In this study, the innovative and multi-functional chitosan-based hydrogel beads were immobilized with silver nanoparticles (AgNPs) via polydopamine coating to simultaneously enhance antimicrobial and adsorption activity. The morphological observation under scanning electron microscopy along with elemental mapping by energy disperse X-ray spectrometer indicated that AgNPs were successfully synthesized and immobilized not only on the surface but also the interior of PDA-coated chitosan beads. The covalent silver–carboxylate linkage along with hydrophobic and Van der Waals forces was evidenced by Fourier transform infrared spectroscopy to further confirm the in situ synthesis of AgNPs on the surface of beads. The equilibrium swelling rate of the prepared hydrogel beads decreased as pH increased, being 160%, 100%, and 80% at pH 5, 7, and 9, respectively. The adsorption performance of the hydrogel beads was investigated for the removal of an anionic dye and a metal ion (Cu (II)). The presence of AgNPs enhanced the adsorption capacity of the beads for the above-mentioned adsorbates. The antimicrobial activities were determined against potential human pathogens including Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The antimicrobial activity of the obtained beads on the Gram-negative bacteria was higher than on the Gram-positive bacteria. The obtained hydrogel beads could be used for simultaneously controlling chemical and biological contaminants in wastewater.

Graphical abstract

Polydopamine coating on chitosan beads enables the immobilization of in situ synthesized silver nanoparticles for superior adsorption and antimicrobial activity.