230
G.-R. Xu
deterioration, it is still faced a great challenge to synthesize well-dispersed zeolite
nanosheets with high-aspect ratio. Recently, Varoon et al. reported the synthesis of
highly crystallized MWW and MFI nanosheets derived from ITQ-1 and multilamellar
silicalite-1/polystyrene (PS) blending [93]. Thus fabricated nanosheets, which exhibited a highly crystallized flake-like structure with a thickness of 2.6 ± 0.3–3.4 ±
0.3 nm, could be further deposited on the surface of the porous substrate to obtain
sieving membranes.
Zeolite nanosheets could be significantly affected by the thickness and wrinkling.
Taking this under consideration, a 3D mapping method was exploited to precisely
control the wrinkles and thickness of zeolite nanosheets [94]. Thus synthesized MFI
nanosheets exhibited a thickness of 3.0 nm and a surface roughness of 0.8 nm.
In order to decrease the production cost, many other strategies in addition to the
exfoliation with expensive cost and low yielding were explored to synthesize zeolite
nanosheets. For example, MFI, sodalite (SOD), and Linde Type A (LTA) zeolite
membranes have been fabricated by in-situ microwave synthesis and/or microwaveassisted secondary growth methods (SGM) considering its rapid yield [95]. Nonetheless, these methods always require multiple steps including lengthy hydrothermal
synthesis, drying, and calcination for template removal procedure such as drying and
calcination. Thus they are actually labor and energy intensive. Consequently, optimization is needed to make these methods more acceptable. Just recently, tetrapropyl
ammonium cation (TPA) was used as a structure-directing agent (SDA) to fabricate
MFI nanosheets with high-aspect ratio by a bottom-up seeded growth method [96].
Thus fabricated nanosheets displayed thickness of 5 nm and the pores are highly
oriented. This method displayed obvious advantages compared to exfoliation. In
general, the fabrication methods of zeolite membranes include.
(a) lodging of zeolite onto matrices (e.g., silica and polymers).
(b) layering zeolite onto a support (e.g., ceramic, clay, and carbon).
(c) self-supporting film.
Mobil five (MFI) zeolite membrane has been widely prepared by direct in-situ
crystallization.
4.3 MXene Nanosheet
The most usual method to synthesis MXene is etching of A element layers (Al or Si)
from MAX phase by HF (Fig. 4) [32]. In this process, MAX powders are dissolved in
HF aqueous solution, followed by the centrifugation and filtration to separate solid
from suspensions. The solids are then washed till the pH value of suspension reaches
4–6. Various types of MXenes, such as M2X, M3X2, M4X3 MXenes, have been
synthesized via this method [34]. Especially, Ti 3 AlC 2 is the most commonly used
MAX phase for the preparation of Ti 3 C 2 Tx MXene.
MXenes obtained using etching method are always terminated with -F, -OH, and
-O- (Tx) with multilayer structures [97]. Multilayered MXenes can be treated by
G.-R. Xu
deterioration, it is still faced a great challenge to synthesize well-dispersed zeolite
nanosheets with high-aspect ratio. Recently, Varoon et al. reported the synthesis of
highly crystallized MWW and MFI nanosheets derived from ITQ-1 and multilamellar
silicalite-1/polystyrene (PS) blending [93]. Thus fabricated nanosheets, which exhibited a highly crystallized flake-like structure with a thickness of 2.6 ± 0.3–3.4 ±
0.3 nm, could be further deposited on the surface of the porous substrate to obtain
sieving membranes.
Zeolite nanosheets could be significantly affected by the thickness and wrinkling.
Taking this under consideration, a 3D mapping method was exploited to precisely
control the wrinkles and thickness of zeolite nanosheets [94]. Thus synthesized MFI
nanosheets exhibited a thickness of 3.0 nm and a surface roughness of 0.8 nm.
In order to decrease the production cost, many other strategies in addition to the
exfoliation with expensive cost and low yielding were explored to synthesize zeolite
nanosheets. For example, MFI, sodalite (SOD), and Linde Type A (LTA) zeolite
membranes have been fabricated by in-situ microwave synthesis and/or microwaveassisted secondary growth methods (SGM) considering its rapid yield [95]. Nonetheless, these methods always require multiple steps including lengthy hydrothermal
synthesis, drying, and calcination for template removal procedure such as drying and
calcination. Thus they are actually labor and energy intensive. Consequently, optimization is needed to make these methods more acceptable. Just recently, tetrapropyl
ammonium cation (TPA) was used as a structure-directing agent (SDA) to fabricate
MFI nanosheets with high-aspect ratio by a bottom-up seeded growth method [96].
Thus fabricated nanosheets displayed thickness of 5 nm and the pores are highly
oriented. This method displayed obvious advantages compared to exfoliation. In
general, the fabrication methods of zeolite membranes include.
(a) lodging of zeolite onto matrices (e.g., silica and polymers).
(b) layering zeolite onto a support (e.g., ceramic, clay, and carbon).
(c) self-supporting film.
Mobil five (MFI) zeolite membrane has been widely prepared by direct in-situ
crystallization.
4.3 MXene Nanosheet
The most usual method to synthesis MXene is etching of A element layers (Al or Si)
from MAX phase by HF (Fig. 4) [32]. In this process, MAX powders are dissolved in
HF aqueous solution, followed by the centrifugation and filtration to separate solid
from suspensions. The solids are then washed till the pH value of suspension reaches
4–6. Various types of MXenes, such as M2X, M3X2, M4X3 MXenes, have been
synthesized via this method [34]. Especially, Ti 3 AlC 2 is the most commonly used
MAX phase for the preparation of Ti 3 C 2 Tx MXene.
MXenes obtained using etching method are always terminated with -F, -OH, and
-O- (Tx) with multilayer structures [97]. Multilayered MXenes can be treated by