Microfluidic engineering of covalently stabilized dual polysaccharide- graphene oxide microgels for high-capacity adsorption of cationic dyes.

Developing structurally stable, size-controlled, and high-capacity bio-based adsorbents remains important for the efficient removal of synthetic dyes from wastewater. Herein, we report a microfluidic strategy for fabricating covalently stabilized carboxymethyl cellulose/sodium alginate/graphene oxide (CMC/SA/GO: CGS) composite microgels using high-viscosity dual-polysaccharide precursor solutions followed by glutaraldehyde-mediated crosslinking. The novelty of this work lies in combining microfluidic droplet templating with covalent stabilization and GO reinforcement to produce uniform polysaccharide-based microgels with controlled diffusion length, accessible oxygen-rich binding sites, and improved structural integrity. Microfluidic processing generated spherical precursor droplets with an average diameter of approximately 200 μm, which transformed into dried microgels with a narrow size distribution centered at approximately 50 μm after crosslinking and drying. CGS microgels exhibited a porous internal morphology, a BET surface area of 25.86 m2/g, with an average pore diameter of 47.1 nm, supporting efficient dye transport and site accessibility. Batch adsorption experiments performed using 10 mg of adsorbent in 5 mL dye solution at pH 6 for 210 min demonstrated high adsorption capacities toward representative cationic dyes. At an initial dye concentration of 1000 mg/L, the adsorption capacities reached 477.0, 430.5, and 394.4 mg/g for crystal violet, methylene blue, and malachite green, respectively. The adsorption behavior was strongly pH-dependent and correlated with increasingly negative zeta potential of CGS, indicating that electrostatic attraction is the dominant adsorption mechanism. Overall, this study demonstrates that microfluidic engineering of covalently stabilized CMC/SA/GO microgels provides an effective route to uniform, porous, and high-performance bio-based adsorbents for cationic dye removal.