Magnetical multi-walled carbon nanotubes with Lewis acid-base imprinted sites for efficient Ni(II) recovery with high selectivity

The recovery of nickel is crucial for both production and environmental protection. In this work, density functional theory (DFT) was utilized to select a highly affine functional monomer, 2-acetamidoacrylic acid (AAA), for the fabrication of a nickel ion-imprinted adsorbent based on magnetic multi-walled carbon nanotubes. The imprinting technique was used to regulate the electron transfer ability of the N and O atoms, which act as "hard" bases in the functional monomer, facilitating strong interaction with Ni(II) featuring "borderline" acid properties. The adsorption capacity of Ni(II) on adsorbents was high up to 75.06 mg/g, reaching equilibrium in about 50 minutes, and maintaining high recovery efficiency even after six adsorption-desorption cycles. The adsorbent exhibited a high selectivity for Ni(II), with a distribution coefficient of up to 1366. It is noteworthy that the adsorbent's magnetic properties facilitate easy separation under an external magnetic field, reducing the cost of Ni(II) recycling. The use of XPS characterization and DFT analysis provided in-depth understanding of the adsorption and recognition mechanism. Moreover, the recover efficiency of Ni(II) in acidic mining tailwater reaches 97.66%, demonstrating a high practical value. This research presents an effective strategy to enhance the practicability of ion imprinted adsorbents by regulating electron transfer ability of the adsorption sites through the imprinting technique.