Engineering Amine-Containing Adsorbents for Efficient Carbon Dioxide Capture in Closed-Circuit Escape Respirators

In emergencies involving oxygen deficiency or exposure to toxic gases, closed-circuit escape respirators (CCERs) provide prompt and reliable respiratory protection, enabling safe escape from hazardous environments. These devices utilize a self-contained system that recycles exhaled breath by scrubbing CO₂ and replenishing O₂. CCERs require efficient CO₂ adsorbents, as excessive CO₂ accumulation from exhalation can lead to hypercapnia, causing dizziness, confusion, or even loss of consciousness. This study demonstrates that 1,2-epoxybutane-functionalized polyethylenimine supported on gamma alumina (EB-PEI/γ-Al₂O₃) is a very promising CO₂ adsorbent for CCERs, significantly outperforming the conventionally used soda lime. By controlling 1,2-epoxybutane functionalization, the heat of CO₂ adsorption can be precisely tuned, enabling the adsorbent to efficiently capture CO₂ from exhaled breath (5% CO₂ and 3% H₂O) while minimally adsorbing CO₂ from ambient air (400 ppm of CO₂ and 1.5% H₂O). This desirable CO₂ adsorption window allows the CCER device to be stored long-term under ambient conditions without cumbersome airtight packaging and enables the CO₂-saturated adsorbent to be regenerated through simple air exposure at room temperature. The adsorbent also exhibits remarkably faster CO₂ adsorption kinetics and generates less heat and moisture compared to soda lime, thereby enhancing user comfort and safety.