Visible-light-driven g-C₃N₄/AgBiS₂ S-scheme photocatalyst for N₂ fixation and rhodamine B degradation

The design of photocatalysts, which uses free and available sunlight as a driving force to generate ammonia from nitrogen (N₂) and remove organic pollutants from wastewater, is helpful to develop a sustainable chemical industry. The novel g-C₃N₄ nanosheet/AgBiS₂ nanocomposite with visible-light response was successfully fabricated for the first time using a simple heating process. The purity, microstructure, morphology, photoelectrochemical, and electronic features of the obtained photocatalysts were studied using X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, photoluminescence, Brunauer–Emmer–Teller surface area, photocurrent responses, and electrochemical impedance spectroscopy. The g-C₃N₄ nanosheet/AgBiS₂ nanocomposite possessed excellent photocatalytic activity for rhodamine B (RhB) degradation and N₂ fixation upon visible illumination. The photocatalytic ammonium production reached 3780 μmol L⁻¹ g⁻¹ over g-C₃N₄ nanosheet/AgBiS₂ nanocomposite, increases of 3.15- and 2.85-fold compared to that of g-C₃N₄ nanosheet and AgBiS₂, respectively, as well as 99% improvement in degradation efficiency for RhB removal. The improved activity of g-C₃N₄ nanosheet/AgBiS₂ nanocomposite can be ascribed to the formation of suitable heterojunction, suppressing the recombination of photogenerated charges, while facilitating their transfer. A plausible photocatalytic mechanism was proposed based on the experimental outcomes and photoelectrochemical properties. The g-C₃N₄ nanosheet/AgBiS₂ nanocomposite proved to be significantly reusable and stable after five and four runs of N₂ fixation and RhB degradation, respectively.