Figure 3 . (a) Reconstructed volume by electron tomography, (b)
Volume with labelled mesopores embedded and rendered in diverse colors,
(c-f) Labelled mesopores classified by different mesopore volume (from
left to right: > 3 × 104nm3, 1 ~ 3 × 104nm3, 1 ~ 10 × 103nm3 and 1 ~ 10 × 103nm3), (g) mesopores open to the surface and (h)
sequential slices of the reconstructed volume with an interval of 10 nm
for
H-MEL-31;
the red arrow shows the mesopore interconnectivity among slices (i) A
statistical analysis of mesopore volume distribution over different
equivalent spherical pore size. Red and blue bars refer to
constricted/closed and open mesopores respectively.
The “quality” of these intracrystalline mesoporosity, in terms of
interconnectivity and openness, can be directly evaluated in
three-dimensions and real-space by ET. Based on a TEM tilt series of
H-MEL-31 as a typical mesoporous MEL zeolite, the reconstructed 3D
tomogram can be visualized through volume rendering in Fig. 3a and Fig.
S9. From the 3D tomogram, the intracrystalline mesoporosity can be
directly identified, which could even be more clearly observed from
sequential slices of the tomogram as shown in Fig. 3h. These slices with
an interval of 10 nm exhibited highly interconnected voids either within
or between individual slices, implying a high degree of 3D
interconnectivity of mesopores. A thorough segmentation of the tomogram
allowed the precise labeling in 3D of individual interconnected
mesopores with different size and shape as shown in Fig. 3b-3f (rendered
with different colors). These labelled mesopores can be further
classified according to their different equivalent spherical pore size
and quantified statistically in a bar chart as shown in Fig. 3i. Among
these mesopores, those connected to the surface can be further labelled
and quantified as shown in Fig. 3g & 3i, which were defined as “open
mesopores” (otherwise “constricted” or “closed” ones). Accordingly,
it can be observed that majority of the interconnected intracrystalline
mesopores were highly open to the surface (Fig. 3i). Moreover, the
positron annihilation lifetime spectroscopy (PALS) was further employed
to verify the pore connectivity of zeolites