Trivalent Rare Earth Adsorption at Phosphonic Acid Monolayers.
1Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S Cass Ave., Lemont, IL, 60439, USA.
Summary
Neodymium (Nd) adsorption on octadecylphosphonic acid (ODPA) monolayers was studied. Nd ions enhance ODPA deprotonation, revealing complex interactions crucial for rare earth separation technologies.
Area of Science:
- Surface chemistry
- Materials science
- Environmental science
Background:
- Efficient rare earth element separation is critical for numerous technologies.
- Understanding trivalent ion behavior at interfaces is key to optimizing separation processes.
Purpose of the Study:
- To investigate neodymium (Nd) adsorption at the air/water interface using octadecylphosphonic acid (ODPA) monolayers.
- To elucidate the mechanisms governing trivalent ion adsorption at charged interfaces.
Main Methods:
- Sum frequency generation (SFG) spectroscopy to probe interfacial water ordering.
- X-ray fluorescence near total reflection (XFNTR) to quantify interfacial ion density.
Main Results:
- Neodymium ions induce enhanced deprotonation of ODPA headgroups.
- High interfacial ion densities of Nd were observed (1 Nd per 30 Ų).
- Adsorption involves a complex interplay of electrostatic interactions, ion pairing, and hydration.
Conclusions:
- Classical models do not fully capture the observed trivalent ion adsorption.
- Insights gained can inform the development of improved rare earth separation strategies.
