Acidification of Reverse Micellar Nanodroplets by Atmospheric Pressure CO2

Water absorption of atmospheric carbon dioxide lowers the solution pH due to carbonic acid formation. Bulk water acidification by CO2 is well documented, but significantly less is known about its effect on water in confined spaces. Considering its prominence as a greenhouse gas, the importance of aerosols in acid rain, and CO2-buffering in cellular systems, surprisingly little information exists about the absorption of CO2 by nanosized water droplets. The fundamental interactions of CO2 with water, particularly in nanosized structures, may influence a wide range of processes in our technological society. Here results from experiments investigating the uptake of gaseous CO2 by water pools in reverse micelles are presented. Despite the small number of water molecules in each droplet, changes in vanadium probes within the water pools, measured using vanadium-51 NMR spectroscopy, indicate a significant drop in pH after CO2 introduction. Collectively, the pH-dependent vanadium probes show CO2 dissolves in the nanowater droplets, causing the reverse micelle acidity to increase.