Experimental and Dft Study of Adsorption-Reduction Mechanism of Au(Iii) and Cr(Vi) by Β-Cyclodextrin/Polydopamine Coated Uio-66-Nh2 Magnetic Composites

Abstract

Herein, a magnetic metal-organic framework composite was constructed by loading CoFe2O4 nano-particles on β-CD-TEPA/PDA functionalized UiO-66-NH2 for Au(III)/Cr(VI) elimination. The effective synthesis and excellent structural performances of the target materials were proved by advanced characterization technology, and the introduction of β-CD-TEPA/PDA significantly enhanced adsorption-reduction efficiency of Au(III)/Cr(VI). Batch adsorption experiments showed that the water environmental conditions remarkably affected the removal process, while isotherm and kinetic adsorption demonstrated that the elimination process belonged to a uniform chemical adsorption. The maximum adsorption amounts of Au(III) (445.5 mg/g) were greater than that of Cr(VI) (96.2 mg/g), which was probably caused by the differences in the morphology and size of the two target ions. The synthesized adsorbents exhibited good adsorption selectivity for Au(III)/Cr(VI) in a mixed system, and it could easily be removed from the solution by a magnet. The spectroscopic evidence and DFT calculation revealed that Au(III)/Cr(VI) initially was bound with -NH2 andβ-CD-TEPA via electrostatic attraction and chelate action. Subsequently, Au(III) was readily reduced to Au(0) and Cr(VI) was converted into Cr(III) without additional reducing agents. Hence, this study opened up the possibility to expand the applications of MOFs materials for wastewater remediation.

Keywords: UiO-66-NH2, Adsorption, Reduction, Au (III), Cr(VI)