Adsorption Kinetics of Methyl Orange from Model Polluted Water onto N-Doped Activated Carbons Prepared from N-Containing Polymers

This study aimed to assess the role of polymeric sources (polypyrrole, polyaniline, and their copolymer) of nitrogen (N)-doped activated carbons (indexed as PAnAC, PPyAC, and PnyAC, respectively) on their adsorption efficiency to remove methyl orange (MO) as a model cationic dye. The adsorbents were characterized using FTIR, SEM, TGA, elemental analysis, and surface area. The kinetic experiments were performed in batches at different MO concentrations (C-0) and adsorbent dosages. The adsorption kinetic profiles of pseudo-first-order, pseudo-second-order (PSO), Elovich, intraparticle diffusion, and liquid film diffusion models were compared. The results showed a better fit to the PSO model, suggesting a chemisorption process. The adsorption capacity (q(e), mg/g) was found to have increased as MO C-0 increased, yet decreased as the adsorbent quantity increased. At the adsorption operating condition, including MO C-0 (200 ppm) and adsorbent dose (40 mg), the calculated q(e) values were in the order of PAnAC (405 mg/g) > PPyAC (204 mg/g) > PnyAC (182 mg/g). This trend proved the carbon precursor's importance in the final properties of the intended carbons; elemental analysis confirmed that the more nitrogen atoms are in the activated carbon, the greater the number of active sites in the adsorbent for accommodating adsorbates. The diffusion mechanism also assumed a rate-limiting step controlled by the film and intraparticle diffusion. Therefore, such an efficient performance may support the target route's usefulness in converting nitrogenous-species waste into valuable materials.

Automated summary

This study aimed to evaluate the adsorption efficiency of nitrogen-doped activated carbons with different polymeric sources (polypyrrole, polyaniline, and copolymer) in removing methyl orange as a cationic dye. The adsorbents were characterized and compared using various methods. The results showed that the adsorption capacity increased with the initial dye concentration but decreased with the adsorbent dosage. Among the samples tested, PAnAC exhibited the highest adsorption capacity due to its higher nitrogen content. The diffusion mechanism was found to be controlled by film and intraparticle diffusion. Therefore, nitrogen-doped activated carbons have the potential to convert nitrogenous waste into valuable materials.