Efficient Nanostructured Co ₃ O ₄ /ZnO Heterojunction for Enhanced Heterogeneous Photocatalytic Degradation of Organic Dye

In this work, a p–n heterojunction thin film composed of zinc oxide (ZnO) and cobalt oxide (Co 3 O 4 ) was fabricated using a facile nebulized spray pyrolysis (NSP) process to enhance ZnO's optical and photocatalytic properties. X‐ray diffraction analysis confirmed a polycrystalline hexagonal wurtzite structure with a rough and porous morphology. The Co 3 O 4 /ZnO bilayer exhibited optical features arising from inter‐band transitions in the spinel Co 3 O 4 layer and the direct bandgap of ZnO. Photoluminescence (PL) analysis indicated suppressed radiative recombination of photogenerated electron–hole pairs in the heterojunction, demonstrating efficient charge separation at the interface. Photocatalytic tests using methylene blue dye under sunlight showed that the Co 3 O 4 /ZnO heterojunction achieved ~81% degradation efficiency. These results demonstrate that the Co 3 O 4 /ZnO bilayer heterojunction is a cost‐effective and efficient photocatalyst for solar‐driven environmental remediation.