A Novel Biphasic Absorbent for Liquid–Solid Phase Separation Induced by Nanoparticle Polarity Difference and Application in DAC

Liquid absorption represents a technologically mature and immediately scalable approach for direct air capture (DAC), demonstrating a validated effectiveness in atmospheric CO₂ removal. However, its practical deployment is hindered by the high energy consumption and cyclic stability. The core advantage of the biphasic solvent system is the low-energy regeneration of CO₂ through liquid-solid phase transition, but its application in DAC faces bottlenecks due to environmental humidity sensitivity and susceptibility to oxidative degradation. In this work, we developed a stable nanoparticle-coupled biphasic ionic liquid system ([AEP][1,2-DMI]-DMSO-H₂O/MgO) for DAC, where the introduced nanoparticles significantly enhanced the CO₂ transport and phase transition kinetics. Through its unique liquid-solid transition mechanism, 79.5% of captured CO₂ was concentrated in a minimal solid phase (15.1% of system mass), while maintaining high loading capacity (total loading: 0.65 mol·mol⁻¹, solid phase loading: 0.30 g·g⁻¹). This system can achieve an ultralow regeneration energy (0.94 GJ·t⁻¹CO₂) and exceptional cycling stability (>96.5% efficiency retention over 7 cycles). The nanoparticle-enhanced biphasic ionic liquid system developed in this study has led to a breakthrough in new liquid DAC technology, pushing the technology into a new stage of development by unifying ultralow energy consumption and excellent stability.