PNNL

The Science

Separating critical materials, particularly rare earth elements (REEs), from dilute, chemically complex aqueous feedstocks is essential for building resilient domestic supply chains. Graphene oxide (GO) laminate membranes offer a promising route that leverages interfacial chemistry within angstrom-to-nanometer-scale interlayer transport channels. Researchers developed diethylenetriamine-functionalized GO (DETA-GO) membranes to probe how amine grafting chemistry alters membrane structure and, in turn, REE transport and capture. By maximizing nitrogen incorporation while preserving GO dispersibility, the team fabricated ordered multilayer laminates and showed that functionalization modifies nitrogen-bonding configurations and interlayer channel organization. This yielded membranes with enhanced stability and water transport pathways. Permeation and adsorption experiments with representative lanthanum (La³⁺) and ytterbium (Yb³⁺)solutions demonstrated stronger REE affinity and improved water transport in DETA-GO, while molecular dynamics simulations provided atomistic evidence linking amine coordination sites and nanochannel architecture to regulated ion exclusion and uptake as well as increased water flux, key mechanisms governing efficient REE separation.

The Impact

REEs are difficult to separate efficiently because they have very similar chemical and physical properties and often occur at low concentrations in complex domestic feedstocks. Conventional REE separation methods, such as solvent extraction, ion exchange, and precipitation, are widely used but are energy- and chemical-intensive and frequently employ hazardous reagents. DETA-GO membranes and adsorbents offer a more benign, atom- and energy-efficient alternative by combining high-surface-area sorption with tunable, nanoscale transport pathways. Understanding how DETA functionalization modifies GO provides a predictive handle to increase REE affinity through Lewis-basic amine coordination and to stabilize and tune the interlayer transport nanochannels that govern ion-selective sieving, water throughput, and membrane stability. These fundamental scientific insights will enable the rational design of GO-based separations that reduce reagent consumption and waste while improving performance for REE recovery from domestic aqueous feedstocks.

Summary

Developing atom- and energy-efficient methods to recover REEs from dilute, compositionally complex feedstocks is critical for strengthening domestic supply chains, yet separation is hindered by the similar chemical properties and low concentrations of REE ions. Researchers developed DETA-GO as a multilayer laminate that couples enhanced REE adsorption with improved water transport and membrane stability. Multimodal characterization from a suite of complementary microscopy and spectroscopy techniques revealed that DETA incorporation via epoxide ring opening and amide coupling to carboxyl groups alters nitrogen-bonding configurations and reorganized interlayer channels, improving structural integrity and transport behavior. Ion permeation and adsorption experiments with representative La³⁺ and Yb³⁺ solutions showed that DETA-GO membranes exhibit strong affinity for multivalent REEs and high water flux. Molecular dynamics simulations provided atomistic-level insight into the relationships among functionalization, nanochannel architecture, transport, and stability.

The enhanced separation performance of DETA-GO membranes stems from four factors: 1) increased density of Lewis-basic nitrogen sites that promote strong coordination with multivalent REEs; 2) functionalization-dependent nitrogen-bonding configurations that tune the spatial arrangement and accessibility of adsorption sites; 3) increased hydrophobicity and higher water flux induced by amine functionalization, which increase water throughput and overall separation capacity; and 4) improved long-term membrane stability against swelling, delamination, and defect formation, which preserves ordered transport pathways and adsorption capacity during operation. Collectively, these results position DETA-GO as a durable membrane material and provide design rules for coupling tailored binding chemistry with optimized nanochannel structure for REE recovery from aqueous feedstocks.

Contact

Grant Johnson, Pacific Northwest National Laboratory, grant.johnson@pnnl.gov

Oliva M. Primera-Pedrozo, Pacific Northwest National Laboratory, oliva.primerapedrozo@pnnl.gov

Funding

This work was supported by the Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences program, Chemical Sciences, Geosciences, and Biosciences Division, project 81462 (Harnessing Confinement Effects, Stimuli, and Reactive Intermediates in Separations). This work was supported in part by the DOE-SC, Office of Workforce Development for Teachers and Scientists under the Science Undergraduate Laboratory Internships program. Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle for the DOE under Contract DE-AC05-76RL01830. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a DOE-SC user facility, using NERSC award BES-ERCAP0027218.