Avaliação da adsorção do herbicida 2,4-D por carvão ativado em pó e quitosana

Abstract

The purpose of this study was to evaluate and compare the adsorption of the 2,4-D herbicide in water by powder activated carbon and chitosan between kinetics and isotherms adsorption analysis. There were used four adsorbents: a) commercial activated carbon from coconut shell (CAC), b) laboratory produced activated carbon from microalgae origin from wastewater treatment plant (CAM), c) commercial chitosan from crustacean fibers (QUIC) and d) laboratory produced chitosan from crab shell (QUIU). The adsorbents were characterized by specific superficial area, thermal gravimetric analysis, infrared spectroscopy, scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance techniques. The values of specific superficial area found for the activated carbon samples were 625,5 m².g-1 for the CAC sample and 621,2 m².g-1 for the CAM sample, while for the chitosan samples were 3,11 m².g-1 for the QUIC sample and 0,66 m².g-1 for the QUIU sample. Pseudo-first order, Pseudo-second order and Elovich Kinect models were applied in order to study the effect of contact time between adsorbent-adsorbate during adsorption. It was observed that reaching the adsorption equilibrium of 2,4-D with chitosan samples occurred faster than with activated carbon samples, with adsorption equilibrium being noted at around 1 hour with QUIC, around 2 hours with QUIU and around 4 hours with CAC and CAM. For the evaluation of the adsorption capacity of each sample there were applied Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and compared to each other. All the adsorbent materials studied showed good adsorption capacity of the 2,4-D herbicide in aqueous media, and the order of the adsorbent materials that presented the best results in terms of removal efficiency, adsorption capacity and specific surface area was equal to: CAC > CAM > QUIC > QUIU.