A novel bimetallic UiO-66 loofah sponge adsorbent prepared in situ for the efficient removal of methyl orange and Cr(VI): Batch experiments and DFT calculations

Abstract

The detrimental effects of azo dyes and heavy metal ions on human ecosystems remain an ongoing issue, and so the development of methods for their removal is a growing area of research. In this study, a Ce-UiO-66-NH₂@LS composite (LS = loofah sponge) with a multisite adsorption function was prepared by an in situ growth method. This combination of an LS carrier with a metal–organic framework (MOF) was found to effective in the removal of methyl orange (MO) and hexavalent chromium (Cr(VI)). At a low pH, the maximum adsorption amounts of MO and Cr(VI) were 930.58 and 282.77 mg/g, respectively, with 96.70 and 94.90 % removal being achieved under these conditions. In the presence of multiple anions, Ce-UiO-66-NH₂@LS demonstrated a strong anti-ion interference ability for the adsorption of MO and Cr(VI), and maintained a high adsorption performance in a mixed MO–Cr(VI) system. Four adsorption isotherms and kinetic models were used to evaluate the adsorption process, and it was deduced that chemisorption was the dominant process. The adsorption mechanism was further analyzed by X-ray photoelectron spectroscopy and using the density functional theory approach. Consequently, electronic interactions and coordination effects were found to be the main mechanisms of adsorption. Importantly, Ce-UiO-66-NH₂@LS exhibited a removal efficiency of > 80 % after four cycles of continuous reuse. This study therefore provides a feasible method for improving the recovery capacities and adsorption performances of MOFs.