Utilisation of CO2 as “Structure Modifier” of Inorganic Solids

Utilisation of CO₂ as a chemical reagent is challenging, due to the molecule's inherent chemical stability. However, CO₂ reacts promptly at high temperature (～1000 °C) with alkaline-earth oxides to form carbonates and such reactions are used towards capture and re-utilisation. In this work, this concept is extended and CO₂ is utilised as a reagent to modify the crystal structure of mixed-metal inorganic solids. Modification of the crystal structure is a “tool” used by materials scientists to tailor the physical property of solids. CO₂ gas was reacted with several isostructural mixed-metal oxides Sr₂CuO₃, Sr_1.8Ba_0.2CuO₃ and Ba₂PdO₃. These oxides are carefully selected to show anion vacancies in their crystal structure, to act as host sites for CO₂ molecules, leading to the formation of carbonate anions, (CO₃)^2?. The corresponding oxide carbonates were formed successfully and the favourable formation of SrCO₃ as secondary phase was minimised via an innovative, yet simple synthetic procedure involving alternating of CO₂ and air. We also derived a simple model to predict the kinetics of the reactions for the cuprates, using first-principles density functional theory and assimilating the reaction to a gas-surface process.