Regulating the Electronic Band Structure of the Ti-Based Metal–Organic Framework toward Boosting Light-Driven Hydrogen Evolution

Abstract

The photocatalytic H₂ evolution rate on the isomorphic nanosheet-based Ti metal organic-frameworks (MOFs) is regulated through changing the length of aromatic carboxylate ligands. For the series of Ti-MOFs, when increasing the length of organic linkers, the band gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) narrow based on density functional theory (DFT) calculation, accompanied by a degree of increase of organic ligand involvement in the LUMO. When increasing the linker length, both the intensities of photoluminescence (PL) and electron paramagnetic resonance (EPR) signals related to Ti³⁺ gradually decrease, which are opposite to their photocatalytic performance, where the longer the linkers, the higher the hydrogen evolution rate. It is suggested that the bound photoelectrons by Ti³⁺ compete with the transfer of photoelectrons for H₂ evolution. When increasing the length of the organic linker, more photoelectrons could be generated, in addition to electron transfer overwhelming electrons bound by Ti³⁺. Both of them engender the super photocatalytic hydrogen evolution. This work highlights a specific way of regulating the electronic structure of Ti-based photocatalysts toward promoting the utilization efficiency of photoelectrons, which will shed light on the design of efficient photocatalysts for the generation of solar fuels.