Aging impact on silver-functionalized silica aerogel (Ag0-aerogel) in the off-gas streams including dry air, humid air, 1% NO/N2, and 2% NO2/dry air were studied. Aged Ag0-aerogel was prepared through a continuous-flow aging system by exposing Ag0-aerogel (unaged) to the off-gas streams at different aging temperatures and time. Iodine loading capacity on the aged Ag0-aerogel was obtained through a continuous-flow adsorption system. Iodine loading capacity losses were observed after the Ag0-aerogel was exposed to the off-gas streams. Characterization studies were conducted to observe the physical and chemical changes of the Ag0-aerogel after exposed to gas streams. According to iodine adsorption data and analyses, it was revealed that iodine loading capacity on the aged Ag0-aerogel in the off-gas streams decreases with increasing aging temperatures and time. The pseudo reaction model describes experimental data well and the oxidation of Ag0 is the rate determining step in the aging process.

To understand the effect of temperature to the adsorption, 104 ppbv and 1044 ppbv methyl iodide (CH3I) adsorptions on reduced silver-functionalized silica aerogel (Ag0-Aerogel) at 100, 150 and 200 ℃ were performed. In the experiments, a significantly high uptake rate (3 – 4 times higher than that at 100 and 150 ℃) was observed for the 104 ppbv adsorption at 200 ℃. To explain such behavior, a potential reaction pathway was proposed and multiple physical analyses including nitrogen titration, x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were performed. Based on the results, the contributing factors appear to be the formation of different Ag-I components induced by temperature, higher silver site availability, decreasing diffusion limitation, and increasing reaction rate described by the Arrhenius relationship.

Aging effects of off-gas streams including dry air and humid air on reduced silver exchanged mordenite (Ag0Z) were studied. Aged Ag0Z was prepared by exposing Ag0Z to dry air and humid air at different aging temperatures, time, and water vapor concentrations. Iodine loading capacity on the aged Ag0Z was obtained through a continuous-flow adsorption system. Significant iodine loading capacity losses were observed after the Ag0Z was exposed to dry air and humid air. Physical and chemical analyses were conducted to observe the physical and chemical changes of Ag0Z after being aged. From iodine adsorption data and sample analyses, it was found that iodine loading capacity on the aged Ag0Z in dry air and humid air decreases with increasing aging temperatures, time and water vapor concentrations. The pseudo reaction model describes experimental data well and the oxidation of Ag0 is the rate determining step in the aging process.

The low concentration methyl iodides (CH3I) adsorption process on reduced silver-functionalized silica aerogel (Ag0-Aerogel) was studied. The kinetic data were acquired using a continuous flow adsorption system. Because the corresponding physical process was observed, the shrinking core model (SCM) was modified and applied. An average CH3I pore diffusivity was calculated, the CH3I-Ag0-Aerogel reaction was identified as a 1.37 order reaction instead of first order reaction, and the nth order reaction rate constant was determined. This modified SCM significantly increases the accuracy of adsorption behavior prediction at low adsorbate concentration. Modeling results indicate that the overall adsorption process is controlled by the pore diffusion. However, at low adsorbate concentration (<100 ppbv), the CH3I adsorption is limited to the surface reaction due to the low uptake rate in a predictable time period.