Morphological Design of Mesoporous Hybrid Materials - Mesoporous Organic-Inorganic Non-Siliceous Hybrid Materials - page 65

can affect the thickness of thin films. Besides the two approaches, mesoporous
thin films can also be made by pulsed laser deposition and electrochemi-
cal deposition. In accordance with these strategies, a great diversity of hybrid
organic-inorganic materials with controllable morphologies can be achieved by
combination with existing techniques. Ordered mesoporous aluminum phospho-
nate films with high transparency were prepared through the spin coating of an
ethanol-water solution containing methylene diphosphonic acid, aluminum
chloride, and an EO n PO m EO n -type triblock copolymer [ 15 ]. The amount of
EO 80 PO 30 EO 80 in the precursor solution strongly influenced the mesostructural
ordering of the aluminum phosphonate films (Fig. 4.4 ), and careful heating was
essential to maintain the mesostructure after surfactant removal. The mesostruc-
tural ordering was gradually decreased with an increase in the added amount of
EO 80 PO 30 EO 80 , leading to the formation of other phases that are not defined by
assemblies of EO 80 PO 30 EO 80 . Much larger pores were formed over the entire
films and would be formed through a phase separation by the presence of excess
EO 80 PO 30 EO 80 .
4.3 Nanorods
The formation of phosphonate-based hybrids in a microemulsion system could
also result in mesoporous materials with various morphologies. If HEDP and
tetrabutyl titanate were used as precursors, the multicomponent microemulsion
drops were mainly composed of alkoxide, water, ethanol from the solvent, and
butanol from the hydrolysis of tetrabutyl titanate. The interfacial microemulsion
polymerization of titanium phosphonate sols and titanium oxo clusters caused
the formation of mesostructured titania phosphonate nanorods with a length of
80-150 nm and a thickness of 18-38 nm, possessing homogeneously attached
organophosphonate units. The nanorods formed aggregates with the microemul-
sions to give a hierarchical macroporous structure [ 16 ]. The multipoint BET sur-
face area was 257 m 2 g − 1 , with a BJH pore size of 2.0 nm and a total pore volume
of 0.263 cm 3 g − 1 .
A low-temperature hydrothermal method was developed for the synthesis
of lanthanide phenylphosphonate nanorods that are expected to exhibit some
novel properties [ 17 ]. The mechanism of synthesis and shape control of lantha-
nide phenylphosphonates is proposed from a kinetic perspective. On one hand,
the used p-toluenesulfonate could form loose complex through the electrostatic
action with La 3 + cations to direct the crystal growth process. On the other hand,
the addition of p -toluenesulfonate can significantly decrease the viscosity of
the solution, which increases the mobility of the components in the system and
allows atoms, ions, or molecules to adopt appropriate positions in developing
crystal lattices [ 18 ].
A coordination modulation method, in which acetic acid is used to directly
influence the coordination equilibria, can be used to control the crystal growth of