Solar concentrated-light driven direct air capture with fast desorption kinetics using amine-modified monolithic composites

A concentrated-light driven monolithic PEI/Ni/ γ -Al 2 O 3 offers mechanical robustness, humidity tolerance and enhanced heat and mass transfer for DAC. • DAC desorption completes within 2 min at 70 °C with a CO 2 desorption enthalpy of 45.9 kJ/mol, showing competitive regeneration performance. • Humidity switches the CO 2 capture pathway from carbamate to bicarbonate, achieving 2.35 mmol/g uptake and stable cycling over 18 cycles. The practical deployment of direct air capture (DAC) is hindered by insufficient mass and heat transfer, along with high energy consumption during regeneration, which are intrinsic drawbacks of conventional powdered amine adsorbents. To mitigate these bottlenecks, this work constructs a concentrated-light driven DAC system using a monolithic PEI/Ni/ γ -Al 2 O 3 adsorbents. The monolithic architecture offers a combination of mechanical robustness, humidity tolerance, and enhanced mass and heat transport. The optimized monolith exhibits a CO 2 adsorption capacity of 2.35 mmol/g from 420 ppm CO 2 in air, with an amine efficiency of 0.31 mol CO 2 /mol amine and a regeneration efficiency of 96.92% ± 1.49%. Notably, concentrated light enables complete adsorbent desorption within 2 min at a moderate temperature of 70 °C, and the intrinsic CO 2 desorption enthalpy is 45.9 kJ/mol. Moreover, in-situ FT-IR and DFT calculations reveal two distinct reaction mechanisms under dry and humid conditions, where humidity redirects the reaction pathway from the carbamate route to the stronger-bonded bicarbonate mechanism, driven by efficient electron transfer within water-mediated hydrogen-bonded networks. After 18 consecutive adsorption-desorption cycles, the PEI/Ni/ γ -Al 2 O 3 monolith maintains a steady CO 2 capacity of 1.94 mmol/g, verifying its cycling stability. This study offers a promising strategy for concentrated-light driven DAC, which could provide insights for further development of negative carbon emission techniques. Figure caption. Schematic diagram of CO 2 capture from air using the monolithic PEI/Ni/ γ -Al 2 O 3 absorbent. Download: Download high-res image (415KB) Download: Download full-size image