Photocatalytic, Antioxidant, Energy Storage, and Sensing Applications of rGO Loaded MnO₂ Nanoparticles

A reduced graphene oxide/manganese dioxide (rGO/MnO₂) was prepared via a reflux method. MnO₂ was prepared by the combustion method using neem leaf extract as a biogenic fuel. The materials were characterized using X-ray diffraction, Brunauer-Emmett-Teller, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, EDS, XPS, UV-vis, and photoluminescence spectroscopy. The rGO/MnO₂ exhibited outstanding photocatalytic degradation of methyl violet (MV), achieving ~99.21% removal within 70 min under UV irradiation. The radical scavenging assays demonstrated markedly improved antioxidant activity for rGO/MnO₂, with a half-maximal inhibitory concentration (IC₅₀) of 186.77 μL/μg compared to rGO and MnO₂. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) revealed a specific capacitance of 132.71 F/g for the composite electrode, nearly double the performance of bare MnO₂. The electrode also demonstrated superior electrochemical sensing toward Hg²⁺ and Cr²⁺ metal ions, with lower limits of detection (LOD: 5.94 and 12.42 μM). These results collectively establish rGO/MnO₂ as a nanocomposite with strong potential for environmental and energy storage studies.