Removal performance and the underlying mechanisms of plasma-induced CD/MWCNT/iron oxides towards Ni(II)

• Magnetic CD/MWCNT/iron oxides were synthesized by low-temperature plasma technique.
• CD/MWCNT/iron oxides exhibited high physicochemical stability in aqueous solution.
• CD/MWCNT/iron oxides exhibited favorable removal performance towards Ni(II) in the simulated effluent.
• XAFS analysis suggested that Ni(II) was retained on the surface-coated β-CD and the inner iron oxides.
• CD/MWCNT/iron oxides can be repeatedly used for cost-effective purification of Ni(II)-bearing wastewater.

Herein, a novel low-temperature plasma technique was adopted to graft β-cyclodextrin (β-CD) on the surfaces of magnetic MWCNT/iron oxide particles. The as-prepared CD/MWCNT/iron oxides exhibited high saturation magnetization and good physicochemical stability in solution. Batch experiments and X-ray absorption fine structure (XAFS) spectral technique were combined to verify the removal performance and the underlying mechanisms of CD/MWCNT/iron oxides towards Ni(II) from single-solute system and the simulated Ni(II)-bearing effluent. The sorption kinetics of Ni(II) on CD/MWCNT/iron oxides can achieve equilibrium in a time period of 4 h. The surface-coated β-CD improves the dispersion property of CD/MWCNT/iron oxides and therefore enhances its removal performance towards Ni(II). The maximum sorption capacity of Ni(II) on CD/MWCNT/iron oxides is higher than a series of adsorbent materials. XAFS analysis suggests that Ni(II) can bind on the hydroxyl sites on the surface-coated β-CD and also the FeO6 octahedra of iron oxides in an edge-shared mode, forming strong inner-sphere complexes with high thermodynamic stability. Considering its high physicochemical stability, high removal performance, high separation convenience and favorable regeneration property, the prepared CD/MWCNT/iron oxides can support long-term use as a cost-effective material in the purification of Ni(II)-bearing effluents.