Abstract
Both long chain alkyl thiols and alkyl amines behave as size focusing agents for gold nanoparticles, a process that is under thermodynamic control. However, amines do not oxidize surface gold atoms while thiols do oxidize surface gold to gold(I) with evolution of hydrogen gas. Therefore, alkyl amines participate in digestive ripening by a different mechanism. The efficiency of alkyl amines for this process is described and compared, and ultimate gold particle size differences are discussed. Reported herein is a detailed investigation of alkyl chain lengths for alkyl amines, aromatic amines (aniline), and unusually reactive amines (2-phenylethyl amine). Also, two methods of preparation of the crude gold nanoparticles were employed: gold ion reduction/inverse micelle vs. metal vaporization (Solvated Metal Atom Dispersion—SMAD).
Highlights
The fascinating and unique behavior of ligand capped nanoparticles toward certain preferred sizes has been observed by many workers
Alcohols, phosphines, silanes, halides, and thiols have been compared as ligands for digestive ripening [1,2,34,38,40,41,42] and thiols are the most effective at yielding monodisperse gold, but amines work well too, yielding nanoparticles somewhat larger, but reasonably monodispersed
We determined that hydrogen gas is evolved when thiols attack and ripen gold nanoparticles, and the hydrogen was provided by sacrifice of surface nanoparticle gold [43]
Summary
The fascinating and unique behavior of ligand capped nanoparticles toward certain preferred sizes has been observed by many workers. Size and monodispersity can be affected by a thermodynamic process called digestive ripening, which can be controlled by ligand choice, solvent choice, and temperature [1,2,3,4,5,6]. Alcohols, phosphines, silanes, halides, and thiols have been compared as ligands for digestive ripening [1,2,34,38,40,41,42] and thiols are the most effective at yielding monodisperse gold, but amines work well too, yielding nanoparticles somewhat larger, but reasonably monodispersed. Slightly different processes are involved with thiols vs amines
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