In this study, cerium nitrate hexahydrate was used as a precursor to create nanocrystalline ceria nanoparticles, which were then created utilizing a simple and economical sol-gel method by adjusting the pH of the reactants between 6 and 12. Under direct sun radiation, wastewater containing methyl orange (MO) was photodegraded using the produced CeO2 NPs. For recent photocatalysis experiments, the degree of crystallinity, shape, dimensions, and degree of MO photodegradation were characterized and analyzed using XRD, FTIR, SEM, and UV–Vis spectrometry. According to the results, the pH of the synthesis solutions had a significant impact on the ceria-based photocatalysis of MO. Ceria NPs synthesized at a pH of 8 demonstrated optimal photocatalytic activity. Moreover, the results showed that variation in catalyst loading, initial concentration of MO, pH of MO-wastewater as well as exposure time have significantly impacted on photocatalytic performance of optimized CeO2. The optimum percentage degradation of around 75 % of MO was achieved in 80 min exposure of sunlight. Optimized low-cost ceria NPs prepared herein may be employed for dyes containing industrial wastewater treatment throughout the year using ordinary sunlight.