The development of CO₂ capture materials has faced significant challenges due to limitations in current sorbent technologies. Many existing approaches, including those based on porous polymers and frameworks, suffer from complex and costly syntheses, low surface area and pore volume, and issues with stability and durability — particularly under humid or contaminated conditions, which often lead to diminished uptake performance and poor selectivity. Additionally, traditional sorbents frequently exhibit slow kinetics and suffer from active component leaching, making them less reliable and efficient for rapid CO₂ capture at low pressures. These limitations underline the need for innovative sorbent systems that combine high porosity, stability and rapid sorption kinetics while being scalable and cost-effective for industrial applications.

NETL has developed a new sorbent material for CO₂ capture. The sorbent’s two main components are an amidoxime functionalized PIM and molecular amines such as diethylenetriamine (DETA), tris(2-aminoethyl) amine (TAEA), and Tris(3-aminopropyl) amine. The sorbent is synthesized via a simple, low-cost, scalable process. PIM-1, chosen for its high surface area and porosity, is initially functionalized with amidoxime under conditions that allow the degree of amidoxime functionalization to be controlled. This subsequently allows the level of amine tethering (i.e., amine loading) to be regulated as the amidoxime groups are responsible for binding the molecular amines. Prior to amine tethering, the PIM-amidoxime particles are “spun” into porous fiber form using conventional methods. The PIM-amidoxime fibers are then impregnated with primary amines (e.g., DETA and TAEA), leveraging the amidoxime groups’ high affinity for amines. This strong interaction also serves to limit the amine leaching prevalent among conventional sorbents. Primary amines are used due to their rapid CO₂ adsorption kinetics and mild desorption requirements. To enable rapid transport of CO₂ within the sorbent, amine loading is limited to < 25 wt%.

Relative to other polymeric sorbents, the bifunctionalized PIM sorbent fibers display very high CO₂ capture performance at low temperatures and CO₂ pressures, conditions associated with CO₂ capture from natural gas and coal-fired power plants, natural gas purification, and biogas upgrading. Relative to direct air capture, the sorbent fibers show efficient CO₂ uptake under atmospheric conditions. The sorbents also exhibit rapid CO₂ adsorption rates and very high CO₂/N₂ selectivity. Significantly, the sorbents can be regenerated via a low-temperature/low-energy process and maintain performance following multiple adsorption/desorption cycles. Such attributes are essential for reducing the cost of CO₂ capture.