In Situ Polymerization Electrospinning of Amine–Epoxy/Poly(vinyl alcohol) Nanofiber Webs for Direct CO₂ Capture from the Air

To achieve carbon neutrality by 2050, there is a growing need to actively capture carbon dioxide (CO₂) from the atmosphere. As a method to capture CO₂ directly from the atmosphere, direct air capture (DAC) is attracting attention and amine-based compounds have been extensively studied as CO₂ adsorbents. In this research, we developed thermosetting DAC nanofibers with excellent low-temperature desorption properties and good heat resistance by polymerizing an amine with epoxy. For the fabrication of epoxy-cross-linked amine nanofibers through the electrospinning process, poly(vinyl alcohol) (PVA) was added for the improvement of spinnability, and the direct spin-line heating was conducted for the in situ thermal polymerization. As a result, nanofiber webs with fiber diameters of approximately 300-400 nm were fabricated successfully. The investigation of the CO₂ adsorption and desorption performance of the obtained amine/epoxy/PVA (AE/PVA) nanofiber webs verified the high adsorption amount of 1.8 mmol/g at a CO₂ concentration of 400 ppm. Additionally, 93% of adsorbed CO₂ could be desorbed at a low temperature of 65 °C. These results suggested the possibility of low-energy-consumption CO₂ recovery. By improving the adsorption rate and by making desorption possible at low temperatures, the adsorption/desorption cycle can be repeated more quickly, increasing the amount of CO₂ that can be recovered in a day. The prepared webs also exhibited an excellent adsorption retention ratio of 75% after 100 h of operation at 85 °C, while general amine-filled mesoporous silica usually shows a retention ratio of only 13%. In addition, FT-IR, DSC, and elemental analysis of amine/epoxy/PVA nanofibers were carried out to analyze the reaction mechanism during fiber production. It was revealed that PVA was not involved in the reaction, and as in the bulk state, almost all primary amines were converted to secondary amines due to the in situ polymerization of amines and epoxy to form nanofibers.