Heterogeneous ozonation kinetics of 4-phenoxyphenol in the presence of photosensitizer

Abstract

Abstract. In this work we have quantitatively measured the degradation of 4-phenoxyphenol adsorbed on silica particles following oxidative processing by gas-phase ozone. This was performed under dark conditions and in the presence of 4-carboxybenzophenone under simulated sunlight irradiation of the particles surface. At the mixing ratio of 60 ppb which corresponds to strongly polluted ozone areas, the first order of decay of 4-phenoxyphenol is k1=9.95×10−6 s−1. At a very high ozone mixing ratio of 6 ppm the first order rate constants for 4-phenoxyphenol degradation were the following: k1=2.86×10−5 s−1 under dark conditions and k1=5.58×10−5 s−1 in the presence of photosensitizer (4-carboxybenzophenone) under light illumination of the particles surface. In both cases, the experimental data follow the modified Langmuir-Hinshelwood equation for surface reactions. The Langmuir-Hinshelwood and Langmuir-Rideal mechanisms for bimolecular surface reactions are also discussed along with the experimental results. Most importantly, the quantities of the oligomers such as 2-(4-Phenoxyphenoxy)-4-phenoxyphenol and 4-[4-(4-Phenoxyphenoxy)phenoxy]phenol formed during the heterogeneous ozonolysis of adsorbed 4-phenoxyphenol were much higher under solar light irradiation of the surface in comparison to the dark conditions.

Could triplet-sensitised transformation of phenolic compounds represent a source of fulvic-like substances in natural waters?

“…Further irradiation of phenol dimers is then expected to produce higher oligomers, as recently proposed by Net and coworkers (2010). Several papers report on the possible formation of atmospheric HULIS upon photoinduced oligomerization of phenolic compounds (Net et al, 2010). Here we show that a similar process would produce compounds that could be classified as "M-like" fulvic material on the basis of their EEM spectra.…”

“…In particular, several papers advance the hypothesis that atmospheric HULIS might be formed upon photoinduced oligomerization of smaller molecules (see e.g. Net et al, 2010, andLiu et al, 2012).…”

The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges

“…Photosensitized processes of atmospheric relevance have been evidenced at the surface of aerosol proxies in laboratory, such as the photo-induced formation of HONO, 511 uptake of ozone, 512 or heterogeneous ozonolysis reactions. 513 More recently similar processes were also evidenced in the aerosol bulk, and shown to contribute to SOA growth via bulk radical reactions. 428,514 In these studies the organic photosensitizers used were humic acids, 511,514a benzophenone and benzoic acid-related compounds, [512][513][514] and imidazoles.…”

“…513 More recently similar processes were also evidenced in the aerosol bulk, and shown to contribute to SOA growth via bulk radical reactions. 428,514 In these studies the organic photosensitizers used were humic acids, 511,514a benzophenone and benzoic acid-related compounds, [512][513][514] and imidazoles. 428,514b While humic substances and their proxies, benzophenone and benzoic acid, might not be present in all aerosols, the fact that secondary products of simple precursors, such as imidazoles from glyoxal, can also act as a photosensitizer indicates that such processes could be more common in the atmosphere than previously thought, and might be a source for radicals both in the particulate and in the gas phase, which remains to be evaluated.…”

Alternative pathway for atmospheric particles growth

“…Isoprene was used as VOC and seed particles contained succinic acid and 4-(benzoyl)benzoic acid (10∶1 in weight), a model compound found in biomass burning (42-46) also known to behave as a photosensitizer (31,44,47,48). In the aerosol stopped-flow approach, the mass spectrum of the seed-isoprene mixture after irradiation shows new fragments formation at high m∕z values when the seed particles are exposed to 900 ppbv of isoprene (Fig.…”