Visible-Light-Driven Photocatalytic H₂ Production over an EDTA-TiO₂/DHBA Hybrid Photocatalyst

Visible-light-driven photocatalytic H₂ production using TiO₂ remains challenging due to the wide bandgap (~3.2 eV) and limited visible-light absorption. In this study, EDTA-modified TiO₂ loaded with Pt co-catalyst was employed for photocatalytic H₂ production. Under visible light (450 nm), EDTA molecules coordinated to surface Ti⁴⁺ sites form charge-transfer complexes capable of visible-light absorption and electron transfer from HOMO of EDTA to the TiO₂ conduction band through a ligand-to-metal charge (LMCT) transfer process. Notably, the incorporation of 2,3-dihydroxybenzoic acid (DHBA) significantly enhanced H₂ production rate. The strong chelating ability of catechol-type DHBA, arising from its adjacent hydroxyl and carboxyl functional groups improved visible-light harvesting, and enhanced charge separation efficiency. The photogenerated electrons subsequently migrate to Pt active sites on the TiO₂ surface for H₂ evolution. At the same time, MeOH, EDTA, and DHBA consume photogenerated holes and suppressing electron-hole recombination. It was demonstrated experimentally that 40 mg TiO₂ in a 300 ppm EDTA solution containing 0.375 wt% Pt and 10 vol% MeOH produced H₂ at 59 µmol g⁻¹h⁻¹ under 450 nm irradiation at 50°C temperature. Furthermore, the addition of 0.71 mM DHBA significantly increased the H₂ production rate to 98 µmol g⁻¹h⁻¹. The generated H₂ was detected by GC-TCD. From the UV-vis DRS spectra, a clear red shift was observed for EDTA-TiO₂ and EDTA-TiO₂-DHBA compared to TiO₂, suggesting the improved light absorption capability and Tauc plot analysis revealed a reduced bandgap, which further facilitated the transition of photogenerated electrons from HOMO to the conduction band. These findings demonstrate that the combination of EDTA surface modification and aromatic hydroxyl-carboxylic additives can effectively improve visible-light-driven H₂ production over TiO₂.