Fabrication of CoTiO3/g-C3N4 Hybrid Photocatalysts with Enhanced H2 Evolution

Hydrogen (H₂) has gained much attention as a sustainable and carbon-neutral fuel carrier. Since Fujishima and Honda reported H₂ evolution from water splitting by using TiO₂ electrode under light irradiation in 1972, photocatalytic water splitting has become one of the most fascinating and promising technologies. Among numerous photocatalysts, graphitic carbon nitride (g-C₃N₄) has been rapidly developed due to its non-toxic, proper energy band level for H₂ production (2.7 eV), ability of absorbing visible light, good physicochemical stability and facile fabrication via one-step polymerization. Unfortunately, the pure g-C₃N₄ seriously suffers from poor photocatalytic efficiency because of a high recombination rate of photo-generated charge carriers. To settle this problem, g-C₃N₄-based heterojunctions were prepared. However, the redox ability of photoexcited electrons and holes would be declined as the typical heterojunction forms.

This work reports a novel direct Z-scheme CoTiO₃/g-C₃N₄ (CT-U) photocatalytic system with different weight percentage of CoTiO₃ using a facile in-situ growth method for H₂ evolution from water splitting. The as-prepared CT-U composites composed of 1D CoTiO₃ microrod and 2D g-C₃N₄ nanosheet were characterized by various techniques including XRD, SEM, TEM, XPS, FTIR and UV-vis. Results demonstrate that the CT-U composite photocatalysts were successfully fabricated, with intimate interfacial contact and heterojunction interaction between g-C₃N₄ and CoTiO₃ which can significantly boost the photocatalytic activity compared with prinstine g-C₃N₄ and CoTiO₃. The most enhanced H₂ evolution rate of 858 μmol·h^-1·g^-1 and high quantum efficiency (38.4% at 365 nm, 3.23% at 420 ± 20 nm) are achieved at an optimal 0.15% CT-U. Meanwhile, the 0.15% CT-U sample exhibits good photocatalytic stability in recycling H₂ evolution. Accordingly, direct Z-scheme mechanism capable of leading efficient charge carrier separation and strong reduction ability for enhanced H₂ production was proposed, and further evidenced by PL, Photoelectrochemical analysis and ESR assay.