Dispersive X-ray Absorption Spectroscopy for Time-Resolved In Situ Monitoring of Mechanochemical Reactions

Abstract

X-ray absorption spectroscopy (XAS) provides a unique, atom-specific tool to probe the electronic structure of solids. By surmounting long-held limitations of powder-based XAS using a dynamically averaged powder in a Resonant Acoustic Mixer (RAM), we demonstrate how time-resolved in situ (TRIS) XAS provides unprecedented detail of mechanochemical synthesis. The use of a custom-designed dispersive XAS (DXAS) set-up allows us to increase the time resolution over existing fluorescence measurements from ca. 15 min to 2 sec, for a complete absorption spectrum. Hence, we here establish TRIS-XAS as a viable method for studying mechanochemical reactions and sampling reaction kinetics. The generality of our approach is demonstrated through RAM-induced (i) bottom-up Au nanoparticle mechanosynthesis, and (ii) synthesis of a prototypical metal organic framework, ZIF-8. Moreover, we demonstrate that our approach also works with the addition of a stainless steel milling ball, opening the door to using TRIS-DXAS for following conventional ball milling reactions. We expect our TRIS-DXAS approach will become an essential part of the mechanochemical tool box.

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying – retrospect, achievements and challenges

“…There were some rare exceptions, mainly related to the studies of the processes in single crystals or polymers at the moment of extension, or cleaving, by detecting temperature pulses, light emission or− evolution of gasses. A significant achievement of the last decades is that in situ monitoring of reactions 403 is becoming more common (using X-ray diffraction at synchrotron sources, 9,26,71,411–418 Raman spectroscopy, 413,414,418–420 XAS, 421,422 solid state NMR, 423 following the temperature evolution, 394,395,424,425 or the release of gases 424,426 ). An obvious advantage of in situ studies is the possibility to monitor the process without disturbing it, to fast track the changes in the sample, to observe the intermediate states and products.…”