Fig. 1: CO₂ adsorption in 4 nm C-S-H slit pores under different RHs.

a Effect of RH on the total CO₂ amount in C-S-H slit pores with different Ca/Si ratios. b Effect of water saturation degree on the total (dissolved and gaseous) CO₂ amount for different C-S-H slit pores. c Further classification of fully dissolved and interfacially dissolved CO₂ amount based on their water coordination numbers (see Supplementary Note 4). The water saturation degree is defined as the ratio of the water amount to the maximum amount that fills up the entire pore. Error bars are from the standard deviation resulting from the last 1 ns simulation of CO₂ adsorption. The unit is the number of molecules. d, e Molecular simulation snapshots showing CO₂ adsorption into the C-S-H (Ca/Si = 1.8) pores at RH = 0.40 and 0.54, respectively. These images were generated using Visual Molecular Dynamics software⁶¹. f Normalized CO₂ adsorption capacity as a function of RH and Ca/Si ratios of C-S-H. The white dashed line outlines the onset of pore water condensation states, below and above which are the unsaturated pore with an adsorbed water film and the fully saturated pore, respectively. g–i Water density distributions along the Z direction of the C-S-H nanochannels with varying Ca/Si ratios at different RHs. Red lines show the water density distribution at the critical RHs where capillary condensation initiates. Source data are provided as a Source Data file.