Mesoporous NiFe₂O₄@g‐C₃N₄‐Based <i>p–n</i> Heterostructures for Boosting Solar‐Driven Photocatalytic Dye Degradation and Hydrogen Evolution

Mass-fraction-optimized heterojunction composites featuring precisely engineered interfaces and mesoporous structures are crucial for improving light absorption, minimizing electron-hole recombination, and boosting overall catalytic efficiency. Herein, highly efficient mesoporous-NiFe₂O₄@g-C₃N₄ heterojunctions were developed by embedding p-type NiFe₂O₄ nanoparticles (NPs) within n-type porous ultrathin g-C₃N₄ (p-uCN) nanosheets. The optimized NiFe₂O₄@g-C₃N₄, loaded with 20 wt % magnetic counterparts, exhibits exceptional photocatalytic methylene blue (MB) degradation, achieving the highest performance in both photocatalytic and photo-Fenton processes with rate constants of 0.062 min^-1 and 0.161 min^-1, respectively. These performance metrics are 1.3 and 2.55 fold higher than p-uCN (0.048 min^-1 and 0.063 min^-1) and 51.6 and 17.4 fold higher than NiFO (0.0012 min^-1 and 0.009 min^-1). Notably, mp-NiF@uCN-20 % with 1.0 wt % of Pt loading achieves the highest H₂ evolution rate of 2294 μmolg^-1h^-1, which is 3.72, 1.52, and 13.49 times higher than that of pure CN, p-uCN, and NiFO, respectively. The enhanced performance is corroborated by increased surface area, improved separation of charge carriers, and effective charge transfer, which enables simultaneous reduction and oxidation processes. Further, the magnetic nanocomposite exhibits remarkable stability even after multiple runs, indicating their reusability. The experimental findings emphasize the importance of p-n heterojunctions, interfacial band alignment, and mesoporous architecture in enhancing the photocatalytic efficiency of NiFe₂O₄@g-C₃N₄ nanocomposites.