The sustainable synthesis of functionalized magnetic carbon nanotube adsorbent derived from steel waste for high-efficiency sequestration of tetracycline: Optimization, kinetics, isotherms and regeneration performance

Antibiotic pollution from tetracycline (TC) poses severe environmental and public health hazards. This study investigates the synthesis, characterization, and adsorptive performance of sustainable, magnetically recoverable functionalized magnetic multi-walled carbon nanotubes (FMWCNTs) adsorbent catalyzed by steel-mill waste. The adsorbent exhibits superior surface area (385 m 2 /g), mesoporosity (2.2 nm), and superparamagnetic behaviour (30 emu/g), enabling efficient TC adsorption and facile recovery. Optimization using response surface methodology yielded 98.7% TC removal under optimal conditions (400 mg/L FMWCNTs, 45 mg/L TC, pH 6.5, 23 min). Adsorption followed pseudo-second-order kinetics and Langmuir isotherm (maximum capacity: 21.7 mg/g at 303 K), with thermodynamic analysis indicating a spontaneous, endothermic, and entropy-driven process. The adsorbent material retained 87% efficiency after four regeneration cycles and achieved over 90% TC removal from simulated municipal effluent. Adsorption mechanisms included π-π interactions, hydrogen bonding, electrostatic attraction, and surface complexation. These findings demonstrate the promising potential of low-cost, regenerable FMWCNTs as practical adsorbents for antibiotic-polluted water. • Functionalized multiwalled carbon nanotube catalyzed by steel mill scale waste was synthesized with an elevated surface area of 385 m 2 /g. • RSM optimized TC removal to 98.7% in 23 min under pH 6.5. • Adsorption follows PSO kinetics and Langmuir isotherm; qₘₐₓ = 21.7 mg g- 1 . • FMWCNTs retained 87% efficiency after four adsorption–desorption cycles. • Magnetic recovery presents a low-cost, sustainable route for antibiotic remediation.