Photoinduced Oxidation Reactions at the Air–Water Interface

Abstract

Chemistry on water is a fascinating area of research. The surface of water and the interfaces between water and air or hydrophobic media represent asymmetric environments with unique properties that lead to unexpected solvation effects on chemical and photochemical processes. Indeed, the features of interfacial reactions differ, often drastically, from those of bulk-phase reactions. In this Perspective, we focus on photoinduced oxidation reactions, which have attracted enormous interest in recent years because of their implications in many areas of chemistry, including atmospheric and environmental chemistry, biology, electrochemistry, and solar energy conversion. We have chosen a few representative examples of photoinduced oxidation reactions to focus on in this Perspective. Although most of these examples are taken from the field of atmospheric chemistry, they were selected because of their broad relevance to other areas. First, we outline a series of processes whose photochemistry generates hydroxyl radicals. These OH precursors include reactive oxygen species, reactive nitrogen species, and sulfur dioxide. Second, we discuss processes involving the photooxidation of organic species, either directly or via photosensitization. The photochemistry of pyruvic acid and fatty acid, two examples that demonstrate the complexity and versatility of this kind of chemistry, is described. Finally, we discuss the physicochemical factors that can be invoked to explain the kinetics and thermodynamics of photoinduced oxidation reactions at aqueous interfaces and analyze a number of challenges that need to be addressed in future studies.

Tight electrostatic regulation of the OH production rate from the photolysis of hydrogen peroxide adsorbed on surfaces

“…The significance of heterogeneous photochemistry has been highlighted by different authors, in particular in relation to the study of organic matter oxidation in the atmosphere (23)(24)(25)(26)(27)(28). Many processes appear to be accelerated compared to the same processes in the gas phase or in bulk solution.…”

“…Many processes appear to be accelerated compared to the same processes in the gas phase or in bulk solution. Absorption energy shifts, band broadening, surface accumulation, or the diminution of solvent-cage effects operating in bulk solution are plausible causes for the photochemical rate increase, although the mechanisms of surface-enhanced photochemistry remain to be fully understood (23,26,29).…”

Photosensitization mechanisms at the air–water interface of aqueous aerosols

“…Photosensitization appears to be particularly meaningful at surfaces and interfaces. [5][6][7][8][9] The study of photochemical processes at aqueous interfaces has deserved numerous recent theoretical and experimental studies because the solvation effects at the interface appear to enhance the reactivity, compared to gas phase or bulk water solution (for recent reviews and perspectives, see for instance Ref 8,[10][11][12][13] ). This heterogeneous chemistry has great atmospheric and environmental significance, 3,[14][15][16] but presents also strong implications for the development of efficient technologies in photocatalysis.…”

Amplification of light within aerosol particles accelerates in-particle photochemistry

“…Photochemical reactions can also be promoted at the surface of atmospheric aerosol particles (14)(15)(16). It has been reported that interface effects and surface charging can cause acceleration of chemical reactions in microdroplets and nanodroplets (14,(17)(18)(19)(20), observations that have especially sparked interest in the use of microdroplets as new powerful reactors for chemical synthesis (15,16).…”