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-(A 1 -π-A 2 ) 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 -C 3 N 4 ) via π-π interactions to form the CBP/ g -C 3 N 4 and CBCN/ g -C 3 N 4 composites. CBCN/ g -C 3 N 4 showed a superior H 2 evolution rate of 3211 μmol h –1 g –1 and CBP/ g -C 3 N 4 (1003 μmol h –1 g –1 ) surpassed the performance of g -C 3 N 4 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 -C 3 N 4 were 11.3%, 4.68%, and 2.04% at 400, 450, and 500 nm, respectively. The improved performance of CBCN/ g -C 3 N 4 and CBP/ g -C 3 N 4 compared to only g -C 3 N 4 is attributed to their enhanced visible-light absorption and efficient charge transfer at the heterojunction, boosting their photocatalytic potential.