Through the application of mechanochemistry, controlled forces may be used to drive specific reactions by altering reaction states and pathways. Two-dimensional (2D) materials can serve as model platforms for studying the impact of mechanical forces on chemical reactivity. Graphene, a 2D material, is a viable platform as the single layer of sp2-hybridized C atoms provides a means of seeing how applied forces are distributed across a well-organized atomic lattice. Using Raman micro-spectroscopy and first-principles calculations, we have elucidated the influence strain has on a radical addition reaction of graphene with 4-nitrobenzenediazonium tetrafluoroborate (4-NBD). With increased out-of-plane distortion (transitioning the C atoms from sp2 to sp3 electronic states), the reactivity increases, where greater out-of-plane distortions leading to greater reactivity. Through density functional theory (DFT), it is revealed that the increase in graphene curvature decreases the activation barrier and increases the thermodynamic favorability of 4-NBD functionalization. To expand on these results, we have developed an apparatus that allows for performing Raman and atomic force microscopy (AFM) measurements of suspended graphene films under tailorable amounts of backing pressure, provided by either flowing gas or liquid. This will allow us to study in real time the chemical and physical changes occurring with graphene during mechanochemically-induced reactions, as a result of controlled force. Lastly, a study on the influence that out-of-plane distortion has on the reactivity of molybdenum disulfide (MoS2), a more rigid 2D material than graphene, was performed, where it was found that the susceptibility of MoS2 to oxidation increases with the surface roughness of an underlaying Au substrate.

Mechanochemically-induced reactivity of 2D materials: Using graphene and MoS2 as model systems for elucidating the impact of directionality on reactivity

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ACS Fall 2022

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