Photochlorination of Polycyclic Aromatic Hydrocarbons in Acidic Brine Solution

Abstract

The potential for the formation of chlorinated polycyclic aromatic hydrocarbons via photochlorination of PAHs has been investigated in milli-Q water/synthetic water containing NaCl and PAHs with either UV or visible light. The photochlorination of pyrene occurred under acidic conditions in the presence of both UV and visible light, resulting in 1-chloropyrene as the main product. Benzo[a]pyrene yielded 6-chlorobenzo[a]pyrene following visible light irradiation; however the reaction was dependent upon solution pH. The photochlorination of PAHs was proposed to proceed via a consecutive reaction model. The rate constants associated with the photochlorination and photodecay processes were determined with the observed and theoretical values displaying similar trends, whereas the observed values were approximately 50-1000 times lower than the theoretical values. The lower observed values could be due to undergo photodecay rather than photochlorination of PAHs. Therefore, as photochlorination of PAHs appears to be significantly affected by solution pH, this information may allow for minimizing the impact on the environment.

Self-sensitized photochlorination of benzo[a]pyrene in saline water under simulated solar light irradiation

“…2A, an increase in the pH from 2.2 to 10.3 led to a decrease in the degradation rate of BaP and an increase in the amount of 6-ClBaP formed. Formation of 6-ClBaP at pH 4.3 was different from the previous results (Ohura and Miwa, 2016), the lower Cl − concentration (1.28 mM) and different light source (mercury lamp) used in that study may responsible for the absence of 6-ClBaP. To better understand the formation mechanism of 6-ClBaP in alkaline solution, a high pH of 10.3 was used in subsequent experiments.…”

“…The amount of chlorinated product formed increased with decreasing pH because the reaction rates between the chlorine radicals and various organic compounds increased at lower pH values (Remucal and Manley, 2016). Ohura and Miwa reported the formation of 6-ClBaP at pH 2 and 3 but not at pH 4 and 5 in Cl − -containing solutions under visible light irradiation (Ohura and Miwa, 2016). They proposed that the excited states of BaP initiated the generation of superoxide and hydroxyl radicals (O 2…”

“…Due to its multiple aromatic ring system, BaP can absorb sunlight in the visible and ultraviolet regions of the solar spectrum (290-900 nm), resulting in its structure modification (Teranishi et al, 2010). Photochlorination of BaP in acid brine solutions was observed before, and chloride radicals initiated by excited states of BaP were proposed to involve in the chlorination mechanism (Ohura and Miwa, 2016). This mechanism is only suitable for acid brine solutions.…”

Oxidation of 1-chloropyrene by human CYP1 family and CYP2A subfamily cytochrome P450 enzymes: catalytic roles of two CYP1B1 and five CYP2A13 allelic variants

“…1-Chloropyrene and 6-chlorobenzo[ a ]pyrene are the most commonly occurring chlorinated PAHs in the environment, and approximately 15% of chlorinated PAHs are in the nanoparticle phase (<0.1 µm) in the air (Ohura et al, 2008; Kakimoto et al, 2014; Kakimoto et al, 2017;Ma et al, 2013). Ohura et al (2016) reported that photochlorination of pyrene under acidic conditions in the presence of both UV and visible light causes formation of 1-chloropyrene as the main product, whereas 6-chlorobenzo[ a ]pyrene is formed through irradiation of benzo[ a ]pyrene by visible light.…”

Cation Radical Induced Photochlorination of Naphthalene in Saline Water under UV Light Irradiation

“…A multitude of substances present in natural water can affect the photochlorination of PAHs. Some substances can either facilitate or hinder the formation of active intermediates like Cl·, − 1 PAH*, 3 PAH*, , and PAH + · . Consequently, examining the impact of environmental factors on the photochlorination of PAHs is of great significance.…”