Preparation and characterization of chitosan clay beads for water adsorption

The microstructure of beads composed of 50 mass% α-chitosan and either montmorillonite, a clay minerals mixture (illite, pyrophyllite, and kaolinite), or palygorskite was investigated using X-ray diffraction and scanning electron microscopy. Moreover, the kinetics of water adsorption and desorption by the beads were studied at temperatures ranging from 25 to 45 °C. Adsorption-desorption cycles were conducted to assess the beads performance. The findings revealed that chitosan and montmorillonite were linked by electrostatic forces, with no intercalation of chitosan observed. Additionally, attractive electrostatic forces were noted between the clay minerals assemblage and chitosan. Conversely, repulsive electrostatic forces occurred between chitosan and palygorskite, with the clay fibers acting as fillers. The study also showed that the maximal adsorption kinetic constants for montmorillonite-containing beads, palygorskite-containing beads, and chitosan beads were 13.6 × 10^-3 s^-1, 16.7 × 10^-3 s^-1, and 31 × 10^-3 s^-1, respectively. As for the beads composed of the clay minerals assemblage, the maximum adsorption kinetic constant was 2.8 × 10^-2 mg s^-1. Notably, high water adsorption capacities were measured for the beads consisting of palygorskite and the clay minerals assemblage (22% and 34% mass/mass, respectively). Regarding desorption kinetics, relatively high rate constants were determined for beads composed of montmorillonite and the clay minerals assemblage (38.6 × 10^-2 s^-1 and 39 × 10^-2 s^-1, respectively). In addition, more than 90% of adsorbed water was released by all studied beads at 45 °C, and the adsorption/desorption performances of the beads were not significantly affected by the applied cycles.