Cu (II) decorated thiol-functionalized MOF as an efficient transfer medium of charge carriers promoting photocatalytic hydrogen evolution

Abstract

Herein, a new photocatalyst (UiOS-Cu-CdS/ZnS, abbreviated as SCu-CZS) with hierarchical structure is well-designed by loading CdS/ZnS quantum dots (QDs) onto Cu (II) decorated thiol-functionalized UiO-66 (UiOS-Cu) metal-organic frameworks (MOFs) for water splitting, where CdS and ZnS QDs are evenly distributed on the surface and in the channels of MOF, respectively, and Cu (II) ions are connected with thiol groups. We find that the UiOS-Cu, as an efficient medium for the separation and transfer of charge carriers between CdS and ZnS, successfully transforms the I-type transfer mechanism of charge carriers in CdS/ZnS heterojunction into II-type transfer mechanism, in which the decoration of Cu (II) plays a key role. Due to the decoration of Cu (II), the highest occupied molecular orbital (HOMO) of UiOS-Cu is markedly lifted to the position higher than the valence band (VB) of CdS, promoting the smooth transfer of photoinduced holes from the VB of CdS to the HOMO of UiOS-Cu. Thanks to this II-type transfer mechanism, the photogenerated electrons and holes are effectively separated and transferred, significantly improving the photocatalytic H2 evolution performance. The optimized SCu-CZS sample exhibits a high H2 generation rate of 425.5 μmol/h (10 mg of catalyst) with an apparent quantum efficiency of 24.6% at the wavelength of 365 nm in the absence of noble metal co-catalyst. This work indicates that MOF can be used as an efficient transfer medium of charge carriers, promoting photocatalytic hydrogen evolution by transforming the transfer mechanism of photogenerated electrons and holes, which provides a new idea for the construction of MOF-based photocatalysts.