  A novel system containing nanoporous materials and carbonate ions is
proposed, which is capable to capture CO2 from ambient air simply by
controlling the amount of water (humidity) in the system. The system absorbs
CO2 from the air when the surrounding is dry, whereas desorbs CO2 when wet. A
design of such a CO2 absorption/desorption system is investigated in this paper
using molecular dynamics and quantum mechanics simulations, and also verified
by experiments. Its working mechanism is revealed as the reduction of free
energy of the carbonate ion hydrolysis with the decrease of the number of water
molecules in confined nano-pores. The influences of pore size, spacing of
cations, surface hydrophobicity and temperature on CO2 capture efficiency are
elucidated. The study may help to design an efficient direct air capture system
and contribute to the negative carbon emission.
