Chitosan aerogel

Fig. 9 MEB pictures of chitosan aerogels obtained in hydroalcoholic medium...

The deuterating agent is a probe of the accessibility of the materials to small polar molecules. The FTIR spectra of chitosan aerogel submitted to increasing pressures of D2O are reported in Fig.l2. The admission of D2O vapor brings about a progressive decrease of the intensity of all O-H and N-H bands. At a D2O pressure of 13 mbar, the O-H and N-H bands have virtually disappeared. 

As previously described, the parameters which affect the properties of the hydrogel affect the texture of the aerogel. Chitosan aerogel surface area can be doubled but the benefit of such an increase, which is clear in the first catalytic test (98% conversion, 12 h), becomes a drawback in the successive re-uses of the catalyst (second run 47% conversion). Therefore a balance has to be met between dispersion of the material (surface area) and the mechanical stabiUty of the chitosan beads. 

With its high surface area and the accessibility to the amino groups, chitosan aerogel appeared as a good candidate to play the double role of support for metal complexes and organic base. Silica supported metallophthalocyanine are efficient catalysts for the oxidation of aromatic compounds [139]. The immobilization of hydrosoluble metallophthalocyanines (MPcS with M = Fe or Co) on chitosan aerogels afforded new heterogeneous catalysts for the aerobic oxidation of p-isophorone [140]. 

The catalysts (MPcS chitosan) were obtained by impregnation of chitosan aerogel beads with an aqueous solution of sulfonated metal phthalocyanine. After impregnation, the solids were dried again under supercritical CO2 conditions. The textural properties are maintained and surface areas were greater than 140 m g (Table 4). 

Rinki K, Dutta PK, Hunt AJ et al (2011) Chitosan aerogel exhibiting high surface area for biomedical applications preparation, characterization and antibacterial study. Int J Polym Mater Article ID 553849 (GPOM-2010-0362.R1)... 

Fig. 5 N2 physisorption isotherms of an aerogel empty squares) and a xerogel filled lozenges) of chitosan...

In Fig. 10, the N2 sorption isotherms of the aerogels of an alkali-gelled chitosan from p-chitin and the same chitosan gelled by TMP (2% molar cross-linker with respect to the number of amine groups) are compared. The aerogel of the... 

Fig. 10 N2 sorption isotherms of aerogels of chitosan empty squares) and cross-linked chitosan (filled squares)...

Transmission FT-IR spectroscopy has been used to monitor the deuteration by D2O vapor at room temperature of wafers of aerogels of chitosan from p-chitin... 

The accessibility of the primary amine functions of chitosan has been quantified in organic solvent by formation of a salicylaldimine Schiff base upon treatment with salicylaldehyde. When contacting salicylaldehyde the aerogel beads of chitosan become yellow and their UV-visible diffuse reflectance spectra exhibit the absorption band at 318 nm, characteristic of the Schiff base. Quantitative GC analysis of the remaining salicylaldehyde in the solution allows calculation of the fraction of reacted amino groups, which corresponds to the fraction of accessible sites. In the aerogel formulation, up to 70% of the amine groups are accessible [92]. 

Different chitosan-based catalysts are compared in Table 3. The reactions were performed at 70°C due to the thermal stability of the catalyst. The first ones focus on the influence of the drying procedure in comparison with an uncatalyzed reaction and a known heterogeneous catalyst (Table 3, entries 1-5). Lyophilized chitosan (Cl) does not display any activity when the aerogel is as efficient as the functionalised silica (C3). This result illustrates the accessibility to the amino groups of chitosan in its aerogel form. 

Bifunctional catalysts can be obtained which couple the presence of a metal complex immobiUzed on the aerogel with the activity of the intrinsic functions of the polysaccharide. Metallophthalocyanine supported on chitosan is an example. 

Antimicrobial Activity of sc-C02-Treated Chitosan-L-Glutamic Acid Aerogel... 

Singh, J., Dutta, P. K., Dutta, J. et al., 2008. Physiochemical and bioactivity behavior of highly soluble chitosan-L-glutamic acid aerogel derivative. Asian Chitin Journal, 4 9-18. 

Kuthirummal N, Dean A, Yao C, Risen W (2008) Photo-formation of gold nanoparticles Photoacoustic studies on solid monoliths of Au(III)-chitosan-silica aerogels Spectrochim Acta A Mol Biomol Spectroscopy 70A 700-703... 

Singh J, Dutta PK, Dutta J, Hunt, Macquarrie DJ, Clark JH (2009) Preparation and properties of highly soluble chitosan-L-glutamic acid aerogel derivative. Carbohydrate Polymers 76 188-195. 

Biopolymer-Containing Aerogels Chitosan-Silica Hybrid Aerogels... 

The idea of attempting to synthesize chitosan-silicsL aerogels was pursued beginning in the late 1990s by groups at Brown University and at the E. O. Lawrence Berkeley National... 

The general approach taken was to incorporate chitosan and silica-forming compounds, such as tetraethyl orthosilicate (TEOS), to form hybrid aerogels under acidic conditions. These conditions lead to open silica structures. Chitosan, shown in Figure 18.1, has a random coil configuration under these conditions [3], so it can be present throughout the open silica structure. This is shown schematically in Figure 18.2. 

Figure 18.2. Conceptual model of a chitosan-silica aerogel. The solid line represents chitosan.

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