Effect of organic groups on hydrogen adsorption properties of periodic mesoporous organosilicas

• Published in: Microporous and mesoporous materials Vol. 147; no. 1; pp. 194 - 199
• Main Authors: Kubo, Masaru, Ishiyama, Keisuke, Shimojima, Atsushi, Okubo, Tatsuya
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 2012; Elsevier
• Subjects: Adsorption; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Hydrogen storage; Isosteric heat of adsorption; Molecular order; Periodic mesoporous organosilicas; Porous materials; Surface physical chemistry; Hydrogen storage; Molecular order; Adsorption; Isosteric heat of adsorption; Periodic mesoporous organosilicas; Polarizability; Force; Hydrogen; Adsorption site; Crystals; Density; Porous material; Dispersion; Mesoporosity; Storage; Pore; Affinity; Thermodynamic properties; Heat of adsorption; Electrons
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2011.06.014

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► Hydrogen adsorption properties of various periodic mesoporous organosilicas (PMOs) were investigated. ► PMOs with π electrons on the pore surface exhibit high affinity to hydrogen molecules. ► Molecular orders of organic groups affect the affinity to hydrogen molecules as well as the location of adsorption sites.
We investigate the hydrogen adsorption properties of periodic mesoporous organosilicas (PMOs) and focus, in particular, on how these properties are affected by diverse organic groups embedded in the walls. PMOs with π electrons on the pore surface adsorb more hydrogen molecules per unit area and have a higher isosteric heat of hydrogen adsorption (
Q
st). The number of adsorbed hydrogen molecules per unit area correlates well with the density of organic groups on the pore surface. We attribute the high
Q
st to the high polarizability of organic groups with π electrons, which enhances the dispersion force. The molecular order of organic groups affects the adsorption-site affinity to hydrogen molecules as well as the location of adsorption sites. For phenylene-bridged PMOs with crystal-like pore walls,
Q
st decreases rapidly with increasing hydrogen loading, which indicates two types of adsorption sites with different affinities to hydrogen molecules: one is an exposed CH bond and the other is a siloxane bond. However,
Q
st for phenylene-bridged PMOs with amorphous pore walls exhibits a moderate slope, which might be caused by the random order of organic groups; this results in several types of adsorption sites with various affinities.