Adsorption Mechanism of Substituted Pyridines on Silica Suspensions:  An NMR Study

Abstract

Adsorption isotherms of 2,5-dimethylpyridine (2,5-DMP) on Aerosil 200 silica from water-2,5-DMP binary mixtures are known to exhibit special features indicative of surface phase transitions in the adsorbed layer. We have made similar observations on another substituted pyridine, 2,4,6-trimethylpyridine (2,4,6-TMP). By using 1D and 2D NMR spectroscopy, we investigated adsorbed layers on silica in suspension in water/substituted-pyridine mixtures and demonstrated the existence of adsorbed species specific signals. Comparison of signals with those displayed on NMR spectra of liquid binary mixtures under various pH conditions rules out adsorption via interaction of the surface silanol group and the lone electron pair of the nitrogen atom. A mechanism of adsorption through the interaction of surface siloxane oxygen and the aromatic pi-system is proposed; it is consistent with both thermodynamic measurements and stacking of substituted pyridines within the adsorbed layer.

Adsorption of organic molecules on silica surface

“…1D and 2D NMR spectroscopic investigations on adsorption mechanism of 2,4,6-trimethyl pyridine (2,4,6-TMP:16) were carried out on silica in suspension in water/substituted pyridine mixture by Andrieux et al [103] and the existence of adsorbed species specific signal was demonstrated.…”

Inversion of particle-stabilized emulsions of partially miscible liquids by mild drying of modified silica particles

“…Here we are interested in the small organic molecule 2,6-dimethylpyridine which is quite similar to 2,5-dimethylpyridine and 2,4,6-trimethylpyridine which were studied by Privat et al [22,23]. The fumed silica used in those experiments had <3 OH nm À2 compared to the 4.6 OH nm À2 typical for solution-prepared silica [20].…”

Enhanced metal adsorption on solid suspensions by organic molecules

“…Such interactions are also possible with carbofuran. A previous study of the adsorption of 2,5-dimethyl pyridine (DMP) on silica from solutions [48] highlighted the role of these p quantum levels on the molecule orientation at the interface, but given the configuration of the carbofuran molecule, this is certainly more difficult with it than with DMP.…”