Solvent filtration through the use of monolayer-protected gold nanoparticles

Abstract

Chemical purification is typically approached by taking advantage of the constituent molecules' sizes, densities, phase transitions, or bonding capabilities to isolate individual chemical components from one another. Here, a novel approach for solvent filtration is proposed based on localized geometric constraints and bonding capabilities through the use of mixed monolayer ligand coated nanoparticles. Gold nanoparticles were synthesized and coated with octane thiol and mercaptoproprionic acid in a 3:1 ratio. Such nanoparticles have been reported to form an interesting grooved surface morphology, and it has been shown that their solubility varies according to the ability for individual solvent molecules to penetrate these grooves. Here, a system of filtration was designed, aimed at using these nanoparticles to remove a small quantity of ethanol from a solution of methanol. Solubility tests were performed on the synthesized nanoparticles and additional possible contaminants were isolated for testing including toluene, chloroform, and trihydrofuran. Titration columns were run to test the ability of the synthesized nanoparticles to separate the candidate contaminants above from a methanol solution. NMR spectroscopy of both the filtered and unfiltered solutions was performed and the results compared. Although far from conclusive, the evidence presented in this paper indicates that it very may well be possible to remove specific solute molecules from solution by flowing them through a group of nanoparticles with very clearly defined surface morphologies.