title: Exfoliation and intercalation of montmorillonite by small peptides.
abstract: 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.
authors.affiliation: Department of Earth and Atmospheric Sciences, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Karin A
authors.initials: KA
authors.lastname: Block
authors.affiliation: Department of Earth and Atmospheric Sciences, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Adrianna
authors.initials: A
authors.lastname: Trusiak
authors.affiliation: Department of Physics, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Al
authors.initials: A
authors.lastname: Katz
authors.affiliation: Sophie Davis School of Biomedical Education, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Alimova
authors.affiliation: Sophie Davis School of Biomedical Education, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Hui
authors.initials: H
authors.lastname: Wei
authors.affiliation: Sophie Davis School of Biomedical Education, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Paul
authors.initials: P
authors.lastname: Gottlieb
authors.affiliation: Department of Earth and Atmospheric Sciences, The City College of New York, 160 Convent Ave, New York, NY, 10031.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Steiner
keywords: Clay exfoliation; High resolution TEM; Intercalation; Montmorillonite; Organic matter; Peptides
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