Influence of ammonia on the morphologies and enhanced photocatalytic activity of TiO2 micro/nanospheres

TiO2 micro/nanospheres were synthesized by a combination process contains hydrolysis of titanium tetra-n-butyl in mixed solution of anhydrous ethanol/ammonia and the subsequent calcination under 550 °C for 7 h. The pH values of the mixed solution were tuned to be 10.4, 11.0 and 11.6, respectively, by adding different amounts of ammonia. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the morphologies and the crystallinity. X-ray diffraction (XRD) patterns indicated that pH value of the precursors has an important effect on the crystal phase composition. UV-vis diffuse reflectance spectrum was applied to characterize the optical properties of samples. Degradation of methylene blue under the irradiation of 300 W Hg lamp confirmed the enhanced photocatalytic activity of TiO2 micro/nanospheres. In addition, the formation mechanism was proposed.

Addition of ammonia during the hydrolysis of titanium tetra-n-butyl resulted in the formation of TiO2 micro/nanospheres. In addition, it was found that with different pH values of the hydrolysis solutions, TiO2 micro/nanospheres with different crystallinities (anatase/rutile composition) and different photocatalytic activities were obtained. (a) The obtained TiO2 micro/nanospheres and (b) different photocatalytic activities of TiO2 micro/nanospheres with tuned pH values of hydrolysis solutions.Research highlights▶ Addition of ammonia in precursor results in the formation of TiO2 micro/nanospheres. ▶ Ammonia has a crucial effect on the crystallinity of obtained TiO2 samples. ▶ Ammonia has a crucial effect on the photocatalytic activity of TiO2 samples.