microporosities

Microporosity is the portion of a porous material's pore volume contained in micropores, typically defined as pores with diameters below 2 nanometers. Some definitions use 1 nm as the cutoff. Micropores occur in many materials, including activated carbons, zeolites, metal-organic frameworks, clays and fine-grained rocks, as well as polymers and composites. They are distinct from mesopores (2–50 nm) and macropores (>50 nm).

Microporosity strongly influences adsorption capacity, surface area, and selective sorption of gases and liquids. It affects storage and diffusion in catalysis and separations, and it can regulate capillary pressure and low-saturation water storage in soils and rocks. However, high microporosity can reduce pore connectivity and bulk permeability, influencing flow properties.

Quantification usually relies on gas adsorption measurements at cryogenic temperatures, most commonly nitrogen or argon. By analyzing adsorption isotherms, researchers estimate micropore volume (V_micro) and pore-size distributions using methods such as t-plot, Dubinin–Radushkevich (DR) or Dubinin–Polanyi (DP) analyses, or density functional theory (DFT) models. The reported V_micro and surface area depend on the chosen pore-size cutoff and modeling approach.

Applications include activated carbons for filtration and purification, zeolites and MOFs for catalysis and gas separation, and nanostructured minerals where microporosity governs storage. Because definitions and analysis methods vary, comparisons should specify the cutoff and method used.