- 學位論文
氣固相反應生長金紅石與銳鈦礦二氧化鈦與其應用
Vapor-solid reaction growth of rutile and anatase titanium dioxide and application
摘要
在此研究中，我們發現了一個全新的二氧化鈦合成方法，首先我們利用四氯化鈦與氧化鈣進行一步驟的氣固成長反應，反應完後，在載具的中間與尾端能得到兩種不同晶相與形貌的二氧化鈦，分別為一維線狀形貌的金紅石相二氧化鈦與十面體形貌的銳鈦礦相二氧化鈦。不只這樣，我們發現在反應的過程中會出現鈣鈦礦的中間體，於是，我們將起始藥劑氧化鈣置換成鈣鈦礦並修改一些參數後，能得到一維奈米柱狀的金紅石相二氧化鈦。之後我們對三種不同形貌的二氧化鈦奈米材料進行不同應用的測試，分別有鋰離子電池、光催化反應、場發射。此外，本研究也會對二氧化鈦奈米結構的成長機進行制詳細的探討。 第一部分探討金紅石相二氧化鈦，我們利用兩種不同的起始藥劑，分別是氧化鈣與鈣鈦礦，經過不同參數的調整，分別得到兩種不同的金紅石相二氧化鈦單晶一維結構，分別是奈米線(長: 4 - 15微米;寬: 80 - 120奈米)與奈米柱(長:1-4微米;寬: 80 - 120奈米)，並沒有人可以長出這麼長的單晶結構。可以得知兩種一維結構的二氧化鈦是具有氧缺陷的，並且它們的一維結構是以[001]方向成長，根據實驗所觀察之結果，提出成長機制，並嘗試了解成長過程。進一步應用這兩種不同的一維結構形貌之二氧化鈦於鋰離子電池上，電池測試方面，以鈣鈦礦做出的一維柱狀結構擁有較好的表現，在1C (170 mA/g)的充電速率下，擁有143 mAh/g的電容值，其表現優異。主要原因源至自生長方向[001]的幫助，因為在鋰離子擴散在ab-軸方向面只有10-15 cm2s-1的擴散速率，但在c-軸也就是[001]方向擁有10-6 cm2s-1的擴散速率，這有效地提升鋰離子的電容值表現。 在第一部分過程中，有將上述兩個不同的一維奈米結構(線狀與柱狀)，應用於場發射的測試，兩種一維材料由於經過TGA的鑑定，可以得知前分別組成為TiO1.65與TiO1.81，並且利用UV-vis分析可知道兩者的能帶小於一般金紅石二氧化鈦 (< 3.2 eV)。得知，具有缺陷的二氧化鈦，它的導電性大於一般的二氧化鈦，經過測試後，顯示出樣品的形貌、物理性質及結晶性與其場發射特性具有相的的關聯性。樣品中，表現最好的是利用起始試劑為氧化鈣所合成出的一維線狀二氧化鈦，其起始電場為6.02 V/μm。最後，可得知，具有較高氧缺陷的一維線狀材料(TiO1.65)，擁有較強的導電性。 第二部分，是使用四氯化鈦與一氧化鈣反應生成第二個產物銳鈦礦二氧化鈦，其形貌為十面體的截短的八面體雙锥體，這個結構是由銳鈦礦的{001}面與{101}面所組成的，長度大小約400 nm與200 nm。根據實驗所觀察之結果，提出成長機制，並了解成長過程及將它應用在對甲基藍的光分解以探討不同{001}面裸露所造成的影響。在光催化測試方面，以45% {001}面裸露的二氧化鈦具有最好的表現，擁有0.0527 min-1的降解速率。主要原因來自於{001}面與{101}面的比例，這兩個面之間會有表面異質結(surface heterojunctions)的現象，這個現象能將電子電洞分離，以降低再結合的速率來提升光催化的性能。
並列摘要
In this study, we found a completely new one-step titanium dioxide (TiO2(s)) synthesis method. At the beginning of the experiment, the titanium tetrachloride (TiCl4(g)) reacted with calcium oxide (CaO(s)) by vapor-solid growth reaction (VSRG). After the reaction, two different crystal phases and morphologies of TiO2(s) can be obtained in the middle and the end on alumina boat, which are one-dimensional nanowires (1-D NWs) morphology of rutile phase TiO2(s) and truncated octahedral bipyramids (TOB) anatase phase TiO2(s). Not only that, we found that there is an intermediate of perovskite (CaTiO3(s)) during the reaction, so we can replace the initial reactant CaO(s) with commercial CaTiO3(s) and modify some parameters to obtain a 1-D nanorods (NRs) rutile phase TiO2(s). After that, we will use three kinds of TiO2(s) nanomaterials for different applications, including lithium-ion batteries (LIB), photocatalytic degradation and field emission (FE). In addition, this study will discuss in detail the growth mechanism of TiO2(s) nanostructures. The first part will discuss the rutile phase of TiO2(s). As mentioned above, we used two different reactant, CaO(s) and commercial CaTiO3(s), which are adjusted by different parameters to obtain two different rutile TiO2(s) single crystal 1-D NWs (diameters 80 - 120 nm, lengths 4 - 15 μm) and NRs (diameters 80 - 120 nm, lengths 1 - 4 μm). Fortunately, in many literatures, no one can grow such a long single crystal structure After some basic instrument identification, it can be known that both 1-D structure TiO2(s) are oxygen-deficient, and their one-dimensional structure grows along the [001] direction. According to the results observed in the experiment, the growth mechanism is proposed. It tries to understand the growth process. Moreover, the application of these 1-D structures TiO2(s) in LIBs were examined. The battery testing show that 1-D NRs structure made by CaTiO3(s) has better performance, at 1C (170 mA /g) with a capacitance value of 143 mAh/g. The excellent performance is due to the 1-D structure along [001]. As we know that diffusion rate of lithium ions in the ab-plane is 10-15 cm2s-1, but 10-6 cm2s-1 in the c-axis. The large in the diffusion rate can effectively increase the capacitance of lithium ion battery. In the first part of the process, there are two different 1-D nanostructures (NWs and NRs) applied to the field emission (FE) test. Due to TGA analysis, the two 1-D materials are composed of TiO1.65(s) and TiO1.81(s), respectively. UV-vis analysis show that the energy band of the two materials is smaller than the general rutile TiO2(s) (< 3.2 eV). It can be known that the defective TiO2(s) has higher conductivity than that of the ordinary TiO2(s). It shows that the morphology, physical properties and crystallinity of the sample all have a correlation with its field emission characteristics. Among the samples, the best one is the 1-D NWs TiO2(s). synthesized by using CaO(s). The turn-on field is 6.02 V /μm. Finally, the 1-D wires material (TiO1.65) with higher oxygen defects has strong electrical conductivity. The second part, anatase TiO2(s) crystals composed of truncated octahedral bipyramids (TOB) with exposed {001} and {101} facets (grown at 923 K, average edge length 400 nm, average thickness 200 nm, surface area 4.20 m2/g). In the article, based on the results observed in the experiment, a growth mechanism will be proposed to try to understand the growth process. And further, it is applied to photocatalytic decomposition of methyl blue (MB). Exploring the impact correlation of different {001} face exposures. In photocatalytic examining, the 45% of the {001} exposed TiO2(s), shows a degradation rate constant k, 0.0527 min-1, which has the best performance. The extraordinary performance is attributed to the effective surface heterojunctions between {001} and {101} facets, which would separate photogenerated electrons and holes sufficiently on {101} and {001} surfaces.