ABSTRACT

The extensive growth of nanotechnology has necessitated the development of economical and robust methods for large scale production of nanomaterials. It requires detailed quantitative understanding of lab-scale processes to enable effective scale-up and development of new contacting strategies for their controlled synthesis. In the present work, attempts are made in both the directions using experimental and modelling approaches for synthesis of noble metal nanoparticles. The two-phase Brust–Schiffrin protocol for the synthesis of gold nanoparticles was investigated in detail. The mechanism of transfer of reactants from aqueous to organic phase using phase transfer catalyst (PTC) was investigated using the measurement of interfacial tension, viscosity, SLS, SAXS, 1H NMR, DOSY-NMR, and Karl-Fischer titration. The study shows that the reactants are transferred to organic phase through the formation of hydrated complexes between reactants and PTC rather than through the solubilization of reactants in water core of inverse micelles of PTC, proposed recently in the literature. The particle synthesis reactions thus occur in the bulk organic phase. The extensive body of seemingly disparate experimental findings on Brust–Schiffrin protocol were put together next. The emerging picture ruled out both thermodynamic considerations and kinetics based arguments as exemplified by the classical LaMer's mechanism with sequential nucleation–growth–capping for size control in Brust–Schiffrin protocol. A new model for particle synthesis was developed. The model brought out continued nucleation–growth–capping based size control, a hitherto unknown mechanistic route for the synthesis of monodisperse particles, as the main mechanism. The model not only captured the reported features of the synthesis but also helped to improve the uniformity of the synthesized particles, validated experimentally.

References

• Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. Synthesis of thiol-derivatised gold nanoparticles in a two-phase liquid liquid System. J. Chem. Soc., Chem. Commun. 1994, 801-802.

• Perala, S. R. K.; Kumar, S. On the mechanism of metal nanoparticle synthesis in the Brust-Schiffrin method. Langmuir 2013, 29, 9863-9873.

• Perala, S. R. K.; Kumar, S. On the mechanism of phase transfer catalysis in Brust-Schiffrin synthesis of metal nanoparticles. Langmuir 2013, 29, 14756-14762.

ABOUT THE SPEAKER

Dr. Perala completed B.Tech from Jawaharlal Nehru Technological University College of Engineering Anantpur in 2004, followed by a ME from IISC Bangalore in 2006, both in Chemical Engineering. After his Masters, he worked briefly in IBM India (2006-2009). He rejoined IISc in 2009 and completed his PhD in 2013, with a Kuloor Memorial Medal for the Best PhD Thesis. Currently, he is a postdoctoral scholar at MIT, Cambridge.