Conversion of Argan Nutshells into Novel Porous Carbons in the Scope of Circular Economy: Adsorption Performance of Emerging Contaminants

The present work proposes an experimental strategy to prepare argan nutshell-derived porous carbons using potassium hydroxide (KOH). Several experimental parameters of the activation process were evaluated (temperature, impregnation ratio, and activation time), and an optimized carbon (ACK) was obtained. The surface properties of the ACK sample were determined, and the porous carbon was applied as an adsorbent of diclofenac (DCF) and paroxetine (PARX). A commercial carbon (CC) was used as a benchmark. The ACK porous carbon presented a higher surface area and micropore volume (1624 m² g⁻¹ and 0.40 cm³ g⁻¹, respectively) than CC carbon (1030 m² g⁻¹ and 0.30 cm³ g⁻¹, respectively), but the maximum adsorption capacities of DCF (214–217 mg g⁻¹) and PARX (260–275 mg g⁻¹) were comparable among the two carbons. Besides π-π interactions, H-bonds with the electronegative atoms of the adsorbate molecules and the electropositive H of the oxygen functional groups were appointed as the most probable mechanisms for adsorption onto ACK porous carbon. The electrostatic attraction was also considered, particularly for DCF with CC carbon. The pore size might have also been critical, since CC carbon presented more supermicropores (0.7–2 nm), which are usually more favorable toward the adsorption of pharmaceutical molecules. The reusability of the ACK carbon was tested up to four cycles of adsorption–desorption by using ultrasonic washing with water. The results indicated that no more than one cycle of use of ACK should be performed.