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Metal Chalcogenide Nanocrystal Assembly: From Synthesis To Applications

机译:金属硫属元素化物纳米晶体组装:从合成到应用

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摘要

This dissertation study is focused on (1) the application of an oxidation-induced sol-gel assembly method to formation of CdTe aerogels; (2) extension of existing aerogel compositions and properties by an alternative synthetic approach: cation-exchange reactions; and (3) probing the functionality of CdSe aerogels as optical sensors of Lewis base analytes.Highly porous CdTe aerogels were successfully synthesized by sol-gel assembly of CdTe nanocrystals with thiolate or nonthiolate (phosphine oxide) ligated surfaces by treatment with tetranitromethane. Both phosphine oxide-capped and the thiolate-capped aerogels exhibit similar structure, morphology and porosimetry properties, suggesting that precursor ligation does not have a no major effect on the gelation process and the resultant aerogel properties. These data clearly shows that thiolate capping is not a necessary step in the gelation process; the exposure of reactive sites and the subsequent surface oxidation reaction to form chalcogenide linkages is the key.Cation-exchange reactions in metal chalcogenide gels were explored for the first time. Ag2Se wet gel monoliths were successfully prepared by an ion-exchange reaction of a monolithic CdSe wet gel and converted to an aerogel by drying under supercritical conditions. The newly prepared Ag2Se aerogels adopt the cubic phase and exhibit a typical pearl-necklace morphology and the high surface area characteristics of aerogels. The ion-exchange synthesis route can also be successfully employed for other gel systems, including PbSe and CuSe.The photoluminescence (PL) response of highly porous CdSe aerogels to triethylamine (TEA) is investigated and compared to prior studies on single crystals and nanoparticle-polymer composites. As-prepared CdSe aerogels show significant and reversible enhancement of luminescence intensity upon exposure to TEA relative to the intensity in pure argon carrier gas. The enhancement in the PL response is concentration-dependant and linear over the range of TEA concentration studied (4.7  103 - 75  103 ppm). The sensing response of previously tested samples exhibits saturation behavior that is modeled using Langmuir adsorption isotherms, yielding adsorption equilibrium constants in the range 300 to 380 atm-1. The response is sensitively affected by the surface characteristics of the aerogel; when the wet gels are treated with pyridine prior to aerogel formation, the response to TEA is diminished, and when as-prepared aerogels are heated in a vacuum, no response is observed. Deactivation is attributed to an increase in surface oxide (SeO2) and decrease in surface Cd2+ Lewis acid sites. Sensing runs of approximately one hour have little impact on the morphology or crystallinity of the aerogels, but do result in partial removal of residual thiolate ligands left over from the gelation process.
机译:本论文的研究重点是:(1)氧化诱导溶胶-凝胶组装法在CdTe气凝胶形成中的应用; (2)通过另一种合成方法扩展现有气凝胶的成分和性能:阳离子交换反应; (3)探讨了CdSe气凝胶作为路易斯碱分析物的光学传感器的功能。通过将CdTe纳米晶体与硫醇盐或壬硫醇盐(氧化膦)连接的表面通过四硝基甲烷处理,通过溶胶-凝胶组装成功地合成了高度多孔的CdTe气凝胶。氧化膦封端的和硫醇盐封端的气凝胶都显示出相似的结构,形态和孔隙率特性,这表明前体连接对凝胶化过程和所得气凝胶特性没有重大影响。这些数据清楚地表明,在胶凝过程中,硫醇盐封端不是必需的步骤。活性部位的暴露以及随后的表面氧化反应形成硫族化物键是关键。首次探索了金属硫族化物凝胶中的阳离子交换反应。通过整体CdSe湿凝胶的离子交换反应成功制备了Ag2Se湿凝胶整料,并通过在超临界条件下干燥将其转化为气凝胶。新制备的Ag2Se气凝胶采用立方相,并表现出典型的珍珠项链形态和气凝胶的高表面积特性。离子交换合成路线也可以成功用于其他凝胶体系,包括PbSe和CuSe。研究了高度多孔的CdSe气凝胶对三乙胺(TEA)的光致发光(PL)反应,并将其与先前对单晶和纳米粒子的研究进行了比较。聚合物复合材料。制备的CdSe气凝胶相对于纯氩气载气,在暴露于TEA时显示出显着且可逆的发光强度增强。在所研究的TEA浓度范围内(4.7103-75103 ppm),PL反应的增强是浓度依赖性的并且是线性的。先前测试样品的感测响应表现出饱和行为,该行为使用Langmuir吸附等温线进行建模,得出的吸附平衡常数为300至380 atm-1。响应受到气凝胶表面特性的敏感影响。当湿凝胶在形成气凝胶之前用吡啶处理时,对TEA的响应减弱,并且当将制备的气凝胶在真空中加热时,未观察到响应。失活归因于表面氧化物(SeO2)的增加和表面Cd2 +路易斯酸位点的减少。大约一小时的传感运行对气凝胶的形态或结晶度影响很小,但确实会部分除去凝胶化过程中残留的残留硫醇盐配体。

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    Yao Qinghong;

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  • 年度 2010
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