Periodic Mesoporous Organosilicas (PMOs) were developed in 1999 and are basically ordered templated mesoporous organosilicas, prepared by the combination of a surfactant as template and a silsesquioxane as the organosilica precursor. They were one of the first examples of the so-called “hybrid” organic/inorganic materials. In the years that followed, an amazing variety of functional groups, morphologies and applications has been developed. Some of these high-end applications, like low-k buffer layers in microelectronics, chiral catalysts, chromatographic supports, selective adsorbents and light-harvesting devices, have clearly shown their potential. In this review, we will give a comprehensive overview of all these different functionalities and applications that have been created for Periodic Mesoporous Organosilicas.

IR and NMR spectroscopy were used to determine the silanol content in the most common mesoporous ordered silicas: MCM-41, MCM-48, SBA-15 and SBA-16. In addition, a spray dried MCM-41 and an ethene bridged PMO are investigated. The results are compared with a commercial chromatographic silica (Nucleosil). The complete distribution of surface and bulk silanols, and of isolated, geminal and vicinal silanols for all these materials is presented. A distinction is made between the total silanol number and the reachable or surface silanol content. The latter is determined by controlled reactions with simple silanes. All mesoporous ordered silicas, and especially the thick walled SBA-type materials and the PMO contain a surprisingly high amount of total silanol sites, albeit that up to 90% of these silanols are buried inside the walls and are not reachable for small silanes.

The adsorption of CO₂ on amine modified periodic mesoporous organosilicas (PMOs) has been investigated. An ethenylene-bridged PMO is modified with a wide range of diamines and polyamines. A variety of dangling N-containing functionalities, i.e., diaminobutane, diaminohexane, diaminododecane, diethylenetriamine and tetraethylenepentamine, as nucleophiles in a substitution reaction is used. The CO₂ adsorption capacity of these materials is probed and compared with amine functionalized SBA-15 material, in an effort to reach the maximal CO₂/N ratio of 0.5 when using dry conditions in a chemisorption process. The materials showed good CO₂ adsorption behaviour and this maximum amine efficiency value has been approximated by the PMO material modified with diaminododecane.