Chemical modifications of oxide surfaces

Various synthesis and post-synthesis techniques are described in order to p rovide some insights into the latest developments in pore size engineering. Zeolites with tailor-made micropores can be the result of a controlled che mical surface treatment or the use of structure-directing templates during the synthesis. Various chemical modification methods, based on an ion excha nge process, preadsorption of polar molecules and modification of the frame work were discussed with respect to their mechanism. Furthermore, pillared clays are proposed as a new class of porous materials with properties excee ding those of zeolites. Depending on the synthesis procedure and conditions the micro-and mesoporosity is evaluated. Moreover, the possibilities in po re size engineering using structure-directing templates during the synthesi s are illustrated by the mesoporous MCM and micro-/mesoporous clay heterost ructure (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 shap es an particular important in applications where molecular recognition is n eeded, such as shape-selective-catalysis, molecular sieving, chemical sensi ng and selective adsorption. In general, the pore size engineering of these porous materials can be the result of: (1) a controlled chemical surface t reatment; or (2) the use of structure-directing templates during the synthe sis. (C) 2001 Elsevier Science B.V. All rights reserved.