Researchers using the resources at the Center for Nanoscale Materials (CNM) and the XSD 1-ID-E beamline at the Advanced Photon Source (APS) report, for the first time, the integration of a microwave reactor with a high-energy X-ray synchrotron beamline that enables one to capture the rapid kinetics of nanocrystal formation in large, statistically relevant solutions.
Microwave chemistry, the science of activating chemical reactions through microwave irradiation, represents a greener way to synthesize materials because some attributes of microwave-heating including shorter reaction time, lower energy consumption, high-level thermal management (e.g., uniform temperature distribution), and high product yield.
The fast reaction kinetics presented in the microwave synthesis of colloidal silver nanoparticles was quantitatively studied, for the first time, by integrating a microwave reactor with in situ X-ray diffraction at a high-energy synchrotron beamline. Comprehensive data analysis reveals two different types of reaction kinetics corresponding to the nucleation and growth of the Ag nanoparticles. The formation of seeds (nucleation) follows typical first-order reaction kinetics with activation energy of 20.34 kJ/mol, while the growth of seeds (growth) follows typical self-catalytic reaction kinetics.
Varying the synthesis conditions indicates that the microwave colloidal chemistry is independent of concentration of surfactant. These discoveries reveal that the microwave synthesis of Ag nanoparticles proceeds with reaction kinetics significantly different from the synthesis present in conventional oil bath heating. The in situ X-ray diffraction technique reported in this work is promising to enable further understanding of crystalline nanomaterials formed through microwave synthesis.
Qi Liu, Min-Rui Gao, Yuzi Liu, John S. Okasinski, Yang Ren and Yugang Sun, “Quantifying the Nucleation and Growth Kinetics of Microwave Nanochemistry Enabled by in Situ High-Energy X-ray Scattering,” Nano Letters, Article ASAP, DOI: 10.1021/acs.nanolett.5b04541, Published Online December 1, 2015.