Synthesis of mixed-ligand Cu–MOFs and their adsorption of malachite green

Abstract

Different mixed-ligand MOFs with various ratios of Cu²⁺ and ligands (MOFs-1, MOFs-2, MOFs-3 and MOFs-4) were synthesized and characterized. The mixed-ligand MOFs-2 was the optimal adsorbent, as confirmed by studying the adsorption of malachite green (MG); the adsorption capacity of MOFs-2 for MG was calculated to be 185.4 mg g⁻¹. Based on a combination of surface and pore structure analysis, it was concluded that size match is more important than surface area for adsorption. Adsorption isotherms were acquired, and the results showed that the adsorption is a physical process that obeys the Freundlich model. The adsorption mechanisms were tested, and the results showed that the adsorption has pseudo-first-order kinetics. MOFs-2 was proven to be stable in water and suitable to be recycled for waste water treatments.