Combining Structurally Ordered Intermetallic Nodes: Kinetic and Isothermal studies for Removal of Malachite Green and Methyl Orange with Mechanistic Aspects

Abstract The current research focus is to develop some systematic materials for the removal of hazardous dyes from water to save the aquatic environment. We have reported the in-situ growth of zeolitic imidazolate frameworks (ZIF-8) on zinc layered double hydroxide (ZnAl-LDH) and the developed porous composite material (ZIF-8@ZnAl-LDH) for adsorptive elimination of malachite green (MG) and methyl orange (MO) from water. The adsorption parameters and organic dyes removal efficiency of ZnAl-LDH, ZIF-8 and ZIF-8@ZnAl-LDH has been determined by considering factors such as dye concentration, time for adsorption and pH of dye solutions. Results showed that ZIF-8@ZnAl-LDH has good adsorption capacity (qmax, 194.5 mg. g−1) for MG as compared to ZnAl-LDH (60.6 mg. g−1) and ZIF-8 (155.27 mg. g−1). Furthermore, ZIF-8@ZnAl-LDH also showed good adsorption capacity (qmax, 609.7 mg. g−1) for methyl orange better than that of ZnAl-LDH (86.35 mg. g−1) and ZIF-8 (322.58 mg. g−1). Also, with 180 min contact time 98% MG and 96.9% MO was adsorbed by ZIF-8@ZnAl-LDH. The Langmuir adsorption isotherm model successfully clarified the process of adsorption as monolayer, with relatively high correlation coefficient of (R2 = 0.9988 of ZIF-8 and 0.9992 of ZIF-8@ZnAl-LDH) for MG and (R2 = 0.9973 of ZIF-8 and 0.9990 of ZIF-8@ZnAl-LDH) for MO. After four consecutive cycles ZIF-8@ZnAl-LDH exhibit 96.27% and 95.16% adsorption for malachite green and methyl orange respectively, of the original capacity of pristine ZIF-8@ZnAl-LDH. The best performance of adsorbents is due to the porous structure, greater superficial area for adsorption process and specific morphological inter-layered structure with exposed metallic nodes. The overall results indicate that the as-synthesized ZIF-8 and its composite ZIF-8@ZnAl-LDH are proficient for purification of water by removing dyes such as (MG & MO) from aqueous solutions.