Sphere templating methods for periodic porous solids

This paper reviews methods that employ colloidal crystals, composed of mono disperse silica or polymer spheres. to template periodic porous solids. The resulting structures can be regarded as inverse replicas of the template a rray, or inverse opals. A large number of compositions have been prepared b y various modifications of a colloidal crystal templating process. includin g silicates and organosilicates, metal oxides, metals, metal chalcogenides and carbon allotropes. Regardless of the product composition, the methods i nvolve several common steps. In a first step. colloidal crystals are formed by packing uniform spheres into three-dimensional or sometimes two-dimensi onal 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 forme r interstitial spaces and interconnected voids where the spheres were origi nally located. Each of these steps, together with appropriate synthesis con ditions (or literature references) are outlined for diverse compositions. P otential applications of the macroporous solids include photonic crystals, catalysts, supports, sensors, and porous electrodes or electrolytes. (C) 20 01 Elsevier Science B.V. All rights reserved.