Modification of carbon nanotubes with cationic surfactant and its application for removal of direct dyes

The modification of multi-walled carbon nanotube (MWCNT) with a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) and its application for removal of two direct dyes, direct red 80 (DR80) and direct red 23 (DR23) were investigated. The raw and functionalized samples were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The influence of operational parameters was studied through batch adsorption experiments. For understanding the mechanisms of adsorption, Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich isotherm models were used. Intraparticle diffusion, pseudo-first-order and second-order models were adopted to evaluate data and elucidate the kinetic of the adsorption process. The presence of functional groups: O–H, N–H, C–H and C–N were detected by FTIR spectroscopy. The results showed that CTAB were efficiently immobilized on the surface of the MWCNT. The Langmuir adsorption capacities of surfactant-functionalized carbon nanotubes (SF-CNT) for DR23 and DR80 were established as 188.68 and 120.48 mg/g, respectively. The sorption kinetic of SF-CNT followed pseudo-second-order kinetic model. The experiments indicated that the adsorption capacity of SF-CNT is more significant than raw-CNT; thus, it could be used as an effective adsorbent for removing of anionic dyes from waste waters.