365
The performance of materials in terms of their ability to complex contaminants
was strongly related to their structure and swelling properties and therefore to the
experimental conditions used during cross-linking, notably the reaction temperature, the amount of caustic soda added, the epichlorohydrin dosage, the volume of
water, and the use of a blowing agent or not. The stronger the cross-linking, the
lower the swelling properties, and the less interesting the adsorption performance,
whatever the quantity of cyclodextrin present in the gels. We also observed in our
experiments that performance was independent of the concentration of the pollutant
present in the solutions, as well as, more surprisingly, of the amount of cyclodextrin.
As ECP did not alter the pH of the solutions to be depolluted (no variation during
adsorption), it was not necessary to maintain the initial pH of the solutions during
batch tests. However, performance depended on the pH used. Results obtained at
pH 2 and pH 6 were similar but were different from those obtained at pH 11, suggesting that the inclusion complexes with cyclodextrin and aromatic and phenolic
guests were less stable in basic than in neutral or acidic medium. The results were
explained by the different ionization degree of the guest upon the various pH used
(Crini et al. 1998b; Vecchi et al. 1998).
One of our objectives was to highlight a correlation between the structure of
polymers and their adsorption properties. To do this, we used solid-state
13
C NMR
spectroscopy techniques such as cross-polarization magic angle spinning with dipolar decoupling (CPMAS), magic angle spinning both with and without dipolar
decoupling (DD-MAS and MAS, respectively) and CPMAS with dipolar dephasing
(dd-CPMAS), and relaxation parameter measurements. Two components have been
found, cross-linked cyclodextrin molecules and polymerized epichlorohydrin. We
demonstrated that solid-state NMR techniques were useful to characterize insoluble
cross-linked gels with a limited mobility (Crini et al. 1998a). Two years later, we
confirmed these results by using high-resolution magic angle spinning with gradients (HRMAS) spectroscopy (Crini et al. 2000).
1
H spectra,
13
C CPMAS spectra at
high temperature, and NOESY, TOCSY, HOHAHA, and
1
H/
13
C HSQC spectra are
published for the first time. The HRMAS experiments clearly demonstrated the
presence of two types of structures in ECP materials, in accordance with the results
obtained by CPMAS techniques. The NOESY experiments also demonstrated the
interaction between the β-cyclodextrin molecules present in an ECP material and
the pollutant adsorbed.
Adsorption results were then explained by taking into account just two important
parameters: the presence of cyclodextrin molecules and their degree of crosslinking. The formation of inclusion complexes played the most important role in the
mechanism. HRMAS experiments demonstrated not only the presence of two types
of structures in ECP materials but also the adsorption mechanism by complexation
due to the β-cyclodextrin molecules. NOESY and HOHAHA experiments clearly
demonstrated the interaction between the β-cyclodextrin molecules present in an
ECP material and the contaminant adsorbed. Our results also highlighted the importance of the structure of the 3D network (Crini et al. 1998b; Vecchi et al. 1998;
Bertini et al. 1999). Using solid-state NMR data, we concluded that the mechanism
of adsorption can be explained by the presence of two main interactions: the
8 Water-Insoluble Cyclodextrin-Epichlorohydrin Polymers
The performance of materials in terms of their ability to complex contaminants
was strongly related to their structure and swelling properties and therefore to the
experimental conditions used during cross-linking, notably the reaction temperature, the amount of caustic soda added, the epichlorohydrin dosage, the volume of
water, and the use of a blowing agent or not. The stronger the cross-linking, the
lower the swelling properties, and the less interesting the adsorption performance,
whatever the quantity of cyclodextrin present in the gels. We also observed in our
experiments that performance was independent of the concentration of the pollutant
present in the solutions, as well as, more surprisingly, of the amount of cyclodextrin.
As ECP did not alter the pH of the solutions to be depolluted (no variation during
adsorption), it was not necessary to maintain the initial pH of the solutions during
batch tests. However, performance depended on the pH used. Results obtained at
pH 2 and pH 6 were similar but were different from those obtained at pH 11, suggesting that the inclusion complexes with cyclodextrin and aromatic and phenolic
guests were less stable in basic than in neutral or acidic medium. The results were
explained by the different ionization degree of the guest upon the various pH used
(Crini et al. 1998b; Vecchi et al. 1998).
One of our objectives was to highlight a correlation between the structure of
polymers and their adsorption properties. To do this, we used solid-state
13
C NMR
spectroscopy techniques such as cross-polarization magic angle spinning with dipolar decoupling (CPMAS), magic angle spinning both with and without dipolar
decoupling (DD-MAS and MAS, respectively) and CPMAS with dipolar dephasing
(dd-CPMAS), and relaxation parameter measurements. Two components have been
found, cross-linked cyclodextrin molecules and polymerized epichlorohydrin. We
demonstrated that solid-state NMR techniques were useful to characterize insoluble
cross-linked gels with a limited mobility (Crini et al. 1998a). Two years later, we
confirmed these results by using high-resolution magic angle spinning with gradients (HRMAS) spectroscopy (Crini et al. 2000).
1
H spectra,
13
C CPMAS spectra at
high temperature, and NOESY, TOCSY, HOHAHA, and
1
H/
13
C HSQC spectra are
published for the first time. The HRMAS experiments clearly demonstrated the
presence of two types of structures in ECP materials, in accordance with the results
obtained by CPMAS techniques. The NOESY experiments also demonstrated the
interaction between the β-cyclodextrin molecules present in an ECP material and
the pollutant adsorbed.
Adsorption results were then explained by taking into account just two important
parameters: the presence of cyclodextrin molecules and their degree of crosslinking. The formation of inclusion complexes played the most important role in the
mechanism. HRMAS experiments demonstrated not only the presence of two types
of structures in ECP materials but also the adsorption mechanism by complexation
due to the β-cyclodextrin molecules. NOESY and HOHAHA experiments clearly
demonstrated the interaction between the β-cyclodextrin molecules present in an
ECP material and the contaminant adsorbed. Our results also highlighted the importance of the structure of the 3D network (Crini et al. 1998b; Vecchi et al. 1998;
Bertini et al. 1999). Using solid-state NMR data, we concluded that the mechanism
of adsorption can be explained by the presence of two main interactions: the
8 Water-Insoluble Cyclodextrin-Epichlorohydrin Polymers