Facile Scalable Synthesis of Rectorites

Abstract

Using a synthetic Na-fluorohectorite ([Na 0.5 ] inter [Mg 2.5 Li 0.5 ] oct [Si 4 ] tet O 10 F 2 ), mixed-cation heterostructures with an alternating interstratification pattern are formed under appropriate conditions via simple cation-exchange reactions. The most important requirement for the spontaneous formation of these ordered mixed-layer structures is a high degree of charge homogeneity of the smectite. The partial exchange of cations with largely different hydration enthalpies (Na þ by K þ ) results in the regular interstratification of hydrated (d = 12.4 A ˚) and nonhydrated (d = 10.0 A ˚) interlayers at 40% relative humidity (RH). By combining analytical methods that are sensitive to either hydrated or collapsed interlayers (selective cation exchange, hydrosorption isotherms, and 23 Na MAS NMR spectroscopy), we proposed a novel mechanism that is centered at the interlayers and does not require polar lamellae, as suggested in the literature for rectorite formation. Upon formation of the regular interstratification, the charge density of the interlayers changes from homogeneous to alternating between interlayers in the stacking direction. This simple redistribution of exchangeable interlayer cations is facile and rapid. The cation exchange capacity (CEC) of the collapsed interlayers is higher than the average CEC, while the CEC of the hydrated interlayers will be correspondingly lower. The local CEC of these interlayers deviates by ∼18%-28% from the average CEC, as calculated independently from ion-exchange experiments and hydrosorption measurements. Moreover, this alternating differentiation of the interlayer cation concentration seems to be driven by thermodynamics. Even a mixture of homocationic Na-hectorite and K-hectorite slowly converts to a regularly interstratified material when immersed in water. After the interlayers are differentiated, they may be selectively manipulated, creating dual functional materials, where distinct nanoreactors are separated by a 1-nm-thick insulating lamellae and are arranged in a regular manner.

Molecular Simulation Study of Hydrated Na-Rectorite

“…Several experimental studies showed the hydration and dehydration properties of rectorite with different cations. 38, 39 With the rapid development of rectorite-based composites, industrial applications of rectorite are increasing. 40−44 The complicated structure of rectorite makes it more difficult to obtain exact interlayer information by experiments than that of montmorillonite.…”

Barrier Properties of Synthetic Clay with a Kilo‐Aspect Ratio

“…larger platelets, less impurities and higher homogeneities. [20][21][22] Moreover, designed synthesis allows to adjust crucial parameters controlling accessible aspect ratios: nature of interlayer cation, layer charge, and composition. Colorless materials can easily be produced and the intracrystalline reactivity may be adjusted to a level where switching between shear stiff and shear labile states allows to alter the effi ciency of tactoid exfoliation.…”

Characterization of rectorite from the Beatrix Gold Mine in South Africa

“…In literature, the narrow 23 Na peak at ca. 0 ppm is attributed to trapped Na + ions in symmetric cavities created by a mica-type stacking or to nonexchangeable part of the sodium interlayer cations (Möller et al, 2010). In contrast to that work, the quadrupolar interactions for this peak are not averaged out, and it can tentatively be assigned to a variety of Na-containing mica in the samples under study.…”