XAS investigations into the mechanism(s) of Au(III) binding and reduction by alfalfa biomass

Previous experiments showed that inactivated alfalfa biomass is proficient in the recovery of gold(III) from aqueous solutions. Gold(III) binding to alfalfa biomass is rapid, pH independent, and increases with temperature. Also, X-ray absorption spectroscopy studies showed that alfalfa was able to reduce gold(III) to gold(0), producing nano-particles. This current study was performed to gain a better understanding of the interaction between gold(Ill) and the alfalfa biomass. Through chloride ion release studies, it was found that three moles of Cl- were released per mole of gold adsorbed. Chemical modification of the alfalfa biomass indicated that both amino and carboxyl functional groups on the alfalfa biomass are involved in the reduction process. Finally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies suggested that gold(III)is initially reduced to gold(I) and is eventually reduced to gold(0); in addition, the X-ray spectroscopic studies indicated that binding may be occurring through a nitrogen or oxygen ligand. (C) 2002 Elsevier Science B.V. All rights reserved.