Improving catalytic activity by synergic effect between base and acid pairs in hierarchically porous chitosan@titania nanoreactors

The beneficial effect of the bifunctional character of the chitosan@titania hybrid in heterogeneous catalysis was elucidated: considering a prototypical Henry condensation, Michael addition, and Jasminaldehyde synthesis, the cohabitation of a basic site (NH(2)) and an acidic site (Ti) in the same reactor provided clear activity and selectivity enhancements, with respect to the monofunctional acidic titania and basic chitosan counterparts.

Physicochemical and biological activity study of genipin-crosslinked chitosan scaffolds prepared by using supercritical carbon dioxide for tissue engineering applications

The present study deals with the preparation of porous chitosan scaffolds by using a greener technique i.e., supercritical carbon dioxide (sc.CO2). 0.2 M chitosan (CS) solution in aqueous acetic acid was treated with 4% (w/v) genipin solution; the resulting hydrogels were subjected to solvent exchange prior to the final treatment procedures. Their morphology, pore structure, and physical properties were characterized by thermal analysis, X-ray diffractogram (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the specific surface areas and porosimetry of scaffolds were determined by using N2 adsorption. The biological activity of scaffolds was investigated by immersing them into 1.5 x simulated body fluid (SBF) and cellular attachment study was assessed using Alamar Blue assay by seeding MG63 osteoblastic cells onto the scaffolds. The sc.CO2 assisted chitosan scaffold prepared by using green chemistry approach is highly pure and bioactive and can be served as a potential material for tissue engineering applications.

Chitosan-Based Hydrogels for the Recovery of Precious Metals

Chitosan (an aminopolysaccharide), cross-linked with glutaraldehyde, is very efficient for Pd(II) and Pt(IV) recovery from acidic solutions (pH 2). Due to poorly porous properties, it is necessary to condition the biopolymer as hydrogels. The uncontrolled drying of hydrogels depreciates the diffusion properties of original materials. A different method (to the acidic dissolving/alkaline neutralization procedure) has been used: after chitosan dissolving in acetic acid solution, the viscous solution was dropped into an ionotropic gelling solution (polyphosphate and glutaraldehyde to form stable gel beads with improved porosity. The restriction of diffusion properties due to drying step was less drastic with the modified procedure: a few hours were sufficient for reaching equilibrium while more than two days were required for standard material

Nanostructure of calcium alginate aerogels obtained from multistep solvent exchange route

Ca-alginate materials were studied by small-angle X-ray scattering (SAXS) at different steps of conversion from gel to aerogel in order to determine the relation between the polymer organization at the nanoscale in the gels and the final dry aerogel. In all cases, i.e. before and after the different exchanges of solvents and after the formation of the aerogel, the SAXS patterns exhibit an asymptotic behavior at low q values (in the experimental q range 7x10(-3) up to 2.10(-2) A(-1)) close to I(q) approximately q(-1), indicative of randomly oriented rod-like scattering objects. The evolution of the diameter of such rod-like objects was thus deduced from the maxima observed on Kratky plots, i.e. I(q) q2 vs q. The results are in perfect agreement qualitatively (rod-like anisometry type of the scattering objects) and quantitatively (diameter of the rods) with direct SEM observations of the morphology of aerogels and with the results of N2 adsorption on the aerogel. This is evidence that in the chosen experimental processing conditions, the morphology of the aerogel depends on the morphology of pre-existing objects within the gel, i.e. that the structure of the aerogel provides a correct image of the structure of the parent gel.

Chitosan-based aerogels with high adsorption performance

New natural polymer-based aerogels, cross-linked chitosan aerogels, were prepared by the sol-gel route with glutaradehyde, glyoxal, and formaldehyde as cross-linkers. The alcogels were dried by supercritical carbon dioxide (CO2) fluid extraction. The resulting materials were characterized using scanning electron microscopy (SEM), nitrogen adsorption/desorption analysis, and Fourier transform infrared (FT-IR) spectroscopy. Furthermore, the adsorption of the anionic surfactant sodium dodecylbenzene-sulfonate (SDBS) from aqueous solution by the materials was investigated. The aerogels exhibit high adsorption capability, can remove SDBS from acidic aqueous solutions, and have potential applications in controlling SDBS pollution.

