以微波水熱法製備銀釩氧化物之研究

The preparation of silver vanadates by microwave hydrothermal method

高魁章(Kuei-Chang KAO 高魁章)

指導教授 ： 楊重光 教授

國立臺北科技大學/工程學院/化學工程研究所/碩士(2010年)

摘要

本實驗成功地使用微波法合成銀釩氧化物-SVO(釩酸銀AgVO3、偏釩酸銀Ag3VO4)。為了加速銀釩氧化物的製備程序，因此，將微波輔助電源應用於傳統水熱裝置之中。以實驗級的硝酸銀及偏釩酸銨作為起始原料，而各種影響合成的參數(包括固定加熱溫度微波瓦數、改變pH等)都在本實驗中獲得討論。所有樣品之材料特性，可藉由X光繞射儀 (X-ray) 、電子顯嶶鏡 (SEM)、紅外線光譜(FT-IR)以及紫外/可見光譜 (UV/Vis spectra)進行觀察與量測。樣品在電子顯嶶鏡 (SEM)之研究中，則顯示這些銀釩氧化物的直俓為數個奈米。
在X-ray diffraction patterns值觀察到，固定50瓦的反應功率下，於不同的pH下反應生成的銀釩氧化物粉末有四種不同的形態(α - AgVO3、β - AgVO3、α - Ag3VO4和Ag2O)隨酸鹼值的增加而依序轉變。在電子顯嶶鏡(SEM)分析下可以發現，從pH 6.0到9.0下反應生成的奈米級銀釩氧化物，其產量和長度都是比傳統水熱法高。但隨著反應液的pH值達到10.0和11.0時，其晶相所佔的主要含量則改變為Ag2O，外表形態則是為類似球形。由紅外線光譜(FT-IR)可看到所有的合成產品，在吸收帶500，680，862，895，920，和965 cm-1都有訊號出現。吸收帶在500和680 cm – 1分別是V2O74-離子中對稱和非對稱伸縮振動的V-O-V鍵。使用紫外/可見光譜(UV/Vis spectra)量測結果顯示在pH = 7.0的吸收曲線估計在550 nm時能帶隙值約為2.2 eV。在pH = 6.0和pH = 6.5在可見光區域有一個陡峭的吸收峰，這是不同於pH值為7.0的吸收光譜，這可能是α - AgVO3和β - AgVO3結構上不同造成的分別。
為了製備大量的奈米級銀釩氧化物，一個最佳化的製備條件為功率50 W、溫度140℃反應一小時，再經過80℃烘乾12小時。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銀釩氧化物，而且亦可以相對地降低時間及能源的消耗，相當適合於奈米級銀氧釩化物的合成。最後，基於我們的實驗結果推論，奈米級銀釩氧化物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

光催化劑 ； 微波水熱法 ； 銀釩氧化物 ； 釩酸銀

並列摘要

Preparation visible light photocatalysts were successfully synthesized using microwave-assisted hydrothermal methods. In order to accelerate the preparation of silver vanadate procedure, the power used in traditional microwave-assisted hydrothermal contained unit. An experimental-grade ammonium nitrate silver and vanadium as the starting material, while the various effects of synthesis parameters (including heating temperature, reaction time, as well as the number of micro-Bova, etc.) are to be debated in this experiment. All of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-Transform Infrared (FT-IR) and UV/Vis spectra analysis. Scanning electron microscopy(SEM) investigations revealed that these sample have a diameter of several nm.
The XRD patterns of silver vanadate powders obtained by 50 W power at different pH values. That four different phases occur as the pH value pH values increases. α-AgVO3, β-AgVO3, α-Ag3VO4 and Ag2O were obtained by keeping the pH of the reactant solutions at 6.0, 6.5, 7.0, 8.0, 9.0, 10.0, 11.0, respectively. Scanning electron microscopy(SEM) investigations revealed that as the reaction solution was in pH value range from 6.0 to 9.0, the yield and length of rod were surprisingly high. As the pH value of reaction solution reach to 10.0 and 11.0, the dominant crystal phase changed to Ag2O. The morphology of Ag2O was ball-like observed from SEM, which aggregated to construct architectures of several micrometers. The FT-IR spectra of the sample were recorded from 450 to 1200 cm−1 at room temperature. The absorption bands at 500, 680, 862, 895, 920 and 965 cm−1 were observed in all hydrothermal synthesis samples. The absorption bands at 500 and 680 cm−1 correspond to the symmetric and asymmetric stretching vibrations of the V-O-V bridge of the V2O74- group, respectively. In UV/Vis spectra were measured, the spectra patterns of pH = 7.0 to 9.0 were similar; the band gap absorption edge of pH = 7.0 was determined to be 550 nm and the value of band gap estimated by the onset point of the absorption curve was 2.2 eV. The pH = 6.0 and pH = 6.5 has a steep absorption edge in the visible light region, which was different from the absorbance spectra of pH = 7.0, which consisted of structure of α-AgVO3 and β-AgVO3, respectively.Optimal preparation is conditions under 50 W of power at 140℃ for 1h for fabrication of the silver vanadates.
In comparison to conventional hydrothermal methods, these silver vanadates did not only possessing a small size in diameter, but also relatively low energy consumption was observed in manufacturing the silver vanadates using a microwave-assisted hydrothermal process. The study has shown that silver vanadates 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, and it could be used in the large-scale fabrication of silver vanadates. Based on our experimental results, a dissolving-depositing-growing model was proposed for the formation of silver vanadates structure.

並列關鍵字

Photoelectrodes ； microwave-assisted hydrothermal method ； silver vanadates

參考文獻

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