Pore-Size Distribution of Silica Colloidal Crystals from Nitrogen Adsorption Isotherms

Document Type

Article

Publication Date

11-26-2019

Abstract

Silica colloidal crystals are face-centered cubic structures comprised of silica spheres with the diameters ranging between tens and hundreds of nanometers. The voids between the spheres form pores, which can be probed by nitrogen adsorption porosimetry. Here, we prepared two mesoporous samples and a macroporous reference sample and then measured nitrogen adsorption and desorption isotherms for further characterization. We proposed a straightforward procedure for calculation of the pore-size distribution of silica colloidal crystals from nitrogen adsorption isotherms. The procedure is based on the adsorption integral equation solution with a kernel of theoretical isotherms, consistent with the procedure used for many other porous materials. The solution is carried out using the non-negative least squares (NNLS) regression with Tikhonov regularization. The kernel of mesoporous isotherms is built on the basis of the macroscopic Derjaguin-Broekhoff-de Boer (DBdB) theory of capillary condensation considering the voids as a network of spheres. Application of our procedure for the analysis of the adsorption branches of experimental isotherms resulted in bimodal distributions, where the modes matched well with the sizes of the voids in the colloidal crystals face centered cubic structure: the main mode corresponds to the octahedral voids and the second mode to the tetrahedral voids. Furthermore, we modified the surface of the samples with organics and repeated the characterization procedure for the modified samples. The resulting pore-size distribution for the samples with the modified surface matched the original one quite closely. It demonstrates the procedure as a simple and efficient technique to estimate the pore-size distribution and justifies the spherical shape approximation for the voids in the silica colloidal crystals.

Identifier

85074887052 (Scopus)

Publication Title

Langmuir

External Full Text Location

https://doi.org/10.1021/acs.langmuir.9b02252

e-ISSN

15205827

ISSN

07437463

PubMed ID

31633940

First Page

14975

Last Page

14982

Issue

47

Volume

35

Grant

18-13-00149

Fund Ref

Russian Science Foundation

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