本研究利用四氯化鈦(TiCl4)為前驅物，經由沈澱(precipitating)與解膠(peptizing)兩個過程製備二氧化鈦粉體。先將四氯化鈦與氫氧化鈉反應產生白色沈澱後，再加入硝酸在90℃下解膠，經過水解縮合反應，合成二氧化鈦光觸媒。藉由控制硝酸濃度可以合成各種銳鈦礦(anatase)與金紅石(rutile)比例的量身訂做二氧化鈦光觸媒。當硝酸濃度從0增加到0.5M時，二氧化鈦的結晶相態由純的銳鈦礦轉變成純的金紅石；當硝酸濃度從0.5繼續增加到4.0M時，二氧化鈦的結晶相態又由純的金紅石轉變成純的銳鈦礦。上述硝酸濃度對於二氧化鈦結晶相態轉變的雙重影響，本研究分別以pH值及硝酸根離子濃度的效應解釋之。本研究也將量身訂做的二氧化鈦光觸媒進行一系列的甲烯藍水溶液的紫外光催化反應。實驗結果顯示含82.6%銳鈦礦的混合結晶相態二氧化鈦光觸媒具有最佳的光催化轉化效率，這也證明了二氧化鈦的混合結晶相態對光催化具有混合增效作用。此外，本研究也探討以機械混合銳鈦礦與金紅石而成的混合二氧化鈦光觸媒的光催化效率，並與上述合成的相同結晶相態比例的二氧化鈦光觸媒作比較。

In this study, titanium tetra-chloride (TiCl4) was used as precursor to prepare titanium dioxide powders by the process involves two stages: precipitating and peptizing. Firstly, white precipitates of amorphous oxide were produced from the precipitation reaction of TiOCl2 with sodium hydroxide. Then the precipitates were redispersed in aqueous solution of HNO3 at 90oC for peptizing. Tailored titania photocatalysts, which consist biphase titania with various phase compositions of anatase and rutile, can then be synthesized by controlling the concentration of HNO3. With increasing the nitric acid concentration from 0 to 0.5M, the titania crystalline changed from single phase anatase to single phase rutile. With further increasing nitric acid concentration from 0.5 to 4.0M, titania crystalline changed over from single phase rutile to single phase anatase. The reverse trend of crystalline phase formation with HNO3 concentration were explained by pH and nitric ion concentration , respectively. Furthermore, photocatalystic degradation of methylene blue by the synthesized tailored titania catalysts under UV illumination was systematically studied. A synergetic effect between the anatase and rutile particles is observed. The optimal composition of catalyst is found to be 82.6 wt% anatase. Moreover, photocatalystic performance of mechanically mixed biphase titania catalysts was also studied.

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