Adsorption and catalytic degradation of preservative parabens by graphene-family nanomaterials

Abstract

Parabens pose increasing threats to human health due to endocrine disruption activity. Adsorption and degradation of parabens by three types of graphene-family nanomaterials (GFNs) were therefore investigated. For a given paraben, the maximum adsorption capacities (Q0) followed the order of reduced graphene oxide (RGO) > multilayered graphene (MG) > graphene oxide (GO); for a given GFN, Q0 followed the order of butylparaben (BuP) > propylparaben (PrP) > ethylparaben (EtP) > methylparaben (MeP), dominated by hydrophobic interaction. MeP removal by all the three GFNs was highly enhanced (0.55–4.37 times) with the assistance of H2O2 due to additional catalytic degradation process, and MG showed the highest removal enhancement. ∙OH was confirmed as the dominant radicals responsible for parabens degradation. For MG and RGO, the metal impurities (Fe, Cu, Mn, and Co) initiated Fenton-like reaction with H2O2 to generate ∙OH. GO contained oxygen-centered free radicals, which were responsible for ∙OH formation via transferring electron to H2O2. Four degradation byproducts of MeP were identified, including oxalic, propanedioic, fumaric, and 2,5-dihydroxybenzoic acids. Combined with density function theory calculations, the degradation sites and pathways were identified and confirmed. These findings provide useful information on mechanistic understanding towards the adsorption and degradation of parabens by GFNs.