Experimental study of TiO2 hollow microspheres removal on elemental mercury in simulated flue gas

TiO2 hollow sphere was synthesized by hydrothermal method using trifluoroacetic acid (TFA) and Ti(SO4)2 as raw materials, and it was applied to photocatalytic oxidization of elemental mercury (Hg0) in the simulated flue gas. The prepared samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-vis DRS) and nitrogen adsorption/desorption. The results showed that only anatase phase TiO2 hollow sphere was obtained. The average diameter of TiO2 hollow spheres was about 800 nm and the shell thickness was about 200–400 nm. When M, the molar ratio of TFA to Ti(SO4)2, was higher than a certain value, the photocatalytic activity of prepared TiO2 hollow spheres began to reduce. When M = 2, addition TFA content was the best quantity, which got the best TiO2 hollow spheres and provided the most appropriate F− decomposed from TFA during the sample preparation, which was helpful to its photocatalytic ability. In the experimental temperature range, the photocatalytic oxidation efficiency decreased with the increasing of reaction temperature, and the intensity of UV irradiation had an important effect on the photocatalytic reaction. When UV irradiation intensity was 303.45 μW cm−2 and reaction temperature was 55 °C, TiO2 hollow sphere sample prepared at M = 2 had the highest photocatalytic ability and the mercury removal efficiency reached up to 82.75%.