| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 101 === The mixed-phase nanosized TiO2 powders with superior visible-light photocatalytic activity were prepared by high-energy planetary ball- mill-ing of anatase powders followed by annealing at high temperatures. XRD analyses showed that the as-milled TiO2 powders have the phase assem-blage of ~ 30% anatase, ~ 20% rutile and ~ 50% TiO2-II, and the average grain size of ~50 nm.After further annealing at 700° for 120 min, most of the TiO2-II in the as-milled powders transformed to rutile, yielding the final phase assemblage of ~ 30% anatase, ~ 65% rutile and ~ 5% TiO2-II. The rutile phase in the as-annealed powders shows the characteristically large widths at half-peak height in all XRD peaks, indicating the presence of lattice stresses due to the mix-phase effect. High resolution imaging confirmed the presence of three types of mixed-phase grains in the as-milled or the milled and annealed TiO2 powders: anatase-TiO2-II, TiO2-II-rutile and anatase-TiO2(B). Electron diffraction study identified three different crystallographic orientation relationships (COR) for anatase -TiO2-II powders: [111]A || [2 0]II and { 20}A || {002}II;[110]A || [201]II and {004}A || { 02}II; [311]A || [01 ]II and {11 }A || {200}II, two different COR for TiO2-II-rutile powders: [110]II || [111]R and {002}II || {01 }R; [010]II || [010]R and {200}II ||{200}R, as well as one COR for the minor anatase-TiO2(B) powders:[010]A|| [01 ]B and {103}A || {20 }B. The present mixed-phase TiO2 powders have the superior visible- light photocatalytic activity comparable to that of the commercialized P-25 powder.
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