Adsorção do desregulador endócrino 4-octilfenol por óxido de grafeno

Abstract

Among the endocrine disrupting (ED), alkylphenols have wide application, have potential adverse effects on human health and the environment and have already been detected in several environmental matrices. 4-octylphenol (OP) is one of the main by-products of the degradation of non-ionic surfactants from polyethoxylated alkylphenols and has been investigated for having strong chemical stability and being difficult to biodegrade. OP was considered as a persistent toxic chemical contaminant of special concern by the United Nations Environment Programme (UNEP), of high bioaccumulative capacity by the United States Environmental Protection Agency (USEPA) and as a hazardous substance, in Directive 39/2013 of the European Union. Adsorption is an effective water treatment method for ED removal, considering technical and economic aspects. In this perspective, the present research aimed to analyze the process of adsorption in aqueous solution of OP by graphene oxide (GO) in bench scale. The central composite design (CCD) was used to analyze the adsorption through four factors: adsorbate concentration (ADSOP), adsorbent concentration (ADSGO), contact time (CT) and pH. The results helped in the investigation of the adsorption capacity, adsorbate removal, adsorption kinetics – pseudo-first order (PFO), pseudo-second order (PSO), Elovich equation and intraparticle diffusion (IPD) – and equilibrium conditions – Langmuir, Freundlich and Redlich-Peterson – through mathematical models. The results show the maximum adsorption capacity of 158,92 mg∙g-1 (ADSOP of 120 mg∙L-1; ADSGO of 0,2 g∙L-1; CT of 90 min and pH 2) and the removal of adsorbent ranged from 74,58 to 83,75% under all conditions tested (ADSOP from 100 to 120 mg∙L-1; ADSGO from 0,2 to 3,4 g∙L-1; CT from 15 to 90 min and pH from 2 to 10). Regarding kinetics, the Elovich equation was the one that best fitted the experimental data. The IPD indicated that the adsorptive process happened intraparticle and in the boundary layer. In the isotherms, the Redlich-Peterson model showed better fit to the data. The predominant mechanism of adsorption of OP by GO was chemissorption. Finally, the study showed that GO can be used in the adsorption process for the removal of OP in aqueous solution and that the use in a wide range of pH and contact times without significant loss of efficiency, indicates positive aspects in the operational issues in water treatment plants.