New Insight into Ordered Cage-Type Mesostructures and Their Pore Size Determination by Electron Tomography

Abstract

In this work, a new approach based on electron tomography (ET) has been developed to measure the pore size, through which new insight into cage-type ordered mesostructures and their pore size determination has been obtained. It is demonstrated that the accurate pore diameter, especially for cage-type cubic mesoporous materials, can be determined only through our ET approach by considering that the pore geometry is a real 3D space. We use the established ET method to revisit the applicability of different models for the pore size calculation in nitrogen adsorption analysis. Different from the overwhelming understanding that the nonlocal density functional theory (NLDFT) and Derjaguin-Broekhoff-de Boer (BdB) model are recommended to calculate the pore size of cage-type cubic mesoporous materials while the Barret-Joyner-Halenda (BJH) model should not be used, a new understanding is gained through this study. The choice of a suitable model for pore size determination depends on the precise pore structure. For a cage-type cubic mesoporous material with fcc symmetry and a large entrance connecting the cages, the BJH model is more accurate while the other two methods overestimate the pore size (by up to 40%). The DFT model is more appropriate when the pore shape is a perfect sphere than the BJH model, which underestimates the pore size, and the BdB model, which overestimates the pore size. It is our opinion that the unique ET approach should be used to revisit a vast number of large-pore cubic mesoporous materials to provide genuine structural information.

Electron Tomography: A Unique Tool Solving Intricate Hollow Nanostructures

“…Especially for the intricate features hidden inside of a nanoparticle, the accurate structural determination would be rather challenging. As quantified in a recent report, the direct measurement of pore openings through consecutive tomographic analysis of cage-type pores has perfectly matched the spherical hollow void model (Figure 13a), [136] demonstrating reliable information derived from quantitative ET approach. [134] With superior capability on revealing the interior nanostructures, ET has been widely used due to its great advances in determining the true structures of porous nanomaterials.…”

Successful encapsulation of β‐glucosidase during the synthesis of siliceous mesostructured materials

“…S2, in which two well‐resolved peaks, which can be indexed as 111 and 311 reflections, respectively, are indicative of a face‐centered cubic ( fcc ) mesostructure (space group Fm 3 m ). These are similar to the XRD patterns of FDU‐12 reported in the literature . The diffractogram of sample LP‐FDU‐12‐g‐N indicates that grafting of aminopropyl groups on sample LP‐FDU‐12‐C does not affect the structural ordering.…”

“…These are similar to the XRD patterns of FDU-12 reported in the literature. 30,31 The diffractogram of sample LP-FDU-12-g-N indicates that grafting of aminopropyl groups on sample LP-FDU-12-C does not affect the structural ordering.…”

Estimation of Neck Size Distribution in Ordered Cagelike Materials Using Nitrogen and Water Desorption Isotherms

“…On the other hand, the 3D array structures of the cavities and the cavity diameter uniformity were maintained even after the prolonged hydrothermal treatments of the cagelike materials. 13,14,16,17,36 As far as the normal distribution of neck sizes randomly distributed is assumed, the desorption isotherm of a fluid from the model pore network consisting of the fcc array of cavities interconnected through narrow necks is determined only by two parameters of the neck size distribution, that is, the mean diameter (D mean ) and standard deviation (σ) of the necks. The ordered cagelike silica KIT-5 possesses essentially the same pore structure as the model pore network examined here.…”