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    Please use this identifier to cite or link to this item: http://ir.lib.ksu.edu.tw/handle/987654321/6193

    Title: MOx/SBA-15 複合材對甲苯選擇性氧化反應之研究
    Authors: 黃昭銘
    Keywords: Ag3VO4
    Visible-light driven photocatalyst
    DRIFT technique
    Surface hydroxyl group
    Date: 2009-07-31
    Issue Date: 2009-12-29 16:22:49 (UTC+8)
    Abstract: Visible-light-driven silver vanadate photocatalysts were successfully synthesized using a low-temperature hydrothermal synthesis method. Under various hydrothermal conditions, the structures of silver vanadates were tuned by changing the hydrothermal time and with the assistance of a surfactant. X-ray diffraction (XRD) results reveal that the hydrothermal synthesis powders consisted of three kinds of phase: pure Ag4V2O7 or pure α-Ag3VO4 or mixed phases of Ag4V2O7 and α-Ag3VO4. UV-vis spectroscopy indicated that silver vanadate particles had strong visible light absorption with associated band gaps in the range of 2.2-2.5 eV. The powder synthesized at 140 ℃ for 4 h (HT4) exhibited the highest photocatalytic activity among all samples. The reactivity of HT4 (surface area, 2.04 m2 g-1) on isopropanol and benzene was 16.6 times and 16.2 times higher than those of P25 (surface area, 49.04 m2 g-1) under visible light irradiation. The enhanced photocatalytic activity of HT4 is attributed to mixed crystalline phases of Ag4V2O7 and α-Ag3VO4, where α-Ag3VO4 is the major component. In addition, the highest large amount of hydroxyl groups on the surface of α-Ag3VO4, detected by the in-situ FT-IR diffuse reflectance (DRIFT) technique, was considered as the other factor. Detailed DRIFT experiments also revealed that the stability of Brønsted acid sites of HT4 was excellent, as confirmed by NH3 adsorption. Studies of crystalline phase and surface property showed that the photocatalytic activities of the hydrothermal synthesis of silver vanadates are strongly affected by hydrothermal time. Besides, the amount of surface hydroxyl groups and the crystallinity of α-Ag3VO4 phase were verified to be the key factors influencing photocatalytic activity.
    本研究使用水熱法於不同水熱溫度(120~180℃)下製備銀釩氧化物(silver vanadate),由晶型分析可知120℃合成的粉末為混晶(Ag3VO4與Ag4V2O7),隨著水熱溫度上升,晶型從混晶變成單晶(Ag3VO4),180℃合成的粉末,Ag3VO4的晶型有變強的趨勢。量測吸收光譜可合成的粉末能隙值為2.2 ~2.5 eV。以140℃/4h的水熱條件所得到的銀釩氧化物對IPA及苯,有最大的初始反應速率常數,分別為P25的16.6與16.2倍。原位傅立葉散射-反射紅外光譜分析(DRIFT)可知140℃合成的粉末,含有大量的氫氧官能基與Brønsted acid(布忍司特酸);表面氫氧官能基與布忍司特酸的存在,對水熱法製備的銀釩氧化物光催化活性有決定性的影響。本研究後期階段,運用後添加方法製備BiVO4/SBA-15複合光觸媒,探討添加不同重量比例BiVO4(5、10及20%)對甲苯光分解效率之影響。由晶型分析可知複合材料為BiVO4 monoclinic晶型,能隙值約在2.44 eV,表面積約在298~435 m2/g。在10 W可見光燈照射下對濃度為至154 ppm的甲苯氣體進行光分解實驗。分解實驗結果顯示BiVO4添加量在10%以上時,光分解效率並無明顯幫助,與純BiVO4粉末相差不多,於開燈10分鐘後,空氣中殘留的甲苯濃度已趨進飽和,無明顯下降,推測其BiVO4晶粒阻塞SBA-15孔洞,無法利用SBA-15高表面積的優點。當BiVO4 添加量在5%時,其分解效率比起純BiVO4粉末高出約2倍,在開燈40分鐘後,空氣中殘留的甲苯濃度少於10 ppm,SBA-15的高表面積可有效幫助吸附,再利用分散均勻的奈米BiVO4將甲苯光分解。綜合上述,本研究方法成功製備高吸附量且快速分解甲苯的可見光光觸媒材料。
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