In-situ synthesis of ternary heterojunctions via g-C₃N₄ coupling with noble-metal-free NiS and CdS with efficient visible-light-induced photocatalytic H₂ evolution and mechanism insight

The two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheets based composites are prepared in the form of the NiS/g-C₃N₄, CdS/g-C₃N₄ and CdS/NiS/g-C₃N₄ using a facile and reliable method of chemical deposition. The TEM and HRTEM images demonstrated a spectacular representation of the 2D lamellar microstructure of the g-C₃N₄ with adequately attached CdS and NiS nanoparticles. The changes in crystallinity and the surface elemental valence states of composites with the incorporation of two metal sulphides are studied, which confirmed the formation of composites. The photocatalytic response of the composites was estimated by photodegradation of Rhodamine B (C₂₈H₃₁ClN₂O₃–RhB), and the ternary composite CdS/NiS/g-C₃N₄ samples exhibited the superior photocatalytic performance. Further, the free radical capture and electron paramagnetic resonance (EPR) spectroscopy experiments identified the main active species that contributed to the photocatalytic reaction. Besides, the samples’ photocatalytic performance was evaluated by photocatalytic hydrogen production. The stability of the performance-optimized composite was determined by employing cyclic experiments over five cycles. The CdS/NiS/g-C₃N₄ showed the highest efficiency of hydrogen production i.e. about 423.37 μmol.g⁻¹.h⁻¹, which is 2.89 times that of the pristine g-C₃N₄. Finally, two types of heterojunction structures were proposed to interpret the enhanced photocatalytic efficiency.