Water is a critical resource for the survival of life on earth and the development of humanity. More than 4,000 years have passed since the beginning of the textile industry. Yet, textile dyes and the chemicals used in the manufacturing of clothing continue to be ignored, despite the fact that both humans and the environment can be negatively impacted by them. Not only are artificial dyes dangerous to our health, but they are also detrimental to ecosystems and the environment as a whole. They generate hazardous chemical waste, which winds up in rivers and other sources of water and causes havoc on the environment. Toxic pollutants released by the textile industry are a growing problem for water contamination and are linked to dangerous diseases all over the world. Efforts to treat textile industry effluents have been made, however these efforts are failing miserably. Thus, bismuth oxide is commonly employed because of its   stability and proper band structure in photocatalytic processes. It functions as a photo catalyst to degrade organic dyes and has several edges as a catalyst. Although bismuth oxide occurs naturally in a variety of polymorphic forms, Bi₂O₃ has a relatively modest band gap. In this study, sodium hydroxide, bismuth nitrate, and nitric acid were used to hydrothermally produce Bi₂O₃. We first added bismuth nitrate to the water, then added a few drops of nitric acid while stirring the mixture for 45 minutes. To the bismuth nitrate solution, sodium hydroxides were gradually added. The mixture was then transferred to a Teflon-lined autoclave and heated for 24 hours at 160°C. At 450°C, the dried sample was calcined. FTIR, XRD, SEM, UV-Vis spectroscopy, and EDX were used to study morphology as well as size of the bismuth oxide nanoparticles. Bismuth oxide exhibits a potent excitonic absorption band at 380 nm in UV-Vis spectroscopy. 3.26 eV of band gap energy is therefore provided. The Bi₂O₃ stretching peak was observed in the FTIR spectra at 700 - 400 cm^-1. The SEM images shown that synthesized material were agglomerated and round shape. XRD Sherrer's equation was used to determine the average crystalline structure, and the results showed that the average size of the Bismuth Oxide NPs was 25.54 nm. According to the EDX study, bismuth and oxygen, which together make up roughly 94.21% of the elemental composition of bismuth oxide, are particularly high. Moreover, there is 5.79% of the total amount of carbon present that may have come from citric acid. For the bromophenol blue photocatalytic degradation under solar light irradiation, bismuth oxide nanoparticles were examined. UV-visible spectroscopy was used to monitor the reaction's progress and calculate the percentage of photocatalytic degradation. In 120 minutes, Bi₂O₃ NPs effectively degraded almost 98.35% of the bromophenol blue dye.