Mechanochemistry is the process of using mechanical force to effect bulk chemical reactions with small (catalytic) amounts of solvent. Although the process lacks any form of the positional control that is a cornerstone capability of productive nanosystems, understanding how chemical reactions proceed under mechanical force will help lessen the gap between current and future machine-phase synthesis. Recently featured at Phys.org, an international research collaboration led at McGill University is using high-energy synchrotron Xrays to study the chemical transformations that take place during ball milling.
In recent years, ball milling has become increasingly popular in the production of highly complex chemical structures. In such synthesis, steel balls are shaken with the reactants and catalysts in a rapidly vibrating jar. Chemical transformations take place at the sites of ball collision, where impact causes instant “hot spots” of localized heat and pressure. This is difficult to model and, without access to real time reaction monitoring, mechanochemistry remained poorly understood.
The team of scientists chose to study mechanochemical production of the metal-organic framework ZIF-8 from the simplest and non-toxic components. Materials such as ZIF-8 are rapidly gaining popularity for their ability to capture large amounts of CO2; if manufactured cheaply and sustainably, they could become widely used for carbon capture and storage, catalysis and even hydrogen storage.
“The team came to the ESRF because of our high-energy X-rays capable of penetrating 3 mm thick walls of a rapidly moving reaction jar made of steel, aluminium or plastic. The X-ray beam must get inside the jar to probe the mechanochemical formation of ZIF-8, and then out again to detect the changes as they happened”, says Simon Kimber, a scientist at the European Synchrotron Radiation Facility (ESRF) in Grenoble, who is a member of the team. This unprecedented methodology enabled the real-time observation of reaction kinetics, reaction intermediates and the development of their respective nanoparticles.
The work, published in Nature Chemistry (Abstract), allowed the research team to see differences in reaction pathways and kinetics relative to traditional solvent-phase processes.
An excellent introduction to mechanosynthesis and mechanochemistry (and their important distinctions) by Damian Allis of Syracuse University can be found in the Productive Nanosystems Technology Roadmap (see Part 3 Proceedings of the Roadmap Working Group, Atomically Precise Fabrication: 02 Mechanosynthesis).
-Posted by Stephanie C