Alginate-encapsulated ZIF-67 composite gel spheres for enhanced tetracycline removal and fixed-bed application

The pervasive accumulation of tetracycline (TC) in aquatic ecosystems poses severe ecological and health threats, yet conventional technologies rarely achieve reliable removal under continuous-flow conditions. To overcome the intrinsic brittleness, aggregation and leaching of powdered ZIF-67, this study developed novel alginate-encapsulated MOF composite gel spheres (ALG/ZIF-67) via in-situ crystallization. This simple strategy generates hierarchical pores, anchors Co-N active sites and imparts mechanical robustness without sacrificing adsorption kinetics. Comprehensive characterization confirmed a hierarchical porous structure with uniformly dispersed ZIF-67 nanoparticles. Batch experiments demonstrated exceptional TC adsorption (89.45 mg/g), following pseudo-second-order kinetics and the Langmuir isotherm, indicating chemisorption-driven monolayer adsorption via π-π interactions, hydrogen bonding, and coordination with unsaturated Co²⁺ sites. Fixed-bed applications showcased remarkable stability, maintaining > 80 % TC removal over 6 h with negligible ZIF-67 leaching. The alginate matrix enhanced mechanical robustness and recyclability, mitigating MOF limitations in flow systems. This work provides a scalable, eco-friendly adsorbent for antibiotic-laden wastewater, bridging laboratory innovation and industrial deployment while addressing persistent contaminant challenges.