Avaliação da adsorção de contaminantes em solução aquosa pelo carvão ativado impregnado com óxido de grafeno produzido a partir de pilhas zinco-carbono exauridas

Abstract

The objective of this work was to produce graphene oxide from graphite obtained from zinc- carbon batteries exhausted by the modified Hummers' method (GOH) and by the 1-methyl- 2-pyrrolidone method (GOM), these being impregnated with activated carbon from coconut palm shell, aiming to study the production and use of different adsorbents in the removal of pollutants. To this end, FTIR characterization analyses, N2 physisorption, SEM, Raman, XRD, TXRF were performed, which showed the partial formation of graphene oxide. Kinetic and equilibrium tests, in batch system, were performed to remove methylene blue with initial concentration of 100 mg L - 1 and pH 5, under constant stirring (100 rpm) and ambient temperature (25ºC). In the kinetic test there was no change in the overall efficiency of the process for the adsorbent from the impregnation of GOH in activated carbon (CGOH), occurring modification in the equilibrium time, positively impacting the adsorption kinetics of methylene blue, since for the CDA the time was 240 min, and for the CGOH it was 90 min. The adsorbent of activated carbon with GOM (CGOM) in its turn was not feasible, since the capacity of removal of the dye was reduced compared to the CDA, in addition to presenting a slower removal kinetics. The best fit for kinetic data occurred with the pseudo-first order model for adsorbents CDA and CGOH (R2 = 0.9982 and 0.9886, respectively). The intraparticle diffusion parameters obtained for CGOH indicate that the limiting step of the process was the mass transfer in the meso and macropores (zone II). In addition, an average pore diameter was observed for the CDA of 4.0 nm and for the CGOH of 4.4 nm, which may have facilitated the process of mass transfer of the adsorbate into the pores and caused the better kinetics of removal of the CGOH, compared to the CDA. In addition, it was possible to observe the same capacity of removal of Cr (VI) and Cr (III) ions by means of the kinetic test for the adsorbents CGOH and CDA. To evaluate the equilibrium data, the isotherm model that best ajusted the experimental data for methylene blue dye was the Freundlich model, for the adsorbent CGOH with R2 of 0.9887, and for the adsorbents CDA and CGOM, the Redlich-Peterson isotherm (R2 of 0.9783 and 0.9899, respectively). The adsorption capacity for the agrochemical 2.4 D was evaluated with CDA and CGOH (46.9 mg L-1 and 48.3 mg L-1, respectively), and a slight increase in the adsorption capacity for CGOH was observed. Based on the results obtained, the adsorbent CGOH has potential for use in the treatment of industrial effluents, contributing to the removal in a shorter time, in the case of methylene blue dye, and there are also indications of greater efficiency in the case of agrochemicals 2.4 D.