Innovative dual-function system for efficient CO2 absorption and utilization: Local humidity swing fabric and microalgae-embedded hydrogel

In this study, we explored the use of local humidity swing (LHS) adsorption technology for carbon dioxide (CO2) capture from air, leveraging its low energy consumption and cost-effectiveness. By employing a coating technique, we immobilized ion exchange resin (IER) particles on fabrics with different hydrophilicities. The coating, consisting of silk fibroin (silk) and glycerol, formed a thin membrane on the fabric surface, effectively immobilizing the IER particles. The results revealed that hydrophobic polyester fabric with an initial silk concentration of 2 wt% (2 %SF/Gly@IER-PF) exhibited superior CO2 adsorption capacity (11.07 ml/g at 10 % relative humidity) and stability at varying humidities (10–90 %) compared to the hydrophilic cotton fabric. By covering the 2 %SF/Gly@IER-PF with a hydrophilic, highly water-absorbing non-woven fabric, one-way moisture transfer between the two types of fabrics was made, significantly affecting the water content and the release of adsorbed CO2 within the SF/Gly@IER-PF, and CO2 adsorption/desorption cycles could be achieved by detaching and attaching the water-absorbing fabric from the 2 %SF/Gly@IER-PF. The SF/Gly@IER-PF-based LHS system was combined with a silk/alginate composite hydrogel containing live microalgae, forming a dual-function CO2 fixation system. The functionalized fabric efficiently captured CO2 from the air, which was subsequently utilized by the gel-immobilized microalgae. As a result, the microalgae showed a higher proliferation rate compared to the control hydrogel system without the attachment of SF/Gly@IER-PF. This demonstrates the potential application of the dual-function system in effectively reducing CO2 levels from the air.