“…Further, we used the peak-splitting simulation method to understand the chemical properties. In the high-resolution XPS spectra of C 1s ( Figure 6 b), four peaks located at 285.1, 286.0, 288.7 and 294.1 eV were ascribed to graphitic carbon (C=C) of CQDs, a small quantity of C-O species, sp 2 hybridized carbon (N-C=N) of g-C 3 N 4 and π-excitation, respectively [ 42 , 46 ]. The spectra of N 1s ( Figure 6 c) could be fitted into four peaks at 398.9, 399.8, 401.2 and 404.5 eV, which could be assigned to sp 2 hybridized aromatic N (C-N=C) in triazine rings, tertiary N in N-(C) 3 and amino groups (N-H), π-excitation, respectively [ 40 , 47 ].…”