Department of Chemistry and Biochemistry, Montana State University , P.O. box 173400, Bozeman, Montana 59717, United States.
Langmuir. 2017 Apr 11;33(14):3534-3547. doi: 10.1021/acs.langmuir.6b04606. Epub 2017 Mar 28.
Surface modifications fundamentally influence the morphology of kaolinite nanostructures as a function of crystallinity and the presence of contaminants. Besides morphology, the catalytic properties of 1:1-type exfoliated aluminosilicates are also influenced by the presence of defect sites that can be generated in a controlled manner by mechanochemical activation. In this work, we investigated exfoliated halloysite nanoparticles with a quasi-homogeneous, scroll-type secondary structure toward developing structural/functional relationships for composition, atomic structure, and morphology. The surface properties of thin-walled nanoscrolls were studied as a function of mechanochemical activation expressed by the duration of dry-grinding. The surface characterizations were carried out using N, NH, and CO adsorption measurements. The effects of grinding on the nanohalloysite structure were followed using thermoanalytical thermogravimetric/derivative thermogravimetric (TG/DTG) and infrared spectroscopic [Fourier transform infrared/attenuated total reflection (FTIR/ATR)] techniques. Grinding results in partial dehydroxylation with similar changes as those observed for heat treatment above 300 °C. Mechanochemical activation shows a decrease in the dehydroxylation mass loss and the DTG peak temperature, a decrease in the specific surface area and the number of mesopores, an increase in the surface acidity, blue shift of surface hydroxide bands, and a decrease in the intensity of FTIR/ATR bands as a function of the grinding time. The experimental observations were used to guide atomic-scale structural and energetic simulations using realistic molecular cluster models for a nanohalloysite particle. A full potential energy surface description was developed for the mechanochemical activation and/or heating toward nanometahalloysite formation that aids the interpretation of experimental results. The calculated differences upon dehydroxylation show a remarkable agreement with the mass loss values from DTG measurements.
表面修饰从根本上影响了高岭石纳米结构的形态，这取决于其结晶度和污染物的存在。除了形态，1:1 型层状硅铝酸盐的催化性能也受到缺陷部位的影响，这些缺陷部位可以通过机械化学活化以受控的方式产生。在这项工作中，我们研究了具有准均匀、螺旋型二级结构的剥离埃洛石纳米管，以开发组成、原子结构和形态的结构/功能关系。我们研究了薄壁纳米螺旋的表面性质，其表面性质随机械化学活化的持续时间（以干磨时间表示）而变化。使用 N、NH 和 CO 吸附测量对表面特性进行了研究。使用热分析热重/导数热重（TG/DTG）和红外光谱[傅里叶变换红外/衰减全反射（FTIR/ATR）]技术跟踪研磨对纳米埃洛石结构的影响。研磨导致部分脱羟基，其变化与 300°C 以上热处理观察到的变化相似。机械化学活化导致脱羟质量损失和 DTG 峰温降低，比表面积和中孔数量减少，表面酸度增加，表面羟基带蓝移，FTIR/ATR 带强度降低，这与研磨时间的增加有关。实验观察结果用于使用实际的纳米管颗粒分子簇模型进行原子尺度的结构和能量模拟，以指导机械化学活化和/或加热向纳米金属埃洛石形成的方向进行。针对机械化学活化和/或加热向纳米金属埃洛石形成的方向，开发了一个全势能面描述，以帮助解释实验结果。脱羟后的计算差异与 DTG 测量的质量损失值非常吻合。
