Preparation of gas-filled self-floating chitosan capsules and their application in the removal of methyl orange dye

Many adsorbents have been developed, and some of which have demonstrated high adsorption capacity. For their practical application, however, it is essential to consider not only the adsorption capacity but also other properties such as ease of separation, acid stability, and antimicrobial properties. Herein, we developed a novel capsule-type adsorbent composed of chitosan. Its interior was filled with gas, and the shell was made up of chitosan chains. This gas-filled structure allowed the chitosan capsule to float on water and to be easily separable from dye solution. The shell of chitosan capsule can be decorated with silver nanoparticles. Such capsules exhibited not only a significant bacteriostatic reduction rate of 99.9 % against E. coli, but also enhanced adsorption performance for methyl orange dyes in the pH range between 6 and 10. The maximum adsorption capacity of chitosan capsules increased from 547 to 877 mg/g at pH 6 by silver decoration. The polymer chains of silver-decorated chitosan capsules can be further interconnected by glutaraldehyde. Such cross-linker enabled the chitosan capsule to be stable at pH 3. Silver-decorated and glutaraldehyde-interconnected chitosan capsules are suitable for use across a wide pH range, from 3 to 10, but their maximum adsorption capacity at pH 6 decreased to 605 mg/g. This increase and decrease in adsorption performance by silver nanoparticles and glutaraldehyde were discussed through adsorption isotherm and kinetic studies.