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structure-directing agent, the surface area of tin phosphonate could be increased to
723 m
2
g
−
1
, with the formation of micropores due to cross-linking of the ligand
[
79
]. This hybrid demonstrated excellent catalytic activity in the direct one-pot
oxidation of cyclohexanone to adipic acid using molecular oxygen under liquid
phase conditions. The tin in the framework activated the molecular oxygen, help-
ing to form the cyclic six-membered transition state, which further rearranged into
a cyclic ester.
CO
2
can serve as C1 building block for various organic chemicals. One of the
most promising reaction schemes currently seems to be the formation of cyclic
carbonate via coupling of CO
2
and epoxides, which are useful as monomers, sol-
vents, and pharmaceutical/fine chemical intermediates, and in biomedical appli-
cations [
80
]. Carboxylate-based MOFs have been extensively studied in this area
[
81
-
85
]. Song et al. [
81
] reported the coupling reaction of CO
2
with propylene
oxide to produce propylene carbonate catalyzed by MOF-5 in the presence of qua-
ternary ammonium salts. The synergetic effect between MOF-5 and quaternary
ammonium salts had excellent effect in promoting the reaction. The cycloaddition
of CO
2
with epoxides is considered to be catalyzed by basicity and promoted by
the Lewis acidic sites. On the basis of the intrinsic catalytic sites of the metal-
connecting points (weak Lewis acid), the introduction of basic amino groups could
lead to an enhanced catalytic performance [
84
]. Bifunctional hybrid catalysts con-
taining moderate Lewis acidic and basic sites are preferred in the cycloaddition
reactions. The bifunctionality can not only enhance the conversion and selectivity,
but can also simplify the reaction conditions. The attempted bifunctionality can be
obtained through judicious selection of precursors or through pre- and post-modi-
fication of the organic linkers. Up to now, reports concerning metal phosphonates
for the coupling of CO
2
and epoxides have been relatively scarce. Since metal
phosphonates show similar characteristics of composition and structure and higher
stability compared to their carboxylate counterparts, it is meaningful to explore the
catalytic activity of metal phosphonates in this burgeoning area.
Modified Fenton reactions have emerged as promising strategies for water
treatment, especially for persistent and non-biodegradable pollutants. Generally,
homogeneous Co
2
+
/peroxymonosulfate systems have been proven to be consider-
ably efficient due to the powerful oxidizing ability of catalytically generated sul-
fate radicals toward the decomposition of organic molecules. On the other side,
the introduction of multifarious transition metal centers in metal phosphonates can
present distinct catalytic activities. For instance, cubic mesoporous titanium phos-
phonates showed superior photoactivity in degrading organic dyes under simulated
solar light irradiation as compared with commercial P25 catalyst [
11
]. Effective
catalytic hydrogenation of 4-nitrophenol to 4-aminophenol under ambient condi-
tions could be achieved through the use of mesoporous nickel phosphate/phospho-
nate hybrid microspheres as the catalyst [
86
]. Mesoporous vanadium phosphonate
material constructed from a dendritic tetraphosphonate could perform as an excel-
lent catalyst for the aerobic oxidation of benzylic alcohols with high reactivity and
shape selectivity [
26
]. It is reasonably speculated that porous cobalt phosphonate
materials could fit the qualification of the Fenton reaction for oxidizing organic
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