Vijay Krishna

Abstract:

Conventionally, noble metal nanoparticles, such as gold are synthesized using a reducing agent like sodium borohydride (NaBH₄) or sodium citrate at elevated temperatures and alkaline pH, with stabilizers added to control the size and dispersion of the nanoparticles [1]. While sodium citrate is sometimes used as a single reducing and stabilizing agent, it is limited in the range of gold nanoparticle sizes that can be obtained [2]. Fullerenes and polyhydroxy fullerenes have been coated on gold nanoparticles as they can impart excellent electronic properties in addition to providing stability [3, 4].
We have discovered that polyhydroxy fullerenes (PHF) can act as a single reducing and stabilizing agent by simple mixing of the gold chloride with PHF at room temperature [5]. The gold nanoparticles obtained are monodisperse as characterized by dynamic light scattering and high resolution-transmission electron microscopy. The size of gold nanoparticles is controllable by changing to ratio of reactants and range from 1 nm gold nanoclusters to 100 nm nanoparticles. We studied the mechanism of nanoparticle formation with PHF and proposed a three step process. In the first step, electrostatic attraction between negatively charged PHF and gold cations lead to formation of agglomerate. In the second step, PHF reduces gold cations and formation of Au-O-PHF bonds were detected by electron energy loss spectroscopy and x-ray photoelectron spectroscopy. In the third step, agglomerates containing gold nanoparticles disperse to yield monodisperse colloid. The gold nanoparticles obtained with method is stable for at least 2 years.
The novel PHF-mediated synthesis method can also be applied to other noble metals. The surface PHF coating on noble metal nanoparticles integrates the properties of both metal and carbon nanoparticles, resulting in superior functional applications. Our findings open up new opportunities for metallic nanoparticle preparation methods, properties, and applications.