Systematic Study on Swelling/Delamination of Layered Metal Oxides with Quaternary Ammonium Ions: Production of Well-Shaped/Oversized Unilamellar Nanosheets

Enormous swelling of layered host compounds in an aqueous solution of various amines has been investigated as an important step in the synthesis of molecularly thin 2D nanosheets. However, a complete understanding of the reaction process has not been attained, which is the barrier for producing high-quality unilamellar nanosheets. Here, the swelling and delamination behaviors of platelet single crystals of protonated layered metal oxides are systematically examined with a series of tetraalkylammonium (TAA) hydroxide solutions. Upon contact with the solutions, the crystals immediately underwent massive expansion by several tens to hundreds of times. The swollen crystals can be delaminated into elementary layers by the application of external shear force. The exfoliation behavior is dependent on TAA ions, especially in terms of yield and lateral size/shape of the delaminated nanosheets. The swollen crystals with TAA ions with longer alkyl chains are delaminated almost completely, but irregular and fractured small sheets are yielded. Such long alkyl chains become entangled on the oxide layer and resulting hydrophobic interactions may be responsible for the lateral fragmentation. It is found that replacement of aqueous solutions with organic solvents to suppress the hydrophobic interactions is effective to produce oversized nanosheets in rectangular shape with sharp edges.

Forceless spontaneous delamination of high-aspect ratio fluorohectorite into monolayer nanosheets in chloroform

One-dimensional dissolution of a layered compound in a nonpolar organic solvent is reported for the first time. A high-aspect ratio fluorohectorite modified with a cationic surfactant (dioctadecyldimethylammonium) showed spontaneous delamination into monolayer nanosheets in chloroform.

Nematic suspension of a microporous layered silicate obtained by forceless spontaneous delamination via repulsive osmotic swelling for casting high-barrier all-inorganic films

Exploiting the full potential of layered materials for a broad range of applications requires delamination into functional nanosheets. Delamination via repulsive osmotic swelling is driven by thermodynamics and represents the most gentle route to obtain nematic liquid crystals consisting exclusively of single-layer nanosheets. This mechanism was, however, long limited to very few compounds, including 2:1-type clay minerals, layered titanates, or niobates. Despite the great potential of zeolites and their microporous layered counterparts, nanosheet production is challenging and troublesome, and published procedures implied the use of some shearing forces. Here, we present a scalable, eco-friendly, and utter delamination of the microporous layered silicate ilerite into single-layer nanosheets that extends repulsive delamination to the class of layered zeolites. As the sheet diameter is preserved, nematic suspensions with cofacial nanosheets of ≈9000 aspect ratio are obtained that can be cast into oriented films, e.g., for barrier applications.

Hydration and swelling: a theoretical investigation on the cooperativity effect of H-bonding interactions between p-hydroxy hydroxymethyl calix[4]/[5]arene and H2O by many-body interaction and density functional reactivity theory

In order to explore the nature of the hydration and swelling of superabsorbent resin, a theoretical investigation into the cooperativity effect of the H-bonding interactions in the hydrates of four model compounds that can be regarded as the units of hydroquinone formaldehyde resin (HFR) (i.e., O-hydroxymethyl-1,4-dihydroxybenzene, methylene di-O-hydroxymethyl-1,4-dihydroxybenzene, p-hydroxy hydroxymethyl calix[4]arene and p-hydroxy hydroxymethyl calix[5]arene) was carried out by many-body interaction and density functional reactivity theory. The HFR···H₂O···H₂O complexes, in which the H₂O···H₂O moieties are bound with both the hydroxyl groups of HFR, are the most stable. For the HFR(H₂O)_n clusters, the interaction energy per building block is increased as the number of the size n increases, indicating the cooperativity effect. Therefore, a deduction is given that the cooperativity effects of the H-bonding interactions play an important role in the process of the hydration and swelling of HFR, and the swelling behavior is mainly attributed to the cooperativity effects which arised from the interactions between the H₂O molecules. The origin of the cooperativity effect was examined employing several information-theoretic quantities in the density functional reactivity theory. The degree of swelling of HFR was quantitated using a measure of volume. Graphical abstract.