Chemistry Reference
In-Depth Information
the hydrophobic regions of the surfactant micelles based on hydrophobicity-
hydrophobicity interactions, leading to micelle swelling. With C
16
TABr acting
as a structure-directing agent and 1,3,5-trimethylbenzene (TMB) as an auxiliary
one, Qiu et al. [
76
] prepared a series of hierarchically porous HKUST-1 with
adjustable interconnecting micropores and mesopores by the self-assembly of
framework-building blocks in the presence of surfactant micelles. The synthe-
sized mesostructured MOFs possessed a mesopore system with diameters tunable
from 3.8 to 31.0 nm, which depended on the synthetic conditions. Additionally,
the mesoporous walls were constructed by a crystalline microporous network
containing a 3D system of channels with a pore diameter of 0.82 nm, which was
confirmed by the XRD, N
2
sorption, and TEM analysis. The surface area of the
MOFs decreased remarkably from 1,124 to 579 m
2
g
−
1
with the increase of the
TMB/C
16
TABr molar ratio from 0 to 0.50. It is noteworthy that the enlargement of
the pore sizes usually implicates the sacrifice of the specific surface area.
The effect of the nature of surfactant species and the addition of organic swell-
ing agents on the pore size control were systematically studied [
77
]. Spherical
aluminum phosphonate particles were obtained using Pluronic F127 with the
formation of larger mesopores (10.5 nm) than those architectured using Brij58
(4.1 nm) and Pluronic F68 (6.3 nm). Further expansion of the mesopores from
10.5 to 15 and 20 nm was achieved by the addition of typical aromatic com-
pounds 1,3,5-TMB and 1,3,5-tri-isopropylbenzene as organic swelling agents,
respectively. The boiling points of the aromatic compounds were quite important
for the successful fabrication of high-quality spherical particles of the ordered
mesoporous aluminum phosphonates. In addition, when aromatic compounds
are regarded as model molecules, aerosol-assisted fabrication in the presence
of designed and/or synthetic organic compounds such as fine chemicals is quite
potential for the production of spherical supports with ordered mesopores.
These phenomenons have indeed given us a hint. Other substances that can be
dissolved in the micelle cores may also expand pore diameters. Binary surfactant
systems can result in products with tunable pore sizes and bimodal or trimodal
pores. This has been testified in mesoporous siliceous materials. For example,
blending two quaternary cationic surfactants with different carbon chains together
(e.g., C
12
TABr, C
16
TABr, C
16
TABr, and C
22
TABr) can change the pore sizes of
MCM-41 mesostructures to intermediate values between that templated by a sin-
gle surfactant [
78
]. With respect to mesoporous non-siliceous materials, a step fur-
ther involving binary and even ternary surfactant system is full of interest to be
explored.
Additionally, the reaction medium of the synthetic systems, as well as the
crystallization time, is also inevitable to affect the pore size of the resultant mes-
ostructured hybrids. A series of amorphous porous zirconium phosphonate mate-
rials constructed from HEDP, having tunable from micropore to mesopore sizes,
were hydrothermally synthesized in a C
16
TABr-H
2
O-ethanol ternary system
[
79
]. The as-synthesized materials were mesostructured and could be transformed
into (super-)microporous hybrid solids after surfactant-extracted process. It was
observed that ethanol played a role as cosurfactant in assisting the formation of
Search WWH ::
Custom Search