Pore size regulation of ZIFs for adsorptive separation of branched chain and aromatic amino acids

This research endeavour aims to investigate the adsorptive separation of the branched chain (BCAA) and aromatic amino acids (AAA). Based on the different molecular sizes of BCAA and AAA, zeolitic imidazolate frameworks (ZIFs) with different pore structures were prepared by regulating the size of imidazole ligands. The structure and pore shape were characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction (XRD), scanning electron microscope (SEM), and BET surface area (BET). The results indicated the successful synthesis of ZIF-[Co(mIm) 2 ], ZIF-[Co(eIm) 2 ], and ZIF-[Co(pIm) 2 ] with pore size distribution of 7.821, 6.943, and 9.394 Å, and particle size of these ZIFs was approximately 4 μm. ZIF-[Co(eIm) 2 ] was chosen as the optimal ZIFs for the separation of BCAA and AAA. The adsorption experiment was evaluated in the respective single and binary systems. The corresponding data in a single system demonstrated that ZIF-[Co(eIm) 2 ] showed good adsorption performance for BCAA and poor for AAA. Furthermore, the adsorption behaviour under experimental conditions conformed well to the pseudo-second-order kinetic model and Langmuir isotherm. ZIF-[Co(eIm) 2 ] had great separation ability for BCAA/AAA in their binary system. Finally, regeneration studies further manifested that ZIF-[Co(eIm) 2 ] exhibited fine reusability performance with adsorption efficiencies still higher than 70% after five cycles. This study exhibits a novel path for the design of adsorbents for efficient separation of BCAA/AAA.