A new ZnS/CdS heterojunction is constructed through the direct sulfurization of a metal ions exchanged Zn/Cd-MOF precursor(MOF=metal-organic framework material). The composition, structure, morphology, photoabsorption and photoelectric performance of the ZnS/CdS are characterized by powder X-ray diffraction(PXRD), scanning electron microscope(SEM), transmission electron microscope(TEM), diffuse reflection spectrum(DRS), photoelectric current(PEC), electrochemical impedance spectroscopy(EIS) and photoluminescence(PL) technologies. Since the metal ions are highly orderly separated by the organic ligands and the inherent porosity of the Zn/Cd-MOF, the as-synthesized ZnS/CdS possesses a large surface area and intimate contact at the heterogeneous interface with uniform ZnS/CdS nanoparticles. The photocatalytic hydrogen evolution activity of the ZnS/CdS is investigated under visible light irradiation(λ⩾420 nm). It exhibits enhanced photocatalytic performance that the optimal ZnS/CdS achieves a maximum average hydrogen production rate of 2348 µmol·h −1 ·g −1 . A possible electron transfer mechanism is therefore proposed by the analyses of the Mott-Schottky plots.
Graphical Approaching a junction : A monolithic photomembrane by the judicious integration of ZnS/CdS heterojunction nanorods and multilayer graphene sheets has been fabricated and used as monolithic photocatalyst or a freestanding photoanode for efficient hydrogen evolution. Its outstanding performance can be attributed to the efficient charge separation/transfer brought by its unique structural characteristics. Highly efficient and easy recyclable monolithic photocatalysts with ideal separation/transport route for photogenerated charge carriers are much desired. In this work, a ZnO seed-induced growth approach is developed to fabricate a ternary monolithic photomembrane, that is, ZnS/CdS heterojunction nanorods in situ grow into the interspaces of multilayer reduced graphene oxide (rGO) sheets (denoted as ZnS/CdS/rGO). The monolithic ZnS/CdS/rGO photomembrane can serve as an efficient visible-light photoactive membrane for photocatalytic (PC) or photoelectrochemical (PEC) hydrogen generation. The fast electron transport of 1D CdS nanorods, the excellent electronic conductivity of multilayer stacked rGO sheets, the intense visible-light absorption of CdS, the unique hierarchical structure, and double heterojunctions (ZnS/CdS and CdS/rGO) efficiently boost the photogenerated electron-hole pairs separation and transfer across the interfacial domain of the photomembrane under visible-light irradiation. Furthermore, the superior stability and reusability of the photomembrane is achieved by the ideal process of photogenerated electron-hole pair separation/transfer, i.e., holes transfer to ZnS and electrons transfer to rGO to inhibit CdS from photocorrosion.
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