Cobalt oxide–copper oxide heterojunction nanocomposites for efficient UV-driven photocatalytic degradation of Brilliant Blue G dye

In the present study, we have explored the design of heterojunction nanocomposites, focusing on and abundant availability. In this work, Cobalt Oxide–Copper Oxide (Co3O4–CuO), a p–p heterostructure with complementary electronic properties, was synthesized via a facile sol–gel route followed by calcination. The material was systematically characterized by XRD (X-ray diffraction), FTIR (Fourier Transform Infrared), XPS (X-ray Photoelectron spectroscopy), SEM-EDX (Scanning electron microscope-Electron diffraction X-ray), TEM (Transmission electron microscope), UV–Vis (Ultraviolet visible), PL (photoluminescence) spectroscopy, and BET (Brunauer-Emmett-Teller) to establish their structural, morphological, and optical and surface features. The NC exhibited a narrowed band gap of 2.18 eV compared to pristine oxides, suggesting enhanced light-harvesting capability. Photocatalytic experiments under UV irradiation revealed that the Co3O4–CuO heterojunction achieved nearly complete degradation of Brilliant Blue G (BBG) dye within 120 min of irradiation, with a pseudo-first-order kinetic rate constant (0.030 min–1) markedly higher than that of individual Co3O4 and CuO. The superior performance was attributed to efficient charge separation at the heterojunction interface, suppressed electron–hole recombination, and the dominant role of superoxide radicals (•O2⁻) as reactive oxidative species. Electrochemical studies further validated improved conductivity and lower charge transfer resistance of the nanocomposite. Additionally, regeneration tests confirmed excellent structural stability and reusability over multiple cycles. This study underscores the significance of engineering binary transition-metal oxide heterojunctions as cost-effective and scalable photocatalysts for wastewater treatment.