![]() The discovery of metal–organic frameworks (MOFs) in the late 1990s represents a major breakthrough in terms of rational design and molecularly defined tailoring of adsorbents to achieve specific functions 1. Consequently, the magnitude of NGA in terms of amount of gas expulsed and pressure amplification can be tuned, potentially paving the way towards innovative concepts for pressure amplification in micro- and macro-system engineering. In contrast, even the smallest particles show NGA in the presence of n-butane, however, associated with a significantly reduced pressure amplification. Below a critical crystal size, the nitrogen adsorption-induced breathing is completely suppressed as detected using parallelized synchrotron X-ray diffraction–adsorption instrumentation. Adsorbing probe molecules, such as n-butane or nitrogen, gives insights into size-dependent activation barriers and thermodynamics associated with guest-induced network contraction. ![]() Here, by systematically downsizing the crystal dimensions of a mesoporous MOF (DUT-49) from several micrometers to less than 200 nm, counterintuitive NGA phenomena are demonstrated to critically depend on the primary crystallite size. ![]() ![]() Negative gas adsorption (NGA) in ordered mesoporous solids is associated with giant contractive structural transitions traversing through metastable states. ![]()
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