Ionic liquid-multi walled carbon nanotubes composite tablet for continuous adsorption of tetracyclines and heavy metals

Abstract As the new kind of adsorbent, a 0.15 g ionic liquid-multi walled carbon nanotubes (IL-MWCNTs) composite tablet was prepared for the continuous adsorption of tetracyclines (TCs) and heavy metal ions from their aqueous solutions for the first time. Benzothiazole ionic liquid (N-butyl benzothiazole hexafluoroborate, [C4Bth][PF6]) was found selective for these objects, which was loaded into MWCNTs before tabletting under 5∼20 MPa. Preparation operation was easy and the optional magnetic core (0.6 mm × 8 mm) could make it revolve in solution stably for accelerating mass transfer. Then the novel composite tablet was comprehensively characterized by scanning electron microscopy, thermogravimetry, Zeta potential and spectral analysis. Afterwards, the effects of main factors on adsorption results were investigated. Under unoptimized conditions, the adsorption efficiency of TCs, Cr6+ and Cu2+ could reach 99.76%, 94.10% and 84.60% by single tablet, respectively. It was also found that the adsorbed TCs could enhance the subsequent adsorption of copper ions. The experimental data fit well with pseudo-second-order model and Langmuir model (R2≥0.99). By elution with 5 mol/L NaOH solution, the newly prepared composite tablet could be recycled and more than 90% adsorbate could be removed.