Carvão ativado do ouriço da castanha-do-brasil : caracterização e adsorção do herbicida ácido diclorofenoxiacético (2,4-D)

Abstract

“Ouriço” of Brazil nut presents desirable characteristics to produce activated carbon, therefore, it can be a precursor material. The objective was to evaluate the effect of the temperature and the atmosphere of activation on the quality of activated carbon from “ouriço” and to analyze the adsorption capacity of 2,4-D in aqueous solution. The material was carbonized at 600, 700 and 800 °C for five hours and activated in CO2 or steam atmosphere at the carbonization temperature for 40 minutes. The results showed that there was effect of the pyrolysis temperature on the gravimetric yield, ash content, fixed carbon and pH. The atmosphere influenced the water, ash and fixed carbon contents. There was no effect of the temperature x atmosphere interaction on the evaluated parameters. The characterization of Fourier Transform Infrared Spectroscopy (FTIR) indicated that the activation temperatures and the atmospheres affected the functional groups of the activated carbon surface, and the thermogravimetric analysis indicated stability of the material. The temperature of 800 °C and activation with steam presented better qualitative results. Thus, activated carbons produced at 800 °C and activated with CO2 or steam were used to study the adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The specific surface area determined by the Brunauer, Emmett and Teller (BET) method for the activated carbons was 395 and 401 m2g -1 , respectively. The highest pore intensity occurred with 1.17 nm for the carbons activated with CO2 as well as with steam. The plot of the adsorption/desorption isotherms of N2 presented Type I isotherms, independent of the activation atmosphere. The Scanning Electron Microscopy (SEM) analysis showed that, for both activation atmospheres, pore formation occurred in the form of uniform hive-type craters. The adsorption kinetics followed the pseudo-second order model. The activated carbon with steam at 800 °C also presented better results for the 2,4-D adsorption tests, which, together with the best qualitative results and the lowest cost in relation to CO2, characterize the best alternative for the proposed process.