Manganese Cobalt Sulfide-Integrated g-C ₃ N ₅ Heterojunction Nanocomposite for Visible-Light-Driven Photocatalysis and Electrochemical Energy Storage

The pursuit of sustainable technologies for both environmental purification and energy storage has driven the development of multifunctional nanomaterials capable of delivering high performance in diverse applications. In this study, a g-C3N5/MnCo2S4 nanocomposite was successfully fabricated using a simple indirect-hydrothermal method and systematically assessed for its dual functionality in photocatalytic pollutant removal and electrochemical energy storage. Under visible-light irradiation, the composite displayed superior photocatalytic activity toward Congo Red dye, achieving a degradation efficiency of 92.45% within 60 min. In parallel, the material exhibited superior capacitive behavior, delivering a specific capacitance of 1188.57 F g–1 at 1 A g–1 along with long-term cycling stability over 10,000 charge–discharge cycles. Morphological analyses through FE-SEM and HR-TEM indicated a homogeneous integration of MnCo2S4 rock-like structures onto the g-C3N5 layered structures in the nanocomposite, which results in increased surface area, as verified by BET analysis. Impedance measurements confirmed a markedly reduced internal resistance in the nanocomposite, indicating efficient ion transport and improved electrical conductivity compared to their individuals. The fabricated asymmetric device exhibits a high energy density of 22.81 Wh kg–1 at 599.3 W kg–1 power density. Collectively, these findings demonstrate that the g-C3N5/MnCo2S4 nanocomposite is a highly effective, low-cost, multifunctional material with strong potential for synergistic applications in wastewater treatment and energy-storage systems. The work also emphasizes the broader prospects of engineering g-C3N5-based materials for next-generation environmental and energy technologies.