Green-synthesized Co₃O₄/bentonite nanocomposite as an efficient photocatalyst for methyl blue degradation in water

Methyl blue (MB), a synthetic dye widely used in the textile industry, poses a significant environmental threat due to its improper disposal, toxicity that endangers human health and aquatic ecosystems. This study explored the synthesis and use of a cobalt oxide/bentonite nanocomposite for the photocatalytic degradation and removal of MB in water. The nanocomposite was synthesized through a hydrothermal method at 138 °C and 9.87 atm, employing Millettia ferruginea (Birbira) leaf extract as a green reducing and capping agent. Structural characterization using X-ray diffraction (XRD) revealed an average particle size of 11.7 nm, while scanning electron microscopy (SEM) confirmed successful nanoparticle deposition on the bentonite surface. The synthesized nanocomposite demonstrated high photocatalytic performance, achieving 98% MB removal efficiency under optimal conditions of pH 8, catalyst dose of 15 mg, reaction time of 24 min, and initial MB concentration of 30 mg/L. Reusability assessments showed strong stability, with removal efficiency declining modestly to 85% after four consecutive cycles. Thermogravimetric analysis (TGA) indicated good thermal stability, with only 3% mass loss observed up to 700 °C. These findings underscore the potential of the nanocomposite as an effective and environmentally friendly photocatalyst for treating industrial wastewater containing dye pollutants.