The main N 1s signal of the three samples displays a shoulder at a lower binding energy of 399.3 eV that have been described for -C-NH2, 61,62 indicating the simultaneous presence of small amounts of neutral alkyldiamine, which can be assumed as non-interacting with the V2O5 host via ionic or covalent bonds. Overall, XPS results demonstrate the predominantly ionic interaction between partially reduced V2O5 host and cationic ammonium groups, while a small residue of non-interacting amine groups is also found.