FIGURE 4. Gas adsorption isotherms of ZIF-95 (left) and ZIF-100 (right).

a, b, N₂ at 77 K for ZIF-95 (a, left); Ar at 87 K for ZIF-100 (a, right); CO₂ (black, circles), CH₄ (red, triangles), CO (blue, diamonds) and N₂ (pink, rectangles) at 298 K for ZIF-95 (b, left) and ZIF-100 (b, right); the filled and open shapes represent adsorption and desorption, respectively. P/P₀, relative pressure at the saturation vapour pressure of the adsorbate gas. c, Breakthrough curves, N₂ (pink, rectangles) and CO₂ (black, circles) for ZIF-95 using a CO₂/N₂ gas mixture (left); CH₄ (red, triangles) and CO₂ (black, circles) for ZIF-100 using a CO₂/CH₄ gas mixture (right). The relative intensities of each gas passing through the ZIF-95- and ZIF-100-packed column were obtained using a mass spectrometer to detect ion peaks at m/z⁺ = 44 (CO₂), 16 (CH₄), 28 (N₂) and 12 (CO). Mean value from multiple parallel experiments (n  3, standard deviation   5% for all isotherms and 6% for breakthrough curves) was adopted for each data point. Owing to the slow diffusion, ZIF-100 does not exhibit a stepped isotherm as expected for a mesoporous material.