Fig. 3 XRD patterns of (a) CoP,
Co3O4 QDs, and (b) ZCS, ZCS/CoP-x and
O/ZCS/P-x samples; XPS spectra of (c) Co 2p and O 1s for
Co3O4 QDs, and (d) Co 2p and P 2p for
CoP.
In Fig. 4a, the XPS signals of Co 2p in
Co3O4 QDs/ZCS and ZCS/CoP is quite weak
due to the extremely low content of
Co3O4 QDs and CoP in composite samples.
It is worth noting that the binding energies of
Co
2p in
Co3O4QDs/ZCS and ZCS/CoP exhibit a
negative shift in comparison with those of Co 2p in alone
Co3O4 QDs and CoP, which suggests that
it is charges that migrate from ZCS to
Co3O4 QDs and CoP. On the contrary, the
binding energies of Zn 2p, Cd 3d and
S 2p in all composite samples present remarkable positive shift in
comparison with those of Zn 2p, Cd 3d and S 2p in original ZCS (Fig.
4b-d), which also indicate that it is ZCS that is the electron donor for
highly-efficient photocatalytic hydrogen evolution. In addition, it also
can be observed from the XPS spectrum of Zn 2p, Cd 3d and S 2p that
their binding energies in O/ZCS/P bi-heterostructure cages increase more
compared with those in Co3O4 QDs/ZCS and
ZCS/CoP, which strongly reveal that
Co3O4 QDs and CoP simultaneously
transfer electrons from ZCS.
Consequently, the construction of hierarchical O/ZCS/P
bi-heterostructure cages can rapidly migrate charges from photo-excited
ZCS, so the recombination of electron-hole pairs can be greatly
inhibited, thereby the hydrogen evolution performance is enhanced
seriously.