Article pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX-XXX
Photooxidation of Aniline Derivatives Can Be Activated by Freezing Their Aqueous Solutions Pablo Corrochano,† Dana Nachtigallová,*,§ and Petr Klán*,†,‡ †
RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 62500 Brno, Czech Republic Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, 62500 Brno, Czech Republic § Institute of Organic Chemistry and Biochemistry, Flemingovo nam. 2, 16610 Prague, Czech Republic ‡
S Supporting Information *
ABSTRACT: A combined experimental and computational approach was used to investigate the spectroscopic properties of three different aniline derivatives (aniline, N,N-dimethylaniline, and N,N-diethylaniline) in aqueous solutions and at the air−ice interface in the temperature range of 243−298 K. The absorption and diffuse reflectance spectra of ice samples prepared by different techniques, such as slow or shock freezing of the aqueous solutions or vapor deposition on ice grains, exhibited unequivocal bathochromic shifts of 10−15 nm of the absorption maxima of anilines in frozen samples compared to those in liquid aqueous solutions. DFT and SCS-ADC(2) calculations showed that contaminant−contaminant and contaminant−ice interactions are responsible for these shifts. Finally, we demonstrate that irradiation of anilines in the presence of a hydrogen peroxide/O2 system by wavelengths that overlap only with the red-shifted absorption tails of anilines in frozen samples (while having a marginal overlap with their spectra in liquid solutions) can almost exclusively trigger a photochemical oxidation process. Mechanistic and environmental considerations are discussed.
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INTRODUCTION The phototransformation of organic compounds is an important degradation pathway naturally occurring in surface waters as well as in natural ice and snowpack in the cold regions.1,2 Organic molecules cannot be incorporated within the ice lattice but are trapped and concentrated at the air−ice (disordered or a quasi-liquid) interface region. 3,4 The physicochemical properties of ice impurities depend on their location, speciation and ice surface morphology.2,3 Many studies showed that snow and ice can play a specific role in heterogeneous surface (photo)chemistry, which can affect the composition of the overlying atmosphere or the aquatic environment.1,2 The incorporation of organic micropollutants into snow and ice can alter their absorption spectra due to specific substance− ice or substance−substance interactions,5−12 which do not necessarily coincide with those of the same substances in liquid water.6 Simple aromatic compounds, such as benzene,10,13 naphthalene11 or anisole,14 do not exhibit any significant spectral changes, whereas more complex aromatic molecules bearing polar amino or nitro substituents show considerable shifts at grain boundaries of ice.6 The spectroscopic analyses can give valuable information about the concentration, solvation,6 aggregation,5 conformational dynamics,15 dynamic cooperative hydration,16 acid−base properties,7 and mutual orientations in aggregates5,11 of these ice contaminants. In addition, computational simulation methods were used to study © XXXX American Chemical Society
the interactions of aromatic compounds with ice or within their molecular associates.10,11,13,14 Aromatic amines are common environmental pollutants because of industrial production of dyes, pigments, herbicides and pharmaceuticals.17 Their absorption spectra are limited to the far-UV region (
