Nanoporous carbons prepared from argan nutshells as potential removal agents of diclofenac and paroxetine

Argan nutshells from Northern Africa were selected for a noble valorization: conversion into nanoporous carbon (ACH) through H₃PO₄ activation for the removal of diclofenac (DCF) and paroxetine (PARX). The performance of ACH carbon was compared to that of a commercial carbon (CC), through kinetic, equilibrium, and thermodynamic studies. An extensive characterization of the materials allowed to gain insight about the adsorption mechanisms. The biomass carbon presented a high surface area (1542 m² g⁻¹) and total pore volume (1.04 cm³ g⁻¹) that corresponds mainly to mesopore volume. Despite the acidic activation, ACH surface was enriched with phenolic groups while the CC sample presented much less oxygen, mainly carbonyl-quinone groups. CC sample was also enriched with high concentrations of Si, Al, Fe, Ca, and K. CC carbon presented a higher uptake capacity of DCF (214 mg g⁻¹) and PARX (260 mg g⁻¹) than the ACH carbon (149 mg g⁻¹ for DCF, and 168 mg g⁻¹ for PARX), despite its lower surface area. DCF and PARX adsorption isotherms were best fitted to the Sips model on both carbons indicating some heterogeneous distribution of the active sites. The wide micropores developed on ACH do not provide an optimum size for adsorbates adsorption. It was established that π - π interactions and H-bonding were the main adsorption mechanisms with ACH carbon, while CC removed both molecules through interaction with the metallic elements present at the carbon and π - π interactions. In addition, electrostatic attraction of DCF by CC carbon was also an important mechanism.