Enhancing Visible-Light Driven Photocatalytic Hydrogen Evolution through Carbazole-Benzothiadiazole Conjugates Integrated with Graphitic Carbon Nitride

This study reports two donor–acceptor (D-A) conjugates in the (D-(A1-π-A2)2 architecture, namely, CBP and CBCN, based on carbazole (D), benzothiadiazole (A1), a phenyl π-spacer, and carbaldehyde/cyanoacrylic acid (A2). Replacing carbaldehyde in CBP with cyanoacrylic acid in CBCN enhances the latter’s charge-transfer properties. These conjugates were integrated with graphitic carbon nitride (g-C3N4) via π-π interactions to form the CBP/g-C3N4 and CBCN/g-C3N4 composites. CBCN/g-C3N4 showed a superior H2 evolution rate of 3211 μmol h–1 g–1 andCBP/g-C3N4 (1003 μmol h–1 g–1) surpassed the performance of g-C3N4 alone by 32- and 10-fold, respectively, using triethanolamine (TEOA) as a sacrificial electron donor and platinum as a co-catalyst. Apparent quantum efficiencies (AQEs) for CBCN/g-C3N4 were 11.3%, 4.68%, and 2.04% at 400, 450, and 500 nm, respectively. The improved performance of CBCN/g-C3N4 and CBP/g-C3N4 compared to only g-C3N4 is attributed to their enhanced visible-light absorption and efficient charge transfer at the heterojunction, boosting their photocatalytic potential.