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

Adsorption and desorption of atmospheric gases (N 2 , O 2 , Ar, CO 2 , and H 2 O) 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 SiO 2 aerogel sample V = 42.8 cm 3 in volume and ρ = 0.34 g/cm 3 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(N 2 ) = (9 ± 3)% (nine N 2 molecules adsorbed by pore surface to 100 N 2 molecules in the gas at equilibrium), γ(O 2 ) = (7 ± 3)%, and γ(CO 2 ) = (222 ± 8)%; for water vapor, γ(H 2 O) = (5.9 ± 0.3) × 10 4 % 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 SiO 2 aerogel to determine the amount of adsorbate in a sample. A sum of two exponential functions of kinetic parameters τ 1 and τ 2 is used to fit the P ( t ) dependence, where τ 1 and τ 2 values are estimated during the adsorption and desorption of each gas under study.