Recyclable carbon nanotube/silicone oil emulsion with NaOH aqueous solution for indoor CO₂ capture

Emulsion solvents (ES), which are liquid absorbent-based CO₂ capture materials, are developed as simple and expandable droplets to control CO₂ capture performance. An aqueous NaOH solution, which is a chemical absorbent, is encapsulated by functionalized carbon nanotubes (CNTs) to form a solid adsorbent by enhancing the high lipophilicity and high-viscosity silicone oil. The ratio of each component controls the CO₂ capture performance of the solvent. It is shown that droplets of NaOH aqueous solution formed in fine sizes improve the efficiency of the chemical reaction capacity of NaOH and CO₂, and thus, even when crystallization occurs, they can be used in a stationary environment, and NaOH can be used at a high concentration. It is found that the optimum concentration of CNTs required to minimize the size of the emulsion is 0.075 wt%, while the CO₂ capture capacity is 2.23 mmol_CO2 g⁻¹_ES-NaOH at a pure CO₂ concentration and 1.31 mmol_CO2 g⁻¹_ES-NaOH at a low CO₂ concentration (2000 ppm, 50% relative humidity). The oil phase can be recycled continuously by separating the crystallized aqueous phase after the CO₂ capture. These results demonstrate that chemical absorbents with excellent CO₂ capture performance can be used safely and for a long time in order to reduce indoor CO₂, and the CO₂ capture performance can be flexibly controlled.