gelation. Such gels are often relatively stable and do not show thermoreversible
gel–sol transitions due to the polymeric nature.
4.2.1 Imine Gels
A series of gels based on imine chemistry were reported by Zhang and co-workers
(Scheme 4.17) [2, 47–49]. The imine gels are synthesized by polycondensation of
bridging amines (50–53) and aldehydes (54–61). The corresponding aerogels are
obtained by subcritical CO 2 (l) drying. These imine aerogels consist of
three-dimensional networks of interconnected nanometer-sized particles. Bridging
amine and bridging aldehyde polymerize to yield microporous nanoparticles. Then
the nanoparticles aggregate to form meso- and macropores. Finally, a 3D matrix is
formed to trap the solvent (Fig. 4.15). The effects of building blocks, precursor
concentration and solvent have been investigated on the porosity of the aerogels.
The porosity of the aerogel is controlled by the structural features of precursors,
precursor concentration and reaction solvent. Among these aerogels, the aerogel
synthesized by 50 and 54 (50–54 aerogel) in H 2 O exhibited highest BET surface
areas up to 1021 m
2 g
−1 . Imine bonds and residual amino groups decorate the pore
channels so that the aerogel possesses CO 2 uptake of 1.5 mmol g
−1 at 298 K and
1.0 bar with the isosteric heat of 38.1 kJ mol
−1 and displays high CO 2 /N 2 selectivity up to 70.9, which is derived from the ideal adsorbed solution theory, thus it
has potential for capture and recovery of CO 2 . This aerogel shows a good capacity
for the uptake of aromatic molecules from aqueous solutions due to its aromatic
network and hierarchically porous structure. The aerogel also has great performance
in enrichment of large molecule PAHs/OCPs as the coating adsorbent in
solid-phase microextraction (SPME) fibres.
The gas sorption properties of the imine aerogels are readily modulated. A series
of metalloporphyrin (M-tapp, 53) imine aerogels show sponge-like porous networked structures consisting of interconnected nanoparticles with hierarchical
porosity, high-specific surface areas (up to 719 m
2 g
−1 ) and large pore volumes (up
to 2.60 cm
3 g
−1 ) [48]. The H 2 tapp-59 aerogel prepared from H 2 tapp and 59 showed
good adsorption ability for both aromatic benzene and polar methanol at saturated
vapour pressure and room temperature. Among the investigated M-tapp imine
aerogels, Pd-tapp-59 prepared from Pd-tapp and 59 is the best to increase the CO 2
adsorption and shows improved adsorption capacities for H 2 and C 2 H 4 .
Various functional moieties such as tetraphenylethene (TPE) have been incorporated in these imine gels, and it widely expands their application in various fields.
The 50–60 gel synthesized from 50 and 1,1,2,2-tetrakis-(4-formyl-(1,10-biphenyl))
ethane (60) shows high hierarchical porosity and remarkable aggregation-induced
emission enhancement [2]. Introducing the TPE luminescent units is a modular
approach towards functional gels with novel sensing properties, and 60 is used for
the construction of light-emitting materials due to its AIE characteristics. The gel
exhibited a response towards electron deficient nitroaromatic compounds and
4.2 Dynamic Covalent Polymer Gelators
143
gel–sol transitions due to the polymeric nature.
4.2.1 Imine Gels
A series of gels based on imine chemistry were reported by Zhang and co-workers
(Scheme 4.17) [2, 47–49]. The imine gels are synthesized by polycondensation of
bridging amines (50–53) and aldehydes (54–61). The corresponding aerogels are
obtained by subcritical CO 2 (l) drying. These imine aerogels consist of
three-dimensional networks of interconnected nanometer-sized particles. Bridging
amine and bridging aldehyde polymerize to yield microporous nanoparticles. Then
the nanoparticles aggregate to form meso- and macropores. Finally, a 3D matrix is
formed to trap the solvent (Fig. 4.15). The effects of building blocks, precursor
concentration and solvent have been investigated on the porosity of the aerogels.
The porosity of the aerogel is controlled by the structural features of precursors,
precursor concentration and reaction solvent. Among these aerogels, the aerogel
synthesized by 50 and 54 (50–54 aerogel) in H 2 O exhibited highest BET surface
areas up to 1021 m
2 g
−1 . Imine bonds and residual amino groups decorate the pore
channels so that the aerogel possesses CO 2 uptake of 1.5 mmol g
−1 at 298 K and
1.0 bar with the isosteric heat of 38.1 kJ mol
−1 and displays high CO 2 /N 2 selectivity up to 70.9, which is derived from the ideal adsorbed solution theory, thus it
has potential for capture and recovery of CO 2 . This aerogel shows a good capacity
for the uptake of aromatic molecules from aqueous solutions due to its aromatic
network and hierarchically porous structure. The aerogel also has great performance
in enrichment of large molecule PAHs/OCPs as the coating adsorbent in
solid-phase microextraction (SPME) fibres.
The gas sorption properties of the imine aerogels are readily modulated. A series
of metalloporphyrin (M-tapp, 53) imine aerogels show sponge-like porous networked structures consisting of interconnected nanoparticles with hierarchical
porosity, high-specific surface areas (up to 719 m
2 g
−1 ) and large pore volumes (up
to 2.60 cm
3 g
−1 ) [48]. The H 2 tapp-59 aerogel prepared from H 2 tapp and 59 showed
good adsorption ability for both aromatic benzene and polar methanol at saturated
vapour pressure and room temperature. Among the investigated M-tapp imine
aerogels, Pd-tapp-59 prepared from Pd-tapp and 59 is the best to increase the CO 2
adsorption and shows improved adsorption capacities for H 2 and C 2 H 4 .
Various functional moieties such as tetraphenylethene (TPE) have been incorporated in these imine gels, and it widely expands their application in various fields.
The 50–60 gel synthesized from 50 and 1,1,2,2-tetrakis-(4-formyl-(1,10-biphenyl))
ethane (60) shows high hierarchical porosity and remarkable aggregation-induced
emission enhancement [2]. Introducing the TPE luminescent units is a modular
approach towards functional gels with novel sensing properties, and 60 is used for
the construction of light-emitting materials due to its AIE characteristics. The gel
exhibited a response towards electron deficient nitroaromatic compounds and
4.2 Dynamic Covalent Polymer Gelators
143