Chemistry Reference
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ordered, hexagonal, mesoporous metal (Ti, Zr, V, and Al) phosphonate materials
with microporous crystalline walls using a microwave-assisted procedure in the
presence of triblock copolymer F127 as a template. Corresponding metal chlo-
rides and ethylene diamine tetra(methylene phosphonic acid) were chosen as the
inorganic precursors and the coupling molecule, respectively. The most important
benefit of applying microwave irradiation here is probably the fast dissolution of
the gel and the simultaneous abundant nucleation in the synthetic mixture, caused
by the rapid heating and efficient heat transfer using this technique, which conse-
quently results in the fast crystallization and high crystallinity [
85
,
86
]. During the
microwave treatment, the small nascent metal phosphonate crystals are formed.
However, the microwave treatment seems hardly contributive to the formation of
ordered mesopores. Thus, the periodic assembly of phosphonate crystals along the
surfactant F127 micelles to form a hexagonal mesophase could only be realized
after a hydrothermal aging process, which helps the further crystallization of small
crystals. The prepared metal phosphonates possessed a hierarchical porous struc-
ture with pore sizes of 7.1-7.5 nm for mesopores and 1.3-1.7 nm for micropores,
respectively, and were thermally stable up to approximately 450 °C, with the pore
structure and hybrid framework well preserved. The ordered hexagonal mesopores
and one-dimensional pore channels could be confirmed using TEM images, and
crystal lattice fringes could be observed in the magnified image of the pore walls
(Fig.
3.14
). The crystalline phase of these phosphonate-based hybrids could be
attributable to the corresponding metal phosphonates crystals formed by the exten-
sive coordination of phosphonic claw groups with metal ions rather than tiny metal
oxide particles. The phosphonate groups are homogenously incorporated into the
hybrid framework of the obtained materials.
The pivotal factor to obtain well-defined mesoporosity and fine crystalliza-
tion is to slow down the coordination rates between the metal centers and organic
linkers so as to allow the assembly of nanosized building blocks and surfactant
micelles. Acetic acid can chelate many metal ions, such as Cu
2
+
, to form a deriva-
tive of metal-acetate bidentate bridging [
87
]. Namely, the acetic acid could com-
pete with the carboxylate linkers to coordinate with metal ions and influence the
deprotonation of the linker as well. Under the synergic effect of both factors,
phase segregation was limited thus to fit the liquid-crystal templating mecha-
nism. N
2
adsorption-desorption, TEM, and XRD indicated the generation of well-
defined mesopore channels within the microporous copper carboxylates, which
presented high crystallinity assigned to the HKUST-1. However, the mesostructure
possessed no long-range order.
The positively charged surfactants (S
0
H
+
) and cationic inorganic species (I
+
)
are assembled together by a combination of electrostatic, hydrogen-bonding, and
van der Waals interactions (S
0
H
+
) X
−
I
+
(X
−
=
Cl
−
, NO
3
, HySO
2
−
y
, etc.). If
X
−
was substituted by disulfonate anions, an analogous mechanism was pro-
posed to be accomplished to form a series of highly ordered mesoporous metal
sulfonates [
88
]. The coordination expansion based on X
−
I
+
could form pillared-
layered metal disulfonates in the mesoporous wall (Fig.
3.15
, a kind of cadmium
disulfonate crystal is taken as a representative). In a typical synthesis procedure
−
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