microporities

Microporosity is the property of a solid material to contain micropores, pores with widths below 2 nanometers. It is a key feature of many porous materials used for adsorption and catalysis, including zeolites, activated carbons, porous polymers, silica, and metal-organic frameworks. The micropore volume, a portion of the total pore volume, characterizes the extent of microporosity and strongly influences surface area and adsorption behavior. Materials with high microporosity typically exhibit large internal surface areas and strong uptake of small molecules at low pressures.

Micropores predominantly control adsorption at low relative pressures and contribute to selectivity for small molecules such as hydrogen, carbon dioxide, and methane. However, diffusion of larger species through micropores can be slow, which may limit rate processes. In hierarchical materials, microporosity is combined with meso- or macroporosity to balance surface area with accessible transport pathways.

Microporosity is quantified using gas adsorption techniques. Nitrogen adsorption at liquid nitrogen temperature provides overall surface area (BET method) and pore size distribution, while carbon dioxide adsorption at higher pressure and lower temperature is used to probe micropores. Analyses such as NLDFT, t-plot, and Horvath–Kawazoe models yield pore size distributions and micropore volumes.

Common microporous materials include zeolites, activated carbons, covalent organic frameworks (COFs), a subset of metal-organic frameworks (MOFs), and microporous polymers. Synthesis and processing conditions determine pore size and connectivity; activation, templating, and post-synthetic modification can tailor microporosity.

Applications span gas storage and separation (notably CO2 capture, H2, and CH4 separations), catalysis, and energy storage (supercapacitors) where microporous carbons maximize capacitance per surface area. Microporosity is also relevant to sensor design and drug delivery in certain porous polymers.

Limitations include diffusion hindrance for bulky molecules and potential structural instability under certain conditions. In heterogeneous materials, microporosity is often complemented by larger pores to create hierarchical porosity.