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Fig. 3.3
View of the pentanuclear loop in 1. Symmetry codes: A:
x
,
−
y
,
z
+
1/2; B:
x
,
−
y
−
1,
z
+
1/2; C:
x
,
y
,
z
+
1. Reprinted with permission from Ref. [
15
]. Copyright 2011, Wiley-VCH
3.1.2 Microemulsion Method
Ligand extension strategy is an effective and simple way to expand micropores to
the mesoporous regime in hybrid materials; though the most complicated organic
linkers are not commercially available and in order to gain them, complicated
fabrication processes are generally required. More recently, a new method to pre-
pare mesoporous hybrid metal phosphonates, via employing microemulsions, was
reported [
16
]. Mesostructured pores of several nanometers in size existed in the
vicinity of the surface in a wormhole-like assembly (2.5-5.8 nm), whereas in the
core, close to the wormhole-like mesoporous surface layers of the particle, a new
mesocellular foam structure (8-10 nm) similar to the previously reported meso-
structured cellular foam (MCF) silica materials was observed (Fig.
3.4
). During
the period of synthesis, hydrolysis of titanium tetrabutoxide in EDTMP aque-
ous solution resulted in the rapid formation of nanometer-sized titanium phos-
phonate and butanol molecules at the same time. Thereafter, microemulsion
drops formed in the multicomponent system of alkoxide/organophosphonate-
alcohol-water while stirring. The phosphonate sols aggregated along with the
microemulsions, evolving to a mesocellular foam structure. The interactions
between the sols caused the formation of mesostructured nanoclusters of sev-
eral nanometers in size. At this stage, due to the presence of a large amount of
butanol by-products, the reaction mixture was transferred to phosphonate-based
mesophases and water-alcohol domains by microphase separation, induced
by aging, leading to discrimination of them and even some macrovoids [
17
]. If
1-hydroxy-ethylidene-1,1-diphosphonate (HEDP) was chosen as the organic pre-
cursors, according to microemulsion methodology, the interfacial polymerization
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