A General Strategy to Immobilize Single‐Atom Catalysts in Metal–Organic Frameworks for Enhanced Photocatalysis

Abstract

Single‐atom catalysts (SACs) are witnessing rapid development due to their high activity and selectivity toward diverse reactions. However, it remains a grand challenge in the general synthesis of SACs, particularly featuring an identical chemical microenvironment and on the same support. Herein, a universal synthetic protocol is developed to immobilize SACs in metal–organic frameworks (MOFs). Significantly, by means of SnO2 as a mediator or adaptor, not only different single‐atom metal sites, such as Pt, Cu, and Ni, etc., can be installed, but also the MOF supports can be changed (for example, UiO‐66‐NH2, PCN‐222, and DUT‐67) to afford M1/SnO2/MOF architecture. Taking UiO‐66‐NH2 as a representative, the Pt1/SnO2/MOF exhibits approximately five times higher activity toward photocatalytic H2 production than the corresponding Pt nanoparticles (≈2.5 nm) stabilized by SnO2/UiO‐66‐NH2. Remarkably, despite featuring identical parameters in the chemical microenvironment and support in M1/SnO2/UiO‐66‐NH2, the Pt1 catalyst possesses a hydrogen evolution rate of 2167 µmol g–1 h–1, superior to the Cu1 and Ni1 counterparts, which is attributed to the differentiated hydrogen binding free energies, as supported by density‐functional theory (DFT) calculations. This is thought to be the first report on a universal approach toward the stabilization of SACs with identical chemical microenvironment on an identical support.

Considering single-atom catalysts as photocatalysts from synthesis to application

“…For MOF itself, its unsaturated coordination sites, defects, and the porous structure can be utilized to anchor metal SAs, making it an ideal substrate for anchoring the SAs ( Jiao and Jiang, 2019 ). For example, the Pt 1 /SnO 2 /UiO-66-NH 2 catalysts were successfully synthesized by Sui et al., applying for the visible-light-driven HER ( Sui et al., 2021 ). The obtained Pt 1 /SnO 2 /UiO-66-NH 2 SAPs showed a superior H 2 evolution rate of 2167 μmol g −1 h −1 .…”

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Figure 12 Different substrates for the synthesis of single-atom photocatalysts (A) Schematic illustration of metal/SnO 2 /UiO-66-NH 2 . Reproduced with permission from Ref ( Sui et al., 2021 ). Copyright 2021, Wiley.

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“… (A) Schematic illustration of metal/SnO 2 /UiO-66-NH 2 . Reproduced with permission from Ref ( Sui et al., 2021 ). Copyright 2021, Wiley.…”

“… (D–E) The Pt L 3 -edge XANES spectra for Pt 1 /SnO 2 /UiO-66-NH 2 , PtO 2 , and Pt foil, and (e) Fourier transformed (FT) k 2 -weighted χ(k)-function of the EXAFS spectra for Pt 1 /SnO 2 /UiO-66-NH 2 , PtO 2 , K 2 PtCl 4 , and Pt foil. Reproduced with permission from Ref ( Sui et al., 2021 ). Copyright 2021, Wiley.…”

“…For instance, Sui et al. performed XAS to determine the coordination environment and chemical state of Pt species in Pt 1 /SnO 2 /UiO-66-NH 2 SAPs ( Sui et al., 2022 ). From the L 3 -edge image, it could be seen that the peak intensity of Pt 1 /SnO 2 /UiO-66-NH 2 was closer to that of PtO 2 , implying the presence of a highly oxidized Pt state ( Figure 14 D).…”