Sphere templating methods for periodic porous solids

This paper reviews methods that employ colloidal crystals, composed of monodisperse silica or polymer spheres. to template periodic porous solids. The resulting structures can be regarded as inverse replicas of the template array, or inverse opals. A large number of compositions have been prepared by various modifications of a colloidal crystal templating process. including silicates and organosilicates, metal oxides, metals, metal chalcogenides and carbon allotropes. Regardless of the product composition, the methods involve several common steps. In a first step. colloidal crystals are formed by packing uniform spheres into three-dimensional or sometimes two-dimensional arrays. In a second step, the interstitial space is filled by a fluid that is subsequently converted into a solid skeleton. In a final step, the spheres are removed, creating a solid skeleton in the location of the former interstitial spaces and interconnected voids where the spheres were originally located. Each of these steps, together with appropriate synthesis conditions (or literature references) are outlined for diverse compositions. Potential applications of the macroporous solids include photonic crystals, catalysts, supports, sensors, and porous electrodes or electrolytes. (C) 2001 Elsevier Science B.V. All rights reserved.