Graphitic carbon nitride/CoTPP type-II heterostructures with significantly enhanced photocatalytic hydrogen evolution

Abstract

Graphitic carbon nitride (g-C₃N₄) is among the most promising metal-free photocatalysts for hydrogen (H₂) evolution from water splitting under visible-light irradiation. However, the fast recombination rate of its photogenerated electron–hole pairs limits the photocatalytic activity of g-C₃N₄. Herein, we have developed highly efficient visible light driven C₃N₄/CoTPP type-II heterostructures by decorating cobalt(II) meso-tetraphenylporphine (CoTPP) on the surface of the g-C₃N₄ catalyst through π–π supramolecular interaction. The introduction of CoTPP enhances the migration and transfer of photogenerated charge carriers and inhibits the recombination of electron–hole pairs through the formation of C₃N₄/CoTPP type-II heterojunctions. The C₃N₄/CoTPP heterostructured photocatalyst exhibits efficient spatial separation of photogenerated electrons and holes due to the well-matched overlapping band structures of two semiconductors, thus facilitating more electrons to be released for H₂ evolution. When 4 wt% (weight ratio) CoTPP is loaded onto g-C₃N₄, the H₂ evolution rate of the C₃N₄/CoTPP heterostructured photocatalyst is significantly increased up to 46.93 μmol h⁻¹ under visible light irradiation (λ ≥ 420 nm), which is 2.73 times higher than that of bare g-C₃N₄ (17.21 μmol h⁻¹). Moreover, the C₃N₄/4 wt% CoTPP type-II heterostructured photocatalyst shows good stability for H₂ evolution after five consecutive cycles of continuous irradiation of up to 20 h. Conclusively, the g-C₃N₄ photocatalyst coupled with CoTPP conjugated molecules substantially improves the photocatalytic performance and stability for H₂ evolution from water under visible light irradiation. This novel strategy sheds light on developing other highly efficient photocatalytic systems for clean energy production.