Engineering g-C₃N₅/MnCo₂S₄ Heterojunction Nanocomposites for Highly Efficient Visible-Light Photocatalytic Dye Degradation and Electrochemical Energy Conversion

Abstract

The growing global demand for the sustainable technologies to combat environmental pollution and fulfil clean-energy requirements has sparked intense interest in the multifunctional nanomaterials. Designing a single material that simultaneously addresses both challenges remains a highly promising yet formidable goal. In this study, a g-C3N5/MnCo2S4 nanocomposite was successfully synthesized via a facile indirect-hydrothermal route. The composite achieved 98.88% of photocatalytic degradation efficiency towards indigo carmine (IC) dye within 60 minutes under visible light, outperformed the pristine g-C3N5 and MnCo2S4. Moreover, the as-synthesized nanocomposite exhibited outstanding hydrogen evolution reaction (HER) activity in 0.5 M H2SO4, achieving a current density of 10 mA cm-2 at a low overpotential of -131 mV. Furthermore, in 1M KOH, the nanocomposite demonstrated excellent oxygen evolution reaction (OER) performance, requiring an overpotential of only 205 mV to reach the same current density. In both the reactions, the nanocomposite maintained excellent stability over 20 h of continuous operation. The electrochemical impedance spectroscopy (EIS) revealed significantly reduced charge transfer resistance, indicating the enhanced charge transport and electrical conductivity. The superior bifunctional activity was attributed to the strong interfacial synergy between the individual materials, which ensured uniform dispersion of MnCo2S4 nanostructures over exfoliated g-C3N5 layers, as supported by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and Brunauer–Emmett–Teller (BET) analyses. Overall, the g-C3N5/MnCo2S4 nanocomposite demonstrated excellent structural stability, a high surface area, and efficient charge transfer, establishing it as a highly promising, cost-effective bifunctional material for the wastewater remediation and sustainable hydrogen and oxygen evolution.