Synthesis And Photoreactivity Of Three Types Of TiO₂ And The Effects Of Fluoride Modification In Brookite TiO₂ Suspensions

Photocatalytic technology based on TiO₂ has provided an effective and promising means for remediation of environmental pollutants in air and water. Among the three polymorph phases of TiO₂, i.e. anatase, rutile and brookite, only the first two have been widely studied and their photoactivity was tested and compared. It was generally accepted that the photoreactivity of anatase was better than that of rutile. On the contrary, only a few recent papers dealing with the photoreactivity of pure brookite owing to the difficulties of obtaining its pure form, though it seems to have marked photocatalytic activity (comparable to anatase). Contrary conclusions were usually drawn in the literatures on the relative photoreactivity of the three types TiO₂. The photoreacitivty of TiO₂ was a complex function of the phase, purity, particle size, specific surface area, density of surface hydroxyl groups of TiO₂, and solution pH. These parameters above usually interfere with each other.In the second part of the thesis, three type of TiO₂ were prepared on a large scale through hydrothermal treatment of Ti(SO4)2 or TiCl4 at certain pH. The photooxidation activity evaluated from the photocatalytic degradation of X3B , an anionic organic dye , revealed that the relative photoreactivity of the TiO₂ samples was as follows : AT >> RT >>BT , which is consistant with the adsorption ability of the catalysts. The reasons that caused the differences in photoreactivity among the three types TiO₂ were also discussed.Among various efforts for improvement of photocatalytic efficiency, the surface modification of TiO₂ by fluoride seems mostly interesting. Several studies have shown that surface modification of anatase TiO₂ can result in significant enhancement in the photocatalytic degradation of organic pollutants. However, the effects of fluoride surface modification in brookite TiO₂ has not been reported, which deserves to be investigated. In the third part of the thesis, the phase transformation of brookite as the sintering temperature increase, and the effects of fluoride on the photoreactivity of the sintered brookite TiO₂ were studied. It was found that brookite was transformed to rutile via anatase as the sintering temperature increase, but the photoreactivity of brookite TiO₂ decreased in the presence of fluoride.