Harnessing g-C₃N₄ and rGO synergistic effects for superior photocatalysis in CuO/NiO nanocomposite

This study presents a comparative investigation of a binary CuO/NiO nanocomposite (NC) and two ternary nanocomposites (NCs), CuO/NiO/g-C₃N₄ (CNG) and CuO/NiO/rGO (CNR), for the photocatalytic degradation of Congo red (CR) dye. XRD analysis revealed crystalline phases with crystallite sizes (D) of 37.89 nm for CuO/NiO, 17.77 nm for CNG and 21.76 nm for CNR. Morphological differences among the samples were observed through SEM and TEM, while EDX, XPS and elemental mapping validated the presence of the expected elements, their chemical states and homogeneous distribution, indicating successful composite formation. Zeta potential measurements at 25 °C showed values of 14.1 mV for CuO/NiO, 16.8 mV for CNG and 17.3 mV for CNR, suggesting good colloidal stability. The optical bandgap (E_g) of the NCs was calculated as 1.41 eV for CuO/NiO, 1.48 eV for CNG and 1.13 eV for CNR. Photocatalytic evaluation revealed that the CNG NC achieved the highest degradation efficiency of 95.24% with a rate constant (k_obs) of 3.07 ± 0.19 × 10^–2 min⁻¹, whereas the CNR NC showed 83.05% degradation with k_obs = 1.64 ± 0.05 × 10^–2 min⁻¹. While CNG exhibited superior photocatalytic activity, CNR demonstrated enhanced recyclability over multiple cycles. The scavenger effect of isopropyl alcohol caused a notable reduction in degradation efficiency, dropping to 20.15% for CNG and 18.36% for CNR, which clearly indicates that hydroxyl radicals (^•OH) play a dominant role in the degradation process. A detailed photocatalytic mechanism is proposed to explain the charge transfer and synergistic effects within the ternary NCs systems.