It is noteworthy that the nitrogen loss during carbonization of
the biomass studied is reasonable as compared to other
nitrogen-containing carbons [41,42], suggesting that nitrogen is
structurally bonded and distributed in the carbon. XPS analysis
shows the presence of nitrogen as shown in Fig. 4(B–D) with the
high resolution XPS spectra (N1s) further revealing the form of
nitrogen in the carbon model. The deconvoluted spectra for N1s
with two binding energies except GSK1-700 displays three binding
energies at 398.6, 400.3 and 402.7 eV attributed to pyridinic,
pyrrolic, and pyridone-type nitrogen, respectively. Interestingly,
GSK1-700 showed the signal in the binding energy of the
pyridine-type nitrogen and is larger than that of GSK0.5-700 and
GSK2-700.