Adsorption of atrazine on hemp stem-based activated carbons with different surface chemistry

Surface-modified hemp stem-based activated carbons (HACs) were prepared and used for the adsorption of atrazine from aqueous solution, and their adsorption performance was examined. A series of HACs were prepared by potassium hydroxide activation of hemp stems, followed by subsequent modification by thermal annealing, oxidation with nitric acid and amination. The resultant HACs differed in surface chemistry, while possessing similar porous structure. The surface group characteristics were examined by X-ray photoelectron spectroscopy and measurement of the point of zero charge (pH(PZC)). The adsorption of atrazine from aqueous solution was performed in static conditions. The Langmuir-Freundlich and Langmuir models gave a better fit for equilibrium isotherms compared with the Freundlich model. The atrazine adsorption process was controlled by an intraparticle diffusion mechanism with a significant contribution from film diffusion. The presence of oxygen and nitrogen functionalities on the carbon surface was found to be undesirable for atrazine adsorption. The superior adsorbent was obtained by heat treatment of HAC in an inert atmosphere at 700 A degrees C, resulting in a very high adsorption capacity due to its enhanced hydrophobicity. The adsorption of atrazine on the studied HACs mainly involves pi-pi dispersive interactions between the atrazine ring and the graphene layers of carbon.