Sorption of Atmospheric Gases (N2, O2, Ar, CO2, and H2O) by Silica Aerogel

Resumo

Adsorption and desorption of atmospheric gases (N₂, O₂, Ar, CO₂, and H₂O) in silica aerogel is studied. Static parameters of adsorption and kinetic parameters of adsorption and desorption are determined based on the pressure vs time dependence P(t) in the buffer vacuum chamber of an experimental setup during adsorption and desorption of gases in a SiO₂ aerogel sample V = 42.8 cm³ in volume and ρ = 0.34 g/cm³ in density. The ratios of adsorbate molecular density to aerogel molecular density at room temperature T = 293 K and equilibrium pressure P_e ≈ 1 bar are found: γ(N₂) = (9 ± 3)% (nine N₂ molecules adsorbed by pore surface to 100 N₂ molecules in the gas at equilibrium), γ(O₂) = (7 ± 3)%, and γ(CO₂) = (222 ± 8)%; for water vapor, γ(H²O) = (5.9 ± 0.3) × 10⁴% at P_e = 5.7 mbar. It is ascertained that Ar atoms are not adsorbed by the aerogel. It is suggested to use argon as a “zero” gas in spectroscopy of molecules adsorbed by SiO₂ aerogel to determine the amount of adsorbate in a sample. A sum of two exponential functions of kinetic parameters τ₁ and τ₂ is used to fit the P(t) dependence, where τ₁ and τ₂ values are estimated during the adsorption and desorption of each gas under study.