Spontaneous Iodide Activation at the Air-Water Interface of Aqueous Droplets

We present experimental evidence that atomic and molecular iodine, I and I2, are produced spontaneously in the dark at the air-water interface of iodide-containing droplets without any added catalysts, oxidants, or irradiation. Specifically, we observe I-3( -) formation within droplets, and I-2 emission into the gas phase from NaI-containing droplets over a range of droplet sizes. The formation of both products is enhanced in the presence of electron scavengers, either in the gas phase or in solution, and it clearly follows a Langmuir-Hinshelwood mechanism, suggesting an interfacial process. These observations are consistent with iodide oxidation at the interface, possibly initiated by the strong intrinsic electric field present there, followed by well-known solution-phase reactions of the iodine atom. This interfacial chemistry could be important in many contexts, including atmospheric aerosols.

Automated summary

Experimental evidence shows that I and I2 can be spontaneously generated at the air-water interface of iodide-containing droplets without the need for any catalysts, oxidants, or irradiation. This interfacial chemistry process, possibly initiated by the intrinsic electric field present at the interface, could be significant in various contexts, including atmospheric aerosols.