PNNL

Abstract

Porous materials have received enduring interest in chemical science because of their suitability for many applications, including host materials for molecular separation and storage, catalysis, molecular sensing, magnetism, and drug delivery systems. These porous solids are broadly classified into two major categories: (i) amorphous and (ii) crystalline. Porous amorphous solids (e.g., plastics, gels) do not exhibit any ordered repeated units within their structures, but it is beneficial to work with them as they are usually less expensive and easy to prepare. Their primary disadvantages are the potentially wide range of molecular architectures with non-predictable channels or topologies and the lack of long-range order that results in low mechanical stability. In contrast, the porous crystalline solids are more advantageous because of their ordered structures with reproducible pores/channels and topologies, which give them high thermal and mechanical stability. Nanoporous silica and zeolites are characteristic examples of such ordered porous solids that have predictable structural features with reproducible pores/channels, dimensions, and topologies. These porous solids are subdivided into three categories based on their pore size. According to the International Union of Pure and Applied Chemistry, the porosity of the crystalline solids is usually given by the diameter of the pore size and is categorized as microporous (5-20 Å), mesoporous (20-500 Å) and macroporous (>500 Å).1