Table 2. Parameters and results of the SCM.
It can be visualized that, at 200 ℃, certain abnormal behaviors exist for both 104 and 1044 ppbv CH3I adsorption. To explain such observation, the nitrogen titration, XPS and SEM-EDX analyses were performed and a potential reaction pathway was proposed.

Water Equilibrium in Drying Process

Because of multiple factors including the pellet size of Ag0-Aerogel, the internal structure of Ag0-Aerogel, etc., the water concentration in the pellets after 350 ℃ vacuum drying may not be constant. Therefore, a final drying is still required before the CH3I adsorption and the pellets may adsorb or desorb water in different trials. The water adsorbed was from the trace amount of moisture contained in the carrier gas (Airgas Inc. Air, Ultra Zero). According to the manufacturer, the air contains approximately 2 ppmv of water and the value was also validated by experimental measurement using a dewpoint meter. By selecting a water adsorption curve with the highest uptake (therefore the initial water concentration in the pellet can be assumed to be zero) , the water adsorption process can be modeled using multiple models including the 1-D spherical Fick’s Law26 (Eq. 10), differential form of the diffusion term of the shrinking core model (SCM)26 (Eq. 11), and the micropore term of the pore diffusion model (Micro PD)13 (Eq. 12). For Fick’s law and the shrinking core model, it is assumed that an equilibrium is established on the surface immediately.
q(r,t) is the sorbate concentration (mol/cm3) at radius r (cm) at time t (s), and the average sorbate concentration q(t) can be calculated using . D is the pore diffusivity (cm2/s), r is the radius at timet , V is the volume of the pellet (cm),Di is the micropore diffusivity (cm2/s) and Ri is the radius of the micropore (cm). Ri was measured by the nitrogen adsorption method using ASAP 2020 and the value is approximately 6.6 Å.