Fabrication of metal-doped graphite phase carbon nitride-based membrane and its application

Metal-doped (Cu, Zn, Mn) g-C₃N₄ was synthesized by a simple high-temperature process, followed by the insertion of one-dimensional nanofibrillar cellulose (CNF) into the two-dimensional g-C₃N_4. Photocatalytic composite membranes were then prepared using a vacuum-assisted filtration method. A series of characterization techniques, including XRD, SEM, FT-IR, and UV–vis DRS, were employed to systematically analyze the microstructure, chemical composition, and physicochemical properties of the designed g-C₃N₄/CNF composite membranes. The results indicated that the visible photocatalytic activity of the metal-doped photocatalysts was enhanced, which is beneficial for pollutant degradation by reducing the bandgap and extending the absorption of visible light. Notably, the composite membrane prepared with Mn-doped g-C₃N₄ demonstrated the highest photocatalytic performance in degrading rhodamine B dye, achieving a 42.6% degradation rate within 7 h. Additionally, the water flux and retention rate of the composite membranes were improved after metal doping, with Zn-doped g-C₃N₄ showing approximately six times the water flux of undoped g-C₃N₄, reaching a rate of 293.64 L·m⁻²·h⁻¹·bar⁻¹.