زهرا صولتی دالکی

A straightforward and efficient multiphase combustion method was employed to prepare ZnO nanoparticles using cystoceira baccata algae powder as a fuel. Calcination was performed at 600 °C (ZnO-1), followed by re-calcination at 900 °C (ZnO-2). X-ray diffraction of ZnO-1 and ZnO-2 revealed a pure hexagonal wurtzite structure for both samples. Fourier-transform infrared spectroscopy confirmed the presence of chemical functional groups in ZnO-1, whereas no significant residual compounds were found in ZnO-2. The average crystallite sizes of ZnO-1 were calculated using Debye–Scherrer, modified-Scherrer, and Williamson-Hall formulas, yielding values 13.7 nm, 13.9 nm, and 14.8 nm, respectively. The corresponding data for ZnO-2 were obtained as 40.8 nm, 42.0, and 48.3 nm, respectively. Also, ZnO-1 demonstrated a larger surface area (25.28 m2/g vs 8.92 m2/g) and wider band gap (2.78 eV vs 2.62 eV) in comparison to ZnO-2. Field emission scanning electron microscopy revealed spherical nanograins for ZnO-1 and agglomerated particles for ZnO-2. The photoluminescence spectra of ZnO-1 showed only UV emission at 392 nm, whereas ZnO-2 displayed both UV (392 nm) and visible emission bands (419.0 nm, 440.0 nm, 490.3 nm, 533.4 nm and 541.0 nm), indicating higher vacancy defects in its crystal. ZnO-2 exhibits better photocatalytic activity than ZnO-1 for degradation of methylene blue under sunlight (degradation of 99.2 % against 52.8 % after 30 min of irradiation, respectively). The higher photocatalytic activity of ZnO-2 was attributed to its higher vacancy defects.