Defect engineering is av ersatile approach to modulate band and electronic structures as well as materials performance.H erein, metal-organic frameworks (MOFs) featuring controlled structural defects,n amely UiO-66-NH 2 -X(Xrepresents the molar equivalents of the modulator,acetic acid, with respect to the linker in synthesis), were synthesized to systematically investigate the effect of structural defects on photocatalytic properties.R emarkably,s tructural defects in MOFs are able to switch on the photocatalysis.T he photocatalytic H 2 production rate presents avolcano-type trend with increasing structural defects,w here Pt@UiO-66-NH 2 -100 exhibits the highest activity.U ltrafast transient absorption spectroscopyu nveils that UiO-66-NH 2 -100 with moderate structural defects possesses the fastest relaxation kinetics and the highest charge separation efficiency,while excessive defects retard the relaxation and reduce charge separation efficiency. Angewandte Chemie Communications Conflict of interestTheauthors declare no conflict of interest.

Well-organized photosensitive units and catalytic sites in proximity are crucial for improving charge separation efficiency and boosting photocatalysis. Herein, a general and facile strategy for the construction of high-loading (>4 wt %) single-atom catalysts (SACs) with a tunable coordination microenvironment has been developed on the basis of metal–organic frameworks (MOFs). The neighboring −O/OH x groups from a Zr6-oxo cluster in the MOFs provide lone-pair electrons and charge balance to immobilize the extraneous single metal atoms. The well-accessible and atomically dispersed metal sites possess close proximity to the photosensitive units (i.e., linkers), which greatly accelerates charge transfer and thereby promotes the redox reaction. The coordination environment of the representative single-atom Ni sites significantly modulates the electronic state and the proton activation barrier toward hydrogen production. As a result, the optimized Ni1–S/MOF with a unique Ni­(I) microenvironment presents excellent photocatalytic H2 production activity, up to 270 fold of the pristine MOF and far surpassing the other Ni1–X/MOF counterparts. This work unambiguously demonstrates the great advantage of MOFs in the fabrication of high-content SACs with variable microenvironments that are in close proximity to photosensitive linkers, thereby facilitating the electron transfer and promoting photocatalysis.

Photocatalytic water splitting for H2 production becomes one of the most favorable pathways for solar energy utilization, while the charge-separation dynamics in composite photocatalysts is largely elusive. In the present work, CdS-decorated metal–organic framework (MOF) composites, namely, CdS/UiO-66, have been synthesized and exhibit high H2 production activity from photocatalytic water splitting, far surpassing the MOF and CdS counterparts, under visible light irradiation. Transient absorption (TA) spectroscopy has been adopted in this report to unveil the charge-separation dynamics in CdS/UiO-66 composites, a key process that dictates their function in photocatalysis. We show that, in addition to the preferable formation of fine CdS particles assisted by the MOF, effective electron transfer, which occurs from excited CdS to UiO-66, significantly inhibits the recombination of photogenerated charge carriers, ultimately boosting the photocatalytic activity for H2 generation. This report on charge-separation dynamics for CdS–MOF composites affords significant insights for future fabrication of advanced composite photocatalysts.