Experimental and Theoretical Estimations of Atrazine's Adsorption in Mangosteen-Peel-Derived Nanoporous Carbons

Abstract

Nanoporous carbons were prepared via chemical and physical activation from mangosteen-peel-derived chars. The removal of atrazine was studied due to the bifunctionality of the N groups. Pseudo-first-order, pseudo-second-order, and intraparticle pore diffusion kinetic models were analyzed. Adsorption isotherms were also analyzed according to the Langmuir and Freundlich models. The obtained results were compared against two commercially activated carbons with comparable surface chemistry and porosimetry. The highest uptake was found for carbons with higher content of basic surface groups. The role of the oxygen-containing groups in the removal of atrazine was estimated experimentally using the surface density. The results were compared with the adsorption energy of atrazine theoretically estimated on pristine and functionalized graphene with different oxygen groups using periodic DFT methods. The energy of adsorption followed the same trend observed experimentally, namely the more basic the pH, the more favored the adsorption of atrazine. Micropores played an important role in the uptake of atrazine at low concentrations, but the presence of mesoporous was also required to inhibit the pore mass diffusion limitations. The present work contributes to the understanding of the interactions between triazine-based pollutants and the surface functional groups on nanoporous carbons in the liquid-solid interface.

Keywords: DFT estimations; atrazine removal; isotherms; kinetics; nanoporous carbons.

Figure 1

(a) N₂ adsorption–desorption isotherms at −196 °C; (b) pore size distributions. The figure inset shows the cumulative pore volume on the activated carbons.

Figure 2

SEM images of the homemade carbons: (a) MPB-CO₂; (b) MPB-P50.

Figure 3

Evolution of pH of activated carbons as a function of contact time.

Figure 4

Kinetics of atrazine adsorption (q_t) as a function of the initial concentration: (a) AC_M; (b) AC_PC; (c) MPB-CO₂; (d) MPB-P50.

Figure 5

Adsorption isotherms of atrazine: (a) ACM; (b) ACPC; (c) MPB-CO₂; (d) MPB-P50.

Figure 6

Optimized geometries of adsorbed systems in 1/1 monolayer using one atrazine molecule on a 5 × 5 graphene surface unit cell. O, N, Cl, and H atoms correspond to red, blue, green, and grey spheres, respectively.

Figure 7

DOS (black line) and projected DOS on the pristine G_Pristine graphene (green line) and atrazine (blue line) with the PBE functional.

Figure 8

Schematic model for the atrazine adsorption on porous carbons: (a) low ATZ concentration. (b) high ATZ concentration.