Metal Ion (Cr3+, Eu3+, UO22+) Adsorption on Gibbsite Nanoplates

Abstract

Gibbsite is a common and important aluminum hydroxide mineral in natural environments and various industries, but the mechanisms by which metal ions sorb on the gibbsite surface, and their impact on surface reactivity, is not well understood. Here we examined Cr3+, Eu3+ and UO22+ cation sorption on synthetic nanoplatelet gibbsite using vibrational sum frequency generation (VSFG) spectroscopy along with time-resolved laser-induced fluorescence spectroscopy (TRLFS), Raman/Fourier Transform Infrared (FTIR) spectroscopy, and electron microscopy. Batch sorption experiments show uptake across a broad pH range. VSFG spectra reveal cation-specific participation of surface OH groups in metal binding. For Cr3+, uniform loss of spectral intensity with increasing cation loading indicates equal involvement of the six distinct hydroxyls. But sorption of Eu3+ and UO22+ alters its spectral profile where the reduction of the intra-layer OH bands was more pronounced and the correlation between the spectral reduction and metal ion concentration is weaker, indicating a different sorption mechanism. The latter was confirmed by the results of TRLFS analysis of both Eu3+ and UO22+ adsorbed on gibbsite.