Effective capture of CO2 facilitates the resolution of intensified global warming. This paper describes a novel material design by capturing and storing CO2 as carbonic acid. 2,2,6,6-Tetramethylpiperidine (TP), a hindered secondary amine, lacks a nucleophilic attack ability as do tertiary amines. A polymer supporting TP as the pendant groups captured carbonic acid in water by introducing gaseous CO2. The TP ammonium bicarbonate produced insoluble complexes with poly(sodium 4-styrenesulfonate) (PSS) through their ion exchange. The reversibility of the complexation was dependent on the molecular weight of PSS. The complexes with a low-molecular-weight PSS were reversibly dissociated by introducing N2, whereas those with a high-molecular-weight PSS stored the carbonic acid in their tight structures. The PSS chain length also dominated the morphology of the complex aggregates. The short PSS produced linear and rigid aggregates with a ribbon-like morphology, while the long PSS provided a planar morphology of the aggregates. An amphiphilic diblock copolymer supporting TP produced micron-sized giant vesicles having TP on their shells. The vesicles were transformed into micelles by capturing carbonic acid in an aqueous methanol solution. This vesicles-to-micelles transformation was reversible, responding to alternative CO2/Ar introductions based on electroconductivity (EC), transmittance, and light scattering studies. Furthermore, CO2 capture-induced electrolytes were created using the tertiary diamines. The diamines captured carbonic acid in an aqueous solution to produce electrolytes through the formation of the diammonium carbonate followed by transformation into the bicarbonate. This electrolyte formation caused no viscosity increase, whereas the electrolytes with acetic acid or glutaric acid instead of carbonic acid increased the viscosity. The EC of the electrolytes was dependent on the diamine basicity and structure. The diamine bicarbonate was transformed into the carbonate by Ar introduction, however, the second introduction of CO2 caused an inverse transformation, suggesting the possibility of repeated use of the electrolytes. These findings indicated that the capture and storage of carbonic acid by the hindered secondary amine and tertiary diamines are helpful in preserving the marine ecosystem from ocean acidification and creating new materials composed of carbonic acid.

CO2 capture-based material design

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