Expanding the Mechanochemical Toolbox: Combining X-Ray Absorption Spectroscopy and Scattering for in Situ Time-Resolved Monitoring of Gold Nanoparticle Mechanosynthesis

The development of time-resolved in situ approaches for monitoring mechanochemical transformations has revolutionized the field of mechanochemistry. Currently, the established in situ approaches greatly limit the scope of investigations that are possible. Here we develop a new approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au nanoparticles in the presence of three different reducing agents. Moreover, we demonstrate how X-ray absorption spectroscopy offers unprecedented insight into the early stage generation of growth species (e.g. monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. The approach is general, and not limited to monitoring NP mechanosynthesis. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.