Hydrophobic Core–Shell ZIF-90@ZIF-71 Nanoparticles for Butanol-Water Separation

Separating alcohol from water using highly efficient adsorbents with exceptional flux and separation factors remains a significant challenge, garnering widespread interest in the field of biofuel production. In this study, we developed several nanoscale hydrophobic zeolitic imidazolate framework (ZIF) composites, including core–shell structures like ZIF-90@ZIF-8 and ZIF-90@ZIF-71, as well as polydimethylsiloxane (PDMS)-coated ZIFs (ZIF-8, ZIF-71, and ZIF-90), to separate tert-butanol from water. We assessed the external hydrophobicity of these materials by using water contact angle tests. Comprehensive characterization of the core–shell ZIF composites was conducted by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (NMR). ZIF-8 and ZIF-71 demonstrated hydrophobic properties, whereas ZIF-90 was found to be hydrophilic. Notably, ZIF-90 exhibited a significantly higher uptake capacity for tert-butanol compared with ZIF-71 and ZIF-8. Two-dimensional (2D) 1H–1H spin diffusion homonuclear correlation NMR was employed to distinguish in-pore and ex-pore water and tert-butanol in various core–shell ZIF composites. Additionally, 1H magic angle spinning (MAS) NMR experiments were conducted to determine the separation factor of tert-butanol/water mixtures and the uptake capacity of tert-butanol. Our solid-state NMR measurements revealed that the core–shell ZIF-90@ZIF-71 composite exhibited outstanding separation selectivity exceeding 500 for tert-butanol/water mixtures and a superior uptake capacity of 1.14 mmol/g for tert-butanol among the tested ZIF composites. The combination of a hydrophilic core and a hydrophobic shell in ZIF-90@ZIF-71 enhances the separation efficiency of tert-butanol from water.