(b) EDS spectrum of silicalite-1 after iodine adsorption
Figure 8 EDS Spectra of (a) silicalite-1 and (b) silicalite-1after iodine adsorption
For studying the phase structure changes of the adsorbent after iodine adsorption, the X-ray diffraction analysis results of shaped silicalite-1 before and after iodine adsorption are shown in Figure 9. After iodine adsorption, the diffraction peaks of the two crystal planes [101] and [200] became smaller, indicating that shaped silicalite-1 adsorbed iodine and affected the long range order of the two crystal planes. It might be caused by the blocked pores of adsorbed iodine. Meanwhile, there was no new phase produced after adsorption, indicating probably that the mechanism was physical adsorption, which was proved by subsequent desorption experiment. In addition, there was no obvious diffraction peak of elemental iodine on the adsorbent after adsorption. It might be due to the elemental iodine had better dispersion on the adsorbent or the peak was weaker and annihilated, thus no obvious diffraction peak could be formed.
Figure 9 XRD patterns of silicalite-1
To investigate the existing form of iodine on the adsorbent after adsorption, the results measured by XPS are shown in Figure 10. The scan of I3d showed that binding energy were 618.7eV and 630.3eV, which confirmed the iodine existed in a neutral state39.
Figure 10 XPS Spectrum of silicalite-1 after iodine adsorption