NMR spectroscopy of silica surfaces

IR and NMR spectroscopy are powerful techniques for following the modification of silica surfaces. 

G.E. Maciel, C.E. Broimimann, R.C. Zeigler, I-Ssuer Chuang, D.R. Kirmey, and E.A. Keiter, Multinuclear NMR Spectroscopy Studies of Silica Surface, in The Colloid Chemistry of Silica, ACS Advances in Chemistry Series no. 239, pp. 269 282, 1994. 

Turov, V.V, Leboda, R., Bogillo, V.I., and Skubiszewska-Zi ba, J. 1997b. Study of hydrated structures on the surface of mesoporous silicas and carbosils by H NMR spectroscopy of adsorbed water. Langmuir 13 1237-1244. 

Cyclopentadienyl compounds , which contains Sn NMR data, Solid-state NMR spectroscopy of microporous materials , Characterisation of porous media using NMR methods , NMR imaging of materials , which contains He and Xe NMR data, Adsorption and dynamics of sodium alkylbenzenesul-fonates on alumina , which contains H NMR data, Rubber rubber blends Part II. New developments , which contains Xe NMR data, and Infrared and NMR characterisation of the silica surface , which contains 0 and Si NMR data. ... 

The immobilisation of optically active alkenes on the silica surface by combined hydrosilation and sol-gel technology has been studied. The silanol and silyl groups in silicas which have been silylated with Cg chains have been estimated by Si NMR spectroscopy. Dehydroxylation and silanisation of the surfaces of sihca have been investigated. A A1 and Si NMR study of silane surface modified calcined kaolin has been reported. C NMR spectroscopy has been used to establish the bonding trihydrosilane to Ti02 particles. ... 

Si-NMR spectra of bulk hydrolyzed y-APS and silica treated with different amounts of y-APS are shown in Fig. 9.25a [84]. The resonances are assigned as shown in Fig. 9.25b. In addition, the resonances at — 1(X) and —110 ppm are due to (=Si—0)3Si—OH and (=Si—0)4Si—OH moieties of the silica surface. No peak is observed at —45 ppm, which is the Si chemical shift of liquid APS. For the bulk hydrolyzed y-APS, the line widths are narrow, and the resonance at —58 ppm appears. For the 100% APS-treated silica, the resonances are much broader, and the band at —59 ppm appears as a shoulder. The results indicate that CP-MAS Si-NMR spectroscopy of the solid state is a very powerful tool for studies of silane coupling agents. 

The second approach consists of synthesizing first the complex MLra 1(L X) with the desired ratio (L )/(M) this complex bears the reactive fragment X which then reacts with the surface of the silica. This method is of limited interest, because the synthesis and isolation of these functionalized complexes is not straightforward. One of the successful examples concerns the synthesis of nickel carbonyl complexes anchored to the surface via two bonds in an attempt to increase the stability through a sort of chelate effect. Initial attempts to achieve this by the methods described in Equation(5) (initial functionalization of silica) and Equation(6) (initial functionalization of complex) failed, as demonstrated by 29Si and 31P CP MAS NMR spectroscopies.51... 

ESR spectroscopy can be used with adsorbed paramagnetic ions to study the liquid associated with mineral surfaces. Cu(II) and Mn(II) have been used in his type of investigation, although difficulties are encountered with observing a resonance from Mn(II) in distorted environments. Measurements of Cu(II) on silica at room temperature and above have shown that adsorbed water behaves in the same manner as bulk water, but at lower temperatures it experiences a decreased mobility (61). On freezing two types of water are found one which is freezable and undergoes crystallization and the other which is unfreezable, in which the ice structure cannot be formed because of the surface interaction. NMR, IR and differential thermal... 

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