Substituted Benzoxazole and Catechol Cocrystals as an Adsorbent for CO₂ Capture: Synthesis and Mechanistic Studies

We report the synthesis of cocrystals of a substituted benzoxazole and catechol from a primary amine and 3,5-di-<i>tert</i>-butylbenzoquinone. Fourier transform infrared and NMR spectroscopy studies revealed that cocrystals <b>2</b> could be synthesized in excellent yield from <b>1</b> and 3,5-di-<i>tert</i>-butylbenzoquinone. Introduction of an amine into the cocrystal structure enhanced the CO₂ adsorption capacity of the cocrystals at room temperature from 15.69 to 44.21 mg/g. Our results indicated the ability to use cocrystals for CO₂ capture and to easily modify them to enhance their CO₂ adsorption capacity

Harvesting CaCO₃ Polymorphs from In Situ CO₂ Capture Process

The in situ sequestration of CO₂ using alkanolamine and organometallic calcium (OMC) offers an ecofriendly method for synthesizing a diverse range of calcite, vaterite, and aragonite polymorphs of CaCO₃. Aqueous <i>N</i>-methyldiethanolamine (MDEA) has high CO₂ loading capacity with low regeneration energy, but rate of CO₂ absorption was found to be slow. The driving force for the binding between CO₂ and MDEA could be enhanced by the presence of bovine carbonic anhydrase (bCA). The absorbed CO₂ was converted to stable carbonates through the addition of an OMC. The bCA enzyme both accelerated the CO₂ absorption and mineralization in the amine–CO₂–OMC system and improved the catalytic efficiency to 1.07 × 10⁴ M^–1 s^–1. The enthalpy of in situ mineralization, the mechanism underlying the CO₂ absorption process, and the formation of an aggregated composition of CaCO₃ were examined using calorimetric, NMR, and X-ray diffraction techniques, respectively. The crystal formation depended crucially on the mineralization process involving the anions of the OMC precursors. The CaO-based sorbents derived from the CaCO₃ polymorphs shows good CO₂ capture capacity on combustion process, and the consecutive re-formation–regeneration cycles of the CaO sorbents followed the trend aragonite > vaterite > calcite. Hence, the MDEA–OMC–bCA system offers a promising method for transitioning between CaCO₃ polymorphs