Covalently crosslinked carboxymethyl chitosan beads containing SiO2 and ionic polymer for efficient adsorptive removal of methylene blue.

Abstract

The carboxymethyl chitosan (CMCS)-based porous beads are still criticized for their limited number of binding sites, which impairs their efficacy in removing aqueous pollutants. To overcome this challenge, this work introduces the production of covalently crosslinked CMCS-based beads containing SiO₂ and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The porous composite beads not only possess remarkable stability under acidic conditions, but also have abundant active binding sites for adsorption. By using methylene blue (MB) as a representative pollutant, adsorption experiments have demonstrated that the presence of SiO₂ and PAMPS significantly enhances the adsorption performance of the CMCS-based beads. The adsorption behavior aligns with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating the occurrence of chemical adsorption and monolayer adsorption phenomena. The optimal sample, CCMCS-SiO₂@PAMPS, exhibits a maximum adsorption capacity of 606.06, 649.35, and 684.93 mg g^-1 at 25, 35, and 45 °C, respectively, as calculated from the Langmuir isotherm model. The effects of pH, ionic strength, and adsorbent dosage on adsorption performance are investigated, and the porous composite beads exhibit robust reusability, maintaining their efficiency even after four adsorption-desorption cycles. The significant findings of this research confirm the superior performance of the functionalized CMCS-based beads for the effective removal of organic dyes from aqueous environments.