Introduction
7
shapes (3D) of MOF could be octahedra, irregular polyhedral, dodecahedra, etc.
These 3D shapes have two major drawbacks, such as the requirement of activation
treatment and poor solvents dispersibility. Therefore, recent studies are focusing on
2D MOF nanosheets synthesis either from 3D bulky MOFs using exfoliation methods
or others. Compared with 3D MOFs, 2D MOF nanosheets have ultrathin thickness,
accessible reactive/active sites, high surface area, etc., which are unique properties to
develop industrial-grade separation techniques. Because of thin thickness and tunable
pore size, the selectivity and permeability of 2D MOFs nanosheets are completely
suitable for fabricating membranes with unprecedented advantages [19].
Zeolite is popular for acting as a host framework towards various solutes. It is
mainly due to their microporous structure, high aspect ratio, thinner nanosheets
(short diffusion distance), hydrophilicity, etc. [21]. It mainly consists of ‘cornersharing TO 4 tetrahedra where T means tetrahedrally coordinated framework atoms,
for example, Si and Al or other heteroatoms [22]. Roth et al. reported that 213
different types of zeolite are possible to synthesize and/or naturally available by
tuning a range of reaction parameters, such as pressure, time, temperature, reactant
types and structure-directing agents as indicated by the yellow color in Fig. 6. Among
these structural variations, nearly 200 types belong to 3D structure and only 10 cases
can be prepared before the condensation of monolayers to 3D zeolite as revealed
in the left and right sides of Fig. 6, respectively [22]. Figure 7 reveals a few 2D
zeolite nanosheets synthesis methods including hydrothermal, surfactant-templated,
and partial zeolite hydrolysis.
MXenes (general formula: M n+1 X n ) are transition metal carbides or nitrides. They
are the new member of the 2D materials family which could be obtained by etching
of A atomic layer from MAX ternary (M n+1 AX n ) where M is an early transition metal
(e.g., Ti, Zr, Hf, W, V, Nb, Ta, Cr, Sc, etc.), A is a non-metal element (i.e., Si, Al, Ga,
etc.) and X is C or/and N. Yury’s research group reported the MXene (i.e., Ti 3 C 2 )
using HF as etchant at first in 2011 from Ti 3 AlC 2 [23]. This Ti 3 C 2 is commonly
expressed by Ti 3 C 2 T X , where T X depicts surface functional groups, such as = O, −
OH, −F, etc. Subsequently, various MXenes are reported in the literatures including
V 4 C 3 TX, Nb 4 C 3 T X , Zr 3 C 2 T X , Ta 4 C 3 T X , Ti 4 N 3 T X , V 2 CT X , Ti 2 CT X and Cr 2 CT X,
etc. Li et al. reported halides-terminated MXenes by using ZnCl 2 salts as the etchant
and Zn-based MAX as a precursor as shown in Fig. 8. Such 2D nanosheets are used
to fabricate membrane which shows extremely short transport pathway and many
nanochannels. These properties ensure a very high water transport (>1000 L m
−2
h
−1 bar
−1 ) and solute rejection (over 90 %) [24]. Therefore, MXenes nanosheets
are promising fashioned 2D materials for fabricating advanced water purification
membranes.
2 Conclusions
Based on these preceding materials, this book consists of eight chapters, excluding
this introductory chapter. These chapters bring meaningful information, focusing
7
shapes (3D) of MOF could be octahedra, irregular polyhedral, dodecahedra, etc.
These 3D shapes have two major drawbacks, such as the requirement of activation
treatment and poor solvents dispersibility. Therefore, recent studies are focusing on
2D MOF nanosheets synthesis either from 3D bulky MOFs using exfoliation methods
or others. Compared with 3D MOFs, 2D MOF nanosheets have ultrathin thickness,
accessible reactive/active sites, high surface area, etc., which are unique properties to
develop industrial-grade separation techniques. Because of thin thickness and tunable
pore size, the selectivity and permeability of 2D MOFs nanosheets are completely
suitable for fabricating membranes with unprecedented advantages [19].
Zeolite is popular for acting as a host framework towards various solutes. It is
mainly due to their microporous structure, high aspect ratio, thinner nanosheets
(short diffusion distance), hydrophilicity, etc. [21]. It mainly consists of ‘cornersharing TO 4 tetrahedra where T means tetrahedrally coordinated framework atoms,
for example, Si and Al or other heteroatoms [22]. Roth et al. reported that 213
different types of zeolite are possible to synthesize and/or naturally available by
tuning a range of reaction parameters, such as pressure, time, temperature, reactant
types and structure-directing agents as indicated by the yellow color in Fig. 6. Among
these structural variations, nearly 200 types belong to 3D structure and only 10 cases
can be prepared before the condensation of monolayers to 3D zeolite as revealed
in the left and right sides of Fig. 6, respectively [22]. Figure 7 reveals a few 2D
zeolite nanosheets synthesis methods including hydrothermal, surfactant-templated,
and partial zeolite hydrolysis.
MXenes (general formula: M n+1 X n ) are transition metal carbides or nitrides. They
are the new member of the 2D materials family which could be obtained by etching
of A atomic layer from MAX ternary (M n+1 AX n ) where M is an early transition metal
(e.g., Ti, Zr, Hf, W, V, Nb, Ta, Cr, Sc, etc.), A is a non-metal element (i.e., Si, Al, Ga,
etc.) and X is C or/and N. Yury’s research group reported the MXene (i.e., Ti 3 C 2 )
using HF as etchant at first in 2011 from Ti 3 AlC 2 [23]. This Ti 3 C 2 is commonly
expressed by Ti 3 C 2 T X , where T X depicts surface functional groups, such as = O, −
OH, −F, etc. Subsequently, various MXenes are reported in the literatures including
V 4 C 3 TX, Nb 4 C 3 T X , Zr 3 C 2 T X , Ta 4 C 3 T X , Ti 4 N 3 T X , V 2 CT X , Ti 2 CT X and Cr 2 CT X,
etc. Li et al. reported halides-terminated MXenes by using ZnCl 2 salts as the etchant
and Zn-based MAX as a precursor as shown in Fig. 8. Such 2D nanosheets are used
to fabricate membrane which shows extremely short transport pathway and many
nanochannels. These properties ensure a very high water transport (>1000 L m
−2
h
−1 bar
−1 ) and solute rejection (over 90 %) [24]. Therefore, MXenes nanosheets
are promising fashioned 2D materials for fabricating advanced water purification
membranes.
2 Conclusions
Based on these preceding materials, this book consists of eight chapters, excluding
this introductory chapter. These chapters bring meaningful information, focusing