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Hybrid organic-inorganic silica gel is a new class of high performance liquid
chromatographic packings in recent years. Hybrid organic–inorganic particles combine the
best properties of silica with the best properties of organic polymers. It not only combines
excellent mechanical stability of inorganic materials and hydrothermal stability in acid and
alkali medium of organic materials, but also derives a lot of new properties, which has
optimistic prospects.[1] Currently, organic-inorganic hybrid silica spheres are mainly
prepared by functional modification on the basis of sol-gel method[2], including grafting
method, co-condensation method and periodic mesoporous organosilicas (PMOs)[3]. Most of
the reports about the synthesis of monodispersed organic-inorganic hybrid silica materials
have poor spherical shape and undesirable pore structure parameters, which are difficult to
meet the requirements of chromatographic stationary phases, especially the large diameter (>
3 nm) spherical silica, and greatly limit their application as chromatographic packings.
Among the various hybrid mesoporous materials reported so far, periodic mesoporous
organosilicas (PMOs) have evoked considerable interests of the scientists in the fields of
adsorption and separation since these novel materials were developed by Inagaki[4], Stein[5]
and O’zin[6] three research groups independently in 1999. PMOs exhibit unique properties,
such as high surface area, ordered mesostructure, uniform distributed organic moieties in the
framework, and high mechanical and chemical stabilities[7].
The ethane-bridged PMOs have been widely investigated, such as the control of
morphology and mesoporous structure. Froba et al.[8] prepared monodisperse spherical
ethane-bridged PMOs with an average particle size between 0.4 and 0.5 mm, relatively
low-ordered mesostructure and small pore-size (0.3 nm). Hamoudi and Kaliaguine prepared
spherical ethane-bridged sulfonic acid-functionalized PMOs with particle size of 10 mm and
pore size of 3.6 nm. However, reports on their application in HPLC are limited. It is difficult
to synthesize the spherical PMOs with particle size distribution of 3–10 mm [10], which is a
barrier for their potential use in HPLC [11]. Yang and co-workers[12] synthesized spherical
ethane-bridged periodic mesoporous silica in acidic medium by condensation of
1,2-bis(trimethoxysilyl)ethane (BTME). Highly efficient and rapid separation of the mixtures
of polycyclic aromatic hydrocarbons was obtained on the column packed with the
ethane-bridged periodic mesoporous silica.
Previously, Huang synthesized aminopropyl-functionalized ethanebridged periodic
mesoporous organosilica spheres (APEPMOs) by the co-condensation of
1,2-bis(triethoxysilyl)ethane (BTSE) and 3-aminopropyltriethoxysilane (APTES). The
column packed with APEPMOs exhibited reduced back pressure and good chemical stability
and was tested as a potential stationary phase for HPLC. These characteristics show the
advantages of PMOs used for HPLC.
However, particle distributions and the degree of order were needed to be improved. And
how to expand the pore size is a big challenge as well.
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