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.