Bi-doped HKUST-1 encapsulated in copper alginate matrix: A novel composite adsorbent for enhanced removal of chlortetracycline and oxytetracycline from aquatic systems.

The persistent presence of tetracycline antibiotics such as chlortetracycline (CTC) and oxytetracycline (OTC) in aquatic environments has emerged as a critical environmental concern. To address this challenge, we developed a novel composite adsorbent through strategic doping of bismuth into the HKUST-1 metal-organic framework (MOF), followed by encapsulation within a copper alginate (SA-Cu) hydrogel matrix. This innovative synthesis protocol yielded BiHKUST-1/SA-Cu, which was characterized using SEM, XRD, FT-IR, and XPS to elucidate its structural and chemical properties. Remarkable adsorption capacities of 577.34 mg g for CTC and 538.18 mg g for OTC were achieved at 298 K. The adsorption process was best described by the Langmuir isotherm model and exhibited pseudo-second-order kinetics, indicating monolayer adsorption dominated by chemisorption mechanisms. Thermodynamic analysis revealed the spontaneous and endothermic nature of the adsorption process. Mechanism studies demonstrate that adsorption arises from multiple interactions, including coordination, hydrogen bonding, π-π stacking, cation bridging, electrostatic attraction, electron donor-acceptor (EDA) interactions (via n-π and π-π pathways), and hydrophobic interactions. Notably, the composite demonstrated exceptional anti-interference capability against coexisting species and acceptable adsorption-regeneration abilities. These superior properties position BiHKUST-1/SA-Cu as a highly promising candidate for practical water remediation applications.