N modified uniform Fe0 nanoparticles within CNT for efficient removal of methylene blue from wastewater

Fe and N co-loaded carbon nanotubes were synthesized through a coordination-assisted strategy for methylene blue MB removal. Structural characterization confirmed that Fe-N modification increased the defect density of CNT, improved pore accessibility, and promoted the dispersion of iron species. The I D /I G value increased from 1.08 for CNT to 1.10 for Fe-N/CNT, while the specific surface area of Fe-N/CNT reached 209.7 m 2 g −1 . Under the optimized conditions, MB concentration of 100 mg L −1 , adsorbent dosage of 25 mg, and contact time of 120 min, Fe-N/CNT exhibited an adsorption capacity of 108.98 mg g −1 . This value was much higher than those of pristine CNT (60.67 mg g −1 ) and Fe/CNT (41.43 mg g −1 ). The adsorption behavior fitted well with the pseudo-second-order kinetic model (R 2 = 0.9998) and the Langmuir isotherm model (R 2 = 0.9977). Mechanism analysis suggested that electrostatic attraction, hydrogen bonding, π-π stacking, pore filling, and Fe-N x sites jointly contributed to MB adsorption. Fe-N/CNT retained 81% of its adsorption efficiency after five cycles and showed stable performance in cation-containing solutions, multi-dye systems, and fixed-bed column operation. These results demonstrate that Fe-N/CNT is a promising adsorbent for practical dye wastewater treatment.