Formation of phenoxy-type Environmental Persistent Free Radicals (EPFRs) from dissociative adsorption of phenol on Cu/Fe and their partial oxides

Abstract

The interplay of phenolic molecules with 3d transition metals, such as Fe and Cu, and their oxide surfaces, provide important fingerprints for environmental burdens associated with thermal recycling of e-waste and subsequent generation of notorious dioxins compounds and phenoxy-type Environmental Persistent Free Radicals (EPFRs). DRIFTS and EPR measurements established a strong interaction of the phenol molecule with transition metal oxides via synthesis of phenolic-and catecholic-type EPFRs intermediates. In this contribution, we comparatively examined the dissociative adsorption of a phenol molecule, as the simplest model for phenolic-type compounds, on Cu and Fe surfaces and their partially oxidized configurations through accurate density functional theory (DFT) studies. The underlying aim is to elucidate the specific underpinning mechanism forming phenoxy-or phenolate-type EFPRs. Simulated results show that, the phenol molecule undergoes fission of its hydroxyl's O-H bond via accessible activation energies. These values are lower by 46.5 -74.1% when compared with the analogous gas phase value. Physisorbed molecules of phenol incur very low binding energies in the range of -2.1 --5.5 over clean Cu/Fe and their oxides surfaces. Molecular attributes based on charge transfer and geometrical features are in accord with the very weak interaction in physisorbed states. Thermo-kinetic parameters established over the temperature region of 300 and 1000 K, exhibit a lower activation energy for scission of phenolic's O-H bonds over the oxide surfaces in reference to their pure surfaces (24.7 and 43.0 kcal mol -1 vs 38.4 and 47.0 kcal mol -1 ).

Environmentally persistent free radicals in PM2.5 from a typical Chinese industrial city during COVID-19 lockdown: The unexpected contamination level variation

“…The existence of oxide of Cu was proven to be beneficial for the EPFR generation ( Yang et al, 2017b ). Intriguingly, the results of computational simulation elucidated Cu could mediate the formation of oxygen-centered EPFRs ( Ahmed et al, 2020 ), which may explain the occurrence of the same type of EPFRs in this work. Hence, the higher concentration of Cu might promote the Cu-mediated secondary formation of EPFRs in PM 2.5 , resulting in their unreduced contamination level during city lockdown in Linfen.…”

Phenolic Compounds in the Built Environment

“…Phenolic common derivatives such as Bisphenol A (BPA), chlorophenols (CPs), and phenolic endocrine disrupting compounds (EDCs) are often listed at the top of lists of environmental pollutants. Phenolic compounds and their halogenated derivatives can also produce dioxin compounds [40]. Dioxins are notorious for their persistency in the environment and their high toxicity, so much so that they usually are at the top of "dirty dozen" lists.…”

Formation of Environmentally Persistent Free Radicals from the Irradiation of Polycyclic Aromatic Hydrocarbons

“…Incomplete combustion of organic materials, such as fuel and biomass, provides the main source of EPFRs. Previous studies have reported EPFR concentrations of 10 16 to 10 18 spins g –1 in various samples, including cigarette smoke, biochars, coal, electronic waste, residential and vehicle fuel, and industrial activity. ,− The organic substituents in these materials can also react during combustion and form a variety of fused, multi-ringed aromatic compounds known as polycyclic aromatic hydrocarbons (PAHs). ,,− The formation of PAHs has been previously explained by various reaction pathways, e.g., hydrogen abstraction acetylene addition, hydrogen abstraction vinylacetylene addition, and methyl addition cyclization. ,− These pathways involve free radical reactions, which can form other free radical molecules. Due to the aromaticity of the PAH present in combustion particles, the resulting free radicals become resonance-stabilized in the structure of the particles. ,,,,,,, Because PAHs are ubiquitous in combustion particles, PAHs and PAH-derived EPFRs can be transported into the body and lodged in the heart and lungs, contributing to chronic disease, cardiopulmonary dysfunction, and a decrease in life expectancy. ,,− …”