Figure 10. The SEM images including SED, BEC, Ag mapping and I mapping of (a) fresh, (b) 104 ppbv/150 ℃ CH3I partially loaded, (c) 1044 ppbv/150 ℃ CH3I partially loaded, (d) 9585 ppbv/150 ℃ CH3I fully loaded and (e) 50 ppmv /150 ℃ I2 fully loaded Ag0-Aerogel. (Full resolution images are available in Supplementary Materials )
The SED and BEC (including the corresponding mappings of Ag and I) images are shown in Figure 10. The images show that the fresh Ag0-Aerogel (a) does not contain any notable Ag clusters in the micrometer scale on the surface. After reacting with 104 (b) and 1044 ppbv (c) CH3I (partially loaded), the surfaces of the adsorbent become coarser, whereas the distributions of Ag and I remain relatively uniform. As the concentration of the adsorbate increases, certain surface structures were formed and some bright spots can be observed in the SED image of the 9585 ppbv CH3I fully loaded Ag0-Aerogel(d). These spots appear to be AgI clusters since the same spots were also observed in the BEC image and the corresponding Ag and I mappings. The change of surface structure is more significant for the 50 ppmv I2 fully loaded sample. A layer consisting of AgI in polygon shape may be formed during the adsorption process.

Surface Composition

Observed in the XPS results (Figure 9), the spectra of 104 ppbv/ 200 ℃ CH3I adsorbed Ag0-Aerogel are significantly different from all others, which may further explain the abnormal high uptake rate. Figure 11 is the Ag(a) and I(b) regional scans of the 104 ppbv/200 ℃ CH3I adsorbed pellets with the spectra of CH3I fully loaded sample as references. Both Ag and I spectra of 104 ppbv/ 200℃ sample consist of three groups of peaks, which are marked as 1, 2 and 3 in the figure. For Ag spectrum, 3 Ag3d5/2 peaks are located at 366.6, 368.2 and 369.45 eV, which the second group is well agreed with the peaks of CH3I fully loaded sample. Similarly, the I spectrum also contains 3 groups of peaks and the binding energies of the second group are close to those of the fully loaded sample. The compositions of three groups of peaks were also determined, and the results are, approximately 52-55%, 15-20% and 28-29% for group 1, 2 and 3 respectively. Since the compositions acquired in both fittings are relatively similar, the additional peaks appear to be some form of Ag-I (not AgI, silver iodide) compounds.