Linker Engineering of Sandwich-Structured Metal-Organic Framework Composites for Optimized Photocatalytic H2 Production

Abstract

While the microenvironment around catalytic sites is recognized to be crucial in thermocatalysis, its roles in photocatalysis remain subtle. In this work, a series of sandwich-structured metal-organic framework (MOF) composites, UiO-66-NH₂ @Pt@UiO-66-X (X means functional groups), is rationally constructed for visible-light photocatalytic H₂ production. By varying the ─X groups of the UiO-66-X shell, the microenvironment of the Pt sites and photosensitive UiO-66-NH₂ core can be simultaneously modulated. Significantly, the MOF composites with identical light absorption and Pt loading present distinctly different photocatalytic H₂ production rates, following the ─X group sequence of ─H > ─Br > ─NA (naphthalene) > ─OCH₃ > ─Cl > ─NO₂ . UiO-66-NH₂ @Pt@UiO-66-H demonstrates H₂ production rate up to 2708.2 µmol g^-1 h^-1 , ≈222 times that of UiO-66-NH₂ @Pt@UiO-66-NO₂ . Mechanism investigations suggest that the variation of the ─X group can balance the charge separation of the UiO-66-NH₂ core and the proton reduction ability of Pt, leading to an optimal activity of UiO-66-NH₂ @Pt@UiO-66-H at the equilibrium point.

Keywords: hydrogen production; linker engineering; metal-organic frameworks; photocatalysis.