Facet-engineering of NH₂-UiO-66 with enhanced photocatalytic hydrogen production performance

Sluggish charge transfer is the major problem which restricts the development of metal-organic framework (MOF)-based photocatalysts. Recently, facet-engineering has been proven to be an effective method for solving this issue. However, due to difficulties in regulating the exposed facets of MOFs, there are few reports about the facet-engineering of MOF-based photocatalysts. Here, we firstly report facet-engineering for promoting the photocatalytic activity of NH₂-UiO-66 crystals. In this study, by regulating the influence of kinetics and thermodynamics, cubic, tetra-decahedral, and octahedral forms of NH₂-UiO-66 are synthesized. The photocatalytic hydrogen evolution rate of tetra-decahedral NH₂-UiO-66 with co-exposed (100) and (111) crystal facets reaches 64.06 μmol g^-1 h^-1, which is approximately 2 and 1.5 times greater than that of the cubic and octahedral forms of NH₂-UiO-66, respectively. The density functional theory (DFT) calculation and ultrafast spectroscopy results indicate that a slight staggering exists in the band structure of (100) and (111) facets, causing the facets junction to appear. The facet junction promotes the charge separation efficiency and prolongs the lifetime of the charge carriers, thereby giving tetra-decahedral NH₂-UiO-66 optimal photocatalytic performance. This study demonstrates the feasibility and potential of facet-engineering for photocatalytic applications of MOFs.