Amorphous coordination polymers based on Cr and phenol for efficient and selective recovery of Au(III)

Abstract

The recovery of gold from secondary resources has significant implications for both the environment and the economy. In this paper, using four types of polyphenols including 4,4′-oxydiphenol, 4,4′-methylenebisphenol, 4,4′-thiodbisphenol, and 2,2′,4,4′-tetrahydroxybenzophenone as the organic ligand and Cr(NO3)3·9H2O as the metal center, four kinds of amorphous coordination polymers (aCPs), namely Cr-ODP, Cr-MBP, Cr-TDP, and Cr-TDBP were directly synthesized by solvothermal method. Each of the four aCPs exhibits remarkable selectivity and reusability for Au(III) adsorption. The adsorption processes of Au(III) adsorption by the four aCPs are spontaneous, endothermic and entropy increasing. All of the adsorption kinetics follows the pseudo-second-order model, and the adsorption isotherms fit well with Redlich-Peterson isotherm model. Cr-TDBP has faster adsorption rate than the other three aCPs, and only needs 8 min to completely adsorb Au(III) at 12 mg/L. The adsorption capacities of Cr-ODP, Cr-MBP, Cr-TDP and Cr-TDBP at 298 K are up to 1943 mg/g, 2015 mg/g, 1807 mg/g, and 2046 mg/g, respectively. At 328 K, the adsorption uptake of Cr-TDBP could be increased significantly to 3455 mg/g. The excellent adsorption performance of the four aCPs mainly are attributed to their abundant phenolic hydroxyl group, which could act as active sites for adsorbing Au(III) through a redox reaction.