Micropore

Micropores are the smallest size class of pores in a porous material, defined by a width or diameter of less than 2 nanometers. They are distinguished from mesopores (2 to 50 nm) and macropores (greater than 50 nm) and contribute a material’s high surface area and strong adsorption capability. Microporosity occurs in a range of substances, including activated carbons, zeolites, and some metal-organic frameworks, where the pore structure is dominated by tiny cavities.

Materials with microporosity are often used for adsorption, separations, and catalysis. Activated carbons achieve microporosity through activation processes that develop a network of sub-nanometer to nanometer pores, while zeolites and many MOFs possess intrinsically microporous crystalline frameworks. The micropore volume and distribution largely determine a material’s capacity for gas uptake, dye or impurity adsorption, and selective separation based on molecular size and shape.

Characterization of microporous materials relies on gas adsorption techniques, typically using nitrogen at 77 K or other probe gases. Analyses such as BET surface area, t-plot methods, and density functional theory (DFT) based pore-size distributions are used to quantify micropore volume and size distribution. Interpretation may require models that separate micropore filling from meso- or macropore contributions.

Applications include hydrogen and methane storage, carbon dioxide capture, catalytic supports, and adsorption-based purification in water and air streams. In hierarchical materials, abundant microporosity is complemented by larger pores to improve diffusion and overall performance.