222
G.-R. Xu
2.3 MXene Nanosheets
MXene is a new family of 2D layered membranes based on transition metal carbides
and/or nitrides. The general chemical formula of MXene is M n+1 X n T z (n is in the
range of 1–3), M is transition metals, such as Ti, Zr, Hf, V, Nb, Ta, Cr, and Sc, X
is C and/or N, T z is surface groups, such as O
2− , OH
− , F
− , NH 3 , NH 4
+ . Presently,
fabrication of MXenes is mainly realized via exfoliation of A element such as Al of
its precursor of M n+1 AX n with weak combination by hydrofluoric acid solution or
mixed solution of hydrochloric acid and fluoride [32, 33]. MXene has emerged and
exhibited promising potential in electrochemical energy storage area via controlling
ions insertion between the atomically thin layers [34].
Besides, it should be noted that excellent characters, such as high flexibility,
mechanical strength, and hydrophilicity, enable MXenes with controllable thickness
from nanometers to micrometers, which are very promising in separation science. The
most studied MXene is Ti 3 C 2 T x . Ti 3 C 2 T x displays comparable mechanical strength
with GO. For example, Ti 3 C 2 T x film with thickness of 3 μm exhibits a tensile strength
of 22 MPa [35], while GO membrane with thickness of 2.5 μm shows 55 MPa [36].
Moreover, hydroxyl groups on alkalization interacted MXenes make them suitable
for removing heavy metal ions from wastewater [37]. For instance, high surface area
and hydrophilic surface endow Ti 3 C 2 T x great potential in removing various heavy
metal ions and organic pollutants [38–40].
3 Computer Simulation
3.1 MOF Nanosheets
Hg 0 and HgCl 2 adsorption on UiO-66 was investigated using computer simulation
[41]. A reliable force fields (FFs) stemmed from plane-wave-density functional
theory (DFT) calculations was introduced to describe interactions between Hg 0 ,
HgCl 2, and UiO-66. Grand Canonical Monte Carlo (GCMC) calculations were used
to indicate the single and/or multi adsorption of Hg 0 , HgCl 2 , and other components into UiO-66. The interaction energies between mercury species and UiO66 were researched. HgCl 2 has a stronger affinity than Hg0 for UiO-66 with a
heat of adsorption of ~ 60 kJ/mol. Considering that MOFs materials are always
limited by the low chemical stability compared with that of zeolites [42]. Tb with
higher chemical stability and facile functionality with abundant functional groups
was used to construct MOFs. Adsorption of Pb
2+ onto Tb-MOFs was theoretically
studied recently (Fig. 1) [43]. Carboxylate-based ligands of H3TATAB (4,4
,4
-
(1,3,5-triazine-2,4,6-triyltriimino) tris-benzoic acid, containing amino, imine, and
carboxylic acid groups and Tb
3+ were assembled into Tb-MOFs with nanotubular
shapes via solvothermal method. N groups seem to be the most prospective ligands
to remove heavy metal ions, while they did not react with constitutive metal ions.
G.-R. Xu
2.3 MXene Nanosheets
MXene is a new family of 2D layered membranes based on transition metal carbides
and/or nitrides. The general chemical formula of MXene is M n+1 X n T z (n is in the
range of 1–3), M is transition metals, such as Ti, Zr, Hf, V, Nb, Ta, Cr, and Sc, X
is C and/or N, T z is surface groups, such as O
2− , OH
− , F
− , NH 3 , NH 4
+ . Presently,
fabrication of MXenes is mainly realized via exfoliation of A element such as Al of
its precursor of M n+1 AX n with weak combination by hydrofluoric acid solution or
mixed solution of hydrochloric acid and fluoride [32, 33]. MXene has emerged and
exhibited promising potential in electrochemical energy storage area via controlling
ions insertion between the atomically thin layers [34].
Besides, it should be noted that excellent characters, such as high flexibility,
mechanical strength, and hydrophilicity, enable MXenes with controllable thickness
from nanometers to micrometers, which are very promising in separation science. The
most studied MXene is Ti 3 C 2 T x . Ti 3 C 2 T x displays comparable mechanical strength
with GO. For example, Ti 3 C 2 T x film with thickness of 3 μm exhibits a tensile strength
of 22 MPa [35], while GO membrane with thickness of 2.5 μm shows 55 MPa [36].
Moreover, hydroxyl groups on alkalization interacted MXenes make them suitable
for removing heavy metal ions from wastewater [37]. For instance, high surface area
and hydrophilic surface endow Ti 3 C 2 T x great potential in removing various heavy
metal ions and organic pollutants [38–40].
3 Computer Simulation
3.1 MOF Nanosheets
Hg 0 and HgCl 2 adsorption on UiO-66 was investigated using computer simulation
[41]. A reliable force fields (FFs) stemmed from plane-wave-density functional
theory (DFT) calculations was introduced to describe interactions between Hg 0 ,
HgCl 2, and UiO-66. Grand Canonical Monte Carlo (GCMC) calculations were used
to indicate the single and/or multi adsorption of Hg 0 , HgCl 2 , and other components into UiO-66. The interaction energies between mercury species and UiO66 were researched. HgCl 2 has a stronger affinity than Hg0 for UiO-66 with a
heat of adsorption of ~ 60 kJ/mol. Considering that MOFs materials are always
limited by the low chemical stability compared with that of zeolites [42]. Tb with
higher chemical stability and facile functionality with abundant functional groups
was used to construct MOFs. Adsorption of Pb
2+ onto Tb-MOFs was theoretically
studied recently (Fig. 1) [43]. Carboxylate-based ligands of H3TATAB (4,4
,4
-
(1,3,5-triazine-2,4,6-triyltriimino) tris-benzoic acid, containing amino, imine, and
carboxylic acid groups and Tb
3+ were assembled into Tb-MOFs with nanotubular
shapes via solvothermal method. N groups seem to be the most prospective ligands
to remove heavy metal ions, while they did not react with constitutive metal ions.