Controlled Construction of Hierarchically Porous UiO-66 by Adjusted Partial Linker Thermolysis with Enhanced CO₂ Photoreduction Activity

Abundant porosity, sufficient active sites, and appropriate stability are crucial factors for metal-organic frameworks (MOFs) designed for photocatalysis. Herein, a controllable partial pyrolysis strategy was employed to synthesize hierarchically porous UiO-66-<i>X</i> (<i>X</i> denotes the mass ratio of H₂BDC-NH₂ in ligands) with adjustable coordinated unsaturated zirconium sites and interconnected mesoporous structure. By taking full advantage of linker instability in MOFs, which is usually viewed as an undesirable trait of MOFs, this controllable thermolysis involved heat treatment of the original UiO-66-<i>X</i>, leading to selective partial decomposition and permanent mesopores within the structure. Meanwhile, dangling functional amino groups could serve as anchoring sites for cocatalyst and CO₂ molecules. Cu nanoclusters were successfully incorporated into hierarchically porous MOFs by a structure engineering approach, yielding a novel photocatalyst. A mutually active mechanism was put forward and illustrated in this work. Mechanistic investigation reveals that mesoporous structures in a catalyst not only offer three-dimensional (3D) interconnected gas transport channels but also provide sufficient space for accommodating the introduced Cu nanoclusters, which served as active sites and efficiently induced a CO₂ photoreduction reaction. At the optimal ratio, the photocatalyst exhibited superior photocatalytic activity, achieving a CO yield of 121.64 μmol g^-1 under 5 h of the stimulated solar irradiation without any photosensitizer.