In situ growth of MOF crystals to synthesize a graphene oxide/ZIF-7 gel with enhanced adsorption capacity for methylene blue

Abstract

A graphene oxide gel containing ZIF-7 (Z_x@GoG) was synthesized by immersing graphene oxide gel (GoG) in a DMF solution of Zn²⁺ and a DMF solution of organic ligands, respectively, and characterized by powder XRD, FT-IR spectroscopy, SEM, TEM, TGA, and BET. The growth of ZIF-7 crystals on GoG was controlled by the concentration of Zn²⁺ and benzimidazole. In particular, when the concentration of Zn²⁺ ranged from 0.05 to 0.067 mol L⁻¹ and the molar ratio of Zn²⁺ to benzimidazole was kept at 4 : 25, ZIF-7 crystals were well grown on GoG and some ZIF-7 crystals were trapped in the networks of GoG. Particularly, with the increase in the concentration of Zn²⁺ and benzimidazole, the aggregation of ZIF-7 crystals on the surface of GoG was observed. The coordination of Zn²⁺ with both the oxygen-containing groups of GoG and benzimidazole played a major role in the in situ growth of ZIF-7 crystals on GoG. In addition, Z_x@GoG was explored to remove methylene blue (MB) from wastewater. Compared with GoG and the pure ZIF-7 crystals, the equilibrium adsorption capacity of Z_x@GoG for MB was increased by 156.78% and 72.29%, respectively. The result of the kinetic simulation indicated that the adsorption of Z_x@GoG for MB belonged to the chemical action.