Enhanced Green Hydrogen Generation via Photocatalytic Water Splitting Using V-Doped Ti-Squarate MOFs

Herein, defect engineering strategies were applied to enhance the photocatalytic activity of squarate-based MOFs (IEF-11) for green hydrogen generation via water splitting. The textural properties of pristine IEF-11(Ti) were significantly improved using microwave (MW)-assisted synthesis, leading to a four-fold increase in surface area (350 m² g^-1) due to the formation of mesopores associated with defect aggregation, primarily arising from linker vacancies (24%). Vanadium doping (0-100%) progressively reduced the optical band gap (2.44-1.87 eV), shifting absorption toward the visible region. The IEF-11 series was evaluated as photocatalysts for the hydrogen evolution reaction under simulated sunlight irradiation, revealing a volcano-type trend correlating activity with V content. Doped with 11% V, the MW-synthesized IEF-11(Ti_0.89V_0.11)_MW solid exhibited the highest activity (1053 <i>vs</i>. 536 μmol g^-1 h^-1 H₂ for IEF-11(Ti)), attributed to optimized band alignment, enhanced charge separation, and structural robustness. It also showed activity in photocatalytic overall water splitting (83 μmol g^-1 h^-1 H₂, 30% higher than the undoped IEF-11(Ti)). Theoretical calculations further confirmed band gap narrowing and the generation of new electronic states upon V-doping, facilitating charge transfer and reducing electron-hole recombination. These findings highlight the relevance of inducing artificial porosity and V-doping of IEF-11(Ti) to prepare efficient MOF-based photocatalysts. Importantly, this work not only reports the first V-squarate frameworks but also represents one of the first systematic studies addressing the effect of metal doping in MOFs for photocatalytic water splitting, achieving competitive efficiencies operating in the absence of cocatalysts.