 The synthesis of undoped cobalt oxide and cobalt oxide with 4% nickel doping was studied using hydrothermal techniques. After heating to 300 degrees Celsius, X-ray diffraction analysis showed the formation of cobalt spinel oxide with complete nickel substitution in the lattice. Crystallite sizes of 42 nanometers and 31 nanometers were observed for Co3O4 and Co3XNXO4, respectively. Retvelled refinement yielded good agreement between the experimental and simulated patterns, with values of X2 equals 1.25 and GOF equals 0.90 for Co3O4. The energy band gap was measured by UVvis spectroscopy in two different regions, ranging from 1.54 to 2.04 EV for samples doped with nickel. Scanning electron microscopy, SEM, revealed the formation of nanostructures with semi-cubic shapes and irregular rods. The crystallite size, particle size, surface area, and morphology of the final product all depended on the amount of nickel doping. This article was authored by Lady Julieta Cardenas-Fletchis, Angela Mercedes-Rovapáez, and Miriam Rincon Joya. We are article.tv, links in the description below.