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 modify 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 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-, 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.