Covalent surface modification of single-layer graphene-like BC₆N nanosheets with reactive nitrenes for selective ammonia sensing via DFT modeling

Abstract

Novel graphene-like nanomaterials with a non-zero bandgap are important for the design of gas sensors. The selectivity toward specific targets can be tuned by introducing appropriate functional groups on their surfaces. In this study, we use first-principles simulations to investigate the covalent functionalization of single-layer graphitized BC6N with azides to yield aziridine-functionalized adducts and explore their possible use to realize ammonia sensors. First, we determine the most favorable sites for physical adsorption and chemical reaction of methylnitrene, arising from the decomposition of methylazide, onto a BC6N monolayer. Then, we examine the thermodynamics of the [1+2]–cycloaddition reaction of various phenylnitrenes and perfluorinated phenylnitrenes para-substituted with (R = CO2H, SO3H) groups, demonstrating a favorable energetics. We also monitor the effect of the functionalization on the electronic properties of the nanosheets via density of states (DOS) and band structure analyses. Finally, we test four dBC6N to gBC6N substrates in the sensing of ammonia. We show that, thanks to their hydrogen bonding capabilities, the functionalized BC6N can selectively detect ammonia, with interaction energies varying from –0.541 eV to –1.371 eV, even in presence of competing gas such as CO2 and H2O, as also confirmed by analyzing the change in the electronic properties and the values of recovery times near ambient temperature. Importantly, we model the conductance of a selected substrate alone and in presence of NH3 to determine its effect on the integrated current, showing that humidity and coverage conditions should be properly tuned to use HO3S-functionalized BC6N-based nanomaterials to develop selective gas sensors for ammonia.