Alginate vs chitosan composites loaded with halloysite/molecularly imprinted polymer hybrids for tetracycline removal: Comparative studies of adsorption behaviour.

Tetracycline (TC) is a broad-spectrum antibiotic but poses a significant threat to ecosystems. In this study, a series of alginate-based (ALG) hydrogel beads were synthesized with the incorporation of halloysite (Hal), a molecularly imprinted polymer (MIP), and a Hal-deposited polymer (Hal@MIP). The adsorption properties of these materials were evaluated and compared with those of their chitosan-based (CS) counterparts. The findings demonstrate a significant improvement in TC removal, highlighting the potential of the alginate-based hydrogels as superior adsorbents than chitosan-based ones. The maximum TC adsorption capacity reached 281 mg g-1 for ALG_Hal@MIP, which was approximately 100 mg higher than that obtained for CS_Hal@MIP. The hydrogel beads with Hal@MIP demonstrated higher thermal stability and better accessibility to the imprinted cavities than those with MIP. The high adsorption efficiency was attributed to pore-filling, accompanied by the simultaneous contributions of electrostatic interaction, complexation, H-bonding and π-π electron donor-acceptor effect. The hydrogel beads containing imprinted polymers exhibited high selectivity and maintained their functionality in real water samples. The advantage of alginate-based adsorbents over chitosan-based ones was evident in water and soil samples. Hence, ALG_Hal@MIP emerged as the most promising material for the selective remediation of TC contamination in different environments compared to the other adsorbents.