Heterointerface Connection with Multiple Hydrogen-Bonding in Z-Scheme Heterojunction SiW9Co3@UiO-67-NH2 Deciding High Stability and Photocatalytic CO2 Reduction Performance

Merging metal-organic frameworks (MOFs) and polyoxometalates (POMs) into heterogeneous heterojunction photocatalysts through in situ encapsulation is an effective approach to suppress the leachability of POMs and enhance their electron supply. The heterointerfacial connection in POMs@MOFs directly determines the performance of stability and charge separation, and the suited interaction between MOFs and POMs for POMs@MOFs heterojunctions photocatalyst is of vital importance. Here, a distinctive Keggin-type POM [(n-C₄H₉)N]₁₀[SiW₉Co₃ (H₂O)₃O₃₇]·17H₂O (SiW₉Co₃) with near-total visible region absorption, narrow band gap of 2.23 eV, and powerful electron supply activity was prepared and tightly immobilized in the cavities of UiO-67-NH₂ and UiO-68-NH₂ to construct two Z-scheme heterojunctions SiW₉Co₃@UiO-67-NH₂ and SiW₉Co₃@UiO-68-NH₂, which were used for photocatalytic reduction of CO₂ to CO. Their compositions, structures, and energy band features were fully characterized by a series of tests including XRD, FT-IR, SEM, XPS, UV-vis-DRS, UPS, and so forth. SiW₉Co₃@UiO-67-NH₂ showed optimal photocatalytic performance with an excellent CO yield of 153.3 μmol^-1·g^-1·h^-1 and a selectivity of 100%, which is 3.3-fold higher than that of SiW₉Co₃@UiO-68-NH₂ and far superior to most reported POM-based heterojunctions. Comprehensive investigations with extensive photoelectric characterizations and microcalorimetric experiments demonstrated that the exceptional photocatalytic performances of SiW₉Co₃@UiO-67-NH₂ could be attributed to the fact that (i) strong host-guest interactions were formed due to the well-matched dimensions between SiW₉Co₃ cluster and MOF cavity, which generated an intimate heterointerface to effectively accelerate interface electron transfer; (ii) the intimate heterointerface promoted SiW₉Co₃ to yield multielectron supply for efficient interfacial carrier neutralization owing to its donor-acceptor structure and narrow band gap. Additionally, the excellent durability of SiW₉Co₃@UiO-67-NH₂ was also supported by the solidly locked SiW₉Co₃ and a stable MOF framework.