Spectroscopic characterization of phenol in frozen aqueous solution and on the ice surface

Phenol is one of the omnipresent pollutants in the environment, frequently detected in ambient air, water, soil, snow, and ice. Due to its low aqueous reactivity and inability to undergo direct photolysis under typical tropospheric conditions, phenol can be widely distributed and accumulated in the environment for an extended period of time. However, the reactivity of phenol can be influenced by a number of factors, including temperature, pH, and phase transitions. The present study examines the impact of the ice matrix and ice surface on the photophysical properties of phenol via UV-VIS, fluorescence, and Raman spectroscopies. We demonstrate that the freezing of an aqueous solution results in the vitrification or crystallization of the freeze-concentrated solution. The latter case is accompanied by a bathochromic shift of the absorption spectrum above 290 nm. The most pronounced red-shifts were obtained for deprotonated and crystalline samples, which suggests that direct photolysis under tropospheric conditions would be significantly enhanced in these cases. The study further demonstrates the difference in the molecular arrangement in freeze-concentrated solutions as compared to the surface of Ih ice.