ZnO Modified g‐C3N4–MnO2 Composite for Photodegradation of Methylene Blue

Single ZnO (NM1), MnO2 (NM2) nanoparticles, and MnO2–g‐C3N4–ZnO (NM4) nanocomposite were synthesized by the sol–gel method, whereas g‐C3N4 (NM3) was synthesized by polymerization of urea. The as‐synthesized materials were characterized by thermogravimetric‐differential thermal (TGA‐TDA), Fourier transformer (FTIR), X‐ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and high‐resolution transmission electron microscopy (HRTEM).The bandgap of the NM4 nanocomposite was lower than those of NM1, NM2, and NM3 photocatalysts, which is applicable in the visible region. The photocatalytic activities of the synthesized materials were studied under visible light radiation. The efficacy of NM4 composite is 5, 3.4, and 3‐fold higher than those of NM1, NM2, and NM3 materials. This enhancement might be ascribed to the synergistic effect. Besides, the NM4 nanocomposite degraded 94% of methylene blue (MB) and 81% of the real sample. The rate constant (k) for NM1, NM2, NM3, and NM4 nanocomposite was also studied and resulted in 0.00327, 0.0046, 0.0056, and 0.0156 min−1, respectively. The reusing of NM4 nanocomposite was carried out for four sequential rounds and resulted in 94%, 92.6%, 91%, and 89% degradation efficiency for 1st, 2nd, 3rd, and 4th round, respectively. This result suggests that the synthesized NM4 is cost‐effective and stable. This work provides an overview of composite photocatalysts for degrading methylene blue dye under visible light. The MnO2–ZnO–g‐C3N4 photocatalyst features a unique band structure that reduces electron‐hole recombination. Superoxide radicals attack methylene blue, producing CO2 and H2O, whereas photoexcited electrons generate H2O2, and holes create hydroxyl radicals, enhancing degradation efficiency.