Cross-linkable chitosan-based hydrogel microbeads with pH-responsive adsorption properties for organic dyes prepared using size-tunable microchannel emulsification technique

- Novel method for preparing highly-uniform chitosan hydrogel beads is proposed.
- Particle formation process by microchannel emulsification was characterized.
- Adsorption properties for an anionic dye were evaluated based on the Langmuir model.
- The chitosan hydrogel beads showed very good stability for long-term use.

Cross-linked chitosan hydrogel microbeads were prepared from monodisperse water-in-oil (W/O) emulsions and their adsorption properties for an anionic organic dye, Acid Orange 7 (AO7), were investigated. Preparation of monodisperse W/O emulsions with a mean diameter of 22-28 μm and coefficient of variation below 10% were achieved by microchannel (MC) emulsification. The mean diameter and diameter distribution were affected by the viscosity and flow rate of the chitosan solution pressed into MCs. Chitosan gel microbeads were formed by gelation of chitosan-containing water droplets by alkali treatment followed by cross-linking treatment. The resulting microbeads still had a narrow diameter distribution. The pH-responsive adsorption property of chitosan gel microbeads was studied using AO7. The experiment results indicated that negatively charged AO7 molecules adsorbed onto positively charged chitosan gel microbeads via electrostatic interaction. The chitosan gel microbeads were stable for more than 100 days and could be reused in repetitive adsorption-desorption cycles.

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