External optimization of Zr-MOF with mercaptosuccinic acid for efficient recovery of gold from solution: Adsorption performance and DFT calculation

Abstract

A novel sulfhydryl-modified MOF (UiO-66-MSA) was prepared by externally optimizing UiO-66-NH2 with mercaptomalic acid (MSA) and its capacity in selective recovering of Au(III) from solution was examined. Tests indicated that external modification of UiO-66-NH2 by MSA increased its theoretical maximal adsorption capacity at pH 5 by 24.57% from 578.0 to 720.0 mg/g. Simulation of the kinetics data revealed that Au(III) binding on both UiO-66-MSA and UiO-66-NH2 followed the pseudo-second-order model, with the former material having significantly higher kinetics. In the existence of competing ions, Au(III) recovery by sulfydryl-modified UiO-66-NH2 (UiO-66-MSA) was increased from 72.06% to 98.59% at an initial Au(III) concentration of 56.9 mg/L. This material also had a fairly good reusability. At 5 times of regeneration, it was still able to capture 99.42% Au(III) from solution. Analysis of the changes in XPS patterns and the electrokinetic properties of UiO-66-MSA suggested that Au(III) binding on this MSA-modified MOF was complex. The electrostatic interaction, reduction and chelation may have all actively participated in the adsorption process. DFT calculation revealed that Au(III) binding was attributed to the -SH, -NH and C=O functional groups residing on the repeating unit of UiO-66-MSA, with its sulfhydryl functional group being the strongest binding site.