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首页> 外文期刊>Crystal growth & design >High-Speed Morphology Control of Boehmite Nanoparticles by Supercritical Hydrothermal Treatment with Carboxylic Acids
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High-Speed Morphology Control of Boehmite Nanoparticles by Supercritical Hydrothermal Treatment with Carboxylic Acids

机译：羧酸超临界水热处理对勃姆石纳米颗粒的高速形貌控制

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摘要

This study demonstrates that the morphology of boehmite (AlOOH) nanoparticles can be controlled over a short timespan by supercritical hydrothermal treatment in the presence of alkyl carboxylic acids including hexanoic, octanoic, decanoic, tetradecanoic, and octadecanoic acids. Boehmite nanoparticles were treated with carboxylic acid in supercritical water at 400 degrees C and at a water density of 0.35 g/cm(3) in a batch-type reactor. When the carboxylic acid was not added, the particles were shaped as rhombic plates. However, the addition of carboxylic acid changed the crystal morphology to hexagonal plates. The aspect ratio (i.e., [length along the a-axis]/[length along the c-axis]) of the rhombic plates increased with a treatment time of 2-30 min, which is a much shorter timespan than that used for conventional hydrothermal crystallization. The aspect ratio of the hexagonal plates increased with increasing concentration of alkyl carboxylic acids. These results clearly indicate that carboxylic acids enhance the dissolution and recrystallization of boehmite. The aspect ratio increased with decreasing length of the alkyl chain of alkyl-carboxylic acid added to the system. Thermogravimetric analysis (TGA) showed that carboxylic acids modified the surface of the boehmite particles. The coverage of the alkyl carboxylic acid on the surface of the nanoparticles was evaluated from the weight loss curve obtained from TGA, and the surface area was evaluated from transmission electron microscopy, which showed that the aspect ratio of the particles increased with increasing the coverage. The results suggest that the carboxylic acid suppresses crystal growth along the shorter axis through surface-capping, thus enhancing dissolution and crystal growth along the a-axis.
机译：这项研究表明，在存在己酸，辛酸，癸酸，十四烷酸和十八烷酸的烷基羧酸存在下，超临界水热处理可以在短时间内控制勃姆石（AlOOH）纳米颗粒的形貌。勃姆石纳米颗粒在间歇式反应器中于400摄氏度和水密度0.35 g / cm（3）的超临界水中用羧酸处理。当不添加羧酸时，颗粒成形为菱形板。然而，羧酸的添加将晶体形态改变为六边形板。菱形板的长宽比（即[a轴的长度] / [c轴的长度]）随着2-30分钟的处理时间而增加，这比传统的处理时间要短得多水热结晶。六边形板的纵横比随烷基羧酸浓度的增加而增加。这些结果清楚地表明，羧酸增强了勃姆石的溶解和重结晶。长径比随着添加到体系中的烷基羧酸的烷基链长度的减小而增加。热重分析（TGA）表明，羧酸修饰了勃姆石颗粒的表面。根据由TGA获得的重量损失曲线评价烷基羧酸在纳米颗粒表面上的覆盖率，并且根据透射电子显微镜评价表面积，这表明颗粒的纵横比随着覆盖率的增加而增加。结果表明，羧酸通过表面封端抑制了沿短轴的晶体生长，从而增强了沿a轴的溶解和晶体生长。

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