The main source of commercial chitosan is the extensive deacetylation of its parent polymer chitin. It is present in green algae, the cell walls or fungi and in the exoskeleton of crustaceans. A novel procedure for preparing chitosan from shrimp shells was developed. The procedure involves two 10-minutes bleaching steps with ethanol after the usual demineralization and deproteinization processes. Before deacetylation, chitin was immersed in 12.5 M NaOH, cooled down and kept frozen for 24 h. The obtained chitosan was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV, X-ray diffraction (XRD) and viscosimetry. Samples of white chitosan with acetylation degrees below 9% were obtained, as determined by FTIR and UV-first derivative spectroscopy. The change in the morphology of samples was followed by SEM. The ash content of chitosan samples were all below 0.063%. Chitosan was soluble in 1% acetic acid with insoluble contents of 0.62% or less. XRD patterns exhibited the characteristic peaks of chitosan centered at 10 and 20 degrees in 2θ. The molecular weight of chitosan was between 2.3 and 2.8 ×0.166667em105 g/mol. It is concluded that the procedure developed in the present work allowed obtaining chitosans with physical and chemical properties suitable for pharmaceutical applications.

Ni(1-x)FexO nanoparticles have been obtained by the co-precipitation chemical route. X-ray diffraction analyses using Rietveld refinement have shown a slight decrease in the microstrain and mean particle size as a function of the Fe content. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves show superparamagnetic behavior at high temperatures and a low temperature peak (at T = 11 K), which is enhanced with increasing Fe concentration. Unusual behavior of the coercive field in the low temperature region and an exchange bias behavior were also observed. A decrease in the Fe concentration induces an increase in the exchange bias field. We argue that these behaviors can be linked with the strengthening of surface anisotropy caused by the incorporation of Fe ions.

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Developing new technologies for carbon sequestration and long-term carbon storage is important. Clay minerals are interesting in this context as they are low-cost, naturally abundant, can adsorb considerable amounts of CO 2 , and are present in storage sites for anthropogenic carbon. Here, to better understand the intercalation mechanisms of CO 2 in dehydrated and hydrated synthetic Na-fluorohectorite clay, we have combined powder X-ray diffraction, inelastic and quasi-elastic neutron scattering, and density functional theory calculations. For dehydrated Nafluorohectorite, we observe no crystalline swelling or spectroscopic changes in response to CO 2 , whereas for the hydrated case, damping of the librational modes related to the intercalated water was clearly observed. These findings suggest the formation of a more disordered water coordination in the interlayer associated with highly confined water molecules. From the simulations, we conclude that intercalated water molecules decrease the layer−layer cohesion energy and create physical space for CO 2 intercalation. Furthermore, we confirm that interlayer confinement reduces the Na + hydration number when compared to that in bulk aqueous water, which may allow for proton transfer and hydroxide formation followed by CO 2 adsorption in the form of carbonates. The experimental results are discussed in the context of previous and present observations on, a similar smectite, Ni-fluorohectorite, for which it is established that CO 2 attaches to the edge of nickel hydroxide islands present in the interlayer.

We present a systematic study of the coercive field of CoFe2O4–SiO2 nanocomposites. The samples were prepared via the sol-gel method by using the Tetraethyl Orthosilicate as starting reagent. Results of X-ray diffraction, transmission electron microscopy, and X-ray fluorescence confirm the dispersion of the magnetic nanoparticles inside the silica matrix. In addition, the shift in the maximum of Zero-Field-Cooled curves observed by varying the weight ratio of CoFe2O4 nanoparticles to the precursor of silica is consistent with the increasing of average interparticle distances. Because our samples present a particle size distribution, we have used a generalized model which takes account such parameter to fit the experimental data of coercive field extracted from the magnetization curves as a function of applied field. Unlike most of the coercive field results reported in the literature for this material, the use of this model provided a successful description of the temperature dependence of the coercive field of CoFe2O4 nanoparticles in a wide temperature range. Surprisingly, we have observed the decreasing of the nanoparticles anisotropy constant in comparison to the bulk value expected for the material. We believe that this can be interpreted as due to both the migration of the Co2+ from octahedral to tetrahedral sites.