Lehrstuhl für Anorganische Chemie I, Universität Bayreuth , D-95440 Bayreuth, Germany.
Bayerisches Polymerinstitut, D-95440 Bayreuth, Germany.
Langmuir. 2017 May 16;33(19):4816-4822. doi: 10.1021/acs.langmuir.7b01008. Epub 2017 May 4.
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 (NaMgLiSiOF, 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 SiOF. 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.
由于强库仑相互作用，随着电荷密度的增加，带电层状材料的分层变得越来越困难。例如，高电荷密度的钠氟羟硅镁石（NaMgLiSiOF，Na-Hec）不能直接通过渗透压膨胀在水中分层，因为其层电荷超过了渗透压膨胀的既定限制，即每个 SiOF 单元 0.55。令人惊讶的是，我们发现这种处于蒙脱石和蛭石族边界的羟硅镁石可以通过两步法完全分层成具有高纵横比（24000）的 1nm 厚薄片。羟硅镁石首先通过部分离子交换转化为一维有序的、层间交替的杂结构，其中严格交替的 Na 和正丁基铵（C4）层间。然后，当将这种杂结构浸入水中时，它会自发地分层成均匀的单层，而均相离子相（Na-Hec 和 C4-Hec）不会发生渗透压膨胀。更高度荷电合成层状硅酸盐的分层是推动纵横比超过当前限制的关键步骤。
