As-synthesized multi-walled carbon nanotubes for the removal of ionic and non-ionic surfactants

This research deals with the application of untreated multi-walled carbon nanotubes (MWCNT) in their agglomerates form for the removal of non-ionic (TX-100), cationic (CTAB) and anionic (SDBS) surfactants from aqueous media. In order to optimize the removal process, the influence of several key parameters was investigated including contact time under different solid/liquid ratios, initial solution pH, temperature, along with ultrasonication assistance and desorption assays. Experimentations revealed that pH variation enhanced the removal capacities at optimum values of 6, 2 and 8 for TX-100, SDBS and CTAB, respectively, and that hydrophobic interaction is a major adsorption factor, especially for non-ionic surfactant with possible electrostatic interactions occurring for the ionic ones. As well, removal efficiencies peaked for an optimum temperature range between 35 and 45. °C. As for the ultrasonication assistance, it enhanced the overall removal capacities, especially that of the ionic surfactant, with an enhancement of 52% for the case of SDBS after 1. h of treatment. The modeling results revealed that the pseudo-second order model provided the best correlation of the dynamic data and that the process was controlled by intraparticle diffusion phenomena. At equilibrium, and under optimized experimental conditions, untreated MWCNTs showed promising removal capacities with 359, 312 and 156. mg/g for TX-100, SDBS and CTAB, respectively.