Figure 1 . XRD patterns of different MEL zeolite samples.
The chemical state of these species was characterized by XPS, and the
results were displayed in Fig. S1. For Fe containing MEL zeolites, two
peaks at 711.8 and 725.4 eV were observed corresponding
Fe2p3/2 and Fe2p1/2 in
Fe3+,
respectively.25,26Moreover, the additional satellite peaks at ~716.3 eV
and 729.9 eV can also be observed in P-MEL@Fe (Fig. S1a) and
H-MEL@Fe-x (Fig. S1b-S1d), which represented the binding energy
of Fe2p3/2 and Fe2p1/2 in Fe(III) of
Fe2O3.27The UV-vis spectroscopy of resultant zeolite samples was given in Fig.
S2, and the corresponding percentages of different iron species of
zeolites were listed in Table S1, it was found that
Fe3+ species occupied the majority. Moreover, The EPR
analysis was further carried out to detect the structure and
coordination environment of Fe species in Fe-containing MEL zeolites,
where the two distinct resonance signals at g = 4.3 and 2.0 referred to
Fe3+ species in a distorted tetrahedral and a highly
symmetric coordination respectively (Fig.
S3).28,29Based on the above analysis, it deduced that most of iron species loaded
in the P-MEL@Fe, H-MEL@Fe-34, H-MEL@Fe-23 and H-MEL@Fe-20 samples
existed in the form of Fe(III).