Nanoporous materials

Nanoporous materials consist of a regular organic or inorganic bulk phase in which a porous structure is present. Nanoporous materials exhibit pore diameters that are most appropriately quantified using units of nanometers. The diameter of pores in nanoporous materials is thus typically 100 nanometers or smaller. Pores may be open or closed, and pore connectivity and void fraction vary considerably, as in other porous materials. Most nanoporous materials can be classified as bulk materials or membranes. Activated carbon and zeolites are two examples of bulk nanoporous materials, while cell membranes can be thought of as nanoporous membranes.
A porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas).
There are many natural nanoporous materials, but artificial materials can also be manufactured. One method of doing so is to combine polymers with different melting points, so that upon heating one polymer degrades. A nanoporous material with consistently sized pores has the property of letting only certain substances pass through, while blocking others.
Nomenclature.
The term nanomaterials covers diverse forms of materials with various applications. Microporous and mesoporous materials are distinguished as separate material classes owing to the distinct applications afforded by the pores sizes in these materials. Confusingly, the term microporous is used to describe materials with smaller pores sizes than materials commonly referred to simply as nanoporous. More correctly, microporous materials are better understood as a subset of nanoporous materials, namely materials which exhibit pore diameters smaller than 2 nm . Having pore diameters with length-scales of molecules, such materials enable applications that require molecular selectivity such as filtration and separation membranes. Mesoporous materials, referring generally to materials with average pore diameters in the range 2-50nm are interesting as catalyst support materials and adsorbents owing to their high surface area to volume ratios. 
According to IUPAC Nanoporous materials are subdivided into 3 categories: