Deep eutectic solvent-mediated, energy-efficient synthesis of copper terephthalate metal-organic framework and its application in degradation of an azo dye

Abstract

The flexible topology, high surface area, porous structure, and unsaturated metal sites of metal-organic frameworks (MOFs) renders them promising candidates for the remediation of organic pollutants. An environmentally benign, safe, and energy-efficient synthesis process of copper and benzene dicarboxylic acid-based MOF (Cu-BDC) in choline chloride/urea deep eutectic solvent (DES), a promising green solvent, is described. The present protocol for Cu-BDC synthesis conserved 97% of the energy input as compared to the traditional process. The MOF prepared was characterized following different spectrometric techniques such as Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), BET surface area, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The characterization is in good agreement with those of reported Cu-BDC MOF. The subsequent heterogeneous Fenton-like catalytic application of the Cu-BDC MOF in C.I. Acid orange 7 (AO-II) dye removal from water showed promising efficiency under mild reaction conditions. The effect of initial pH, catalyst loading, H2O2 concentration, and temperature on the catalyst performance was investigated. The best catalytic efficiency (99% dye degradation and 74% COD removal) was achieved for 20 mL of 30 mg/L of AO-II dye concentration for the condition of 5 mM H2O2, 0.05 g/L of Cu-BDC, pH = 6.8, and room temperature. Under optimum reaction conditions, the pseudo-first-order kinetics model was well fitted with the experimental data. The HRLC-MS analysis was performed to identify degradation products and a plausible degradation pathway. The Cu-BDC exhibits recyclability without much loss in its catalytic activity.