Hantzsch ester as hole relay significantly enhanced photocatalytic hydrogen production

Abstract

Polymeric graphitic carbon nitride (g-C₃N₄) has emerged as a promising semiconductor photocatalytic material, which can convert solar energy into chemical energy under visible-light irradiation. However, because of the issue of recombination of photogenerated electron–hole pairs, the photocatalytic efficiency of g-C₃N₄ is dissatisfactory. Herein, we constructed a novel system of graphitic-C₃N₄ composite photocatalyst (C₃N₄/DHPE) through π–π interactions and hydrogen bonds for efficient visible light-driven H₂ evolution. The Hantzsch ester (diethyl 1,4-dihydro-2,6-3,5-pyridine dicarboxylate, denoted as DHPE) not only speeds up the transfer rate of photogenerated charge carriers, but also retards the recombination of electron–hole pairs through extracting holes from g-C₃N₄. C₃N₄/DHPE hybrid photocatalyst exhibits efficient spatial separation of photogenerated electrons and holes and thus, more electrons can be released for hydrogen production. When 4% DHPE was introduced, the hydrogen production rate of C₃N₄/DHPE photocatalyst drastically increased up to 1345.0 μmol h⁻¹ g⁻¹, which is 4.7 times higher than that of pure g-C₃N₄ (286.0 μmol h⁻¹ g⁻¹). Moreover, there is no significant decrease in H₂ production after a long time reaction (20 h, five test cycles), confirming that the C₃N₄/DHPE photocatalyst has excellent stability. Our study offers a simple, cost-effective, and powerful route to promoting efficient separation of photogenerated charge carriers and a novel strategy to design other highly efficient photocatalytic systems for solar energy conversion.