Innovative Design of PEI-Modified AMO-Layered Double Hydroxide for Efficient and Stable Direct Air Capture of CO₂

Emerging as a critical technology for atmospheric carbon dioxide (CO₂) removal, the mass deployment of direct air capture (DAC) demands breakthrough innovations in efficient and stable adsorbent materials that simultaneously achieve high capacity, oxidative durability, and low cost. Herein, a hydroxyl-rich Mg_0.55Al layered double hydroxide (LDH) support is developed via aqueous miscible organic solvent treatment, circumventing energy-intensive calcination while engineering mesopores for efficient polyethyleneimine (PEI) loading. The optimized 60 wt.% PEI modified Mg_0.55Al-CO₃ AMO-LDH achieves a CO₂ uptake of 3.92 mmol g^-1 under simulated wet air at 25 °C and retains 90.8% capacity over 20 cycles. Crucially, the abundant surface hydroxyls of uncalcined LDH, validated by ¹H Nuclear Magnetic Resonance and in situ X-ray Photoelectron Spectroscopy, form hydrogen bonds with PEI, suppressing oxidative degradation. After 3 h at 120 °C in simulated air, PEI-LDH retains a CO₂ capacity of 1.06 mmol g^-1, significantly outperforming PEI/mixed metal oxide and conventional silica-based adsorbents. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy further reveals that hydroxyl-mediated amine anchoring minimizes water co-adsorption. This work establishes a dual strategy of hydroxyl preservation and mesopore engineering to design cost-effective DAC adsorbents, achieving both high capacity and exceptional stability under realistic operating conditions.