Bio-hybrid magnetic [email protected] nanocomposite for efficient tetracycline adsorption: Synthesis, mechanistic insights, and reusability

• Magnetic MA–Fe 3 O 4 @ E.coli bio-hybrid nanocomposite from Sargassum macroalgae • FTIR–XRD–FESEM–EDX verify E. coli immobilization with optimal loading at 300 ppm • TC adsorption obeys PSO kinetics and Langmuir isotherm (q m = 2.51 mg/g) • Adsorption is spontaneous, mildly endothermic, via dual chemisorption–physisorption • MA– Fe 3 O 4 @ E.coli enables facile magnetic recovery, 87.7% desorption and 59% reuse The persistence of tetracycline in aquatic systems poses a serious environmental and health concern, necessitating efficient and sustainable removal technologies. This study developed a bio-hybrid magnetic nanocomposite (MA-Fe 3 O 4 @ E.coli ), synthesized by immobilizing Escherichia coli biomass onto Fe 3 O 4 nanoparticles derived from Sargassum filipendula . FTIR, XRD, and FESEM-EDX analyses confirmed the successful integration of magnetic and biological components. FTIR showed Fe-O vibrations (∼580 cm -1 ) and intensified C=O and amide bands, verifying microbial immobilization; XRD displayed characteristic Fe 3 O 4 peaks with minor broadening, indicating structural integrity with slight lattice strain; and FESEM-EDX revealed uniform bacterial attachment forming a stable biofilm at 300 ppm E. coli , the optimal loading for adsorption performance. Batch adsorption followed pseudo-second-order kinetics (R 2 = 1.000) and the Langmuir isotherm (R 2 = 0.997) with a maximum adsorption capacity (q m ) of 2.51 mg g -1 , indicating monolayer chemisorption as the primary mechanism, supported by secondary physisorption through hydrogen bonding and electrostatic interactions. Thermodynamic analyses confirmed a spontaneous (ΔG° < 0) and mildly endothermic (ΔH° = +7.76 ± 3.43 kJ mol -1 ) process. The adsorbent achieved 87.7% desorption efficiency using methanol-water and retained 59% capacity after five cycles, highlighting excellent reusability. Compared to chitosan-Fe 3 O 4 composites, MA-Fe 3 O 4 @ E.coli offers a low-cost, environmentally benign alternative for antibiotic removal and magnetic recovery in wastewater treatment applications.