Manipulating Carbon Nanotubes for Efficient Removal of Both Cationic and Anionic Dyes from Wastewater

This study explores the application of carbon nanotubes (CNTs) for efficient removal of a mixture of cationic and anionic dyes. The multi walled carbon nanotubes (MWCNT) have been synthesized using a thermal chemical vapor deposition technique and they have been functionalized via acid treatment (ACNT), heat treatment (HCNT) and have also been treated with amine (NH2CNT). Specific surface area, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infra-red (FTIR) spectroscopy, zero point charge (pHzpc) of MWCNT, ACNT, HCNT and NH2CNT have been investigated in this study. The sorption studies have been done using rhodamine B (RhB), methylene blue (MB), malachite green (MG) and methyl orange (MO) dyes. The conditions for optimum adsorption of the dyes onto these CNTs have been determined by investigating the effect of the contact time, pH of solution, and initial solution concentration in batch adsorption process. MWCNT and ACNT showed greater affinity for cationic MB, MG and RhB dyes whereas NH2CNT exhibited better sorption of the anionic dye MO. For adsorption of MG by MWCNT, ACNT and HCNT and MO by NH2CNT, the Langmuir adsorption equilibrium isotherm data provides a better fit than the Freundlich isotherm. Furthermore, the separation factor, RL and the surface coverage, for Langmuir isotherm confirms that the proposed adsorption process is the most suitable for MWCNT, ACNT, HCNT and NH2CNT for these selected dyes. The reusability of the sorbents has also been tested and they have been found to retain their efficiency after three consecutive runs. The composites of NH2CNT with MWCNT/ACNT exhibits good sorption affinity for both cationic and anionic dyes which suggest that these could be effectively used for the removal of dye effluents from waste water.