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  • 學位論文

氧化鈦相關材料之合成及其應用之探討

Syntheses of Titanium Oxide Related Materials and Discussions on Their Applications

指導教授 : 李紫原

摘要


本研究利用水熱法將四異丙基鈦分別與甲酸或乙酸反應以得到各種不同形貌與結構的氧化鈦相關產物。在乙酸的合成環境下,可以合成出三種不同產物,分別是條狀鈦酸鹽 (FT)、菊花狀鈦酸鹽 (CT) 以及橢圓二氧化鈦 (ET)。其中以CT的形狀較特別,其外型是由許多奈米等級的花瓣形薄片聚在一起所構成的微米級的顆粒。在結構方面,FT與CT分別是兩種不同結構的新型鈦酸鹽類,這兩種鈦酸鹽晶體中的層狀結構均有乙酸及乙酸根插層在內,可藉由FTIR及TGA-MS的分析獲得證實。而這些插層在結構中的有機物在溫度高於350 oC時可被碳化並形成一均勻的碳網絡。同時,在高溫煅燒的過程中,CT也會經由相轉換轉變為具有TiO2-B及anatase晶相的二氧化鈦。因此,透過CT的碳化,可以得到碳/二氧化鈦的複合材料,並拿來做為鋰離子二次電池的陽極材料。這種碳/二氧化鈦複合材在鋰離子二次電池的應用上表現相當優異,尤其是在大電流的充放電速率下,仍可保有相當高的電容量。(在10C rate充放電速率下仍有145 mAh/g) 本研究亦將CT在800 oC煅燒1小時,以得到純anatase相的二氧化鈦,在此將其命名為CT800。值得注意的是,CT800的光催化效能非常良好,比市售商用的二氧化鈦 (P25) 還要好上許多,其反應速率常數k值是P25的1.4倍。為了探索究竟是哪些因素造成CT800有如此優異的光催化效能,本研究對CT800進行了一系列的分析。首先將CT800放進硝酸銀的水溶液中並進行照光,觀察銀離子被還原在CT800上的位置,以探討CT800在被光激發後所產生之電子的遷移行為。由HADDF以及EDX對單一顆CT800的顆粒做分析,所得到的結果均顯示銀離子傾向被還原在較靠近CT800的中心位置。再者,由EPR光譜分析也得到相同的結果,顯示電子的遷移行為的確是由CT800的花瓣形薄片之尖端往整個顆粒的中心移動。 這是由於「多重能帶接面」所造成,在本研究中亦將此現象暫名為「串流效應」。而藉由此串流效應使電子傾向集中往顆粒的中心遷移,將可減少其與電洞之再結合反應發生,進而大幅提升其光催化效能。此外,CT800的特殊形貌亦提供兩種好處,其菊花狀的外型不但可誘使入射光在其內發生多次散射,進而更有效的利用入射光能量之外,還可以藉由其花瓣形薄片上之晶界所貢獻的「高活性點」來提高材料的光催化反應活性。 另一方面,在甲酸的合成環境中,若將反應溫度設定在較低的溫度時 (100 oC) 可得到接近非晶型態的柱狀鈦酸鹽。當反應時間拉長後,即可得到繡球花狀的鈦酸鹽類產物,此結果與本實驗室先前在迴流裝置中利用溶膠-凝膠法所得到的的研究成果非常相似。當反應溫度提高至150 oC後,出現了具有{101}露面的二氧化鈦八面體顆粒,藉由TEM及XRD的分析可知其結晶相為anatase。 本實驗亦於合成環境中加入0.1 M之氟離子進行反應,在反應中氟離子會傾向與二氧化鈦{001}面上之五配位鈦原子鍵結,進而抑制晶體在<001>方向上的成長。因此,在150 oC的溫度下我們可以得到露面為{001}之片狀二氧化鈦。若進一步提高反應環境中之氟離子濃度製0.2 M,則可發現片狀顆粒的厚度急遽下降,並且每片薄片傾向聚集在一起長成類似花朵狀的二氧化鈦,其露面也是{001}。由於花朵狀二氧化鈦是由超級薄片所構成的,大幅縮短了鋰離子的擴散路徑,是故我們預期這材料能在鋰離二次電池的效能上有優良的表現。此外,將來亦可針對上述這些材料進行其光催化活性之探討。

並列摘要


In my study, various titanium-oxide related materials were obtained from reacting TTIP with formic acid or acetic acid by solvothermal method. In the case of acetic acid, three kinds of product were synthesized, which are fibrillar titanate (FT), chrysanthemum-like titanate (CT) and elliptic anatase TiO2 (ET). Both FT and CT are the new titanates which have acetic acid and acetate intercalated in the layers of their crystal structure. The intercalated organic species were confirmed by FTIR and TGA-MS spectra, and can be carbonized to form the uniform carbon networks at the temperatures over 350 oC. Additionally, CT can be converted to TiO2-B and anatase by calcinations. Hence, C/TiO2 composites with anatase and TiO2-B can be acquired after the carbonization of CT. The C/TiO2 composites were used as the active material of the anode of Li-ion battery and showed excellent performance (145 mAh/g at 10C rate). CT800 is the material obtained by annealing CT at 800 oC for 1 hour. After annealing, the crystal structure can be converted to anatase TiO2 completely, and was utilized in photocatalyst application. Interestingly, CT800 exhibited higher photoactivity than the commercial TiO2 (P25), the k value of CT800 was 1.4 times higher than P25. In order to discover the key factors that governed the photocatalytic properties, the specific reduction of Ag+ ions was carried out and EPR spectra of CT800 were obtained. Both an HADDF image and EDX mapping indicated that the Ag+ ions tended to be reduced close to the center of the micro matrix of CT800. Moreover, the EPR spectra strongly suggest that the excited electrons tended to migrate toward the center of the micro matrix, resulting from a multiple junction, “cascade effect”, which efficiently reduces the recombination of excited electrons and holes and greatly increases the photoactivity. Additionally, the special morphology of CT800 was responsible for not only multi-scattering around 350 nm, which strongly enhancing the harvesting of light, but also the hot spots at the surface of nano sheets and then contributing to its outstanding photocatalytic activity. Otherwise, in the case of formic acid, as the reaction takes place at low temperature, the rod-like titanate was formed initially and showed poor crystallinity. Once elongating the reaction time at the same temperature, the hydrangea-like titanate appeared and exhibited better crystallinity. These results are similar to the observations of our previous study that the reaction was taken place by sol-gel method using reflux system. When the temperature was arisen, the {101} exposed octahedron TiO2 was observed and was assigned to anatase TiO2 by TEM and XRD. Once the 0.1 M fluorine was contained in the solvents, fluorine bonded to the five-coordinated Ti atoms of the {001} surface and limited the crystal growth along <001>. Hence, the plate-like TiO2 was obtained at 150 oC. Moreover, the thickness of the particle decreased dramatically as the concentration of fluorine increased to 0.2 M. The particles aggregated and became flower-like TiO2, which was also exposed {001} facets. The flower-like TiO2 which is constructed by many ultra-thin nano sheets may have the potential to be used as the active material of the anode of Li-ion battery due to the dramatically decreased in length for Li-ion to intercalate into the material. Furthermore, the photoactivity of these materials could be discovered in the future.

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被引用紀錄


鄭惠珍(2009)。中西圖書分類原理之比較研究〔博士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU.2009.03380

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