Adsorption Kinetic, Isotherm and Thermodynamic of 2,4-Dichlorophenoxyacetic Acid Herbicide in Novel Alternative Natural Adsorbents

The aim of this work was to study the adsorption kinetic, isotherm, and thermodynamic of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in raw and boiling-treated sterile bracts of Araucaria angustifolia as novel alternative natural adsorbents. The sterile bracts were characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. The adsorption and removal of 2,4-D from aqueous solutions were conducted at different contact times, bract granulometries, solution pH, bract masses, initial 2,4-D concentrations, and temperatures. The adsorption kinetic, mechanism, and thermodynamic were evaluated using pseudo-first- and pseudo-second-order kinetic models, non-linear Langmuir, Freundlich, Redlich-Peterson and Sips isotherm models, and Gibbs free energy, enthalpy, and entropy. The maximum removal efficiency of 2,4-D was found with 720 min of contact, 5.0 g of bract containing 31 micron particle sizes, pH = 2.0, and room temperature. The best kinetic and isotherm fits were found with the non-linear pseudo-second-order kinetic model and non-linear Freundlich isotherm model, respectively. Therefore, the adsorption mechanism in the bract structure takes place with multi-layer formation and multi-site interactions due to chemisorption reactions. The adsorption process is thermodynamically favorable, spontaneous, and exothermic. Overall, sterile bract of Araucaria angustifolia could be useful as alternative natural adsorbent for the treatment of water and wastewater contaminated with 2,4-D, mitigating the environmental pollution caused by agricultural crops.