Supplementary information files for An investigation into the adsorption mechanism of <i>n</i>-butanol by ZIF-8: a combined experimental and <i>ab</i> <i>initio</i> molecular dynamics approach

<p dir="ltr">© the authors, CC-BY 3.0</p><p dir="ltr">Supplementary files for article An investigation into the adsorption mechanism of <i>n</i>-butanol by ZIF-8: a combined experimental and <i>ab</i> <i>initio</i> molecular dynamics approach</p><p dir="ltr">The zeolitic imidazolate framework, ZIF-8, has been shown by experimental methods to have a maximum saturation adsorption capacity of 0.36 g g⁻¹ for <i>n</i>-butanol from aqueous solution, equivalent to a loading of 14 butanol molecules per unit cell or 7 molecules per sodalite β-cage. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the presence of hydrogen bonding between adsorbed butanol molecules within the cage; the presence of three different O–H stretching modes indicates the formation of butanol clusters of varying size. <i>Ab initio</i> molecular dynamics simulations show the formation of intermolecular hydrogen bonding between the butanol molecules, with an average hydrogen-bond coordination number of 0.9 after 15 ps simulation time. The simulations also uniquely demonstrate the presence of weaker interactions between the alcohol O–H group and the π-orbital of the imidazole ring on the internal surface of the cage during early stages of adsorption. The calculated adsorption energy per butanol molecule is −33.7 kJ mol⁻¹, confirming that the butanol is only weakly bound, driven primarily by the hydrogen bonding. Solid-state MAS NMR spectra suggest that the adsorbed butanol molecules possess a reasonable degree of mobility in their adsorbed state, rather than being rigidly held in specific sites. 2D ¹³C–¹H heteronuclear correlation (HETCOR) experiments show interactions between the butanol aliphatic chain and the ZIF-8 framework experimentally, suggesting that O–H interactions with the π-orbital are only short lived. The insight gained from these results will allow the design of more efficient ways of recovering and isolating n-butanol, an important biofuel, from low-concentration solutions.</p>