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.

Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites

“…[7][8][9][10][11][12][13][14][15][16][17][18] In this study, we demonstrated that co-spray-drying of lactose and Na-MMT leads to lactose intercalation,…”

“…5 There is significant amount of published research on organic polymer-clay nanocomposites, but only few report on MMT combined with low-molecular-weight organic compounds including peptides and amino acids. [7][8][9][10][11][12][13][14][15][16][17][18][19] In these reports, the most important mechanism involved in intercalation into MMT is cationic exchange. 7-9, 12, 13, 19 Anionic and nonionic compounds have also been demonstrated to interact with MMT.…”

Organo-Mineral Interactions Are More Important for Organic Matter Retention in Subsoil Than Topsoil

“…This may suggest preferential adsorption of N-containing biomolecules [8,14,45] on illite and montmorillonite. Montmorillonitic soils retain peptides and become enriched with amine-N [46,47]. Microbial residues such as secretions and necromass are a component of mineral-associated SOM [31,48] although Vogel et al [49] reported that illite retained more microbial-derived C and N than montmorillonite.…”

Effect of Natural Nanostructured Rods and Platelets on Mechanical and Water Resistance Properties of Alginate-Based Nanocomposites

“…It has been shown that MMT is a 2:1-type layered clay mineral with a sandwiched structure composed of two 2D platelets and interlayer cations (i.e., Na + , Ca 2+ , Mg 2+ ). The strong hydrogen-binding and electrostatic interaction, and van der Waals forces between two platelets make MMT difficult to be exfoliated and tend to be present in a form of agglomeration (Zhang et al, 2014; Block et al, 2015; Liu et al, 2016). In comparison, natural 1D rod-like nanoclays are easy to be dispersed as nanoscale size, and showed great potential to be used to develop polymer/nanoclays composites (Nikolic et al, 2017; Ajmal et al, 2018; Shankar et al, 2018; Zhang P. et al, 2018).…”