Insights into the Electrocatalytic Oxygen Evolution Reaction and Photocatalytic Methylene Blue Degradation of Mixed Spinel NixCu1–xFe2O4 Nanocomposites Anchored at Sulfur-Doped g-C3N4

In consideration of energy conversion and/or environmental protection, it is important to develop electrocatalytic and/or photocatalytic active materials for the oxygen evolution reaction (OER) and photodegradation of methylene blue (MB), respectively. To meet these requirements, mixed spinel ferrites such as NixCu1–xFe2O4 anchored at sulfur-doped graphitic carbon nitride (SCN) nanosheets was developed for the first time via a simple one-pot hydrothermal method for the construction of a novel bifunctional NixCu1–xFe2O4@SCN nanocomposite. Initially, the crystal structure, optical properties, surface morphology, elemental composition, and surface area of different nanocomposites, such as NiFe2O4, Ni0.8Cu0.2Fe2O4, Ni0.5Cu0.5Fe2O4, Ni0.2Cu0.8Fe2O4, SCN, and Ni0.5Cu0.5Fe2O4@SCN, were studied through XRD, UV-DRS analysis, FT-IR, FE-SEM with EDX, HR-TEM, and BET analysis. Furthermore, when compared to other prepared electrode nanocomposites such as spinel ferrites or different proportion mixed spinel ferrites, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite loaded 316 SSL mesh electrode demonstrated exceptional electrocatalytic oxygen evolution performance with a very low overpotential of 250 mV at 10 mA cm–2 current density and outstanding stability. Subsequently, the photocatalytic activities of the prepared mixed spinel ferrites, NixCu1–xFe2O4@SCN nanocomposites, were tested through the degradation of MB under visible-light irradiation. Among the prepared photocatalysts, Ni0.5Cu0.5Fe2O4@SCN nanocomposite showed superior photocatalytic MB degradation under visible light, which is firmly due to the equi-proportion blending of Cu+2 substitutions in mixed spinel ferrites at SCN. Accordingly, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite shows excellent photocatalytic degradation (POD) efficiency of 99.1% for MB in 40 min, while other nanocomposites such as NiFe2O4, SCN, and Ni0.5Cu0.5Fe2O4 show 40.2, 42.5, and 91.2% degradation efficiencies, respectively. Thus, the Ni0.5Cu0.5Fe2O4@SCN nanocomposite could be a promising material for electrocatalytic OER and/or photocatalytic degradation of MB under visible-light irradiation.