Chemical modifications of oxide surfaces

Various synthesis and post-synthesis techniques are described in order to provide some insights into the latest developments in pore size engineering. Zeolites with tailor-made micropores can be the result of a controlled chemical surface treatment or the use of structure-directing templates during the synthesis. Various chemical modification methods, based on an ion exchange process, preadsorption of polar molecules and modification of the framework were discussed with respect to their mechanism. Furthermore, pillared clays are proposed as a new class of porous materials with properties exceeding those of zeolites. Depending on the synthesis procedure and conditions the micro- and mesoporosity is evaluated. Moreover, the possibilities in pore size engineering using structure-directing templates during the synthesis are illustrated by the mesoporous MCM and micro-/mesoporous clay heterostructure (PCH) materials. The pore size engineering in various oxides, such as zeolites and clay minerals is emerging as a new area of great scientific and technological interest. Materials with tailor-made pore sizes and shapes are particular important in applications where molecular recognition is needed, such as shape-selective-catalysis, molecular sieving, chemical sensing and selective adsorption. In general, the pore size engineering of these porous materials can be the result of: (1) a controlled chemical surface treatment; or (2) the use of structure-directing templates during the synthesis.