Chemistry Reference
In-Depth Information
The absence of homocondensation between organic functional groups and the easy
formation of organic-inorganic layers allows the straightforward and reproducible
formation of robust monolayers on an extremely wide range of substrates. On one
hand, the original physicochemical properties of the bulk materials can be pre-
served. On the other hand, diverse novel functional groups with special properties
including bioactivity, electronic conductivity, and photochemical properties can be
incorporated, showing the capacity to be further modified as well.
Mallouk et al. proposed to employ bisphosphonic acids for the formation of
metal phosphonate multilayers on surfaces [
71
]. Later on, Guerrero et al. reported
the anchoring of phosphonate and phosphinate coupling molecules on titania
particles [
72
], with the use of six organophosphorous compounds: phenylphos-
phonic and diphenylphosphonic acids, their ethyl esters, and their trimethylsilyl
esters. In the case of organophosphorus coupling molecules, reaction with the
surface involves not only the condensation with surface hydroxyl groups but also
the coordination of the phosphoryl on Lewis acid sites, and the cleavage of the
M-O-M bonds depending on the anchoring conditions. The hydrolytic stability
of organic monolayers supported on metal oxides was also investigated [
73
]. It
was found that the monolayers of C
18
H
37
P(O)(OH)
2
demonstrated a better hydro-
lytic stability than other octadecyl organosilane modifiers. The high stability of
these phosphonate monolayers is explained by the strong specific interactions of
the phosphonic acid group with the surfaces of metal oxides. On the basis of the
above-mentioned literature reports, the feasibility of grafting phosphonic acids
onto metal oxides is fully confirmed. Soler-Illia et al. prepared organic modified
transition metal oxide mesoporous thin films and xerogels by using dihexadecyl
phosphate (DHDP), monododecyl phosphate (MDP), and phenyl phosphate (PPA)
[
74
]. Dramatic differences were observed for the incorporation of organophospho-
nates in mesoporous versus non-mesoporous solids, demonstrating that the organic
functions were incorporated inside the pore system. Incorporation behaviors were
also observed depending on the mesostructure; cubic 3D mesostructures are more
accessible than their 2D hexagonal counterparts [
75
]. Furthermore, the function-
alized pores were found to be further accessible to other molecules (solvent and
fluorescent probes) or ions (i.e., Hg
2
+
), opening the way for sensor or sorption
applications.
Besides the monophosphonic acids mentioned above, Yuan and co-workers
reported the use of a series of amine-based organophosphonic acids and their salts
as organophosphorus coupling molecules in the one-step synthesis and the appli-
cation exploration of oxide-phosphonates and metal organophosphonate hybrid
materials with mesopores and hierarchical meso-/macroporous architectures
[
76
,
77
]. Claw molecules of ethylene diamine tetra(methylene phosphonic acid)
(EDTMP) and diethylene triamine penta(methylene phosphonic acid) (DTPMP)
were anchored to the titania network homogeneously. The synthesized titania-
phosphonate hybrids showed irregular mesoporosity formed by the assembly of
nanoparticles in a crystalline anatase phase. The synthesis process is quite simple
in comparison with the previously reported two-step solgel processing involving
first the formation of P-O-M bonds by non-hydrolytic condensation of a metal
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