Accelerated carbon dioxide mineralization and polymorphic control facilitated by nonthermal plasma bubbles

Mineralization of carbon dioxide is of interest for developing net-negative carbon technologies that mimic natural carbon cycles by removing and sequestering atmospheric carbon dioxide (CO₂). This study investigates plasma-liquid interactions (PLI) and the impact of modifying electron temperatures of nonthermal CO₂ plasmas to influence the nucleation and growth kinetics of calcium carbonate (CaCO₃). Through optimization of plasma discharge parameters, we show that plasma-liquid interactions can direct the formation of a pure vaterite phase of CaCO₃ over the more thermodynamically stable calcite phase under certain conditions. By varying the mole fraction of the discharge between a mixture of CO₂/Ar in the plasma bubbles, we show that increasing electron temperature enhances CO₂ capture, nucleation rate, and CaCO₃ yields. Increasing the electron temperature of the plasma by varying the Ar mole fraction in the flow increases CO₂ conversion nearly tenfold compared to pure CO₂ yet increases the competitive formation of carbon monoxide through CO₂ dissociation. When average electron energies were ∼1 eV, the greatest selectivity toward CaCO₃ was observed. Our results support a mechanistic picture in which CO₂ mineralization is driven concurrently through gas-phase vibrational excitation of CO₂ and at the plasma-liquid interface by generating reactive hydroxyl species from plasma-activated water splitting. These plasma-generated species react to produce HCO₃^-, which is the rate-determining step in CO₂ mineralization. By demonstrating accelerated mineralization kinetics and polymorphic control of solid carbonate formation at plasma-liquid interfaces, this study could have broader relevance for engineering net-negative carbon sequestration technologies into solid forms for long-duration storage.