Heterointerface engineering of water stable ZIF-8@ZIF-67: Adsorption of rhodamine B from water

Elimination of toxic dye, one of the utmost and usual industrial pollution released in the natural water, is the very serious issue for the modern civilization. In this study, a novel bimetallic (ZIF-8@ZIF-67) zeolitic imidazolate frameworks (ZIFs) have been fabricated by a simple and straight forward technique at room temperature. So-dalite (SOD) cage type structure, morphology and porosity of synthesized bimetallic metal-organic frameworks (MOFs) were characterized by SEM, TEM, XRD and BET. The results of characterizations showed that the ZIF-8@ZIF-67 owns greater nano crystallinity, surface area and porosity. As compared to single metallic MOFs (ZIF-67 and ZIF-8), the physical and chemical properties of ZIF-8@ZIF-67 were improved. Accordingly, the ZIF-8@ZIF-67 potentially analysed for the exclusion of rhodamine B from water and the gained outcomes were compared with the efficiency of mono-metallic MOFs (ZIF-67 and ZIF-8). Several parameters, including initial dye concentrations, sonication time, and pH on dye removal efficiency were investigated. Additionally, Lang-muir, Freundlich, Tempkin and Dubinin-Radushkevich isotherm models were used to explain the process of adsorption onto the surface of MOFs. The results disclosed that the Langmuir model sufficiently explained the adsorption procedure as monolayer with higher R-2 values (R-2 = 0.9924, 0.9822 and 0.9909 of ZIF-67, ZIF-8 and ZIF-8@ZIF-67 respectively). The mean free energy (E) was observed to be 0.551, 0.576 and 0.532 KJ.mol-1 for ZIF-67, ZIF-8 and ZIF-8@ZIF-67, respectively, exposing that the chemisorption dominates the process of adsorption. The qmax premeditated with Langmuir model was comparatively high (143.26 mg.g(-1)) as compared to ZIF-8 (56.40 mg.g(-1)) and ZIF-67 (81.63 mg.g(-1)), accrediting to the intensification in active binding sites. Further, the reusability of bimetallic MOFs was tested for four regeneration cycles and results were outstanding with only 8 +/- 1% decrease in efficiency. It is assumed that, the fabricated ZIF-8@ZIF-67 composite have high applicability for the adsorption of toxic dyes from water.