NaOH-activated carbon of high surface area produced from coconut shell: Kinetics and equilibrium studies from the methylene blue adsorption

Activated carbons (ACs) of coconut shell produced by NaOH activation at impregnation ratios of NaOH:char (w/w) equal to 1:1 (AC-1), 2:1 (AC-2) and 3:1 (AC-3) were prepared. The properties of these carbons, including BET surface area, pore volume, pore size distribution, and pore diameter, were characterized from N-2 adsorption isotherms. It was found that the ACs are essentially microporous and that the BET surface area was in order of 783 m(2) g(-1) for AC-1, 1842 m(2) g(-1) for AC-2, and 2825 m(2) g(-1) for AC-3. Scanning electron microscopy images showed a high pore development while Boehm method and Fourier-transform infrared spectroscopy spectra indicated the presence of acid functional groups which was confirmed by pH drift method. The adsorption equilibrium and kinetics of methylene blue (MB) onto AC-3 were carried out. Experimental data were fitted to the four isotherm models (Langmuir, Freundlich, Toth and Redlich-Peterson), and was found that Langmuir model presented the best fit, showing maximum monolayer adsorption capacity of 916 mg g(-1). The kinetic studies showed that experimental data follow pseudo-second-order model. The mechanism of the adsorption process was described from the intraparticle diffusion model. The AC-3 has a high surface area and showed to be an efficient adsorbent for removal of MB from aqueous solutions. (C) 2011 Elsevier B.V. All rights reserved.