合成Fe3O4及Ag奈米粒子應用於磁性奈米線及光觸媒之研究

Synthesis of Fe3O4 and Ag Nanoparticles for Magnetic Nanowires and Photocatalyst Applications

林秀珠(Hsiu-Chu Lin)

指導教授 ： 王宏文

中原大學/理學院/化學系/博士(2007年)

https://doi.org/10.6840/cycu200700486

摘要

本論文主要研究下列主題:
(一)、以水熱方法處理不同的起始劑[FeCl2、FeCl3、FeSO4、Fe2(SO4)3、Fe(NO3)2、Fe(NO3)3、Fe(OH)2、Fe(OH)3]合成Fe3O4奈米磁性粒子。(二)、合成奈米銀粒子。
(三)、以簡單的氧化還原方法將銀披覆在Fe3O4磁性奈米粒子上。
(四)、以Electrophoretic Deposition(EDP)的方式製備Fe3O4奈米線。(五)、以模板方式經過共沉和共沉後加微波水熱兩種方法來製備Fe3O4奈米線。
(六)、經過銀改質後之自製多孔洞二氧化鈦(TiO2)及商用TiO2分解亞甲基藍的研究。
主要結果簡述如下:
(一)、Fe3O4產物結晶相隨反應溫度、壓力、時間、和起始劑不同而有所不同，分別有Fe3O4 、α-Fe2O3。水熱的前驅溶液必須完全溶解在鹼性條件下。除此之外，二價鐵離子和三價鐵離子的精確莫耳比例是重要反應條件之一。在本研究中成功製備得粒徑約30 nm的Fe3O4奈米磁性粒子。
(二)、以NaBH4及檸檬酸鈉還原銀粒子，NaBH4為還原劑，檸檬酸鈉為保護劑。改變AgClO4的濃度從10-3M到10-4M，銀奈米粒子大小從3 nm變化到20 nm。濃度越大則其奈米銀粒徑越大。硝酸銀、保護劑和還原劑的莫耳比為AgNO3 : PVP : NaBH4 = 1 : 1.5 : 150條件下還原的銀離子，粒徑約為5~10nm，可見光吸收峰在388 nm呈紫紅色。若以無毒的澱粉當保護劑，在鹼性條件下用葡萄糖還原銀離子，黃色透明銀奈米粒子水溶液能保持六個月以上。
(三)、含銀磁性奈米粒子乃透過以Ag+離子氧化Fe2+離子，形成Fe2+與Fe3+共存溶液後，再以鹼液共沉澱出帶銀之磁性粒子。反應中反應溫度、組成物比例、反應時間皆加以探討，所得沉澱物以XRD、SEM、TEM、VSM研究。
(四)、以Electrophoretic Deposition (EDP)的方式製備Fe3O4奈米線。電解液的部份是由分散均勻且為單一相的Fe3O4 奈米粒子組成，所得之Fe3O4奈米線。長度可超過20 慆，而其直徑約在130-150 nm之間。
(五)、以AAO模板方式經過共沉和共沉後加微波水熱兩種方法來製備奈米線。繼共沉之後再進一步做150 °C持續30分鐘做微波水熱處理，可得均勻的、十分平行的尖晶石相Fe3O4奈米線，品質比用PC膜或未作微波水熱者較好。用VSM量測Ms值，發現垂直方向比平行軸方向來得要大。
(六)、自製多孔性TiO2催化活性效果經由UV-visible測試結果，會隨增加銀改質量而提升。相反地，商用TiO2卻隨增加銀改質量而降低其光催化活性的功能。金屬鍍在自製多孔性二氧化鈦TiO2表面上形成電子陷井[ ]，此陷井能有效的延長電子及電洞的的生命週期，因此能增加光催化活性效果。另一方，金屬鍍在商用TiO2表面上，推測造成表面遮蔽效應大於捕捉電子的效果，降低光催化表面積，故而降低光催化活性。

關鍵字

微波水熱 ； 電泳鍍 ； 奈米線

並列摘要

In this research, the following subjects were investigated：
(1) Synthesis of Fe3O4 nanoparticles by hydrothermal method.
(2) Synthesis of Ag nanoparticles.
(3) Deposition of silver on magnetic Fe3O4 nanoparticles.
(4) Formation of Fe3O4 nanowire by electrophoresis deposition.
(5) Synthesis of Fe3O4 nanorod arrays via AAO template precipitation and subsequent microwave hydrothermal process.
(6) Synthesis and photocatalysis of Ag nanoparticle-modified mesoporous TiO2 powders.
The study disclosed following facts: (1) various phases such as Fe3O4 、α-Fe2O3 were obtained and found to be dependent on the temperature, time, and precursors used in hydrothermal process. The hydrothermal process may form single spinel phase only when all precursors were dissolved in a basic solution (pH≥9). In addition, the selection of iron salts and the exact ratio of Fe2+ and Fe3+ are important for the formation of Fe3O4 phase. The size of nanoparticles obtained in this study was about 30 nm.
(2) The silver nanoparticles from 3 to 20 nm were obtained by varying the concentrations of AgClO4 solution. Silver nitrate AgNO3、Poly(vinylpyrrolidone) (PVP) and the reducing agent NaBH4 were employed for the synthesis. Reduction of AgNO3 by D-glucose in the presence of starch gave a stable aqueous of silver nanoparticles. The Ag nanoparticles solution are stable over 6 momths at pH=12.
(3) Synthesis of nano-composites materials Ag - Fe3O4 was carried out. Chemical reduction and oxidation was utilized such as： Ag+ + Fe+2 → Ag0 + Fe+3. Silver ions were used as oxidation agent to oxidize ions of Fe(II) to form a solution containing both Fe(II) and Fe(III) ions. After precipitation with ammonia hydroxide, magnetic nanoparticles containing silver metals were obtained. Our modifications of the magnetic nanoparticles were much easier than literature methods and the procedure to produce magnetic nanoparticles was also simplified.
(4) Template-growth of Fe3O4 nanowires via electrophoretic deposition (EPD) was accomplished. Uniform Fe3O4 nanowires with length more than 20 mm and diameter around 130-150 nm are successfully synthesized.
(5) Template-growth of Fe3O4 nanowires via precipitation and subsequent microwave hydrothermal process was investigated. Fe3O4 precipitates were obtained in a ferrous chloride and ferric chloride mixture (pH>9) followed by microwave hydrothermal process at 150 °C for 30 min. The nanowires have a polycrystalline spinel structure and very smooth surface and extreme parallel rod-shape.
(6) Deposition of Ag nanoparticles on mesoporous anatase TiO2 powders as well as on commercial TiO2 powders via reduction of Ag+ solution was performed and their photocatalytic activities were investigated. Photocatalytic activities of Ag/TiO2 were evaluated by UV-visible test on degrading of methylene blue aqueous solution. For the synthesized mesoporous TiO2 powders, the catalytic activity increased as the amount of Ag nanoparticles increased. However, for the commercial TiO2 powders, the catalytic activity decreased as the amount of Ag increased. It is inferred that the Ag nanoparticles reduce the recombination of electron-hole pairs and therefore enhance the photocatalytic activity of the synthesized mesoporous TiO2 powders. However, the Ag nanoparticles retard the photocatalytic activity of commercial TiO2 powders by shielding their effective surface area for the accessing of light.

並列關鍵字

nanowire ； Microwave hydrothermal ； electrophoretic deposition

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