Photocatalytic activity of ZnO nanoparticles and the role of the synthesis method on their physical and chemical properties

Abstract

Abstract In the present study, we report on the effect of the synthesis method in the photoactivity of ZnO-NPs. The nanoparticles were prepared by precipitation and sol-gel procedures using zinc nitrate and zinc (II) acetylacetonate as ZnO precursors, respectively. The obtained samples were named as ZnO-PP (precipitation method) and ZnO-SG (sol-gel method). The powders were calcined at 500 °C and further characterized by Fourier Transform Infrared spectroscopy, X-ray Powder Diffraction, N2 adsorption, thermal analysis, Diffuse Reflectance UV-Vis spectroscopy, and Electron Microscopy. Both methods of synthesis lead to formation of pure ZnO with hexagonal-wurtzite crystalline structures with average crystallite sizes ∼30 nm. The specific surface area was affected by the synthesis method, since SBET values were 5 m2/g and 13 m2/g for sol-gel and precipitation method, respectively. The electron microscopy revealed significant changes in morphology for the obtained nanoparticles, as sol-gel directed the hexagonal rod-like geometries (∼50 nm in diameter) while quasi-spherical nanoparticles (∼100 nm in diameter) were formed using precipitation method. Photocatalytic activity was estimated by degrading phenol (50 ppm) as probe molecule under UVA irradiation (λ = 356 nm), the results demonstrated that ZnO-PP reached 100 % of degradation after 120 min and 90 % of the pollutant was mineralized, whereas for ZnO-SG the results were 80 % and 48 % respectively. Fluorescence test using terephthalic acid (TA) demonstrated higher formation of OH• radicals for ZnO synthesized by precipitation method, which could explain the higher photodegradation and mineralization observed. These results support that even slight differences in physical and chemical properties of ZnO, have a significant impact on the photocatalytic performance of such nanoparticles.