S-scheme heterojunction between donor-acceptor linear polymer and g-C3N4 via strengthened internal electric field for enhanced photocatalytic activity

The inherent sluggish photo-induced charge carrier separation and transport limit the efficiency of photocatalytic hydrogen evolution (PHE) of graphitic carbon nitride (g-C3N4). To address this, polymer-based heterojunctions (PHJs) are designed by integrating a linear donor-acceptor type polymer (PTSO-T) with g-C3N4 nanosheet at different feed ratios. The results demonstrate that the optoelectronic properties of the PHJs are significantly modulated by the intermolecular pi-pi stacking effect, resulting in a wide light absorption range, enhanced exciton dissociation rate and enhanced transport of charge carriers. Spectroscopic analysis and theoretical calculations confirmed the establishment of a highly efficient charge transfer pathway with an S-scheme and the formation of an internal electric field (IEF) within the PHJs. The optimized PTSO-T/g-C3N4-40 photocatalyst exhibits a remarkable hydrogen evolution rate (HER) of 85.51 mmol g- 1 h- 1 under visible light and with 0.3 % Pd as the co-catalyst. The photocatalyst shows improved HER, which is 1.3 and 83.0 times the HER values of PTSO-T and g-C3N4, respectively. The maximum apparent quantum efficiency (AQY) is 14.13 % at 475 nm for PTSO-T/gC3N4-40. The performance of the PHJs reported in this study ranks the first class among the state-of-the-art PHJs.