surface chemistry toward efficient LOHC separation Download: Download high-res image (333KB) Download: Download full-size image