Selective removal of cationic dyes from aqueous solutions by an activated carbon-based multicarboxyl adsorbent

An activated carbon-based multicarboxyl adsorbent has been synthesized for selective removal of cationic dyes from aqueous solutions. The adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N-2 adsorption measurement and zeta potential. The adsorption behavior of cationic rhodamine 6G on the activated carbon-based multicarboxyl adsorbent from an aqueous medium was studied by varying the parameters such as pH, contact time and initial dye concentration. Dye adsorption was dramatically dependent on solution pH and the optimum pH is 4.45. After being modified by multicarboxyls, the adsorption capacity of rhodamine 6G on the activated carbon dramatically increased from 33.18 mg L-1 to 122.55 mg L-1 at pH 4.45. The multicarboxyl adsorbent has obvious selectivity to cationic dyes. Adsorption isotherms could be well described by the Langmuir model, adsorption kinetics fitted well with a pseudo-second-order kinetic equation and exhibited a 3-stage intraparticle diffusion mode. The electrostatic interaction was the main mechanism for the cationic dye adsorption.