Adsorção da cafeína em carvão ativado da folha de coqueiro (Cocos nucifera L.)

Abstract

The population growth also provides an increase in the consumption of chemical compounds, lack of resources and criteria for treating the generated waste points out to an increasing accumulation of emerging pollutants in the environment, among which, caffeine stands out. Residue from coconut cultivation, the leaves of the coconut palm Cocos nucífera L, are used in this work for biochar production through pyrolysis process at 500 oC and later analysis of this biomass by thermogravimetry (TGA). The biochar generated were activated with potassium carbonate (K2CO3) to be used as an adsorbent for caffeine in aqueous media. The ray diffraction analysis (XRD) performed on activated shows a predominantly amorphous structure and the study of pH at the zero charge point (pHPZC) showed a value of 7.9. In the nitrogen adsorption by the Brunauer, Emmett and Teller (BET) method, the adsorbent under study showed a predominance of mesopores, in the order of 45.48 ηm and a surface area of 678.03 m2 /g, which are quite acceptable data when compared to other processes and biomasses mainly for the time and temperature necessary for the equilibrium, 40 minutes and 30 oC. Using statistical tools to adjust the experiments to models defined in the literature, the adsorption kinetics suggests a pseudo-second order process where the intraparticle diffusion can be neglected, the adsorption isotherms were adjusted for the Redlich-Peterson model and a type L curve in the model proposed by Giles, both models defining that the difference in concentration between adsorbent and adsorbate controls ou conduct the process. The thermodynamic parameters calculated at temperatures of 30, 40 and 50 oC resulted in a system where the Gibbs free energy (ΔG °) with negative values defines that the adsorption occurs spontaneously and the enthalpy (ΔH °) with the value of - 28 , 35 kJ / mol for a process governed by physical adsorption.