Micropore Measurement

Nanoporous materials are essential in regulated pharmaceutical administration, energy conversion, and other uses. Analysing their pore size, surface area, and distribution is crucial to choosing and enhancing their performance in areas like catalyst design and reaction selectivity. Gases like N2, Ar, and CO2 that physically absorb energy are used to describe micropores and mesopores. Specialised equipment is needed to monitor low pressures in micropores.

Controlled medicine delivery, energy conversion, and storage, among other applications, use nanoporous materials in research and industry. To choose and enhance the performance of these materials, a thorough analysis of nanoporous materials about pore size, surface area, and pore size distribution is necessary.

When describing porous materials, the distribution of the size of the pores is crucial. For instance, surface area and porosity are significant characteristics in the design of catalysts. Since they determine the quantity of active sites on the catalyst’s surface, the total surface area is crucial for the performance of solid catalysts. Selectivity in catalyzed reactions is determined by pore size, pore size distribution, and pore volume.

Micropores are pores with internal diameters smaller than 2 nm, while mesopores are pores with internal widths between 2 and 50 nm. To characterize micropores, physically absorbing gasses must be used. The gasses employed are those that are physisorbed or physically bind at the solid surface, such as N2 at 77K, Ar at 87K, and CO2 at 273 K. Specialized equipment is needed to measure these low pressures because micropores are filled at very low relative pressures (P/P0).

Argon is a perfect probing gas for evaluating the pore structure of absorbent substrates because of its outstanding adsorption activity. Compared to nitrogen at 77K, argon fills micropores at a substantially higher relative pressure at 87K, making analysis more effective. The use of CO2 can be made to access the smallest micropores. CO2 molecules can easily enter micropores that are less than 0.7 nm in size when the temperature is close to room temperature. As a result, CO2 has emerged as the preferred gas for characterizing microporous carbons.

On an adsorption isotherm plot, the micropore region is represented by a significant and steep increase of the isotherm close to its origin and a subsequent levelling off to a plateau. A realistic pore-filling model must be used to extract the data on pore size from the experimental adsorption isotherm. The density functional theory (DFT) was created and applied as a result of developments in physical adsorption characterisation. Horvath-Kawazoe (HK) and Dubinin, two earlier, more straightforward macroscopic techniques, have traditionally been employed as the pore-filling models.

The non-local density function theory (NLDFT) pore-size distribution and pore volume data can be estimated using the relevant materials characterization procedures. The NLDFT pore-filling model applies to all types of micro- and mesopores and accurately explains the adsorption at the molecular level. Commercially available NLDFT models for various adsorbent/adsorptive systems.

Read more: Mesopore Measurement

Advantages

• Nitrogen, argon, or CO2 are available for adsorbate gasses.
• There is also a multi-point BET analysis for the micropore and mesopore combo.
• Many alternatives for instruments to achieve the greatest fit for the material

Considerations

• There are options for micropore-only analysis and combination micropore-mesopore analysis.
• suitable primarily for dry materials

Video 01: Micropore Technology