254
catalytic activity widely increased demonstrated by a sharp decrease of the relative
absorbance of methylene blue.
A similar strategy had been reported by Wang et al. (2010) where colloidal silver
hydrosols were synthesized using Pluronic
®
F-68 and then incorporated in situ into
an α-cyclodextrin-assisted supramolecular hydrogel. An absorption peak around
430 nm was observed for the synthesized silver nanoparticles that were attributed to
the characteristic surface plasmon resonance effect, showing the reduction and stabilization performances of the Pluronic
®
F-68. According to transmission electron
microscopy images, the silver nanoparticles were deposited on the surface of
Pluronic
®
aggregates. Pluronic
®
F-68 can also interact with α-cyclodextrin, and it
was shown that the higher the Pluronic
®
concentration, the better the gelation process. The effects of the silver nanoparticles on the gelation process and the hydrogel
strength were investigated through several physicochemical analyses. The catalytic
activity of the resulting hydrogel-embedded silver nanoparticles was evaluated for
the reduction of methylene blue using sodium borohydride. In the presence of the
hybrid hydrogel, methylene blue was consumed (80% converted in 10 min) which
was not the case in the absence of it. Léger et al. (2012) developed a thermoresponsive hydrogel for the synthesis of Ru nanoparticles and their activation for hydrogenation reactions. The hydrogel template properties have been taken to access
size-controlled Ru nanoparticles. More precisely, once metal nanoparticles have
been embedded into the supramolecular matrix, the system was heated above the
sol-gel transition temperature to give a sol phase where the catalytic reaction took
place. First, the polypseudorotaxane template was prepared from the mixture of the
N-alkylpyridinium amphiphilic [py-N-(CH 2 ) 12 OC 6 H 3 -3, 5-(OMe) 2 ]
+
(Br
−
) and
α-cyclodextrin. The self-assembly of these molecules yielded a thermoresponsive
hydrogel with a sol-gel transition temperature of 42 °C. The synthesis of Ru
nanoparticles was realized by classical chemical reduction of ruthenium metallic
salt solubilized in hydrogel at the sol state (50 °C) by an excess of sodium borohydride. Transmission electron microscopy analysis clearly showed homogeneous dispersion of spherical Ru nanoparticles with an average diameter of 1.6 nm within the
hydrogel network, which is smaller than that observed using surfactants or ionic
liquids as Ru nanoparticle stabilizers. This result emphasized the effective control
exerted by the hydrogel internal network structure over the Ru nanoparticle growth.
The catalytic hydrogenation of various substrates, ranging from hydrophobic longchain to hydrophilic olefins such as 2-methyl-3-buten-2-ol, was evaluated. Under H 2
pressure ranging from 10 to 40 bar at 50 °C, turnover frequency comprised between
4 and 350 h
−1
was obtained. At the end of the catalytic test, after cooling to ambient
temperature, the hydrogel spontaneously returned to the gel state, and consequently
the products could be easily recovered (Fig. 5.20). The recycling of the nanoparticles entrapped in the hydrogel had been successfully performed using 1-decene.
The same group had also reported a similar strategy involving the synthesis of
gold nanoparticles embedded into a thermoresponsive hydrogel made from the
combination of Tetronic
®
90R4 and α-cyclodextrin and their use in the catalytic
hydrogenation of alkenes, alkynes, and aldehydes (Chevry et al. 2019). In this case,
the first step consisted into the reduction of AuCl 3 metal precursor in a Tetronic
®
S. Noël et al.
catalytic activity widely increased demonstrated by a sharp decrease of the relative
absorbance of methylene blue.
A similar strategy had been reported by Wang et al. (2010) where colloidal silver
hydrosols were synthesized using Pluronic
®
F-68 and then incorporated in situ into
an α-cyclodextrin-assisted supramolecular hydrogel. An absorption peak around
430 nm was observed for the synthesized silver nanoparticles that were attributed to
the characteristic surface plasmon resonance effect, showing the reduction and stabilization performances of the Pluronic
®
F-68. According to transmission electron
microscopy images, the silver nanoparticles were deposited on the surface of
Pluronic
®
aggregates. Pluronic
®
F-68 can also interact with α-cyclodextrin, and it
was shown that the higher the Pluronic
®
concentration, the better the gelation process. The effects of the silver nanoparticles on the gelation process and the hydrogel
strength were investigated through several physicochemical analyses. The catalytic
activity of the resulting hydrogel-embedded silver nanoparticles was evaluated for
the reduction of methylene blue using sodium borohydride. In the presence of the
hybrid hydrogel, methylene blue was consumed (80% converted in 10 min) which
was not the case in the absence of it. Léger et al. (2012) developed a thermoresponsive hydrogel for the synthesis of Ru nanoparticles and their activation for hydrogenation reactions. The hydrogel template properties have been taken to access
size-controlled Ru nanoparticles. More precisely, once metal nanoparticles have
been embedded into the supramolecular matrix, the system was heated above the
sol-gel transition temperature to give a sol phase where the catalytic reaction took
place. First, the polypseudorotaxane template was prepared from the mixture of the
N-alkylpyridinium amphiphilic [py-N-(CH 2 ) 12 OC 6 H 3 -3, 5-(OMe) 2 ]
+
(Br
−
) and
α-cyclodextrin. The self-assembly of these molecules yielded a thermoresponsive
hydrogel with a sol-gel transition temperature of 42 °C. The synthesis of Ru
nanoparticles was realized by classical chemical reduction of ruthenium metallic
salt solubilized in hydrogel at the sol state (50 °C) by an excess of sodium borohydride. Transmission electron microscopy analysis clearly showed homogeneous dispersion of spherical Ru nanoparticles with an average diameter of 1.6 nm within the
hydrogel network, which is smaller than that observed using surfactants or ionic
liquids as Ru nanoparticle stabilizers. This result emphasized the effective control
exerted by the hydrogel internal network structure over the Ru nanoparticle growth.
The catalytic hydrogenation of various substrates, ranging from hydrophobic longchain to hydrophilic olefins such as 2-methyl-3-buten-2-ol, was evaluated. Under H 2
pressure ranging from 10 to 40 bar at 50 °C, turnover frequency comprised between
4 and 350 h
−1
was obtained. At the end of the catalytic test, after cooling to ambient
temperature, the hydrogel spontaneously returned to the gel state, and consequently
the products could be easily recovered (Fig. 5.20). The recycling of the nanoparticles entrapped in the hydrogel had been successfully performed using 1-decene.
The same group had also reported a similar strategy involving the synthesis of
gold nanoparticles embedded into a thermoresponsive hydrogel made from the
combination of Tetronic
®
90R4 and α-cyclodextrin and their use in the catalytic
hydrogenation of alkenes, alkynes, and aldehydes (Chevry et al. 2019). In this case,
the first step consisted into the reduction of AuCl 3 metal precursor in a Tetronic
®
S. Noël et al.