This study uses the sol-gel method to synthesize and characterize pure zinc oxide (ZnO) and cobalt-doped zinc oxide (Co-ZnO) nanoparticles. ZnO, a wide-bandgap semiconductor, is known for its optical transparency, high exciton binding energy, and antimicrobial properties, making it valuable for various applications in optoelectronics, sensors, and biomedical fields. Incorporating cobalt as a dopant modifies ZnO's structural and optical characteristics, enhancing its functionality in photocatalysis, spintronics, and magnetic storage devices. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure for ZnO and Co-ZnO. However, Co doping led to decreased crystallite size, increased strain, and higher dislocation density, indicating lattice distortions. UV-Vis spectroscopy showed a shift in the absorption edge for Co-ZnO, suggesting bandgap narrowing, improving its visible-light absorption capabilities. This modification enhances the photocatalytic efficiency of Co-ZnO, making it highly suitable for environmental remediation and solar energy applications. The findings demonstrate that while pure ZnO is preferable for UV-blocking, optoelectronic applications, and sensors, Co-ZnO exhibits superior performance in photocatalysis and magnetic-based technologies. The study concludes that cobalt doping enhances ZnO’s properties, expanding its potential applications in energy, environmental, and electronic industries.