Block Karin A, Trusiak Adrianna, Katz Al, Alimova Alexandra, Wei Hui, Gottlieb Paul, Steiner Jeffrey C
Department of Earth and Atmospheric Sciences, The City College of New York, 160 Convent Ave, New York, NY, 10031.
Department of Physics, The City College of New York, 160 Convent Ave, New York, NY, 10031.
Appl Clay Sci. 2015 Apr;107:173-181. doi: 10.1016/j.clay.2015.01.021.
Understanding structural changes in clay minerals induced by complexation with organic matter is relevant to soil science and agricultural applications. In this study, the effect of peptide storage in montmorillonite and the thermal stability of peptide-clay complexes was examined through characterization by X-ray diffraction (XRD), electron microscopy, UV absorption, and thermogravimetric analysis (TGA). XRD analysis of small peptide-montmorillonite clay complexes produced profiles consisting of reflections associated with the smectite 001 reflection and related peaks similar to that produced by a mixed layer clay mineral structure. Shifts in higher order diffraction maxima were attributed to disorder caused by the intercalation with the peptides. Increasing peptide concentrations resulted in greater shifts towards smaller 2θ from 6.37° (1.39 nm) to 5.45° (1.62 nm) as the interlayer space expanded. The expansion was accompanied by broadening of the 001 reflection (FWHM increases from 0.51 to 1.22° 2θ). The XRD line broadening was interpreted as caused by poorer crystallinity resulting from intercalation and tactoid exfoliation. SEM images revealed montmorillonite platelets with upwardly rolled edges that tend toward cylindrical structures with the production of tubules. High-resolution TEM images revealed bending of montmorillonite platelets, confirming exfoliation. The distribution of basal spacings in the micrographs was determined from the spatial frequencies obtained by Fourier analysis of density profiles. The distribution indicated the presence of discrete coherent crystallite domains. XRD and TGA results indicated that higher peptide concentrations resulted in a greater fraction of intercalated peptides and that surface adsorption of peptides mediated intercalation. Therefore, higher peptide concentration led to more stable organoclay complexes. However, UV absorption and TGA found that peptide adsorption onto montmorillonite had a finite limit at approximately 16% by weight.
了解黏土矿物与有机物络合所引起的结构变化与土壤科学及农业应用相关。在本研究中，通过X射线衍射（XRD）、电子显微镜、紫外吸收和热重分析（TGA）等表征手段，研究了肽在蒙脱石中的储存效应以及肽-黏土复合物的热稳定性。对小肽-蒙脱石黏土复合物的XRD分析产生的图谱由与蒙脱石001反射相关的反射峰以及与混合层黏土矿物结构产生的相关峰组成。高阶衍射最大值的位移归因于肽插入导致的无序。随着肽浓度增加，层间空间扩大，2θ从6.37°（1.39纳米）向5.45°（1.62纳米）的位移更大。这种膨胀伴随着001反射的变宽（半高宽从0.51增加到1.22° 2θ）。XRD谱线变宽被解释为插入和片晶剥落导致结晶度变差。扫描电子显微镜（SEM）图像显示蒙脱石片层边缘向上卷曲，趋向于形成带有小管的圆柱形结构。高分辨率透射电子显微镜（TEM）图像显示蒙脱石片层弯曲，证实了剥落现象。通过对密度分布图进行傅里叶分析获得的空间频率确定了显微照片中基面间距的分布。该分布表明存在离散的相干微晶域。XRD和TGA结果表明，较高的肽浓度导致更多的肽插入，且肽的表面吸附介导了插入过程。因此，较高的肽浓度导致形成更稳定的有机黏土复合物。然而，紫外吸收和TGA发现，肽在蒙脱石上的吸附存在约16%重量的有限极限。
