A novel non-covalent functionalized multi-walled carbon nanotubes for the microextraction of bromophenols in kelp and seaweed

Long chain betaine-based deep eutectic solvents (DESs) non-covalent functionalized multi-walled carbon nanotubes (MWCNTs) were successfully prepared by mechanical milling. The structural, optical and morphological properties of functionalized MWCNTs were characterized by means of thermal field emission scanning electron microscope coupled with energy-dispersive X-ray spectrometer, transmission electron microscope, Fourier transform infrared spectroscopy, UV-vis-NIR spectroscopy, X-ray diffraction and thermogravimetric analysis. The results showed that the DESs were adsorbed tightly on the surface of MWCNTs, providing for reduced hydrophobicity and enhanced stability of MWCNTs dispersion. The adsorption capacity, the isotherms (Langmuir and Freundlich models), kinetic models (pseudo-first order and pseudo-second order models) were also evaluated for the adsorption behaviors. The results indicated that the adsorption capacities for 4-bromophenol, 2,4-dibromophenol, 2,6-dibromophenol and 2,4,6-tribromophenol were 155.82, 267.42, 761.19 and 1719.68 mg/g, respectively. The adsorption isotherm of bromophenols fitted well with Freundlich model and pseudo-second-order kinetic, revealing that the adsorption process accorded with the theory of multilayer adsorption and chemical adsorption. Satisfactory recoveries were ranged from 85.34 +/- 3.41% to 98.44 +/- 3.45% with a low RSD% of 2.35-4.95%, demonstrated that DES-1 functionalized MWCNT was an efficient adsorbent for the bromophenols in the kelp and seaweed.