Advanced engineered KNbO3/CoxN/Co3O4/C3N4 nanoflakes via a single-step calcination method: A robust and recyclable photocatalyst for tackling water pollutants

Abstract

To tackle the increasing issue of water contamination caused by industrial dye discharges, a highly efficient, visible-light-active quaternary nanocomposite photocatalyst, KNbO₃/CoₓN/Co₃O₄/C₃N₄, was synthesized via a single-step calcination route. Characterization techniques including EDX, SEM, XRD, FTIR, UV–Vis DRS, XPS, BET, TGA, and DSC confirmed the structural properties and thermal stability. The nanoflake-like composite exhibited excellent optical properties, a high surface area (78.98 m²/g), and a narrow bandgap (∼2.9 eV), contribute to enhanced visible-light absorption. Photocatalytic activity was evaluated against crystal violet (CV) and malachite green (MG) dyes. Under optimized conditions, degradation efficiencies reached 97.21% for CV (pH 10, 7 mmol H₂O₂) and 99.2% for MG (pH 9, 5 mmol H₂O₂) within 90 min. Kinetic analysis followed a pseudo-second-order model (R² = 0.99). Quantum efficiencies were calculated as 1.59 × 10⁻⁶ (CV) and 1.81 × 10⁻⁶ (MG) molecules/photon, with corresponding space–time yields (STY) of 1.59 × 10⁻⁸ and 1.81 × 10⁻⁸ molecules/photon/mg. The total number of dye molecules degraded was estimated at ∼1.48 × 10¹⁸ for CV and ∼1.64 × 10¹⁸ for MG under the given experimental conditions. Reusability tests over three cycles showed consistent performance with negligible structural change, confirming long-term stability. These results demonstrate the potential of KNbO₃-based quaternary composites for efficient and sustainable pollutants removal in wastewater treatment.