Usage of the isotope effect for the synthesis of ultrahigh aspect ratio gold nanorods

• Published in: Journal of materials chemistry Vol. 22; no. 29; pp. 14594 - 1461
• Main Authors: Koeppl, Susanne, Koch, Felix P. V, Caseri, Walter, Spolenak, Ralph
• Format: Journal Article
• Language: English
• Published: 01.01.2012
• Subjects: Ascorbic acid; Aspect ratio; Bonding; Gold; Nanoparticles; Nanorods; Solvents; Synthesis
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/c2jm30648d

The synthesis of gold nanorods is commonly performed via seed-mediated growth processes, where typically tetrachloroaurate( iii ) is reduced with ascorbic acid in the presence of a surfactant (CTAB). However, in most cases nanorods with average aspect ratios below 4 are obtained, and reproducible processes which lead to average aspect ratios above 10 are widely missing. Using a modified seed-mediated method, we show that the average aspect ratio of gold nanorods increased from 8 to 19 when H 2 O was replaced by D 2 O as a solvent. The aspect ratio can be varied between these values by appropriate H 2 O-D 2 O mixtures. The increase in aspect ratio in the presence of D 2 O is established rather by an increase in nanorod length than in diameter. Apparently, the increase in length is not caused by an influence of D 2 O on the seed nanoparticles but is associated with the growth solution. It appears that in D 2 O a slower reduction of gold( iii ) species by ascorbic acid, with involvement of an O-D bond (or an O-H bond in H 2 O) in the rate determining step, is the origin of higher selectivity in the growth processes which lead to the different morphologies in nanoparticle formation. Gold nanorods of aspect ratios around 20 were prepared by a seed-mediated procedure in D 2 O instead of H 2 O. Probably formation of O-D bonds of ascorbic acid in D 2 O led to a decrease in the reduction rate of initially present Au III ions and thus to higher selectivity between the shapes of the nanoparticles.