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Encyclopedia of Nanoscience and Nanotechnology www.aspbs.com/enn Ordered Mesoporous Materials Sebastian Polarz Ruhr-University Bochum, Bochum, Germany CONTENTS 1. Introduction 2. Preparation of Ordered Mesoporous Materials 3. Analysis of Ordered Mesoporous Materials 4. Examples for Ordered Mesoporous Materials 5. Conclusions Glossary References 1. INTRODUCTION Ordered mesoporous materials are a subgroup of, or even prototypes, for so-called nanoporous materials. It is, therefore, necessary to give some comments on (nano)porous materials in general. The most general definition of a porous material is a continuous and solid network material filled through and through with voids. The voids are of the order of ≈1–100 nm in the case of nanoporous materials. A material is obviously porous when the voids are filled with gas. However, the voids might be filled with a liquid or even a solid. Then, some authors prefer to label materials nanostructured instead of using the expression nanoporous. However, for this review, this not very exact distinction will not be made. Once a pore can possibly be emptied without destroying the material, the material is regarded as a porous material no matter what is momentarily in the pores. The general definition given above already indicates that porous materials are actually a classical type of dispersion known for a long time in classical colloid science [1]. This is a solid foam. The voids show a translational repetition in three-dimensional space, while no regularity is necessary for a material to be termed porous. Correlating to this, the most common way is to consider a porous material showing gas-solid interfaces as the most dominant characteristic. This indicates that the creation of interfaces due to nucleation phenomena (in this case, nucleation of wholes), decreasing interface energy, and stabilization of interfaces is of elementa