Effect of nitrogen functionalization on the adsorption performance of commercial charcoal activated with phosphoric acid

This study demonstrates the impact of nitrogen modification on the adsorption properties of activated carbons toward removal of anionic polyazo dye from aqueous solutions. Commercial charcoal was activated with phosphoric acid (ACP) and then modified with mono-aminoethanol (ACP-M), EDTA (ACP-E) and chitosan (ACP-C), respectively. Surface characterizations of samples were carried out using surface pH, total acidity and basicity, zeta-potential, elemental analysis, FTIR, SEM and textural properties. Batch studies were performed to evaluate the influence of pH, contact time, initial dye concentrations and temperature toward removal of solophenyl red 3BL polyazo dye (SR) from aqueous solution. Three common adsorption isotherms including Langmuir, Freundlich and Dubinin-Radushkevich were applied to follow the adsorption process. Langmuir model was found to fit significantly the adsorption of SR dye onto the samples. Among kinetic studies, the pseudo-second-order model well-described the adsorption kinetics and intra-particle diffusion process was not be the rate controlling step. The thermodynamic study showed that the adsorption of SR dye onto activated charcoal and their corresponding modified carbons was spontaneous and endothermic. Modified samples showed better adsorption performance toward dye removal than activated carbon. The adsorption of dye is enhanced on surface of modified carbon samples as the amount of amino groups and specific surface area increased. However, the activated charcoal modified with chitosan (ACP-C) was the best adsorbent where the removal of SR dye was 85%. This result reflects the occurrence of high electrostatic attractions between positively charged surface of ACP-C and negative charges surrounded SR dye.