DFT simulation of structure stability and nitrogen oxide adsorption for nitrogen and oxygen co-modified carbon nanotubes

Abstract

Nitrogen (N) and oxygen (O) co-modified carbon nanotubes (ONCNTs) have demonstrated potential applications in adsorption and catalysis processes, because the oxygen-containing groups and N-doping atoms can provide abundant surface binding sites. However, their structural stabilities and adsorption interactions under different co-modified levels remain to be explored. Herein, for the first time, the density functional theory approach was applied to quantitatively characterize the structural morphologies and thermodynamic stabilities for a series of ONCNTs. Our findings indicate that co-modification levels can significantly affect their structures and stabilities. An increase in the N-doping concentration largely decreases the thermodynamic stability of ONCNTs, whereas the oxygen-containing functional groups can enhance the stability. A suitable co-modification level was proposed, at which the ONCNTs could maintain stable structural morphology. Meanwhile, the interaction energies and electronic mechanisms between the ONCNTs and nitrogen oxides (NO and NO2) were comprehensively investigated. The degree of oxidation is the main factor determining the interaction and the stronger interaction generally occurs at the 20–40 % oxidation degrees, wherein both chemical and physical interactions are exhibited for NO and only physical interaction for NO2. Our simulation results could be important and valuable to the design and application of the modified CNTs.