Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone

Abstract

The reaction of ozone with sea-salt derived bromide is relevant for marine boundary layer atmospheric chemistry. The oxidation of bromide by ozone is enhanced at aqueous interfaces. Ocean surface water and sea spray aerosol are enriched in organic compounds, which may also have a significant effect on this reaction at the interface. Here, we assess the surface propensity of cationic tetrabutylammonium at the aqueous liquid–vapor interface by liquid microjet X-ray photoelectron spectroscopy (XPS) and the effect of this surfactant on ozone uptake to aqueous bromide solutions. The results clearly indicate that the positively charged nitrogen group in tetrabutylammonium (TBA), along with its surface activity, leads to an enhanced interfacial concentration of both bromide and the bromide ozonide reaction intermediate. In parallel, off-line kinetic experiments for the same system demonstrate a strongly enhanced ozone loss rate in the presence of TBA, which is attributed to an enhanced surface reaction rate. We used liquid jet XPS to obtain detailed chemical composition information from the aqueous-solution–vapor interface of mixed aqueous solutions containing bromide or bromide and chloride with and without TBA surfactant. Core level spectra of Br 3d, C 1s, Cl 2p, N 1s, and O 1s were used for this comparison. A model was developed to account for the attenuation of photoelectrons by the carbon-rich layer established by the TBA surfactant. We observed that the interfacial density of bromide is increased by an order of magnitude in solutions with TBA. The salting-out of TBA in the presence of 0.55 M sodium chloride is apparent. The increased interfacial bromide density can be rationalized by the association constants for bromide and chloride to form ion-pairs with TBA. Still, the interfacial reactivity is not increasing simply proportionally with the increasing interfacial bromide concentration in response to the presence of TBA. The steady state concentration of the bromide ozonide intermediate increases by a smaller degree, and the lifetime of the intermediate is 1 order of magnitude longer in the presence of TBA. Thus, the influence of cationic surfactants on the reactivity of bromide depends on the details of the complex environment at the interface.

Emerging investigator series: surfactants, films, and coatings on atmospheric aerosol particles: a review

“…A similar stabilization was seen by Gord et al 363 for N 2 O 5 to Br 2 conversion and by Faust et al 364 for Cl 2 to Br 2 conversion, both on tetrahexylammonium-coated glycerol, and to a lesser extent for Cl 2 to Br 2 conversion on glycerol coated with the zwitterionic phospholipid dihexanoylphosphotidylcholine (DHPC). 363 Chen et al 365 also saw that tetrabutylammonium ions enhanced the reactivity of gas-phase ozone with bromide ions in aqueous solutions, not only because the surfactant draws more Br À to the surface, but also because the surfactant stabilizes the bromide ozonide intermediate, increasing its lifetime by an order of magnitude. In these cases, the quaternary ammonium surfactants brought gas-phase and solution-phase reactants together in close proximity and thereby promoted the multiphase reactions.…”

Mario Molina Memorial Special Issue

“…Photosensitizer chemistry involving light-absorbing dissolved organic matter in seawater is implicated in HONO formation and the release of VOCs . The presence of surface-active organics can impact the oxidation of bromide by ozone . Heterogeneous reactions involving chloride can change the speciation of gaseous oxidized mercury …”

“…34 The presence of surface-active organics can impact the oxidation of bromide by ozone. 35 Heterogeneous reactions involving chloride can change the speciation of gaseous oxidized mercury. 36 Marine aerosols are among the most abundant types of particulate matter globally, and therefore, they play a key role in the climate.…”

The surface composition of amino acid – halide salt solutions is pH-dependent

“…This correlation has implications for chemical reactions at the particle surface, which involve inorganic ions. Prominent examples for such a reaction are the production of Cl 2 from OH• gas and Cl − surf ace , 21 the ozone depletion through a reaction with iodide and bromide 22,23 or the reaction between N 2 O 5 (g) and Br − (aq). 24 The main concern of this work is to learn about the interactions at aqueous surfaces, and thus we used photoelectron spectroscopy (XPS) for our investigation.…”

“…This correlation has implications for chemical reactions at the particle surface, which involve inorganic ions. Prominent examples for such a reaction are the production of Cl 2 from and Cl surface − , 21 the ozone depletion through a reaction with iodide and bromide 22,23 or the reaction between N 2 O 5 (g) and Br − (aq). 24…”