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

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.