Fast adsorptive removal of cationic organic dye by anionic group functionalized carbon nanotubes with high efficiency

In this work, a novel adsorbent, sulfonic acid-functionalized carbon nanotubes (CNT-FA-SA) composite was synthesized by Diels-Alder (DA) chemistry and electrophilic substitution reaction. The adsorption of methylene blue (MB) onto CNT-FA-SA was systematically investigated. Based on the experimental data, MB was rapidly removed by CNT-FA-SA composite with maximum adsorption capacity of 236.55 mg/g under certain conditions. The non-linear relevant fitting result of Langmuir isotherm model fully estimates that the maximum adsorption capacity of monolayer can reach to 1584.22 mg/g. The adsorption kinetic is fitted better with the pseudo-second-order model than the pseudo-first-order kinetic model, and the isotherms were well described by Freundlich isotherm model. The data testified that the adsorption process is monitored by chemisorption and physical adsorption simultaneously. Relevant results also indicate that the adsorption occurred on heterogeneous multilayer surface. The parameters of pH and thermodynamic manifested that adsorption of MB onto CNT-FA-SA composites was pH-dependent and spontaneous endothermic reaction.