Adsorption of pairs of NOx molecules on single-walled carbon nanotubes and formation of NO + NO3 from NO2

The adsorption of NOx(x = 1, 2, 3) molecules on single-walled carbon nanotubes (SWCNTs) is investigated using first-principle calculations. Single NO, NO2 and NO3 molecules are found to physisorb on SWCNTs, but molecules can be chemisorbed in pairs on the top of carbon atoms at close sites of SWCNTs. The adsorption energy for pairs of NO or NO3 molecules is larger than for pairs of NO2 molecules. The local curvature is found to have a sizable effect on adsorption energies. The possibility of a surface reaction NO2 + NO2 → NO + NO3 is examined and the relative pathway and barrier is calculated. The results are discussed with reference to available experimental results.