Delamination by Repulsive Osmotic Swelling of Synthetic Na-Hectorite with Variable Charge in Binary Dimethyl Sulfoxide–Water Mixtures

Abstract

Swelling of clays is hampered by increasing layer charge. With vermiculite-type layer charge densities, crystalline swelling is limited to the two-layer hydrate, while osmotic swelling requires ion exchange with bulky and hydrophilic organic molecules or with Li+ cations to trigger repulsive osmotic swelling. Here, we report on surprising and counterintuitive osmotic swelling behavior of a vermiculite-type synthetic clay [Na0.7]inter[Mg2.3Li0.7]oct[Si4]tetO10F2 in mixtures of water and dimethyl sulfoxide (DMSO). Although swelling in pure water is restricted to crystalline swelling, with the addition of DMSO, osmotic swelling sets in at some threshold composition. Finally, when the DMSO concentration is increased further to 75 vol %, swelling is restricted again to crystalline swelling as expected. Repulsive osmotic swelling thus is observed in a narrow composition range of the binary water–DMSO mixture, where a freezing point suppression is observed. This suppression is related to DMSO and water molecules exhibiting strong interactions leading to stable molecular clusters. Based on this phenomenological observation, we hypothesize that the unexpected swelling behavior might be related to the formation of different complexes of interlayer cations being formed at different compositions. Powder X-ray diffraction and 23Na magic angle spinning-NMR evidence is presented that supports this hypothesis. We propose that the synergistic solvation of the interlayer sodium at favorable compositions exerts a steric pressure by the complexes formed in the interlayer. Concomitantly, the basal spacing is increased to a level, where entropic contributions of interlayer species lead to a spontaneous thermodynamically allowed one-dimensional dissolution of the clay stack.

Tracking the Dissolution Surface Kinetics of a Single Fluorescent Cyclodextrin Metal–Organic Framework by Confocal Laser Scanning Microscopy

“…In 60 and 70% methanol aqueous solutions, the value of n is 0.3304 and 0.2630 ( n < 0.45) for the dissolution of the CD-MOF⊃FL crystal, respectively, implying that the dissolution of the CD-MOF⊃FL crystal maintained a Fickian behavior (case I transport) governed by tiny swelling and diffusion . In 75% methanol aqueous solution, n is 0.745 (0.45 < n < 0.89), indicating that the dissolution of the CD-MOF⊃FL crystal followed a non-Fickian behavior, controlled by both diffusion and erosion. , In 80 and 95% methanol aqueous solutions, n is 1.037 and 4.927 ( n > 0.89), respectively, indicating that the dissolution of the CD-MOF⊃FL crystal exhibited a Fickian behavior (case II transport) controlled by erosion …”

“…The higher the amount of water, the faster the dissolution. In 60 and 70% methanol aqueous solutions, the value of n is 0.3304 and 0.2630 (n < 0.45) for the dissolution of the CD-MOF⊃FL crystal, respectively, implying that the dissolution of the CD-MOF⊃FL crystal maintained a Fickian behavior (case I transport) governed by tiny swelling 50 and diffusion. 51 In 75% methanol aqueous solution, n is 0.745 (0.45 < n < 0.89), indicating that the dissolution of the CD-MOF⊃FL crystal followed a non-Fickian behavior, controlled by both diffusion and erosion.…”

“…51 In 75% methanol aqueous solution, n is 0.745 (0.45 < n < 0.89), indicating that the dissolution of the CD-MOF⊃FL crystal followed a non-Fickian behavior, controlled by both diffusion and erosion. 50,52 In 80 and 95% methanol aqueous solutions, n is 1.037 and 4.927 (n > 0.89), respectively, indicating that the dissolution of the CD-MOF⊃FL crystal exhibited a Fickian behavior (case II transport) controlled by erosion. 53 Additionally, the size influence on the dissolution kinetics was studied by comparing the dissolution kinetics of 160 and 80 μm CD-MOF⊃FL crystals.…”

Trendbericht Festkörperchemie 2023

“…46) Wie Breu, Matjedes, Senker und Mitarbeitende mit Röntgenkleinwinkelstreuung, 23 Na-MAS-NMR-Spektroskopie und Röntgenbeugung zeigten, lässt sich synthetisches Natriumhectorit lösungsmittelgesteuert mit verschiedener oberflächlicher Ladung delaminieren. 47) Abb. Die Gruppe um Schmedt auf der Günne hat das neue frei zugängliche Programm IPReader entwickelt.…”

Gentle, Spontaneous Delamination of Layered Titanate Yielding New Types of Lithium Titanate Nanosheets

“…As the bonding in layered materials is highly anisotropic, the dissolution is restricted to the stacking direction of the charged layers and therefore has been labeled “1-dimensional (1D) dissolution” in a recent review . Among other, antimony phosphate, 2:1 type clay minerals, − ilerite, or lepidocrocite type titanates , and layered perovskites are members of this spontaneously delaminating group of layered materials.…”