Synthesis and Mechanistic Insights into Metolachlor Adsorption on L-Arginine Functionalized Fe₃O₄/Activated Carbon Nanocomposite

Abstract

Metolachlor is one of the most frequently detected herbicides in drinking water sources, posing a significant environmental risk. In this study, an L-arginine functionalized magnetic Fe3O4/activated carbon nanocomposite (Fe3O4/L-Arg@AC) was synthesized and its metolachlor removal performance was evaluated. The kinetic and equilibrium adsorption mechanisms of Fe3O4/L-Arg@AC for metolachlor removal were investigated comparatively with pure activated carbon (AC-Puriss), nitric acid modified activated carbon (AC-HNO3), and Fe3O4/L-Arg. Although Fe3O4-based, L-arginine functionalized, and activated carbon-containing systems have been studied in the literature for different pollutants, the use of Fe3O4/L-Arg@AC composite for metolachlor removal is limited. FTIR analyses confirmed successful binding of L-arginine functional groups to the surface, while SEM images revealed that the composite exhibited a more homogeneous distribution and an improved porous surface morphology. Kinetic analyses showed that adsorption process was not limited to diffusion alone but was based on a multi-stage mechanism where liquid film and intraparticle diffusion processes acted together. The functionalized structure exhibited faster mass transfer and more efficient adsorption behavior compared to Fe3O4/L-Arg. Equilibrium data indicated that Freundlich model was more suitable for the composite structure and that heterogeneous surface properties were dominant. Metolachlor adsorption capacity remained stable under neutral and slightly basic pH conditions, while it was only minimally affected under acidic conditions. In addition, the synthesized adsorbent exhibited good reusability with a regeneration efficiency of 93.2% over five consecutive adsorption-desorption cycles. This study demonstrated the Fe3O4/L-Arg@AC composite as an effective, reusable, functional, and viable adsorbent alternative for metolachlor removal in practical water treatment systems.