Activated carbon from macauba endocarp (Acrocomia aculeate) for removal of atrazine: Experimental and theoretical investigation using descriptors based on DFT

Abstract

In this work the properties of activated carbon obtained from macauba endocarp were evaluated, an agro-industrial waste widely produced in Brazil. This material was applied to remove the herbicide atrazine, an emerging pollutant. The biochar it was produced by vacuum pyrolysis (temperatures of 400 °C and 600 °C; heating rates 10 and 50 °C min−1) and activated with K2CO3. The characterizations of materials were performed by elemental analysis (CNHO), immediate analysis, TG/DTG, density, FTIR, DRX, SEM and surface area analysis by the N2 adsorption and desorption method. Chemical reactivity of the atrazine molecule was investigated using DFT-based reactivity descriptors. For the kinetic profile and mechanism proposal, rate equations of pseudo-first-order, pseudo-second-order and intraparticle diffusion were considered. Activated carbons showed a typical amorphous structure, with an increase in the porous cavity after chemical activation process. Surface areas of 951–1002.5 m2 g−1 were obtained after activation with pores in the range of 1.70–2.67 nm. Activated carbons showed a high affinity with atrazine with a 90–98% removal percentage. The quantum chemical parameters calculated were the energy of the HOMO (EH = −6.4649) and LUMO (EL = −0.4558) orbitals, global chemical hardness (η = 3.0045), chemical potential (μ = 3.4603) and the global electrophilicity index (ɷ = 1.9926). In the kinetic study, the pseudo-second-order model was more predictive in adsorption tests. These results suggest that macauba endocarp activated carbon is efficient in atrazine removal, in addition to being a strategy for using agro-industrial waste.