Scheme 1 . Synthetic Strategy for Fe immobilized hierarchical
single-crystalline MEL zeolites.
and P-MEL@Fe in the region of 3~4.5 nm, which were
attributed to the formation of mesoporous. The above TEM images,
N2 adsorption data combined with textural properties of
zeolites (Table S2) verified that the H-MEL-31 and H-MEL@Fe-xzeolites encompassed a significant amount of mesoporosity, possibly
arising from the orientated crystal transformation process:i) the
silica source (TEOS) and template (TBAOH) assembled with Ferric citrate
through the electrostatic and dispersion interactions between zeolite
precursor and solvated ligand-stabilized Fe
species22, inducing the
formation of Fe containing silicate-2; ii) these Fe containing
silicate-2 underwent the targeted corrosion towards silicon extraction
by interactions between Si–OH groups on the surface of silicate-2 and
TBA+, resulting in the generation of voids in the
silicate-232.
Simultaneously, the Fe containing silicate-2 finished crystal
transformation via directional control of crystallization process
combined with leached silicate oligomers and additional aluminum
isopropoxide species, guiding the formation of acid-redox
co-functionalized single crystalline mesoporous MEL zeolites, as
schematically illustrated in Scheme 1. These mesopores were enclosed by
a series of low-index facets like [011] and [010] as clearly
observed in HRTEM images from an “edge-on” projection (Fig. 2b and
2c). After correcting the defocus effects (Fig. 2d), The HRTEM images of
the crystalline pore walls also well matched the simulated projected
potential and structural projections of a MEL zeolite along the
[100] direction.