ИСТИНА

Typically, to create materials with new functionality, complex, multi-level systems are required. In this work we propose a novel fairly simple concept for creating various 3D modifications of composites based on the natural polymer chitosan and copper. Chitosan is a derivative of chitin, a renewable resource that often ends up in a waste, instead of high-tech industries. At the same time, chitosan has a large number of properties useful for various applications, such as biocompatibility, non-toxicity, hemostatic activity, the ability to effectively stabilize nanoparticles, antimicrobial properties, and so on. We have developed a method for dissolving chitosan in water saturated with CO 2 under high pressure (in other words, in carbonic acid). This high pressure medium is able to efficiently dissolve polycationic polymers without leaving any residue in the polymer after the depressurization, which is important for applications requiring high purity materials. Copper is an accessible alternative to noble metals with a number of promising properties, such as the high activity against both grams-positive bacteria and fungi or catalytic activity, allowing green chemistry reactions to be carried out. The characteristics of the obtained copper-chitosan composites were studied in details using various experimental techniques. Using rheology and FTIR spectroscopy methods, it was found that during the interaction of Cu 2+ with chitosan dissolved in carbonic acid solution, an elastic polymer hydrogel is formed due to the coordination bonds between copper ions and amino and hydroxyl groups of the biopolymer. Using UV-spectroscopy, TEM and XPS, it was found that chitosan partially reduces Cu 2+ to nanoparticles about 2 nm in diameter with a low degree of polydispersity, as well as stabilizes them. We have developed simple methods for creating spherical composites with a hydrogel shell and copper nanoparticles distributed over the surface. The capsules showed good temperature stability up to 55 °C, as well as stability in alkaline medium (up to pH 11). The catalytic activity of such composites was demonstrated on a reaction of nitrobenzene reduction to aniline in the presence of NaBH 4 . It was found out that when using a fairly small amount of catalyst, at room temperature the reaction can be carried out at least five times with the same capsules and the yield of 67-80%. Moreover, a new method of hydrogels foaming was developed, that made it possible to increase several times their porosity and reduce tenfold the pore size by saturating the composites with the mixture of gases H 2 /CO 2 or He/CO 2 under high pressure. The antimicrobial activity of composites was confirmed, and in the case of fungi, activity was even greater than that of the traditional antibiotic, which allows them to be used as waste water filters. Acknowledgments This work was supported by the Russian Science Foundation (grant no. 20-73-10180).