Tuning n-Alkane Adsorption on Mixed-Linker Zeolitic Imidazolate Framework-8-90 via Controllable Ligand Hybridization: Insight into the Confinement from an Energetics Perspective

Linker hybridization provides enormous tunability of structures and properties of zeolitic imidazolate frameworks (ZIFs). We synthesized hybrid ZIF-8-90 structures by using binary organic ligands and examined their compositional and structural evolution using multiple techniques including field emission scanning electron microscopy (FESEM), Raman, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), N-2 adsorption, and H-1 NMR analyses. Well-designed ligand compositions of ZIF structures contribute to the continuously switchable pore structures. The average micropore diameter shrinks from 0.72 to 0.65 nm, while the mesopore width monotonically increases from 2.18 to 3.29 nm as the carboxaldehyde-2-imidazole (OHC-IM) proportion rises from 0.31 for ZIF-8-90-S1 to 0.88 for ZIF-8-90-S5. An increase in framework polarity can lead to the strengthened guest-host interaction and therefore energetically exerts a positive effect on the adsorption affinity of n-hexane on hybrid ZIF-8- 90 structures. The highest n-hexane adsorption capacity is found on the ZIF-8-90-S4 sample (having OHC-IM proportion of 0.82). At a close OHC-IM proportion of 0.792, the simulation result exhibits the strongest guest-host interaction (with the largest van der Waals interaction energy).