Silica-Based Nanoporous Materials

Abstract

Ordered nanoporous structures are among the most fascinating and industrially important materials currently in use. The archetypal zeolite material has now been joined by an eclectic array of new structures that exhibit porosity over a wide range of length scales and with order/disorder expressed in a multitude of ways. This raises the bar in terms of characterization and extends a real challenge to the scientific community to fully understand the properties and potential future applications of such materials. In this review we discuss the importance of modern microscopy tools combined with diffraction in this endeavour and show how the details of even the most complex quasi-crystalline nanoporous architectures can be elucidated. We show by using the appropriate spherical aberration (C-s) corrections in scanning transmission electron microscopy it is possible to decipher all the individual silicon and aluminum atoms in a zeolite structure. Automated routines for using large electron diffraction datasets for crystal structure determination of nanocrystals is described making the need for large single crystal synthesis less-and-less important. The power of complementary combinations of surface tools such as atomic force microscopy and high-resolution scanning electron microscopy is discussed to elucidate crystal growth mechanisms. For mesoporous materials synthesized from self-organized organic mesophases electron microscopy reveals the details of the complex hierarchy of porosity so crucial for the functional performance of the structure.