Figure 9. Regional scans of Ag (a), I (b) XPS spectra of 104 ppbv CH3I adsorbed Ag0-Aerogel and Ag (c), I(d) of 1044 ppbv CH3I adsorbed Ag0-Aerogel, with fresh, 350 ℃ degassed, CH3I fully loaded at 150 ℃ and I2 fully loaded Ag0-Aerogel at 150 ℃ as references.
The XPS spectra collected are shown in Figure 9. The fresh Ag0-Aerogel obtains the Ag3d5/2 peak located at approximately 368.6 eV and the Ag3d3/2 peak at approximately 374.6 eV, which are comparable to the binding energy (BE) reported by Matyáš et al.20 After being degassed at 350 ℃, the Ag BE decreases to 368.1 and 374.1 eV, indicating that certain amount of Ag2S nanoparticles may be generated in this process.41,42 After reacting with CH3I at different concentrations and temperatures, most of the Ag peaks shift to approximately 368.2 and 374.2 eV except those of the pellets at 104 ppbv/ 200 ℃ condition. The trend of iodine BE is slightly different from that of Ag, CH3I fully loaded sample contains the I3d5/2 and I3d3/2peaks at approximately 619.6 and 631.1 eV respectively, I2 fully loaded sample contains I3d5/2and I3d3/2 peaks at approximately 619.3 and 630.8 eV, and the peaks of remaining CH3I reacted samples located in between the values above except the 104 ppbv/ 200 ℃ case.
However, the spectra of the 104 ppbv/200 ℃ CH3I adsorbed Ag0-Aerogel are significantly different. Both Ag3d5/2 and Ag3d3/2 split to at least two peaks, locating at approximately 366.6, 369.5, 372.6 and 375.5 eV and I3d5/2 and I3d3/2 at 618.1, 620.9, 629.6 and 632.4 eV. The variations of the Ag and I spectra at 104 ppbv/ 200 ℃ condition indicate the Ag-I compounds formed may be different.
The SEM-EDX analyses were also conducted to measure the element compositions and potential structure changes on the pellet surface. The SEM-EDX analyses were performed using JEOL JSM IT100LA at SUNY College of Environmental Science and Forestry (SUNY-ESF). The acceleration voltage was 10-15 kV and the probe current is 20-30 mA for secondary electron detector (SED) mode and 55-65 mA for backscattered electron composition (BEC) mode.