Purification of Gold Organosol by Solid Reagent

Straight chain amines of variable chain length offer steric stabilization to gold nanoparticles (AuNPs), and thereby, gold organosol is produced in nonpolar solvent. We have found that dodecylamine (DDA) becomes a preferred ligand over other amines, for extraction, stabilization, and preparation of gold organosol in hexane. In the same context, straight chain thiols also provide steric stabilization to the AuNPs and compete with amines. But, the extracting power of thiols is dramatically reduced while the size of AuNPs is increased, and amines accomplish success for variable sizes of AuNPs. Organosol system always remains admixed with excess free ligands, and it is true for amines also. Hence, free amines (unbound) conjecture false information and pose a problem during further course of investigation. Excess unbound ligands in the organosol system limit application of AuNPs in the organic medium. A simple heterogeneous separation technique is reported here to prepare amine stabilized organosol devoid of unbound (free) amine. A greenish blue solid copper stearate [Cu­(St)₂] has been introduced as the best suited reagent that endorses quantitative removal (97.3 ± 0.12%) of free amine. The solid reagent [Cu­(St)₂] in turn produces a violet solid. The greenish blue to violet color change of the solid reagent indicates selective removal of excess amine from the organosol keeping the properties of amine stabilized organosol unaltered.