Effect of zeolitic imidazole framework (ZIFs) shells of core-shell microspheres on adsorption of Roselle red dye from water

Due to the importance of food safety, natural edible pigments attract more and more attention. Because of the application of adsorption technology in the extraction and purification of natural edible pigments, it is necessary to develop a highly efficient adsorbent. In this paper, we prepared a series of core shell spherical adsorbents (CSS-ZIFs) having different types of zeolitic imidazolate frameworks (ZIF-67, ZIF-7, ZIF-8 and ZIF-9) nanoparticles as the shell on the resin microsphere as the core. The XRD、BET and SEM characterizations proved the core-shell structure of the CSS-ZIFs, and the adsorption performance of the CSS-ZIFs were further studied for removing a natural edible pigment (Roselle red) from water. The CSS-7 (ZIF-7 as the shell) showed the best removal rates of 95.3–97.7% mainly due to the strong π-π attraction and weak cation-cation repulsion between ZIFs and Roselle red molecules. This study demonstrates that novel CSS-ZIFs can be used as a kind of feasible adsorbents for Roselle red extraction and separation, and further applied to the adsorption separation of other natural active substances.