D–π–A-type triphenylamine dye covalent-functionalized g-C3N4 for highly efficient photocatalytic hydrogen evolution

Abstract

Two novel covalent bond photocatalysts, namely, g-C₃N₄NSs/TC1 and g-C₃N₄NSs/TC2 were prepared for the first time via the generation of an amide covalent bond between g-C₃N₄ nanosheets (g-C₃N₄NSs) and acyl chloride synthesized from triphenylamine-type dyes, 2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid (TC1) or 3,3′-(4,4′-(phenylazanediyl)bis(4,1-phenylene))bis(2-cy-anoacrylic acid) (TC2). The experimental results indicated that triphenylamine D–π–A-type organic dye moieties covalently bonded to g-C₃N₄ successfully and the spectral response regions of both g-C₃N₄NSs/TC1 and g-C₃N₄NSs/TC2 could be extended from ∼460 nm to more than 600 nm. Due to the introduced amide covalent bond, the constructed g-C₃N₄NSs/TC1 photocatalyst showed remarkably enhanced H₂ evolution activity with about 73 555.8 μmol h⁻¹ g⁻¹ and exhibited high apparent quantum yields (AQY) of 35.2%, 27.1%, 16.9% and 5.4% at 420 nm, 500 nm, 520 nm and 600 nm monochromatic light, respectively. Compared with the results for pure g-C₃N₄ NSs, about 100 times higher H₂ production rate and 978 times higher AQY value were obtained for g-C₃N₄NSs/TC1 with the amide covalent bond under visible light irradiation. Compared to g-C₃N₄NSs/TC1, g-C₃N₄NSs/TC2 exhibited slightly lower H₂ evolution activity with about 70 986.8 μmol h⁻¹ g⁻¹. Combining the experimental and density functional theory (DFT) calculation results, a possible mechanism can be conjectured that the electronic and geometric structures of g-C₃N₄NSs/TC1 are more conducive to the charge separation and the unidirectionality of electron transport in the excited state than those of g-C₃N₄NSs/TC2. The research reveals that this introduction of simple triphenylamine-type dyes into the surface of g-C₃N₄via covalent links results in a strong covalent interaction between functionalized moieties and g-C₃N₄ to synergistically improve the electronic and optical properties and photocatalytic performance. The present work highlights the potential use of organic dye covalent-functionalized g-C₃N₄via post modification as a novel photocatalyst in applications such as H₂ production.