Release of N2 from the carbon nanotubes via high-temperature annealing

Nitrogen (N)-doped carbon nanotubes (CNTs) were heated to 1000 degreesC under an ultrahigh vacuum. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) reveal three different N structures; graphitelike, pyridine-like, and molecular N-2. The vibrationally resolved XANES peaks of N-2 were first observed, suggesting the existence of molecular N-2 as intercalated and trapped forms. The annealing process can decrease the average N content from 6.3 at. % to 3.3 at. %, mainly by releasing molecular N-2. Electron energy-loss spectroscopy (EELS) confirms that the annealing releases molecular N-2 from the CNTs.