Polyethyleneimine-Impregnated Exfoliated Layered Double Hydroxide-Based Nanosheets for Direct Air Capture of CO2

Accumulation of atmospheric carbon dioxide demands innovations in sorbent technologies capable of direct CO2 removal from ambient air. Herein, we report the aqueous miscible organic solvent treatment (AMOST) of borate-intercalated layered double hydroxides (LDHs), forming highly exfoliated Mg3Al-LDH nanosheets, and evaluate them as high surface area supports for polyethyleneimine (PEI)-based direct air capture (DAC). Compared with carbonate-intercalated Mg3Al-LDH, the borate-intercalated analogue undergoes substantially greater AMOST-induced exfoliation, producing predominantly mono-/few-layer nanosheets with a very high specific surface area of 762 m2 g-1 and a total pore volume of 3.02 cm3 g-1. The high surface area and porosity allow incorporation using a nominal PEI loading of 67 wt %, enabling direct comparison of the carbonate- and borate-derived support architectures. Under humid breakthrough conditions at 400 ppm CO2/N2 and 25 °C, the borate-derived PEI-Mg3Al-LDH composite can achieve a high CO2 uptake of 2.90 mmol g-1, reaching 78% capacity in 20 min, demonstrating fast sorption kinetics. The sorbent also exhibits 96 % capacity retention after 20 adsorption-desorption cycles - competitive with reported PEI-supported solid amine sorbents measured under comparable dry DAC conditions. These results establish borate-assisted LDH exfoliation as a promising strategy for preparing high surface area supports for solid amine DAC sorbents.