Chitosan-derived magnetic nitrogen/selenium-doped porous carbon: A sustainable and high-performance adsorbent for removal of organic pollutants from water and wastewater

The development of effective and sustainable adsorbents for water purification is imperative in the face of growing environmental pollution. In the current study, we report a new magnetic nitrogen/selenium-doped porous carbon nanomaterial (Fe₃O₄/N/SePC-900; abbreviated as FNSC-900), prepared through direct pyrolytic transformation of a deep eutectic solvent system based on choline chloride, urea, iron trichloride, selenium dioxide, and notably the renewable nitrogen-rich chitosan precursor. The addition of chitosan not only offers high nitrogen content and biocompatibility but also enhances porosity and adsorptive ability of the resulting carbon matrix. Exhaustive characterization by XRD, TEM, FE-SEM, EDX, BET, and VSM confirmed the effective synthesis of a highly porous, heteroatom-doped magnetic carbon framework with surface area of 331.07 m²/g and pore volume of 0.2898 cm³/g. FNSC-900 adsorbent showed high adsorption properties towards organic dyes (methylene blue as the model dye) and antibiotics (tetracycline as the model antibiotic) in water solutions. The maximum adsorption capacities under optimal conditions were 529.03 mg/g for methylene blue and 351.43 mg/g for tetracycline, respectively, with more than 98% removal efficiency within 15 minutes of contact time. Kinetic and isotherm experiments revealed that adsorption follows a pseudo-second-order kinetic model and follows the Langmuir isotherm, which is typical of monolayer adsorption on a homogeneous surface. Thermodynamic investigation aided spontaneous and endothermicity of adsorption. Moreover, the magnetic character of the adsorbent gives ease and rapid separability from water, and the material was found to be highly reusable under multiple adsorption-desorption processes. Overall, the current work highlights the pivotal role of chitosan the production of new, engineered, green, and recyclable adsorbents, outlining a future direction towards green water treatment technologies. • Chitosan-derived magnetic N/Se-doped porous carbon was synthesized via green method. • The obtained porous material showed >98% removal for methylene blue and tetracycline in 15 minutes. • The adsorbent high surface area (331 m²/g) and excellent magnetic separability was beneficial in application. • Dual N/Se doping enhanced adsorption and reusability for waters purification. • Adsorption followed pseudo-second-order kinetics and Langmuir isotherm model.