Transformation of Polycyclic Aromatic Hydrocarbons and Formation of Environmentally Persistent Free Radicals on Modified Montmorillonite: The Role of Surface Metal Ions and Polycyclic Aromatic Hydrocarbon Molecular Properties

Abstract

This paper presents the transformation of PAHs (phenanthrene, anthracene, benzo[a]anthracene, pyrene, and benzo[a]pyrene) on montmorillonite clays that are modified by transition-metal ions [Fe(III), Cu(II), Ni(II), Co(II), or Zn(II)] at room temperature (∼23 °C). The decay of these PAHs follows first-order kinetics, and the dependence of the observed rate constants ( k, day) on the presence of metal ions follows the order Fe(III) > Cu(II) > Ni(II) > Co(II) > Zn(II). The values of k show reasonable linear relationships with the oxidation potentials of the PAHs and the redox potentials of the metal ions. Notably, transformation of these PAHs results in the formation of environmentally persistent free radicals (EPFRs), which are of major concern due to their adverse effects on human health. The potential energy surface (PES) calculations using density functional theory were performed to understand the trends in k and the plausible mechanisms for radical formation from the PAHs on modified clays. The yields and stability of these EPFRs from anthracene and benzo[a]pyrene on clay surfaces varies with both the parent PAH and the metal ion. The results demonstrated the potential role of metals in the formation and fate of PAH-induced EPFR at co-contaminated sites.

Formation of environmentally persistent free radicals and reactive oxygen species during the thermal treatment of soils contaminated by polycyclic aromatic hydrocarbons

“…These values are typical of free organic radicals. All spectra are consistent with the characteristics of benzo[a]pyrene-EPFR (Jia et al 2018). According to previous studies, free radicals with g-factor lower than 2.0030 are considered as carbon-centered radicals; the g-factor of oxygen-centered radicals is greater than 2.0040; and free radicals with g-factors in the range of 2.0030-2.0040 are mixed radicals of carbon-and oxygencentered radicals (Zhu et al 2019).…”

“…The preparation of benzo[a]pyrene-contaminated soils was previously described (Jia et al 2018). Briefly, 1 g of soil sample was mixed with 1 mL of acetone solution containing 500 mg L −1 of benzo[a]pyrene.…”

“…The residual concentration of benzo[a]pyrene in soils after thermal treatment was quantified by high-performance liquid chromatography (HPLC, Thermo Fisher Scientific U3000), as described previously by Jia et al (2018), and the specific methods are provided in Text S2.…”

High contribution of hydrocarbon transformation during the removal of polycyclic aromatic hydrocarbons from soils, humin and clay by thermal treatment at 100–200 °C

“…Benzo [a]pyrene-spiked soil samples were prepared with previously described methods (Jia et al 2018;Zhao et al 2017). Samples included three soils: bauxite soil, fluvo-aquic soil and chernozem soil, and pure components: montmorillonite, humic acid and quartz sands.…”

Assessing the effect on the generation of environmentally persistent free radicals in hydrothermal carbonization of sewage sludge

“…Previous studies suggested that the g -factors less than 2.00300 were typical for (C-centered) free radicals 23,24 . Oxygen-centered (O-centered) free radicals usually possess the g -factor larger than 2.00400, such as semiquinone or phenoxyl radicals 25,26 . And radical signals with g -factors of 2.00300–2.00400 are attributed to a combination of the C-centered and O-centered EPFRs 26 .…”