Nonlinear curve fit analysis for Acid blue 92 removal using functionalized carbon nanotubes

Since functionalized carbon nanotubes exhibit enhanced surface chemistry, in this work, boron, nitrogen and sulfur doped carbon nanotubes were prepared through microwave process by treating the oxidized multi-walled carbon nanotubes with appropriate precursors. The carbon nanotubes were characterized using scanning electron microscopy, X-ray diffraction, Raman and Fourier-transform infrared spectroscopy. The study indicated that the functionalized carbon nanotubes with thickness of 50-60 nm retained their structure even after microwave process by showing rather smooth outer surface with I-D/I-G ratio range 0.6-1.2. Co-doping of boron, nitrogen and sulfur on the carbon nanotube layer enhanced the adsorption property. The functionalized carbon nanotubes were evaluated for its adsorption property to remove Acid blue 92 (AB92) from aqueous solution. The kinetics of AB92 adsorption was evaluated using linear and nonlinear mathematical models. Increase in temperature favours the AB92 adsorption on to the adsorbents prepared was supported by Gibbs free energy values (-3 to -10.8 kJ mol(-1)). The thermodynamic parameters substantiate that the adsorption of AB92 onto these adsorbents is more favourable. The adsorbents were effective in removing AB92 at pH 6 following Freundlich isotherm with mass transfer of 1.995 mg g(-1) min(-1). The recyclability tests showed that the spent adsorbents were effective with 90% adsorption for up to 7 cycles.