Investigation of green functionalization of multiwall carbon nanotubes and its application in adsorption of benzene, toluene & p-xylene from aqueous solution

Abstract

The presence of benzene, toluene, and p-xylene (BTX) in an aqueous media imparts harmful effects on the ecosystem. To abate these hydrophobic contaminants, adsorption with the efficient sorbent, multiwall carbon nanotubes (MWCNTs) was selected for the present research. Since the strong oxidizing agents cause the highest degree of degradation (shortening of tubes), severely affect the structural integrity of nanotubes and ultimately result in reduced sorption capacity. Therefore, the surface of MWCNTs was modified with a new combination of green dispersants (citric acid, tartaric acid, malic acid, and salicylic acid) and characterized by surface area analyzer, Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR), Raman spectroscopy, x-ray diffraction (XRD), and variable pressure field emission scanning electron microscope (VPFESEM). The incorporation of oxygen-bearing complexes over the surface of nanotubes, enhanced the surface wettability of MWCNTs that offers more active sites for the sorption process. The impact of governing factors (BTX concentration, contact time, dosage of MWCNTs, temperature, and pH) was systematically studied and optimized using RSM technique. The maximum removal efficiency of oxidized MWCNTs (O-MWCNTs) was up to 99.99% for BTX. The experimental data were best fitted to the pseudo second-order model and Langmuir isotherm models. The thermodynamic study depicted that the sorption process was spontaneous and endothermic. The sorption mechanism was quantitatively evaluated by FTIR-ATR. The successful desorption and regeneration of present surface modified MWCNTs proved the recycling capacity of the modified sorbent. Conclusively, surface modified MWCNTs presented a fast and efficient removal of BTX with the highest adsorption capacity as compared to that reported in existing literature.