The issue of industrial dyes has risen to the forefront of environmental concerns, as they are now recognized as a prevalent form of industrial waste that pollutes our surroundings. As such, it is imperative that efforts be made to address their toxicity, with a view to safeguarding the environment and public health. To this end, the application of nanotechnologies presents a promising solution to the challenge of mitigating the harmful effects of industrial dyes on our environment. Copper oxide nanoparticles (CuO NPs) have been found to possess strong photocatalytic properties and are effective in degrading toxic dyes in polluted water and industrial effluents. In this experimental work, CuO NPs were synthesized using Citrus limon leaves extract as source of bioactive molecules to obtain stable NPs. Microscopic and spectroscopic analyses confirmed the formation of CuO NPs with size range of 20-25 nm with spherical shape. In addition, the prepared NPs utilized as photocatalyst against Remazol Brilliant Blue R (RBBR) dye, which shows remarkable potency within 180 min with degradation efficiency similar to 90%. Thus, CuO NPs can be used as sustainable, cost-effective and efficient alternative for the removal of toxic industrial effluents from water bodies.