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Water Structure Controls Carbonic Acid Formation in Adsorbed Water Films.

Authors :: Miller QRS
Ilton ES
Qafoku O
Dixon DA
Vasiliu M
Thompson CJ
Schaef HT
Rosso KM
Loring JS
Source :: The journal of physical chemistry letters [J Phys Chem Lett] 2018 Sep 06; Vol. 9 (17), pp. 4988-4994. Date of Electronic Publication: 2018 Aug 20.
Publication Year :: 2018
Abstract: Reaction pathways and kinetics in highly structured H <subscript>2</subscript> O adsorbed as Ångstrom to nanometer thick layers on mineral surfaces are distinct from those facilitated by bulk liquid water. We investigate the role of the interfacial H <subscript>2</subscript> O structure in the reaction of H <subscript>2</subscript> O and CO <subscript>2</subscript> to form carbonic acid (H <subscript>2</subscript> CO <subscript>3</subscript> ) in thin H <subscript>2</subscript> O films condensed onto silica nanoparticles from humidified supercritical CO <subscript>2</subscript> . Rates of carbonic acid formation are correlated with spectroscopic signatures of H <subscript>2</subscript> O structure using oxygen isotopic tracers and infrared spectroscopy. While carbonic acid virtually does not form in the supercritical phase, the silica surface catalyzes this reaction by concentrating H <subscript>2</subscript> O through adsorption at hydrophilic silanol groups. Within measurement uncertainty, we found no evidence that carbonic acid forms when exclusively ice-like structured H <subscript>2</subscript> O is detected at the silica surface. Instead, formation of H <subscript>2</subscript> C <superscript>18</superscript> O <superscript>16</superscript> O <subscript>2</subscript> from H <subscript>2</subscript> <superscript>18</superscript> O and C <superscript>16</superscript> O <subscript>2</subscript> was found to be linearly correlated with liquid-like structured H <subscript>2</subscript> O that formed on the ice-like layer.