Studies of the mechanically induced reactivity of graphene with water using a 2D-materials strain reactor.

Abstract

Using mechanical force to induce chemical reactions with two-dimensional (2D) materials provides an approach for both understanding mechanochemical processes on the molecular level, and a potential method for using mechanical strain as a means of directing the functionalization of 2D materials. To investigate this, we have designed a modular experimental platform which allows for in situ monitoring of reactions on strained graphene via Raman spectroscopy as a function of time. Both the strain present in graphene and the corresponding chemical changes it undergoes in the presence of a reagent can be followed concomitantly. As a case study, we have experimentally monitored and theoretically modeled the reactivity of a suspended single-layer graphene membrane under strain with water, where the graphene is strained via an applied backing pressure. While exposure of the unstrained membrane to water does not drive a chemical reaction, distortion of the membrane causes a rise in the I_D/I_G peak ratio, indicating an initial lattice conversion from crystalline to nanocrystalline due to reaction with water. With continued reaction, a decrease in the I_D/I_G peak ratio is then seen, indicative of a nanocrystalline to amorphous lattice transition. Using density functional theory (DFT) calculations, the reaction of water on graphene has been determined to be nucleated by epoxide defects, with the reaction barrier decreasing by nearly 5× for the strained vs. unstrained graphene. While demonstrated here for graphene, this approach also provides the opportunity to examine a host of force-driven chemical reactions with 2D materials.