Template-free preparation and characterization of nanoporous g-C₃N₄ with enhanced visible photocatalytic activity

Highlights: • Nanoporous g-C₃N₄ was prepared via a template-free method. • The combination of ball milling and protonation effect increased the specific surface area of g-C₃N₄. • The more efficient charge separation and prolonged charge carrier life time were achieved in such nanoporous g-C₃N₄. - Abstract: A novel method was proposed to fabricate nanoporous g-C₃N₄ through high energy ball milling process followed by protonation treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET), laser particle analysis, UV–vis diffuse reflection spectroscopy (DRS), photoluminescence spectroscopy, electron paramagnetic resonance (EPR), and photoelectrochemical experiment were adopted to analyze the structure and properties of nanoporous g-C₃N₄ photocatalyst. The photocatalytic activities of the as-prepared samples were also evaluated by decomposing Congo Red (CR) and Rhodamine B (RhB) in aqueous solution under visible light illumination. The results show that the as-prepared nanoporous g-C₃N₄ exhibits high specific surface area, which is about 8.8 times as high as that of the original bulk one, and also shows more efficient exciton collection and charge transfer. Therefore, the visible photocatalytic activity of g-C₃N₄ is significantly improved, and the decomposition rate of congo red is increased from 0.03 to 0.32 h⁻¹. Furthermore, this photocatalyst also displays a selective feature in photocatalysis due to its positive surface charges determined by protonation treatment