Classification of La3+ and Gd3+ rare earth ions using surface-enhanced Raman scattering

TL;DR

This paper demonstrates a novel SERS-based method for qualitative classification of La3+ and Gd3+ ions using citrate-capped silver nanoparticles, supported by DFT calculations revealing the molecular interactions.

Contribution

It introduces the first use of SERS spectra for classifying RE3+ ions and correlates spectral features with molecular coordination through DFT analysis.

Findings

Distinct SERS peak ratios enable classification of La3+ and Gd3+.

Characteristic peaks are linked to citrate coordination with RE3+ ions.

DFT calculations confirm the molecular origin of the observed peaks.

Abstract

In this study, surface-enhanced Raman scattering (SERS) spectra of different rare earth (RE) ion-citrate complexes were investigated for the first time for the qualitative classification of RE3+ ions. With the addition of RE3+ ions to citrate-capped silver nanoparticles in aqueous solutions, the Raman signals of RE-citrate complexes were enhanced, and characteristic peaks appeared near 1065 cm-1 and 1315 cm-1. The I1065/I1315 ratios of La-citrate and Gd-citrate were approximately 1 and 0.5, respectively. Thus, different RE3+ ions were classified based on the ratio of characteristic SERS peaks near 1065 cm-1 and 1315 cm-1. In addition, the effects of RE3+ ions in the RE-citrate complexes were analyzed based on density functional theory (DFT) calculations. Calculation results show that these characteristic peaks are attributed to the coordination of carboxyl and hydroxyl groups of citrates with the RE3+ ions, suggesting that these are spin-related bands of the RE-citrate complexes.