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).