Figure 9 A) Comparison of H2 evolution rates
under visible-light irradiation using different photocatalysts: ZnS
nanorods, CdS nanorods, binary ZnS-CdS hetero-nanorods, ternary
ZnS-(CdS/Au) hetero-nanorods(ZCAu), ternary ZnS-(CdS/Pd)
hetero-nanorods(ZCPd), ternary ZnS-(CdS/Pt) hetero-nanorods(ZCPt). The
insert is the representative geometric model of ternary hetero-nanorods
with four CdS node sheaths. B) The energy-band alignment of a ZnS(111)
nanorod attached by the ZnS()/CdS() hybrid in the periodic binary
heterojunction. C) The energy-band alignment of the periodic ternary
heterojunction with CdS()/Au hybrids attached to a ZnS(111) nanorod. D)
Absorption spectra of the as-prepared samples. a) CIS nanorods, b) ZCIS
nanorods, c) ZCIS–Pt hybrid nanorods, and d) ZCIS–Pd4S
hybrid nanorods. E) Photocatalytic hydrogen production under
visible-light illumination by CIS nanorods, ZCIS nanorods, ZCIS–Pt
hybrid nanorods, and ZCIS–Pd4S hybrid nanorods from an
aqueous solution containing
0.25MNa2SO3 and 0.35MNa2S. Measurements were taken every hour for 6 h. A-C)
Reproduced with permission.[28] Copyright 2015,
Wiley-VCH. D-E) Reproduced with permission.[29a]Copyright 2015, Wiley-VCH.
Ye et al. studied the photocatalytic effect of an alloyed
semiconductor of ZnS-CuInS2(ZCIS).[29a] Actually, the band gap energy of
CuInS2 (CIS) and ZnS are 1.5 eV and 3.7 eV respectively,
which are not suitable for visible light induced photocatalysis to
generate hydrogen from water splitting. However, previous studies by Yeet al. have shown that the band gap of ZCIS is highly correlated
with alloy composition,[29b] so it is possible to
regulate the band gap by alloying, and adjust the ratio of CIS to ZnS to
absorb visible light. Compared with the absorption spectrum of CIS, a
blue shift occurred for ZCIS, indicates the widen of band gap by
introduction of ZnS (Figure 9D). The ZCIS band gap measured was 2.23 eV,
which was between the band gap of ZnS and CIS. Based on this, Pt and
Pd4S were decorated on ZCIS to form hybrid nanorods
nanostructures, and their photocatalytic properties were tested with
Na2S and Na2SO3 as hole
scavengers, as shown in Figure 9E, ZCIS-Pt and ZCIS-Pd4S
hybrid nanorods nanostructures showed better photocatalytic performance
than naked ZCIS nanorods. This indicates that by constructing
heterogeneous structures to regulate the band gap, the materials may
possess unprecedented properties that are not available previously,
which expands the selection of photocatalyst materials. Compared with
traditional photocatalytic materials, it is more feasible to prepare and
control heterogeneous catalysts with excellent performance, low price
and environmental friendliness.[29a]
3.7. Surface ligands