One-Step Exfoliation of Kaolinites and Their Transformation into Nanoscrolls

Abstract

Kaolinite nanoscrolls, rolled kaolinite sheets with a tubular form, were prepared by a one-step route in which intercalation of guest species and swelling with solvent proceed at the same time. A methoxy-modified kaolinite was exfoliated by the intercalation of hexadecyltrimethylammonium chloride. The formation of nanoscrolls by the one-step route proceeded only by several alkyltrimethylammonium salts and 1-hexadecyl-3-methylimidazolium chloride. Intercalation of primary amines caused the formation of nanoscrolls by a two-step route in which the intercalation and swelling proceed separately. The successful one-step route is ascribed to the relatively weak interactions between the head groups of guest species and the interlayer surface of methoxy-modified kaolinite, and the interaction is thought to allow the formation of a flexible array of interlayer guest species for swelling. The tubular structure was mostly retained after the heat treatment at 600 °C to form hierarchically porous aluminosilicates with amorphous frameworks. The nanoscrolls intercalated organic guests species, which are not directly intercalated into methoxy-modified kaolinite, between the scrolled layers. The formation route to nanoscrolls is quite dependent not only on the surface modification of kaolinite but also on the structure of guest species.

Characterization of kaolinite-cetyltrimethylammonium chloride intercalation complex synthesized through eco-friend kaolinite-urea pre-intercalation complex

“…In the XRD pattern of ZK-UMe(wet), the complete displacement of U with Me and the formation of wet kaolinite-Me complex is clearly demonstrated by the shift of the whole (001) reflection from 1.07 nm to 1.11 nm [41]. The 1.11-nm basal spacing of the wet kaolinite-Me intercalation complex synthesized using the kaolinite-U pre-intercalation complex agrees well with the literature results with kaolinite-DMSO and kaolinite-NMF pre-intercalates [10,12,15,19,29,30,[33][34][35][36]41]. After drying the wet kaolinite-Me complexes at room temperature, the (001) reflections of the expanded phase decreased to 0.86 nm (ZK-U-Me(air-dry) sample), which is close to the value (d 001 = 0.88 nm) reported by Cheng et al [38] for similar air-dried complex prepared from kaolinite-U pre-intercalate.…”

“…According to the literature [7,15,35,41], the formation of the 0.86-nm complex from the 1.11-nm one can be attributed to the partial release of mobile Me and/or water molecules from the interlayer spaces during the air-drying process. After treating the wet kaolinite-Me intercalation complex with CTAC, the (001), (002), (003), (004), and (005) reflections of the kaolinite-CTAC intercalation complex [30,35,40] appeared at 3.82, 1.91, 1.27, 0.95, and 0.76 nm, respectively (ZK-U-Me-CTAC(unwashed) sample). The presence of these characteristic reflections, together with the disappearance of the 1.11-nm basal spacing, proves the complete formation of kaolinite-CTAC intercalation complex.…”

“…The preparation of these nanocomposites is usually carried out through multiple intercalations, where the natural platy kaolinite could transform from nanoplates into halloysite-like nanoscorolls. A promising exfoliation method for synthesizing kaolinite nanoscrolls involves the intercalation of cetyltrimethylammonium chloride (CTAC) into a kaolinite-methanol (kaolinite-Me) complex prepared from kaolinite-DMSO or kaolinite-NMF pre-intercalate [19,29,30,34,35,40].…”

“…From the DMSO and NMF pre-intercalates, the formation of a kaolinite-Me complex with basal spacing of 1.11-1.13 nm was established in methanol-wet state [10,12,15,19,29,30,[33][34][35][36]41], but on air-drying, a contraction down to 0.93-0.86 nm was observed [12,15,19,38,41]. Using elemental and thermal analysis results, Tunney and Detellier [7], Komori et al [15], and Matusik and Klapyta [36] calculated the values of x=0.87, x=0.36, and x=0.48, respectively, for the supposed chemical formula of In spite of the more eco-friendly behavior of U, there are only two studies reported in the literature [34,41], where the kaolinite-U pre-intercalate was used to synthesize kaoliniteMe complexes.…”

“…Using elemental and thermal analysis results, Tunney and Detellier [7], Komori et al [15], and Matusik and Klapyta [36] calculated the values of x=0.87, x=0.36, and x=0.48, respectively, for the supposed chemical formula of In spite of the more eco-friendly behavior of U, there are only two studies reported in the literature [34,41], where the kaolinite-U pre-intercalate was used to synthesize kaoliniteMe complexes. In our previous work with U [41], we obtained the same methanol-wet state (with the basal spacing of 1.12 nm) as prepared earlier in the literature using the kaolinite-DMSO and kaolinite-NMF pre-intercalates [10,12,15,19,29,30,[33][34][35][36]. However, the drying of our methanol-wet complex leaded to a somewhat different methoxylated kaolinite structure with x=0.3, which was far below the theoretical upper limit ratio of methoxy functionalization (x=1) of the inner surfaces.…”