In situ construction of metal–phenolic networks in chitosan/polyvinyl alcohol (CS/PVA) hydrogel beads for efficient tetracycline hydrochloride removal with recyclability from complex water systems

The widespread occurrence of antibiotic residues in aquatic environments has become a major water pollution concern, posing ecological risks and accelerating antimicrobial resistance. Metal–phenolic networks (MPNs), eco-friendly functional materials formed via coordination between natural polyphenols and metal ions, exhibit broad application potential in environmental remediation. In this study, a novel composite adsorbent (FTN@CS/PVA) was fabricated by uniformly immobilizing MPN structures within a three-dimensional porous chitosan/polyvinyl alcohol (CS/PVA) gel beads through the in situ coordination of Fe 3+ and tannic acid (TA). The resulting material exhibited excellent adsorption performance toward tetracycline hydrochloride (TCH), achieving a maximum adsorption capacity of 95.5 mg/g at 298 K and pH 3. The adsorption process followed the pseudo-second-order kinetic model (R 2  = 0.9963) and the Redlich–Peterson isotherm model (R 2  = 0.9736). The primary adsorption mechanisms involved synergistic physicochemical interactions, including hydrogen bonding, Fe O coordination, and electron transfer. Notably, FTN@CS/PVA also exhibited high adsorption efficiency toward various dyes and maintained excellent competitive and selective adsorption performance even in a TC–MB binary system. Furthermore, FTN@CS/PVA retained high TCH removal efficiency in real water matrices (lake water, domestic wastewater, and secondary effluent from a wastewater treatment plant) and in complex systems containing various coexisting anions or humic acid (HA), demonstrating superior interference resistance and environmental adaptability. In addition, FTN@CS/PVA demonstrated structural stability and excellent regenerability, maintaining over 80 % of its adsorption capacity after three adsorption–desorption cycles in the presence of humic acid (HA). This study provides a novel design strategy and theoretical foundation for developing highly stable and selective MPN-based composite adsorbents for the efficient removal of antibiotic contaminants.