Tuning the Bandgap of Semi‐Conductive Metal–Organic Framework to Promote Photocatalytic Hydrogen Evolution from Water

The systematic study on the relationship between the bandgap of catalysts and their activity for water reduction under visible-light irradiation is of significant importance. Herein, the design flexibility and modifiability of Metal-Organic Frameworks (MOFs) are utilized to synthesize a series of M₃O-containing MOFs (named NKU-M, M represents Fe, Co, Ni, FeNi, FeCo, Fe-NO₂, and Fe-NH₂) through structure engineering. Upon visible light irradiation, the H₂ production rates of these MOFs exhibit a volcanic curve with bandgap changing, and NKU-Fe with a bandgap of 2.15 eV shows the highest rate of 263.5 µmol g^-1 h^-1. Theoretical calculation suggests that NKU-Fe possesses an optimal conduction and valence band position and a small value of work function, contributing to its excellent hydrogen production performance under visible light. Systematic studies reveal that photocatalysts with wider bandgaps go against absorbing sunlight, leading to unsatisfied hydrogen production. Catalysts with narrower bandgaps have higher light harvesting ability but may exhibit lower space potential, leading to an increased recombination rate of photo-generated electron-hole pairs, which hampers overall photocatalytic performance. This study illustrated that the activity of photocatalysts can be adjusted by tuning the bandgaps at the molecular degree, which may inspire the construction of more efficient catalysts for photocatalysis.