Magnetic biochar from tilapia waste for oxytetracycline removal: Adsorption performance and absence of toxicity on zebrafish embryos

The urgent demand for environmental remediation has generated significant interest in sustainable materials and technologies. Among them, biochar (BC) has recently emerged as a promising material for applications in aquatic and soil environments. Herein, we aimed to develop functionalized biochars derived from Nile Tilapia ( Oreochromis niloticus ) carcasses for the removal of the antibiotic oxytetracycline (OTC) from aqueous solutions linked to ecotoxicity assessment in Zebrafish embryos. The BCs were synthesized via pyrolysis at different temperatures and subsequently subjected to size reduction using high-energy ball milling, referred to as CBC (Crushed Biochar). Magnetization was performed via a co-precipitation method, yielding magnetite-functionalized biochar, resulting in NMBC (Nano-Magnetized Biochar). The chosen equilibration time for adsorption was 24 h, during which CBC600 and NMBC600 displayed adsorption capacity and removal percentage for OTC at 49.17 mg g −1 and 61.8%, and 39.25 mg g −1 and 56.6%, respectively. For both adsorbents, the kinetic model that best fitted the experimental data was the Elovich model, while for the adsorption isotherm the best fit was the Sips model. The negative values of ∆G° confirmed that the adsorption process was favorable, spontaneous, physical, with the system showing an exothermic enthalpy. The ∆S° was negative for CBC and positive ∆S° for NMBC. Ecotoxicity assessment using zebrafish embryos showed absence of acute toxicity effects (until 100 mg L −1 ) to both CBC and NMBC materials. Finally, the results obtained support the development of functional biochars for removal of oxytetracycline from water associated with Nile Tilapia waste valorization by sustainable materials production for environmental technologies and circular economy. • The highest Oxytetracycline removal percentage from water was 61% (39.25 mg g −1 ) for magnetic biochar. • Magnetic properties avoid the centrifugation and filtration steps. • Both crushed biochar and magnetic biochar were not toxic for zebrafish embryos (until 100 mg L −1 ).