Strategies to Incorporate Mesoporosity - Mesoporous Organic-Inorganic Non-Siliceous Hybrid Materials - page 46

Fig. 3.12 a The synthesis condition map of periodic mesoporous titanium phosphonates, mainly
considering the adding amounts of reagents and surfactant, TEM images of cubic ( b , c) and hexag-
onal ( d , e ) mesoporous titanium phosphonate materials. Reprinted with permission from Ref. [ 65 ].
Copyright 2010, Wiley-VCH
regularity, and within the range of 1.9 < C 16 TABr/Ti < 2.3 (Ti/P = 1:4) for a cubic
phase, which was in agreement with the previously reported molecular surfactant
packing parameter theory that the hexagonal phase is formed at a low surfactant/
inorganic species ratio and the cubic phase formed at a high ratio [ 63 ]. Lamellar
mesostructured aluminum organophosphonate with unique inorganic-organic hybrid
network could be synthesized from the reactions of aluminum tri-isopropoxide with
methylene disphosphonic acid with the assistance of alkyltrimethylammonium
when the corresponding atomic ratios decreased to Al/P/C 16 TABr = 1:4:2 [ 66 ].
The organic diphosphonic bridges were embedded in the integrated hybrid sheets
with surfactant micelles inserted between the sheets. The removal of the surfactant
would lead to the irreversible collapse of the lamellar phase, which signified that it
had limited values from a practical applications point of view.
As to the mesoporous siliceous materials, the curvature of the mesostructures
increases from lamellar via hexagonal to cubic phases, and the control of the mes-
ostructure is commonly dependent on the hydrophilicity/hydrophobicity ratio and
the molecular weight of the surfactants [ 67 , 68 ]. The ease in tuning the surfactant
composition via living polymerization paves the way for adjusting the mesophase.
Initially, it is considered that lower hydrophilicity/hydrophobicity ratios lead to
the formation of mesophases with small curvatures (e.g., lamellar), and high ratios
are favorable for the generation of the ones with large curvatures (e.g., hexagonal
and cubic) [ 69 ]. For example, the utilization of EO 80 PO 30 EO 80 with a high EO:PO
ratio led to the preferential formation of cubic IA 3 D phases and cage-type ones
with FM 3 M and PM 3 M structures [ 70 , 71 ]. In the cases of non-silica-based hybrid
materials, the hexagonal mesophases are usually preferred in spite of the molecule
structures and compositions. This may be due to the fact that the hybrid network
condensed incompletely, and the arrangement of surfactant scaffolds containing