Parabens Adsorption onto Activated Carbon: Relation with Chemical and Structural Properties

Abstract

Parabens (alkyl-p-hidroxybenzoates) are antimicrobial preservatives used in personal care products, classified as an endocrine disruptor, so they are considered emerging contaminants. A raw version of activated carbons obtained from African palm shell (Elaeis guineensis) modified chemically by impregnation with salts of CaCl2 (GC2), MgCl2 (GM2) and Cu(NO3)2 (GCu2) at 2% wt/v and carbonized in CO2 atmosphere at 1173 K was prepared. The process of adsorption of methyl (MePB) and ethylparaben (EtPB) from aqueous solution on the activated carbons at 18 °C was studied and related to the interactions between the adsorbate and the adsorbent, which can be quantified through the determination of immersion enthalpies in aqueous solutions of corresponding paraben, showing the lowest-value carbon GM2, which has a surface area of 608 m2 × g−1, while the highest values correspond to the activated carbon GCu2, with a surface area of 896 m2 × g−1 and the highest content of surface acid sites (0.42 mmol × g−1), such as lactonic and phenolic compounds, which indicates that the adsorbate–adsorbent interactions are favored by the presence of these, with interaction enthalpies that vary between 5.72 and 51.95 J × g−1 for MePB adsorption and 1.24 and 52.38 J × g−1 for EtPB adsorption showing that the process is endothermic.