Silica–Chitosan Hybrid Gels: Preparation, Solution Chemistry, Optical and Thermal Properties

Silica–chitosan hybrid gel composites containing up to 3.3 wt% chitosan are prepared by a simple and reproducible sol–gel route based on the acid-catalyzed hydrolysis and condensation of tetraethoxysilane. The resulting materials are characterized by UV–Vis and FTIR spectroscopy, thermogravimetric and differential thermal analysis, scanning electron microscopy, X-ray diffraction, and thermal conductivity measurements. Increasing the chitosan content resulted in densification of the silica network from 1.56 to 1.70 g·cm−3. Even at low chitosan concentrations, its incorporation produces measurable changes in the structural, optical, and thermal properties of the sol–gel-derived silica, thus preserving its amorphous nature. The thermal conductivity of the gels decreases from 0.1 W/m·KW/m·K to 0.09 W/m·K with chitosan doping, combined with an increase in optical absorption at 300 nm. A simple empirical method based on UV–Vis reflectance spectroscopy is proposed for determining the chitosan content in silica powders. Optical properties of low-doped silica gels and chitosan solutions are described. Hydrothermal treatment of the chitosan solution improves optical absorption at 285 nm. Overall, the preparation–structure–property relationships of the hybrid gels demonstrate their potential as optical matrices with tunable properties.