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