Biodegradable Crosslinked Chitosan Gel Microbeads with Controlled Size, Prepared by Membrane Emulsification-External Gelation and Their Application as Reusable Adsorption Materials

Abstract

Gel microbeads composed of chitosan biopolymers were synthesized via membrane emulsification, as novel adsorbents for the adsorption of anionic azo dye (Acid Orange 7 (AO7)) and protein (bovine serum albumin (BSA)). The synthesis route involved the production of size-controlled water-in-oil emulsion droplets containing the chitosan solution using a porous, hydrophobic polytetrafluoroethylene membrane. The resulting size-controlled emulsion droplets were successfully converted into stable gel microbeads via external gelation, followed by chemical crosslinking using ethylene glycol diglycidyl ether (EGDE). Scanning electron microscopy results revealed the size of the gel microbeads having a diameter ranging from 15 to 20 µm, which was comparable to the size of the emulsion droplets. The effect of the crosslinking reaction between the prepared gel microbeads with EGDE was confirmed via Fourier transform infrared spectroscopy. The batch adsorption studies employed the Langmuir adsorption model with maximum adsorption capacities at pH values of 5 and 6 for AO7 dye (q_max=1.84 g/g) and BSA (q_max=0.87 g/g), respectively, with electrostatic interaction being the dominant mechanism of adsorption for both the azo dye and protein. The prepared crosslinked chitosan gel microbeads in this study exhibited excellent recyclability up to 30 times without a decline in their adsorptive capacities, a shelf life of >100 d, and a fair susceptibility toward enzymatic biodegradation, making them some of the most effective and versatile green adsorbents for wastewater treatment.