Several forms of niobium oxide were prepared, including nanostructured mesoporous materials, and their acidity properties were comprehensively investigated and compared with commercially available materials. The composites were characterized by a variety of techniques, including XRD, TEM, N2 adsorption and Hammett acid indicator studies. The acidity of the niobium oxide derivatives was also investigated by the ability of the materials to successfully promote the halochromic ring-opening of an oxazine-coumarin probe that was specifically designed for use in fluorescence imaging studies. The ring-opening reaction was easily monitored using UV-visible, fluorescence and NMR spectroscopy. Single molecule microscopy was employed to gain a more in-depth understanding of the niobium oxide acid catalysis pathway. Using this technique, the rate of niobium oxide mediated protonation was estimated to be 1.8 × 10−13 mol m−2 s−1. Single molecule analysis was also used to obtain a detailed map of Brønsted acid sites on the niobium oxide surface. The active sites, located by multiple blinking events, do not seem to be localized on any area of the material, but rather randomly distributed throughout the solid state surface. As the reaction proceeds, the sites with the highest acidity and accessibility are gradually consumed, making the next tier of acid sites available for reaction. The phenomenon was more closely characterized by using time lapsed reactivity maps.
制备了几种形式的
氧化铌,包括纳米结构介孔材料,并对其酸性进行了全面研究,并与市售材料进行了比较。通过 XRD、
TEM、N2 吸附和 Hammett 酸指示剂研究等多种技术对复合材料进行了表征。
氧化铌衍
生物的酸性还通过这些材料成功促进专门设计用于
荧光成像研究的恶嗪-
香豆素探针的卤代开环反应的能力进行了研究。利用紫外可见光、荧光和核磁共振光谱可以轻松监测开环反应。为了更深入地了解
氧化铌的酸催化途径,我们采用了单分子显微镜技术。利用这一技术,
氧化铌介导的质子化速率估计为 1.8 × 10-13 mol m-2 s-1。单分子分析还用于获得
氧化铌表面布氏酸位点的详细图谱。通过多次闪烁事件定位的活性位点似乎并不集中在材料的任何区域,而是随机分布在整个固态表面。随着反应的进行,酸度和可及性最高的位点逐渐被消耗掉,从而使下一层酸性位点可用于反应。通过使用时滞反应图可以更准确地描述这种现象。