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

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.