Asymmetric Zinc Porphyrin Derivative-Sensitized Graphitic Carbon Nitride for Efficient Visible-Light-Driven H₂ Production

An asymmetric zinc porphyrin (ZnPy) derivative bearing one benzoic acid and three 3-pyridines as <i>meso</i>-position substituents (zinc-5-(4-carboxyphenyl)-10,15,20-tri­(3-pridyl)­porphyrin, ZnMT3PyP) was used to sensitize graphitic carbon nitride (g-C₃N₄) for visible-light-driven photocatalytic H₂ production. It was found that ZnMT3PyP exhibits more excellent photosensitization and stability on g-C₃N₄ than its counterpart bearing one benzoic acid and three phenyls (zinc-5-(4-carboxyphenyl)-10,15,20-triphenylporphrin, ZnMTPP) under visible light (λ > 420 nm) irradiation even though they have very similar physicochemical properties such as optical absorption capacities and energy band structures. Especially, ZnMT3PyP-Pt/g-C₃N₄ gives an apparent quantum yield (AQY) up to 25.1% at λ = 420 nm light illumination, greater than that (11.6%) of ZnMTPP-Pt/g-C₃N₄. The differences in photosensitization and stability between ZnMT3PyP and ZnMTPP are mainly due to the substitution of 3-pyridine for the phenyls in ZnMTPP, which leads to the electron transfers between ZnMT3PyP and g-C₃N₄ faster than that between ZnMTPP and g-C₃N₄. The present results provide a new insight applying porphyrin derivatives to the photocatalytic H₂ production and open up a new path for further improving the conversion efficiency of solar energy to hydrogen energy through molecular designing