Benign preparation of metal organic framework materials with different copper precursors and adsorption of organic dyes

Two different metal organic framework (MOF) materials with Cu2+ as metal center providing by copper nitrate and copper chloride (denoted as MOF-1 and MOF-2, accordingly) were facilely prepared with ethanol and water as reaction solvents at room temperature for several hours. FTIR, XRD, SEM, XPS and pore structures of the MOF materials were characterized to verify that types of copper precursors would affect the structures of the MOF materials, which would also influence the adsorption efficiencies for methyl orange (MO) and methylene blue (MB). The adsorption kinetics and isotherm studies established pseudo-second-order kinetics and Freundlich isotherm with good agreement according to the data. Solution pH greatly affected the adsorption process. Presence of NaCl enhanced the adsorption of MO while it hindered MB removal. The differences in adsorption behaviors of both MOF materials for MO and MB were ascribed to their different structures which may be due to the types of copper salts. The results showed that carboxyl group, aromatic ring and metal center contributed greatly to the removal of MO and MB from aqueous solution. Both MOF materials exhibited higher adsorption efficiencies for the dyes (238.26 mg/g for MO and 217.60 mg/g for MB of MOF-1, 277.02 mg/g for MO and 167.80 mg/g for MB for MOF-2), compared to several reported MOF related materials. This study indicated that the prepared MOF materials could be used as viable candidates to effectively remove MO and MB from aqueous solution.