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Doping enhances the optical properties of high‐band gap zinc oxide nanoparticles (ZnO NPs), essential for their photocatalytic activity. We used the combustion approach to synthesize cobalt‐doped ZnO heterostructure (CDZO). By creating a mid‐edge level, it was possible to tune the indirect band gap of the ZnO NPs from 3.1 eV to 1.8 eV. The red shift and reduction in the intensity of the photoluminescence (PL) spectra resulted from hindrances in electron‐hole recombination and sp‐d exchange interactions. These improved optical properties expanded the absorption of solar light and enhanced charge transfer. The field emission scanning electron microscopy (FESEM) image and elemental mapping analysis confirmed the CDZO′s porous nature and the dopant's uniform distribution. The porosity, nanoscale size (25–55 nm), and crystallinity of the CDZO were further verified by high‐resolution transmission electron microscopy (HRTEM) and selected area electron image analysis. The photocatalytic activity of the CDZO exhibited much greater efficiency (k=0.131 min−1) than that of ZnO NPs (k=0.017 min−1). Therefore, doped heterostructures show great promise for industrial‐scale environmental remediation applications. [ABSTRACT FROM AUTHOR]