Solvothermal synthesis of carbon nitride (g-C₃N₄): bandgap engineering for improved photocatalytic performance

Graphitic carbon nitride (g-C₃N₄) is a metal-free semiconductor material with highly promising photocatalytic properties owing to its unique structural, electronic, and optical characteristics. Herein, the solvothermal synthesis of g-C₃N₄ as a photocatalyst for photoelectrochemical water splitting and the photocatalytic degradation of organic pollutants is reported. The solvothermal synthesis of g-C₃N₄ was carried out using acetonitrile as the solvent at three different temperatures: 160 °C, 180 °C and 200 °C. The chemical structure of the synthesized photocatalysts was characterized using NMR, FT-IR, and Raman spectroscopy. Phase purity was confirmed through X-ray diffraction (XRD), and the morphology was analyzed using transmission electron microscopy (TEM). The optical properties were accessed using UV-visible and diffuse reflectance spectroscopy (DRS). The prepared photocatalysts were tested for photoelectrochemical (PEC) water splitting and the photocatalytic degradation of organic pollutants, with methylene blue used as a model compound. It was observed that the g-C₃N₄ synthesized at 200 °C showed an enhanced anodic photocurrent of ∼25 mA cm⁻² at an applied potential of 1.7 V vs. RHE under exposure to 100 mW cm⁻², AM 1.5 G. Additionally, it exhibited superior performance in the photocatalytic degradation of organic pollutants, with methylene blue as the model compound. The enhanced photoelectrochemical and photocatalytic performance of the g-C₃N₄ synthesized at 200 °C is likely attributed to the improved physicochemical properties of the material, which are linked to its structural features modified by the elevated synthesis temperature.