Strategies to Incorporate Mesoporosity - Mesoporous Organic-Inorganic Non-Siliceous Hybrid Materials - page 50

zirconium organophosphonate mesostructures, by achieving the charge density
matching between the surfactant and hybrid nanoparticles. By varying the hydro-
thermal time from 1 to 72 h at 110 °C, the pore sizes of the obtained zirconium
phosphonates could be efficiently tuned from micropore (0.87 nm) to mesopore
(2.5 nm) range, and their micropore-specific surface areas ranged from 116 to
509 m 2 g − 1 with the pore volumes in the range of 0.11-0.35 cm 3 g − 1 . Considering
the acidity and tunable pore sizes, the prepared porous zirconium phosphonates
may find their potential applications in adsorption, shape-selective heterogeneous
catalysis, ion exchange, and proton conduction.
3.2.5 Improving the Crystallization of Pore Walls
A high degree of crystallinity of the hybrid structures is quite significant for
improving the properties and thus the applicability of these materials in many
fields. Attempts to crystallize the materials through heat treatment always resulted
in the collapse of the periodic mesoporous structures and the deterioration of
the hybrid frameworks, which could impede their extended applications [ 80 ].
Revealingly, using organosilane instead of inorganic precursors, organic-inorganic
hybrid periodic mesoporous benzene-silica was synthesized with a crystalline
wall structure, formed from the structure-directing interactions between the ben-
zene-silica precursor molecules and between the precursor molecules and the sur-
factants [ 81 ], which has supplied scientific researchers with an alternative method
to prepare crystalline mesostructures of hybrid materials.
Kimura et al. [ 82 ] reported the preparation of lamellar mesostructured alu-
minum phosphonates with a crystalline hybrid framework from the reaction of
aluminum triisopropoxide with methylene diphosphonic acid in the presence
of alkyltrimethylammonium C n TMA ( n ≥ 14) surfactants. This was only under
restricted conditions, and the crystal structure of the hybrid framework has not
been defined yet because of the ill-resolved diffraction peaks. In the study, meth-
ylene groups can be embedded in the sheets (integrated hybrid frameworks) of the
lamellar AOP-1 by a surfactant-assisted strategy. Al atoms are six-coordinated,
connected to oxygen atoms only, and bonded to P atoms through oxygen atoms,
and water molecules are ligated to the Al atoms. However, the ethylene groups are
embedded in the hybrid framework, but the framework is not constructed from
Al, P, and the organic group only. P atoms are bonded to AlO 6 units, which is a
common structure for the reported crystalline AOPs. The six-coordinated Al atoms
are surrounded by four oxygen atoms (two Al-O-P bonds and two water ligands)
and two F atoms, meaning that the framework is not pure. On the other side, such
hybrid mesostructures are unstable, and the surfactants could not be removed
without the collapse of the mesostructure.
Microwave-assisted synthesis has been shown to be a facile and moder-
ate approach for promoting the crystallization of porous materials at a relatively
low temperature [ 83 , 84 ]. Ma et al. [ 73 ] reported the successful preparation of