Synthesis of WO(3) nanoparticles using a biopolymer as a template for electrocatalytic hydrogen evolution

Tungsten trioxide nanoparticles were prepared by a simple approach using chitosan biopolymer as a template. These nanoparticles were characterized using x-ray diffraction, Raman spectroscopy, transmission electron microscopy and high resolution transmission electron microscopy. The average size of the WO(3) nanoparticles is 42 nm, and they intercalate a larger amount of hydrogen than tungsten trioxide, which is prepared without chitosan. The materials are tested for their electrocatalytic hydrogen evolution in a sulfuric acid medium, where WO(3) nanoparticles show a fourfold higher activity than bulk tungsten trioxide.

Characterization of a gel in the cell wall to elucidate the paradoxical shrinkage of tension wood

Wood behavior is characterized by high sensibility to humidity and strongly anisotropic properties. The drying shrinkage along the fibers, usually small due to the reinforcing action of cellulosic microfibrils, is surprisingly high in the so-called tension wood, produced by trees to respond to strong reorientation requirements. In this study, nitrogen adsorption-desorption isotherms of supercritically dried tension wood and normal wood show that the tension wood cell wall has a gel-like structure characterized by a pore surface more than 30 times higher than that in normal wood. Syneresis of the tension wood gel explains its paradoxical drying shrinkage. This result could help to reduce technological problems during drying. Potential applications in biomechanics and biomimetics are worth investigating, considering that, in living trees, tension wood produces tensile growth stresses 10 times higher than that of normal wood.

Accessibility of the Functional Groups of Chitosan Aerogel Probed by FT-IR-Monitored Deuteration

Transmission FT-IR spectroscopy allowed us to monitor the deuteration of wafers of chitosan aerogel and xerogel by D2O vapor at room temperature. The complete deuteration of the alcohol and amine groups of the aerogel (surface area 175 m2 g(-1) as measured by N2 volumetry) confirmed the high accessibility of the functional groups of the polymer. The xerogel (surface area 5 m2 g(-1)) was only partially deuterated in more severe conditions. The isotopic shift of the deuterated groups allowed us to confirm or revise some attributions of infrared bands of chitosan.

Pillaring effects in macroporous carrageenan–silica composite microspheres

The impregnation of a carrageenan gel by a silica sol is an efficient method to form a composite material which can be conveniently activated by CO2 supercritical drying. The textural properties of the solids have been characterized by nitrogen adsorption-desorption at 77 K and their composition by thermogravimetric analysis and EDX microprobe. Morphology was examined by SEM. The silica-carrageenan composites present an open macroporous structure. Silica particles retained inside the gel behaved as pillars between the polysaccharide fibrils and form a stick-and-ball network. The stiffening of the carrageenan gel by silica prevented its shrinkage upon drying. The nature of the alkali cations affected the retention of silica particles inside the gel. In the absence of silica, carrageenan fibrils rearrange under supercritical drying and form an aerogel with cavities in the mesopore range.

Magnetic water-soluble cyano-bridged metal coordination nano-polymers

Magnetic water-soluble cyano-bridged metallic coordination polymer nanoparticles of controlled size were prepared by using water-soluble chitosan beads.

From Hydrocolloids to High Specific Surface Area Porous Supports for Catalysis

Polysaccharide hydrogels are effective supports for heterogeneous catalysts. Their use in solvents different from water has been hampered by their instability upon drying. While the freeze-drying process or air-drying of hydrocolloid gels led to compact solids with a low surface area, drying the gel in CO2 beyond the critical point provided mesoporous materials with a high specific surface area. Their effectiveness as a support for catalysis was exemplified in the reaction of substitution of an allyl carbonate with morpholine catalyzed by the hydrosoluble Pd(TPPTS)3 complex. The influence of water on the catalytic activity and the properties of the support was evidenced.