Adsorption of anionic and cationic dyes in aqueous solution by a sustainable and low-cost activated carbon based on...

The objective of this work is to study the adsorption capacity of a natural and low-cost material prepared from argan waste treated with H₃PO₄ towards two dyes of different molecular charges and presenting an acute toxicity, the methyl orange (MO, anionic dye) and the methylene blue (MB, cationic dye). The prepared adsorbent was characterized by SEM, EDX, FTIR, and BET specific surface. These analyses showed the presence of C (42%), O (55%), and P (3%) and a remarkable difference between the morphology of the precursor and that of the obtained material with a specific surface of 475 m²/g and a very porous structure as well as the main functional groups, O-H, C=O, and C-H. The influence of the pH showed a maximum adsorption at pH =2 for MO and at pH = 10 for MB. Investigation of the effect of time on the adsorption of anionic and cationic dyes revealed that the contact time at equilibrium was 240 and 180 min, respectively. The isotherms that best fit the adsorption of MO and MB are the Langmuir model and the Freundlich model respectively. The kinetic study showed that the experimental data are in agreement with the pseudo-second-order model. Regeneration of the saturated material was also studied for the probability of reusing the adsorbent in many experiments. The valorization of argan waste into activated carbon using H₃PO₄ has allowed to obtain an effective adsorbent for the removal of anionic and cationic dyes and create an added value for environmental sustainability.