Preparation of metal organic framework materials with defects via a mixed-metallic centers strategy for enhanced removal of organic dye

Abstract

Metal organic framework (MOF) materials display intriguing potential in wastewater treatment applications. In this study, a series of mixed MOF materials with several defects were designed and prepared via a strategy of mixed-metallic centers and the reaction process was lasted for only several hours at room temperature with water as environmental-friendly reaction medium. The MOF materials were characterized by Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and were employed to enrich organic dyes from aqueous solution with methyl orange (MO) and methylene blue (MB) as model molecules. Several factors influencing adsorption efficiency such as contact time, initial concentration, pH of dye solution and ionic strength were systematically explored. Due to the difference of structure and charge of MO and MB, the adsorption behaviors of the materials for both model dyes were obviously different from each other. The results showed that the adsorption process could be better described by pseudo-second-order kinetics and Freundlich isotherm model. The adsorption capacity of mixed MOF material with the ratio of Co2+ and Ni2+ of 1:1 for MO was 380.91 mg/g, much higher than those of MOF materials with single metallic center (255.15 mg/g of the material with Co2+ and 176.65 mg/g of the material with Ni2+), indicating the advantages of the preparation strategy and defects of the mixed MOF material produced in the preparation process in the adsorption field. However, the adsorption capacities of the prepared MOF materials for MB were close to each other. Furthermore, it would be possible to achieve a highly selective adsorption of MO from the mixed aqueous solution of MO and MB through choosing the appropriate NaCl concentration. This study can provide a method of increasing the diversity and functionality of the MOF materials.