Water Saturated with Pressurized CO2 as a Tool to Create Various 3D Morphologies of Composites Based on Chitosan and Copper Nanoparticles.

Methods for creating various 3D morphologies of composites based on chitosan and copper nanoparticles stabilized by it in carbonic acid solutions formed under high pressure of saturating CO2 were developed. This work includes a comprehensive analysis of the regularities of copper nanoparticles stabilization and reduction with chitosan, studied by IR and UV-vis spectroscopies, XPS, TEM and rheology. Chitosan can partially reduce Cu2+ ions in aqueous solutions to small-sized, spherical copper nanoparticles with a low degree of polydispersity; the process is accompanied by the formation of an elastic polymer hydrogel. The resulting composites demonstrate antimicrobial activity against both fungi and bacteria. Exposing the hydrogels to the mixture of He or H2 gases and CO2 fluid under high pressure makes it possible to increase the porosity of hydrogels significantly, as well as decrease their pore size. Composite capsules show sufficient resistance to various conditions and reusable catalytic activity in the reduction of nitrobenzene to aniline reaction. The relative simplicity of the proposed method and at the same time its profound advantages (such as environmental friendliness, extra purity) indicate an interesting role of this study for various applications of materials based on chitosan and metals.

Green approach for fabrication of bacterial cellulose-chitosan composites in the solutions of carbonic acid under high pressure CO2.

The functionalization of the bacterial cellulose (BC) surface with a chitosan biopolymer to expand the areas of possible applications of the modified BC is an important scientific task. The creation of such composites in the carbonic acid solutions that were performed in this work has several advantages in terms of being biocompatible and eco-friendly. Quantitative analysis of chitosan content in the composite was conducted by tritium-labeled chitosan radioactivity detection method and this showed three times increased chitosan loading. Different physicochemical methods showed successful incorporation of chitosan into the BC matrix and interaction with it through hydrogen bonds. Microscopy results showed that the chitosan coating with a thickness of around 10 nm was formed in the bulk of BC, covering each microfibril. It was found that the inner specific surface area increased 1.5 times on deposition of chitosan from the solutions in carbonic acid.

Structural organization of bacterial cellulose: The origin of anisotropy and layered structures.

In this paper, we perform a systematic analysis of the structural organization of bacterial cellulose (BC). We report four types of organization of the BC mass, produced by Gluconacetobacter hansenii that occur depending on cultivation conditions. Two of those, particularly, plywood type one and layers of micro-sized tubes were observed and described for the first time. In spherical BC particles (pellets), we found the layered structure that had previously been reported for planar geometry only. We suggest a model explaining why layers form in BC films and attempt to reveal the impact of different factors on the BC microscale morphology. We assume that the main factor that has direct impact on the type of structure formed is the rate of BC mass accumulation.

Chitosan composites with Ag nanoparticles formed in carbonic acid solutions.

Chitosan-based hydrogels with stabilized Ag nanoparticles were synthesized in the aqueous solutions of carbonic acid, i.e. water saturated with CO2 under pressure in hundreds of bars. Such a medium is biocompatible and self-neutralizing at decompression. The influence of various parameters, such as chitosan molecular weight, molar ratio of chitosan to silver, additional stabilization of gels by genipin as a cross-linking agent, on the structure of the chitosan/Ag composites was investigated using transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, rheology measurements. The distributions of chitosan-stabilized Ag nanoparticles in a chitosan matrix turned out to be uniform, their average size was in the range of 2-5 nm. The higher degree of Ag nanoparticles reduction could be achieved using self-eliminating gaseous hydrogen as an additional reducing agent being admixed to CO2. This was consistently confirmed by different research methods (TEM, XRDA, UV-vis spectroscopy).

Formation of Easy-to-Recover Polystyrene-block-Poly(4-vinylpyridine) Micelles Decorated with Pd Nanoparticles in Solutions of Self-Neutralizing Carbonic Acid.

It was found out that block copolymers of polystyrene and poly(4-vinylpyridine) with comparable lengths of blocks could be dissolved in a high-pressure reactor containing water phase saturated with carbon dioxide under high pressure at room temperature. This rather effective dissolution occurs due to a protonation of P4VP nitrogen-containing groups together with a plasticization of the polymer material to be dissolved by a compressed dense CO2 being contained in the autoclave. The selected block copolymers form rather monodispersed micelles with well-defined and reproducible spherical geometry. They apparently have a hydrophobic polystyrene core and a polycationic poly-4-vinylpyridine corona. The obtained micelles were characterized by various techniques such as DLS, AFM, TEM, and SEM. Further, it was revealed that the corona of such micelles could be decorated with Pd nanoparticles having the diameter around 3 nm.