Experimental and Theoretical Investigation on the Catalytic Generation of Environmentally Persistent Free Radicals from Benzene

Abstract

Environmentally persistent free radicals (EPFRs) are toxic products deriving from incomplete combustion and are able to generate DNA damage and pulmonary dysfunction. They are formed on particulate matter through interaction with aromatic hydrocarbons, catalyzed by transition metal oxides, and produce reactive oxygen species (ROS) in aquatic media. The processes are already described for substituted aromatic molecules, for example, phenol, but not for unsubstituted aromatic systems, such as benzene. This Article reports on the reaction of benzene with molecular oxygen in the presence of CuxO/SiO2, suggesting a mechanism based on cluster and periodic computational models. The activation of O2 by interaction with silica coordinated Cu(I) centers leads to a peroxy species that yields the phenoxy radical upon reaction with benzene. Dissociation of OH• radical eventually allows for the recovery of the catalyst. The experimental characterization of the CuxO/SiO2 catalyst regarded morphology, crystal structure, copper electronic state, and crystal field around Cu(II). Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of phenoxy radical entrapped in the catalyst upon reaction between benzene and CuxO/SiO2. Moreover, EPR investigation of ROS in aqueous solution evidenced the generation of OH• radicals by benzene-contacted CuxO/SiO2. All of the experimental results nicely fit the outcomes of the computational models

Ab initio Study of Anchoring Groups for CuGaO2 Delafossite-Based p-Type Dye Sensitized Solar Cells

“…To describe the strong-correlated nature of Cu d electrons we applied the rotationally invariant DFT+U approach of Dudarev (Dudarev et al, 1998) as implemented in VASP (Rohrbach et al, 2003). As in previous works on Cu(I)-containing oxides, we applied an average U-J effective value of 6 eV on Cu d electrons (Isseroff and Carter, 2012; D'Arienzo et al, 2017; Schiavo et al, 2018). SCF energy convergence threshold was set to 10 −5 eV, and for minimum-energy structural optimizations the total forces on each atom were set to be all below 0.05 eV·Å −1 .…”

Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants

“…67,68 In neonatal rodents that were exposed to EPFRs, their airway epithelial cells transform into mesenchymal cells, which increases the risk of asthma. 67,68…”

“…68 DFT calculation suggests that the benzene ring donates 0.5 e − to the O atom on the metal oxide surface. 68 In the initial step of formation, O 2 activates the Cu(II)O, which forms an epoxide-like structure with an energy of adsorption of 23.9 kcal/mol. 68 Then, benzene physically interacts with the activated surface, in which the C atom on benzene bonds with the surface O atom on Cu(II)O.…”

“…68 In the initial step of formation, O 2 activates the Cu(II)O, which forms an epoxide-like structure with an energy of adsorption of 23.9 kcal/mol. 68 Then, benzene physically interacts with the activated surface, in which the C atom on benzene bonds with the surface O atom on Cu(II)O. 68 Abstraction (transfer) of H atom from the benzene ring forms a phenolate species, and electron transfer forms a phenoxyl radical.…”

Environmentally persistent free radicals in PM2.5: a review

“…This mechanism also applies to the formation of EPFRs on a hematite-silica surface under ambient conditions using ultraviolet (UV) light irradiation [25]. However, it can neither fully explain the formation of EPFRs from unsubstituted aromatics such as benzene [26] nor the reversed electron transfer from ZnO surfaces to phenols [27]. To solve these problems, Vejerano et al proposed a new formation mechanism of EPFRs on the surfaces of combustion or thermal treatment produced engineering nanomaterials (ENMs) not necessarily supported on micron-sized silica particles or with the presence of transition metals [28].…”