Innovative use of CaO in combination with amino acid salt to convert CO2 as CaCO3 nanoparticles under mild pH and low temperature

The increasing demand for sustainable CO₂ management has driven the development of innovative methods that can convert point source CO₂ into value-added products. In this study, CaO in combination with amino acid salt was used to convert CO₂ into CaCO₃ nanoparticles. Different from the conventional method where CO₂ diffusion presents a major challenge in reacting with CaO to form CaCO₃, amino acid salt solvent was applied to absorb CO₂ first and then rapidly reacted with CaO to form CaCO₃ nanoparticles (∼50 nm) at a low temperature (e.g., 60 °C). Our experiments showed that at a glycine (Gly)/NaOH ratio of 2:1 or 3:1, the solution pH values during the CO₂ absorption and conversion were about 8–9 at 60 °C, while at a ratio of 1:1, the solution pH values were about 9–11; without Gly, the solution pH values were about 12. Gly-optimized solvent substantially reduced corrosion risk to reactors. In addition, the use of amino acid (i.e., Gly) led to much smaller CaCO₃ particles, distinctly different chemical phases, and fundamentally different chemical reactions. Moreover, in the presence of Gly, the solution pH was completely reversed and the solution was regenerated for cyclic use when CaO was added. The solvent was recyclable and reusable, highlighting the cost-effectiveness and sustainability of this approach. The Gly-modulated CaCO₃ nanoparticles may have significant potential for industrial applications in the biomedicine, construction, plastics, and rubber industries.