Adsorption behaviors and kinetics studies of chitooligosaccharides with specific degree of polymerization on a novel ion-exchange resin

Physiological activities of chitooligosaccharides (COSs) are related to their intrinsic structure and purities of products. However, the efficient preparation method of COSs with a specific degree of polymerization (DP) is still lacking, which limits the in-depth research and application of COSs. This work focused on the adsorption characters of COSs on the ion-exchange resin. Static adsorption experiments were conducted to study the effects of initial solution pH and ionic strength on the adsorption behaviors of chitobiose, chitotriose, chitotetraose, chitopentaose, and chitohexaose (COS 2-6). The adsorption equilibrium, thermodynamics, and kinetics of adsorption were investigated, and the molecular dynamics method was used to calculate the interaction energy of COS 2-6 with the resin and the diffusion coefficients of COS 2-6 in solution. The results show that the adsorption equilibrium data of COS 2-6 are satisfied with the Langmuir model, while the adsorption equilibrium capacities decrease with the increase of COSs DP. The COS 2-6 adsorption kinetic data are well fitted to the pseudo-second-order kinetic model. Liquid-film diffusion and intra-practical diffusion are both the adsorption rate-limiting steps. Thermodynamic parameters show that the adsorptions of COS 2-6 on HX-7 resin are spontaneous and feasible. With the increase of DP, the diffusion coefficients of COS 2-6 in solution decrease while the interaction force with resin become stronger, thus leading to more favorable adsorption.