Mesoporosity

Mesoporosity is a characteristic of porous materials whose pore diameters fall within the mesopore range defined by IUPAC (2 to 50 nanometers). Materials with mesoporosity feature networks of interconnected pores that are larger than micropores but smaller than macropores, providing high surface areas and enhanced accessibility for larger molecules.

Common mesoporous materials include silica forms such as MCM-41 and SBA-15, as well as mesoporous carbons, metal oxides, and some polymer networks. Mesoporosity is typically introduced through templating strategies during synthesis: soft templating uses surfactants or block copolymers that assemble into regular mesostructures, while hard templating uses a solid sacrificial template that is removed after the framework is formed.

Characterization relies on gas adsorption techniques, notably nitrogen adsorption-desorption isotherms to obtain surface area (BET) and pore size distributions (BJH or NLDFT). Transmission electron microscopy and small-angle X-ray scattering can reveal pore ordering and structure.

Properties of mesoporous materials include high surface area, tunable pore size, and good accessibility of internal surfaces. The pore architecture influences diffusion of molecules in catalysis and adsorption processes. The stability depends on composition and synthesis conditions; silica-based systems are common but can be susceptible to hydrothermal degradation, while carbon and some oxides may offer better conductivity or redox activity.

Applications span catalysis, adsorption and separation, drug delivery, energy storage, and sensing. In catalysis, mesopores enable diffusion of bulky reactants to active sites. In drug delivery, mesoporous carriers can load and release therapeutic molecules. In energy devices, mesoporous materials serve as electrodes or electrolytic hosts.

Challenges include achieving reproducible pore structures at scale, maintaining stability under operating conditions, and functionalizing pore surfaces for specific interactions. Ongoing research seeks to broaden material types, improve thermal and chemical resilience, and integrate mesoporous components into composite systems.