Plant tannin immobilized Fe3O4@SiO2 microspheres: A novel and green magnetic bio-sorbent with superior adsorption capacities for gold and palladium.

In this paper, a new core-shell nanostructured magnetic bio-based composite was prepared by immobilizing persimmon tannin (PT) onto Fe3O4@SiO2 microspheres, and the as designed Fe3O4@SiO2@PT was utilized for adsorptive recovery of Au(III) and Pd(II). The preparation, morphology, composition and magnetic property of Fe3O4@SiO2@PT were characterized. Adsorption parameters of Fe3O4@SiO2@PT towards Au(III) and Pd(II) including initial pH, reaction time, initial concentration of metal ions, effect of acidity and interference of coexisting metal ions were investigated. It is sufficiently confirmed that silica was coated on Fe3O4 and persimmon tannin was immobilized on aminated Fe3O4@SiO2. The thickness of silica and loaded persimmon tannin are around 18 nm and 14 nm, respectively. With only 1.00 wt% of persimmon tannin, however, the maximum adsorption capacities of Fe3O4@SiO2@PT for Au(III) and Pd(II) were as high as 917.43 and 196.46 mg·g-1, respectively. In addition, after adsorption of Au(III) and Pd(II), the magnetization saturation values (Ms) of Fe3O4@SiO2@PT were high enough to guarantee efficient magnetic seperation. Metallic gold could be facilely recovered from wastewaters containing Au(III).