Absorption and emission spectroscopic investigation of the phyto-extraction of europium(III) nitrate from aqueous solutions by alfalfa biomass

Abstract

Europium(III) is a common product found in nuclear wastes. Recent investigations into the use of europium compounds as cancer therapy treatments have proven promising. In this study, europium(III) nitrate binding studies were performed using unmodified and esterified alfalfa biomass. Batch experiments included pH profile studies and X-ray absorption spectroscopy (XAS) inspection to determine the functional groups responsible for the binding of europium(III) nitrate on alfalfa. Results from the pH profile study showed that approximately 80% of the europium(III) nitrate bound to the native alfalfa biomass while the esterified biomass showed approximately 40% binding at pH 5. XAS consists of two complementary components: X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XAS experiments were performed using the europium L III edge which had an energy of 6.977 KeV. The XANES spectra showed that there were some changes in the characteristics of the europium(III) nitrate when bound to the modified and unmodified alfalfa biomass. No change in the europium(III) oxidation state was observed after europium(III) binding to the alfalfa biomass. EXAFS spectra showed that europium(III) nitrate binds to the alfalfa biomass via a nitrogen or oxygen ligand with bond lengths ranging from 2.44 to 2.49 Å. However, chemical esterification experiments show that oxygen may be the primary ligand for coordination. The coordination numbers for all samples and compounds tested were approximately 9.