High-efficiency adsorption of crude oil and cadmium by bagasse biochar-supported iron ions and carbon nanotubes

Pollution caused by crude oil and heavy metals, particularly cadmium, is a great threat to the environment and human health. In this study, a carbon nanotube-iron composite modified biochar (Fe-CNT-BBC) was successfully prepared. Characterization analysis indicates that the addition of carbon nanotubes increases the carbon content of biochar, enabling it to form a stable porous structure. The main adsorption mechanisms of Fe-CNT-BBC are pore filling, electrostatic attraction, π-π packing interaction and surface complexation and iron ions play a key role in adsorption. The specific surface area (74.06 ± 0.34 m²·g⁻¹), total pore volume (0.24 ± 0.01 cm³·g ⁻¹), and number of surface functional groups of Fe-CNT-BBC were higher. The adsorption of crude oil and Cd(II) by Fe-CNT-BBC is a multi-layered and chemical adsorption process. The maximum theoretical adsorption capacity values of crude oil and Cd(II) adsorption reached 1425.3556 ± 35.7301 and 148.3845 ± 6.8211 mg·g⁻¹, respectively. In addition, when crude oil coexists with cadmium solution, there is a phenomenon of competitive adsorption. The DFT results show that the binding energy of Fe₃O₄-BBC reached 20.3276 kJ·mol⁻¹ with a small energy gap (1.0467 eV), indicating that the addition of iron oxides enhances the chemical activity and electron transfer rate. The multifunctional composite adsorbent Fe-CNT-BBC has achieved a synergistic enhancement in active sites and adsorption performance, surpassing that of single-modified biochar, and can be used for the efficient removal of crude oil and Cd(II) complex system.