Gradient-Aminated Hollow Fiber Membranes Enable Moisture-Synergized Facilitated Transport for Anesthetic Xenon...

Xenon is a superior anesthetic, yet its clinical use is crippled by the high cost of unrecovered gas, a challenge rooted in the inability to selectively remove CO₂ from humid, Xe-rich exhaled streams. Here, we uncover a strategy that turns water from a performance-degrading agent into a synergistic enhancer. By engineering a sub-10 nm gradient-aminated surface on hollow fiber membranes via controlled NH₃ plasma treatment, we create a confined environment where water molecules play a dual role. They promote the reversible CO₂-amine reaction to form mobile bicarbonate species, accelerating CO₂ transport, while simultaneously generating steric and competitive adsorption barriers that selectively suppress Xe diffusion. This moisture-synergized facilitated transport mechanism enables the optimized membrane to achieve an unprecedented mixed-gas CO₂/Xe selectivity of 1105 ± 13 with a CO₂ permeance of 35.3 ± 1.2 GPU under simulated exhaled anesthetic conditions, surpassing all previously reported membranes. The membrane maintains stable operation over 720 h in oxygen-containing feeds, and a home-built module achieves over 99% single-stage CO₂ removal, confirming practical viability. Beyond xenon recovery, this work establishes a scalable plasma-amination platform for engineering molecular-sieving pore architectures, offering a generalizable principle for designing humidity-tolerant membranes.