Adsorption mechanism of substituted pyridines on silica suspensions: An NMR study
Résumé
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 π-system is proposed; it is consistent with both thermodynamic measurements and stacking of substituted pyridines within the adsorbed layer.
Mots clés
Absorption spectroscopy
Adsorption isotherms
Contamination
Gravimetric analysis
Phase transitions
Purification
Thermodynamics
Free induction decays (FID)
Heteronuclear multiple bond correlation (HMBC)
High-resolution magic-angle spinning (HR-MAS)
Molecular adsorption
Silica
pyridine derivative
article
chemistry
comparative study
methodology
nuclear magnetic resonance spectroscopy
pH
solution and solubility
standard
surface property
Adsorption
Hydrogen-Ion Concentration
Magnetic Resonance Spectroscopy
Particle Size
Pyridines
Reference Standards
Silicon Dioxide
Solutions
Surface Properties
Absorption Spectra
Dimethyl Sulfoxide
Isotherms
Nuclear Magnetic Resonance
Phase Transition