Theoretical study on the oxidation of zigzag silicon carbide nanotubes (SiCNTs) by singlet O2

Singlet O2 produced upon photoexcitation is a very important oxidative reagent. The study on its reaction with nanotube might be useful not only to evaluate the stability of the nanotube upon air exposure and sunlight, but also to modify the properties of the nanotube. Considering the unique properties and wide applications of silicon carbide nanotube (SiCNT), in this paper, we performed extensive density functional theory (DFT) calculations to study the oxidation of a series of zigzag (n,0) SiCNTs (n=6 to 12) by singlet O2. It is found that the reaction process contains two steps, namely, (i) [2+2] cycloaddition of a singlet O2 to the Si-C bond, followed by (ii) the dissociation of the O-O bond, leading to the formation of an epoxide configuration with a highly exothermicity (>4.00 eV). Compared with pure SiCNT, the cycloaddition of singlet O2 on tube leads to the decrease of the band gap, while the formation of the stable epoxy structure render band gap increase. Our results indicate that the SiCNT is more prone to be degraded after exposure to air and sunlight.