PNNL

Abstract

The growing demand for rare earth elements (REEs) in high-technology industries necessitates the development of atom- and energy-efficient as well as selective separations to overcome the challenges posed by the similar chemical and physical properties of REEs and their low concentrations in many unconventional domestic feedstocks. In this study, diethylenetriamine (DETA)-functionalized graphene oxide (DETA-GO) was prepared through an optimized synthesis process to incorporate nitrogen-containing functional groups into GO laminate structures. Unmodified neat-GO and DETA-GO multilayer laminate membranes were fabricated via vacuum filtration onto polyvinylidene fluoride (PVDF) supports. To provide insight into the structural and chemical modifications resulting from amine functionalization, the membranes were characterized using Raman, Fourier transform infrared, and X-ray photoelectron spectroscopy, as well as grazing incidence X-ray diffraction. Ion permeation experiments, conducted with representative lanthanum (La³?) and ytterbium (Yb³?) chloride solutions, demonstrated membrane selectivity based on different ion transport rates. Additionally, molecular dynamics (MD) simulations were performed to provide molecular-level insights into the mechanisms by which amine functionalization enhances the ion adsorption and selective transport properties of GO membranes. By comparing neat-GO with amide functionalized DETA-GO, and GO containing both amide and amine groups, the simulations reveal the influence of different chemical functionalization on nanochannel properties and metal cation diffusivity. This multidisciplinary study, combining experimental synthesis and characterization, ion adsorption and permeation studies, and theoretical simulations, demonstrates the potential of DETA-GO membranes for selective REE separations, offering valuable insights into binding mechanisms and nanochannel optimization for advanced critical material recovery.