Electrochemical synthesis of 2D copper coordination-polymers: Layer-stacking deviation induced by the solvent and its effect on the adsorptive properties

Abstract

A 2D Cu-based Metal-Organic Framework (MOF), namely copper-terephthalate (Cu(1,4-BDC)), was successfully synthesized by electrochemical method for effective methylene blue (MB) sorption from aqueous solutions. The composition, morphology, and the presence of functional groups in the obtained material were verified by Fourier Transform Infrared spectroscopy (FTIR), Powder X-Ray Diffraction (PXRD), Thermal (TGA), and Elemental (EA) analysis, as well as Scanning Electron Microscopy (SEM). The effect of electrochemical parameters applied in the synthesis protocol (i.e., a potentiometric or amperometric mode) on the resulting product composition was evaluated. The electric current value was determined as a variable controlling the type of crystal structure present in the obtained MOF. A structure with open channels - CuBDC1 was favored under the current higher than 0.35 A conditions. In contrast, for the lower current values and upon the amperometric mode in the material, a CuBDC2 phase with DMF molecules occupying the grids of the layers was also present. The MB sorption studies were analyzed both with kinetic and equilibrium models. The obtained results showed the time evolution could be fitted with a pseudo-second-order model with the rate constant k2 equal to 0.047 g μmol−1 h−1. According to the Langmuir isotherm model, the maximum sorption capacity was determined as 76.63 μmol g−1. After MB sorption, the MOF material could be easily regenerated under mild conditions with good recyclability up to the four cycles (76.77%).