Phenol adsorption from aqueous solutions by functionalized multiwalled carbon nanotubes with a pyrazoline derivative in the presence of ultrasound

Carboxylated multi-wall carbon nanotubes (MWCNTs-COOH) were functionalized with a pyrazoline derivative (MWCNT-Py) and used for the removal of phenol from aqueous solutions under ultrasound. The resulting materials were characterized by different techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. In batch tests, the influences of solution pH, contact time (ultrasonic time), concentration of the phenol and amount of adsorbents on the sorption of phenol onto MWCNT-COOH and MWCNT-Py were investigated. The kinetic data were fitted with pseudo-first order, pseudo-second-order, Elovich and intra-particle diffusion models. Kinetic studies showed that the sorption process with MWCNT-COOH and MWCNT-Py was well described by pseudo-second-order and pseudo-first-order kinetics, respectively. In addition, the adsorption isotherms of phenol from aqueous solutions onto MWCNTs were studied. The six isotherm models: Langmuir (four linear forms), Freundlich, Tempkin, Halsey, Harkins–Jura, Flory–Huggins and Fowler–Guggenheim models, were applied to determine the characteristic parameters of the adsorption process. The results showed that the interaction among the adsorbed molecules is repulsive and there is no association between them. Also, the adsorption isotherm models fitted the data in the order: Langmuir > Freundlich, Halsey > Fowler–Guggenheim > Tempkin > Harkins–Jura isotherms.