Aldehyde trapping by self-propagating atom-exchange reactions on a gallium nitride monolayer: role of the molecule complexity

The design of novel gas sensors based on two-dimensional systems has grown rapidly in the last few years due to the remarkable reactivity of their surfaces. Formaldehyde trapping has been extensively investigated on diverse 2D substrates by self-propagating atom-exchange reactions. However, it is the smallest of the aldehydes, and its surface chemistry may not be extended to complex aldehydes. To understand the role of the molecule complexity in the surface adsorption and trapping reaction, we have studied the self-propagating reaction of propionaldehyde (C3H6O), and benzaldehyde (C7H6O) on a hydrogenated gallium nitride monolayer with a vacancy. The use of the same substrate allows us to isolate only the molecule effect. Our results show that the two molecules chemically adsorb on the Ga-side of the monolayer, in an exothermic process. Both aldehydes generate a new H vacancy on the monolayer, promoting an atom-exchange self-propagating reaction after overcoming energy barriers of 0.59 and 0.77 eV for C3H6O and C7H6O, respectively. The effect of the aldehyde size on the substrate's electronic and structural properties is studied during the adsorption and the self-propagating process. In this way, our results contribute to the understanding and optimization of a toxic gas sensor with selectivity towards formaldehyde.