Construction of planar-type defect-engineered metal–organic frameworks with both mixed-valence sites and copper-ion vacancies for photocatalysis

Abstract

This manuscript presents a facile paradigm for controllably developing planar-type defect-engineered metal–organic frameworks (DEMOFs) by systematically doping reductive defect linker vanillin (VAN) during the synthesis of HKUST-1. The as-prepared DEMOF variants were designed to carry copper-ion vacancies and mixed-valence Cu¹⁺/Cu²⁺ sites on the {220} and {111} planes of NR-HKUST-1 and {100}, {110} and {111} planes of NS-HKUST-1 via reversible and irreversible growth modes. The photocatalysis results indicate that the mixed-valence Cu¹⁺/Cu²⁺ sites (with special electronic properties) in planar-type defective HKUST-1 have a greater effect on performance improvement than copper-ion vacancies (with special steric properties). The HOMO–LUMO gap of the Cu¹⁺/Cu²⁺ unit is significantly reduced to promote the separation of photogenerated electron–hole pairs and overcome the transfer resistance of electron–hole pairs, leading to an outstanding catalytic activity (3784.2 μmol g⁻¹ h⁻¹). This strategy of creating mixed-valence sites and vacancies by doping a reductive defect linker can provide a new way to prepare catalysts with higher photocatalytic activity.