Equilibrium, kinetics and mechanism of Au, Pd and Ag ions adsorption from aqueous solutions by graphene oxide functionalized persimmon tannin.

In this study, a novel bio-adsorbent (PT-GO) was prepared by functionalization persimmon tannin (PT) with graphene oxide (GO) and the effective adsorption behaviors of Au, Pd and Ag ions from aqueous solution was investigated. The PT-GO was characterized by Fourier transform infrared spectrometer (FTIR), scanning electronic microscope (SEM), thermogravimetric analysis (TGA) and Zeta potential. Many influence factors such as pH value, bio-adsorbent dosage, initial concentration of metal ions and contact time were optimized. The maximum adsorption capacity for Au, Pd and Ag was 1325.09mg/g, 797.66mg/g and 421.01mg/g, respectively. The equilibrium isotherm for the adsorption of Au and Ag on PT-GO were found to obey the Langmuir model, while the Freundlich model fitted better for Pd. The adsorption process of Au, Pd presented relatively fast adsorption kinetics with pseudo-second-order equation as the best fitting model, while the pseudo-first-order kinetic model was suitable for describing the adsorption of Ag. Combination of ion exchange, electrostatic interaction and physical adsorption was the mechanism for adsorption of Au, Pd and Ag onto PT-GO bio-adsorbent. Therefore, the PT-GO bio-adsorbent would be an ideal adsorbent for removal of precious metal ions and broaden the potential applications of persimmon tannin in environmental research.