Comparative study of the surface hydroxyl groups of fumed and precipitated silicas. 4. Infrared study of dehydroxylation by thermal treatments

The elusive silica/water interface: isolated silanols under water as revealed by vibrational sum frequency spectroscopy

“…Thermal treatment, particularly at temperatures above 1000 1C, results in an almost total dehydroxylation of silica surfaces with the interconversion of most silanol groups into siloxane bridges (Si-O-Si). 4,6,7,10,37 During the heating process, the hydrogenbonded and vicinal silanols are the first to disappear, followed later by the geminals. 3,6 On the other hand, isolated silanols first increase in numbers, peaking at B400 1C, before totally dehydroxylating at temperatures above 1100 1C.…”

Combining in Situ NEXAFS Spectroscopy and CO2 Methanation Kinetics To Study Pt and Co Nanoparticle Catalysts Reveals Key Insights into the Role of Platinum in Promoted Cobalt Catalysis

“…Such hydrogen transport processes theoretically involve the presence of surface hydroxyl groups, however it has been shown that silica surfaces typically have 6-7 -OH per nm 2 groups even after 450 ºC treatment in vacuum. 24 This hydrogen migration would reverse the deactivation, increasing the observed rate, as found during the catalytic experiments when Pt nanoparticles are added. To investigate this further, we performed in situ NEXAFS spectroscopy during nanoparticle reduction for analogous 2D samples deposited on silicon wafers (Figure 4).…”

Adsorption of organic molecules on silica surface

“…From the water adsorption study of the surface of fumed silica and precipitated silica [50] two structures of physisorbed water were proposed for precipitated silica before the formation of cluster. According to this proposal the most stable adsorption of water takes place on inner surface and water absorbing at 5315 cm − 1 is due to less stable adsorption on outer surface.…”

“…Chemically modified silica with attached aminopropyl, imidazolyl, and trimethylsilyl groups, with adsorptive and coordinative grafted hemin were synthesized (47)(48)(49)(50)(51)(52)(53)(54)(55) and adsorption of some bile acids on the surface of hydroxylated silica, synthesized siliceous adsorbents and cholestyramine were investigated by Belyakova et al [215]. It was found that the main contribution to the total adsorption is caused by electrostatic attraction between anions of bile acids and positively charged sites of the surface of modified silica and also by dispersion interactions between steroid skeleton of bile acids and functional groups of modified silicon dioxides.…”