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Calcium oxide (CaO), commonly known as quicklime, is a widely used material. It is a white, caustic, alkaline solid at room temperature. There are 3 methods determination of calcium oxide : 1) Gravimetric Method, 2) Volumetric Method, 3) EDTA Method. The present study is proposed with an objective to synthesize CaO nanoparticles by the eco-friendly green synthesis using environmentally benign papaya leaf extract and Green Tea extract as it makes use of pollution free chemicals and encourages the use of non-toxic solvents such as water and plants extracts. The synthesized nanoparticle was characterized by UV-Vis, Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) studies. The antibacterial and photocatalytic activity of the calcium oxide nanoparticles were also analysed. Calcium oxide is widely used in industry, e.g., in making porcelain and glass; in purifying sugar; in preparing bleaching powder, calcium carbide, and calcium cyanamide; in water softeners; and in mortars and cements. In agriculture it is used for treating acidic soils (liming). CaO based material were found effective for thermochemical heat storage by reversible chemical reaction with high energy density and has long storage period.