Modification and Potential Applications of Organic–Inorganic Non-Siliceous Hybrid Materials - Mesoporous Organic-Inorganic Non-Siliceous Hybrid Materials - page 95

contaminants, which has been scarcely reported to the best of our knowledge.
Organic-inorganic hybrid of cobalt phosphonate hollow nanostructured spheres
was prepared in a water-ethanol system through a mild hydrothermal process in
the absence of any templates using DTPMP as bridging molecule [ 87 ]. Cobalt
phosphonate materials possessed amorphous frameworks with alternatively linked
cobalt sites and organophosphonic bridging groups, providing abundant active
sites for the catalytic oxidizing degradation of organic contaminants with the assis-
tance of peroxymonosulfate under ambient conditions. The kinetic study showed
that MB decomposition followed pseudo-first-order model with a heterogeneous
reaction activation energy of 50.2 kJ mol − 1 , and sulfate radicals were confirmed to
be the active species. The experimental results suggested that cobalt phosphonate
material could perform as an efficient heterogeneous catalyst for the degradation
of organic contaminants, providing insights into the rational design and develop-
ment of alternative catalysts for wastewater treatment.
In addition, the activity of hollow frameworks of mesoporous MOFs can be
modified by tailoring the linkers to adjust the overall porosity or include chiral-
ity. Hwang et al. [ 88 ] proposed a way to selectively functionalize coordinatively
unsaturated metal sites (CUS) in MIL-101 by attaching electron-rich functional
groups onto unsaturated chromium sites. Trimeric chromium octahedral clusters in
MIL-101 possess terminal water molecules, removable from the framework after
vacuum treatment at 423 K for 12 h, thereby creating on the CUS Lewis acidic
sites usable for the surface functionalization. The synthesis of the ethylenedi-
amine-grafted MIL-101 (ED-MIL-101) was performed by coordinating ED to the
dehydrated MIL-101 framework in toluene while heating under reflux. The amine-
grafted MIL-101 exhibited a remarkably high activity in the base-catalyzed reac-
tion and behaved as a size-selective catalyst. For example, the conversion of the
condensation of benzaldehyde into trans-ethylcyanocinnamate on ED-MIL-101
was 97.1 %, with a selectivity of 99.1 %. Interestingly, ED-MIL-101 also revealed
size dependency for the catalytic activities when the substituent groups of car-
bonyl compounds in the Knoevenagel condensation changed. Encapsulation of
noble metals, such as palladium, over the amine-grafted MIL-101, has also been
studied. Palladium-loaded APSMIL-101 and ED-MIL-101 have obviously high
activities during the Heck reaction at 393 K that were comparable to those of a
commercial Pd/C catalyst (1.09 wt% Pd) after a certain induction period (0.5-1 h),
probably because of the slow diffusion of the reactants to reach accessible metal
sites in the pores. Gascon et al. [ 89 ] further showed that MOFs with non-coordi-
nated amino groups, IRMOF-3 and the amino-functionalized MIL-53, were stable
solid basic catalysts in the Knoevenagel condensation of ethyl cyanoacetate and
ethyl acetoacetate with benzaldehyde. The catalysts were stable under the studied
reaction conditions and could be reused without significant loss in activity. The
catalytic performance of IRMOF-3 in various solvents suggests that this open,
accessible, and well-defined structure behaves more like a homogeneous basic
catalyst, in contrast to other solid basic catalysts. MIL-101 could act as heteroge-
neous catalyst for the selective allylic oxidation of alkenes with tert -butyl hydrop-
eroxide [ 90 ]. The selectivity toward ʱ , ʲ -unsaturated ketones reached 86-93 %.
The temperature of the catalyst activation strongly affects the ketone yield.