Bio-inspired mineralization of CO2 into CaCO3: Single-step carbon capture and utilization with controlled crystallization

Abstract

CO2 mineralization which involves the reaction of CO2 with alkaline earth metal cations to form carbonates, is a promising pathway that could be crucial for combating global warming via long-term CO2 utilization and storage. However, due to the large abundance of natural calcium carbonate (CaCO3) and advanced milling techniques, micron-ranged CaCO3 is conventionally produced via the top-down method because it is more economically attractive than mineralization or precipitation unless particles with functional properties are generated so that a higher product value is achieved. In this study, inspired by the natural formation of nacre, which is produced naturally via controlled crystallization (using environmental CO2) in the marine environment, we produce CaCO3 particles with different morphologies via single-step CO2 capture and mineralization. We used a gas diffuser reaction setup to bubble CO2 in liquid media containing CO2 absorption promotor, water-soluble polymer, and surfactant as crystal growth modifiers, and Ca2+ to form functional CaCO3. First, different inorganic and organic CO2 absorption promoters and their combinations were investigated for their effectiveness on Ca2+ conversion to CaCO3. Ca2+ conversion and pH of the reaction system with various concentrations of CO2 absorption promoters were monitored every 5 min. Second, the effect of the polymer combined with different concentrations of surfactant on CaCO3 properties was studied. It was found that the combination of triethanolamine and ammonium hydroxide as absorption promotors results in 53.2% Ca2+ conversion into stable CaCO3 particles within 5 min of CO2 bubbling. Absorption promotors themselves could not regulate the particle shape; however, with increasing concentrations, smaller particles agglomerated to form bigger rhombohedral particles. Polymer and surfactant-mediated mineralization of CO2 produces spherical and hollow, stable calcite particles that could serve as dies, heavy metal adsorbents, supports to catalysts, functional composite fillers, etc.