Sorption and Structural Properties of Aerogel Materials Based on Biopolymers

Nowadays aerogel materials (AM) are successfully used as entero-and applicative sorbents to eliminate excessive amounts of heavy metals and toxins from living organisms. Natural biopolymers alginate and chitosan, as well as various lignin derivatives are an inexhaustible raw material base for the creation of AM. A significant number of sorption materials and wound coatings of various types have been developed on their basis, which is associated not only with a wide range of physicochemical properties of these polymers and their already proven biomedical activity, but also with the prevalence and renewability of raw material sources for the production of these polymers, ease of extraction, the possibility of achieving a high degree of purification and relatively low price. The key stage in the AM synthesis is the formation of a strong hydrogel which is the AM framework. One of the technological methods is to obtain interpolyelectrolyte solid hydrogel. The paper proposes two different packaging models for the formation of the structure of interpolyelectrolyte complexes (IPEC) based on biopolymers pairs: sodium alginate (ALNa)-chitosan (CT) and sodium lignosulfonate (LSNa)-CT. The first model is a block model, in which the structure is formed due to ionic bonds between the carboxyl groups of ALNa and amino groups of CT, as well as a cooperative system of hydrogen bonds and dispersion interactions. The second model is an aggregation-tubular model, the structure of which is formed through ionic bonds between sulfogroups (within the rod-shaped supramolecular structures of LSNa) and amino groups of CT, as well as hydrogen bonds and dispersion interactions. Upon the process of IPEC drying under supercritical (SC-) conditions, strong phase contacts are formed, and the changes in the gel structure become irreversible. As a result, hydrophobic micro-and mesoporous two-component AMs differing in internal structure were obtained. AM ALNa-CT are characterized by fibrillar structure, and LSNa-CT - by structural elements of spherical shape. The obtained AM ALNa-CT and LSNa-CT have high sorption activity towards water and a wide range of heavy metals and low molecular weight toxins. The purpose of the work is to study the structural and sorption properties of AM based on biopolymers of various structural organization. A significant increase in the sorption activity of AM ALNa-CT in comparison with LSNa-CT is apparently due to their different supramolecular structure. There is a combination of several sorption mechanisms such as wetting, absorption, diffusion, osmotic phenomena and chemical interaction due to the highly porous structure of AM and the presence of sorption-active centers.