微波輔助水熱法合成二氧化鈦奈米線及形成機構之探討

Synthesis of Titanium Dioxide Nanowires by Microwave-Assisted Hydrothermal Treatment and its Mechanism of Formation

鍾錦軍(Chin-Chun Chung)

指導教授 ： 鍾財王

中原大學/工學院/化學工程學系/博士(2008年)

https://doi.org/10.6840/cycu200800326

摘要

本實驗成功地使用微波輔助水熱法合成具有anatase晶相的二氧化鈦奈米線。為了加速奈米線的製備程序，因此，將微波輔助電源應用於傳統水熱裝置之中。以商業級的二氧化鈦奈米顆粒（ST01, 100% anatase）作為起始原料，而各種影響合成的參數（包括加熱溫度、反應時間、微波瓦數以及原料的總重等）都在本實驗中獲得討論。所有產品的材料特性，可藉由電子顯微鏡（SEM）、X光繞射儀（X-ray）以及表面吸附分析儀（BET）進行觀察與量測。產品在穿透式電子顯微鏡（TEM）之研究中，則顯示這些奈米線的直徑約為80–150 nm，長度範圍從數個微米到數十個微米。
SEM以及TEM的量測結果顯示，奈米線的成長進化是形成在一個微波輔助的條件之下。另外，後處理條件（例如：酸洗處理、超音波處理以及鍛燒處理）與二氧化鈦奈米線形成的關係，在本研究中亦獲得充分的討論。由實驗結果可證明，奈米線的確是形成在微波照射下與氫氧化鈉反應的期間之內，而無須任何的酸洗處理程序；同時，二氧化鈦奈米線的長度與產量可隨著反應時間的延長而增加。至於，奈米線的結晶結構在水熱過程期間以及後處理步驟中，可透過X光繞射顯示其晶相進化的過程，而藉由酸洗以及超音波震盪處理則有利於分散相互集結的奈米線。為了製備具有anatase晶相的二氧化鈦奈米線，一個最佳化的製備條件為沈積物（samples obtained under 350 W of power at 210 °C for 4 h）先以0.1 M HCl水溶液洗滌至pH=1.0後，再經過450 °C鍛燒2小時處理即可完成。
與傳統水熱法相較下，透過微波輔助水熱技術的使用，不但可以合成具有較小尺寸的二氧化鈦奈米線，而且亦可以相對地降低能源的消耗。在350 W的功率及210 °C的溫度條件下，只需2小時（並且再經過450 °C鍛燒2小時）即可產生二氧化鈦奈米線。由於二氧化鈦奈米線能夠以較短的時間以及在較低的熱源下被獲得，因此，這個方法能夠明顯地減少二氧化鈦奈米線合成的反應時間、成本以及所須能源，相當適合於二氧化鈦奈米線的合成。最後，基於實驗結果可推論奈米線最有可能的形成機構是以溶解-沈積-成長模式所構成。

關鍵字

二氧化鈦奈米線 ； 微波輔助水熱法 ； 後處理步驟 ； 奈米顆粒

並列摘要

Titania nanowires in the anatase phase were successfully synthesized using microwave-assisted hydrothermal methods. To accelerate the fabrication procedure of nanowires, microwave-assisted power was applied to the traditional hydrothermal apparatus. Titanium dioxide nanoparticles (ST01, 100% anatase) were utilized as the starting material. Experimental parameters including heating temperature, reaction time, radiation power, and the amount of raw material were studied in the present work. All of the products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analysis. Transmission electron microscopy (TEM) investigations revealed that these nanowires have a diameter of ca. 80–150 nm with a length ranging from several micrometers to tens of micrometers.
SEM and TEM measurements revealed the evolution of nanowires formation under a microwave-assisted condition. In addition, the influence of post-treatment conditions on the formation of TiO2 nanowire was discussed. These results confirmed that the nanowires were definitely formed under microwave irradiation during the NaOH treatment and no acidic treatment is needed. The wire lengths and yields of titanate nanowires were increased with increasing reaction time. Additional post-treatment steps such as acid washing and ultrasonic vibration were beneficial to disperse the aggregated titanate nanowires. X-ray diffraction indicated a remarkable change in crystalline structure during the hydrothermal process and post-treatment steps. Optimal preparation conditions （under 350 W of power at 210 °C for 4 h）for fabrication of the anatase TiO2 nanowires were found to be as follows: rinse with 0.1M HCl to pH=1.0 before calcination at 450 °C for 2 h.
In comparison to conventional hydrothermal methods, these nanowires not only possess a small size in diameter, but also relatively low energy consumption in manufacturing the TiO2 nanowires using a microwave-assisted hydrothermal process. Under the conditions of 350 W of power at 210 °C, TiO2 nanowires could be synthesized in only 2 h (and then calcined at 450 °C for 2 h). The study has shown that TiO2 nanowires can be obtained with a shorter reaction time and lower thermal energy. Therefore, this approach could considerably reduce the synthesis time, cost, and energy required. In additional, it could be used in the large-scale fabrication of TiO2 nanowires. Based on our experimental results, a dissolving-depositing-growing model was proposed for the formation of nanowire structure.

並列關鍵字

microwave-assisted hydrothermal method ； nanoparticle ； post-treatment steps ； TiO2 nanowires

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