XPS has been shown to be useful for analyzing the surface chemical
characteristics of activated carbons. The survey XPS spectra
of various samples are shown in Fig. 6a. It can be seen that the
spectra contained distinct peaks for C and O and weak peaks for
N and P. The relative contents of these elements were calculated
and listed in Table 2. According to the results, the two activated
carbons presented similar elemental compositions. The C content
increased to some extent after activation, while the contents of O
and N decreased notably, implying the elimination of the groups
containing them during the activation process. A small amount of
P was also detected on the surface of the activated carbons. The
possible structure of the phosphorus species was proposed to be
condensed phosphates bound to carbon lattice via C–O–P bonding
(Puziy et al., 2006), which could not be removed easily after
activation.