Surface modification of nanoclays by catalytically active transition metal ions
Surface modification of nanoclays by catalytically active transition metal ions
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DOI：
10.1021/la700908m
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发表时间：
2007-09-11
期刊：
影响因子：
3.9
通讯作者：
Khalid, Syed
中科院分区：
文献类型：
--
作者：
Nawani, Pranav;Gelfer, Mikhail Y.;Khalid, Syed
采用过渡金属离子（TMIs）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（AAS）、元素分析（EA）、扫描电镜（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）等方法研究了tmi改性纳米粘土的组成、结构、形貌和热性能。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，TMI处理可以显著提高有机粘土的热稳定性，在空气中比在氮中更明显。温度分辨SAXS测量显示，tmi的存在增加了结构降解的起始温度。tmi修饰的有机粘土具有较高的热稳定性，这可能是由于热降解机制的改变，导致挥发性产物的产率降低，催化活性tmi的存在促进了炭的形成。
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.