Facile preparation of carbon nitride by binary eutectic KNO3/KCl molten salt and its photocatalytic performance evaluation

Abstract

Graphitic carbon nitride (g-C₃N₄) has been widely investigated and applied in photocatalysis, but it always suffers from unsatisfactory photocatalytic activity performance. In this study, a facile molten salt-assisted heat-treated g-C₃N₄ via binary eutectic KNO₃/KCl was successfully developed. Based on this assumption, the heat treatment temperature has been successfully lowered to 350 °C to modulate and optimize the carbon nitride structure. The obtained target photocatalysts were characterized using various characterization methods (scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and transient photocurrents), confirming the practicability of the proposed strategy. The presence of doped K⁺ ions and the introduction of cyano groups into the main structure can strengthen the photo-induced electron–hole separation and migration ability, suppressing their recombination. Consequently, the much-enhanced photocatalytic activity of the obtained target catalyst was achieved and demonstrated through comprehensive tests such as photocatalytic degradation of organic dyes, photocatalytic degradation of pesticides, photocatalytic degradation of organic flotation reagent, and photocatalytic hydrogen production. Among these, g-CN-A-PN/PC-T350 exhibited the highest photocatalytic activity and the highest recycling usage stability compared with the pure sample. In addition, a possible mechanism for photocatalytic degradation of organic compounds and photocatalytic H₂ evolution was obtained based on comprehensive experimental analysis. Our finding provides a promising way for g-C₃N₄ to manipulate the photocatalytic activity simply by introducing eutectic KNO₃/KCl in the preparation process and provides a comprehensive understanding of the roles of molten salt.