Two-Step Delamination of Highly Charged, Vermiculite-like Layered Silicates via Ordered Heterostructures
journal contributionposted on 28.04.2017, 00:00 by Matthias Daab, Sabine Rosenfeldt, Hussein Kalo, Matthias Stöter, Beate Bojer, Renée Siegel, Stephan Förster, Jürgen Senker, Josef Breu
Because of strong Coulomb interactions, the delamination of charged layered materials becomes progressively more difficult with increasing charge density. For instance, highly charged sodium fluorohectorite (Na0.6Mg2.4Li0.6Si4O10F2, Na-Hec) cannot be delaminated directly by osmotic swelling in water because its layer charge exceeds the established limit for osmotic swelling of 0.55 per formula unit Si4O10F2. Quite surprisingly, we found that this hectorite at the border of the smectite and vermiculite group can, however, be utterly delaminated into 1-nm-thick platelets with a high aspect ratio (24 000) in a two-step process. The hectorite is first converted by partial ion exchange into a one-dimensionally ordered, interstratified heterostructure with strictly alternating Na+ and n-butylammonium (C4) interlayers. This heterostructure then spontaneously delaminates into uniform single layers upon immersion in water whereas neither of the homoionic phases (Na-Hec and C4-Hec) swells osmotically. The delamination of more highly charged synthetic layered silicates is a key step to push the aspect ratio beyond the current limits.
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formula unit Si 4 O 10 F 2Na 0.6 Mg 2.4 Li 0.6 Si 4 O 10 F 2one-dimensionallyNa-Hecinterlayerdelaminationsodium fluorohectoritecharge densityion exchangebutylammonium1- nm-thick plateletsuniformCoulomb interactionsinstancesmectitelayer chargeinterstratified heterostructureHeterostructureTwo-Step DelaminationC 4-Hec swells osmoticallyimmersionmaterialVermiculite-like Layered Silicates0.55delaminatedChargedsilicatehomoionic phasesaspect ratiodelaminatevermiculite group