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