Biotemplate-assisted synthesis of CaO nanoparticles from banana blossom calyx residue for efficient fluoride removal from water.

Fluoride contamination in drinking water poses a significant environmental and public health challenge, necessitating the development of sustainable and efficient remediation materials. In this study, calcium oxide (CaO) nanoparticles were synthesized using banana blossom calyx residue as a renewable biotemplate through a simple precipitation-calcination approach. The porous biomass architecture facilitated calcium ion adsorption and the subsequent formation of nanostructured CaO. Characterization by XRD, TGA/DTA, UV-Vis spectroscopy, photoluminescence spectroscopy, FTIR, FESEM, and EDS confirmed the formation of crystalline CaO nanoparticles with an average crystallite size of 12 nm. FESEM analysis revealed hierarchical surface morphology with well-defined cubic and rhombohedral particle geometries ranging from 1.65 to 2.0 μm, composed of aggregated nanocrystalline domains. The synthesized nanoparticles exhibited effective fluoride removal, achieving 100% removal at an initial fluoride concentration of 3.84 mg L-1 and a maximum adsorption capacity of 25.12 mg g-1. Adsorption equilibrium followed the Langmuir isotherm model (R2 = 0.990), indicating predominant monolayer adsorption. The enhanced fluoride removal was attributed to the synergistic effects of surface adsorption and CaF2 precipitation. These findings demonstrate a facile and environmentally sustainable strategy for converting agricultural waste into functional nanomaterials for water purification applications.