Mechanism of palladium(II) biosorption by: Providencia vermicola

Abstract

The mechanism of biosorption of Pd(ii) from aqueous solution onto Providencia vermicola biomass was elucidated from the aspects of the biosorption process, multi-scale visualization and functional groups for the first time. Kinetic, equilibrium and thermodynamic experiments revealed that the biosorption process was spontaneous, endothermic and limited by chemical reaction. The multi-scale visualization was conducted by using scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy coupled to energy dispersive X-ray spectroscopy (TEM-EDX) and atomic force microscopy (AFM). It was demonstrated that palladium ions were transformed to both the external and internal of P. vermicola biomass, and the morphological properties changed considerably in the nanometer range. The functional groups related to Pd(ii) binding on the cell wall of P. vermicola were confirmed by chemical modification and characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that zero-valent palladium ions were detected in the surface of the biomass, and the most efficient functional groups were carboxylic and hydroxyl groups, followed by phosphate and amine groups.