Mechanochemically synthesized MnO2-gCN nanocomposite for photocatalytic dye and phenol degradation: A combined experiment and DFT study

We present the large-scale synthesis of Manganese dioxide-graphitic carbon nitride (MnO₂-gCN) nanocomposite using a mechanochemical process. Hydrothermally synthesized rod-shaped MnO₂, combined with pyrolyzed gCN powder in appropriate proportions was mechanically ball-milled to form the MnO₂-gCN composite structure. The resulting nanocomposite characterized through X-ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy, UV–Vis spectroscopy, and photoluminesce study revealed the successful anchoring of gCN with MnO₂ nanostructure. Subsequently, the photocatalytic activity of MnO₂-gCN nanocomposite was assessed by studying the degradation of Rhodamine B, Eosin B, Congo red, Methylene Blue dyes and toxic phenol pollutants under UV light exposure. The MnO₂-gCN hybrid catalyst demonstrated impressive degradation efficiency, ca. 90% for Rhodamine B dye and 70% for phenol in 3 h and remarkable stability upto three cyclic runs. The superior performance of the composite, in comparison to its individual counterparts (MnO₂ or gCN), can be attributed to the effective separation of photogenerated electron-hole $(e^{-}-h^{+}$) pairs and the suppression of charge recombination at the interface. First principle based density functional theory calculations also support the experimental findings and the conclusion of this study.