Nawani Pranav, Gelfer Mikhail Y, Hsiao Benjamin S, Frenkel Anatoly, Gilman Jeffrey W, Khalid Syed
Chemistry Department, Stony Brook University, Stony Brook, New York 11794-3400, USA.
Langmuir. 2007 Sep 11;23(19):9808-15. doi: 10.1021/la700908m. Epub 2007 Aug 17.
A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.
通过用过渡金属离子（TMI）对原始粘土或有机粘土（Cloisite C20A）进行改性，制备了一类独特的纳米粘土。采用原子吸收光谱法（AAS）、元素分析（EA）、扫描电子显微镜（SEM）、小角X射线散射（SAXS）、广角X射线衍射（WAXD）、热重分析（TGA）、差示扫描量热法（DSC）和X射线吸收近边结构（XANES）光谱对TMI改性纳米粘土的组成、结构、形态和热性能进行了研究。发现改性粘土中TMI的含量接近离子交换容量的极限值。SEM和X射线结果证实，TMI位于矿物层之间，而不是吸附在粘土颗粒表面。TGA结果表明，对有机粘土进行TMI处理可显著提高热稳定性，在空气中比在氮气中更明显。温度分辨SAXS测量表明，TMI的存在提高了结构降解的起始温度。TMI改性有机粘土的较高热稳定性可归因于热降解机理的改变，导致挥发性产物产率降低，并在具有催化活性的TMI存在下促进了炭的形成。
