Iron oxide (Fe2O3) nanoparticles were synthesized using lemon peel extract with niobium (Nb) doping (2, 4, and 6 mmol) via a hydrothermal method. Characterization techniques included FTIR, UV–Vis spectroscopy, XRD, PSA, and zeta potential measurement. FTIR confirmed Nb integration, with Fe-O and Nb-O bonds at 1.65 Å and 1.34 Å. Nb doping reduced particle size (93.74 nm to 56.01 nm) and enhanced stability (zeta potential −13.04 to −37.31 mV). XRD analysis confirmed phase purity and crystalline structure, while the Scherrer and Williamson-Hall methods revealed decreases in crystallite size and lattice strain with higher Nb concentration. Bandgap analysis showed a red shift (3.08 to 2.28 eV) due to Nb-doped energy levels. Nb-doped Fe2O3 (6 mmol) achieved 87 % degradation of methylene blue (10 ppm) under sunlight in 2 h. Enhanced photocatalysis resulted from prolonged electron-hole recombination, generating reactive radicals. These Nb-doped Fe2O3 nanostructures are promising for pollutant degradation in water environments.
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