Modulating Coordination Environment of Single-Atom Catalysts and Their Proximity to Photosensitive Units for Boosting MOF Photocatalysis.

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/OHx 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.