In situ studies of pyridine adsorption to bare and cyano-derivatized silica sol-gel films using attenuated-total-internal-reflection fourier-transform infrared spectroscopy
D. Rivera et Jm. Harris, In situ studies of pyridine adsorption to bare and cyano-derivatized silica sol-gel films using attenuated-total-internal-reflection fourier-transform infrared spectroscopy, LANGMUIR, 17(18), 2001, pp. 5527-5536
Adsorption of pyridine to silica sol-gel films has been characterized by us
ing attenuated-total-internal-reflection Fourier-transform infrared spectro
scopy (ATR-FTIR). By modeling the accumulation of pyridine in the film usin
g least-squares optimization of simple isotherm models, the pure component
spectra of adsorbed and solution-phase pyridine could be extracted from the
data. Pyridine was found to adsorb to two distinct sites on the sol-gel su
rface. The stronger adsorption site was found to comprise isolated and weak
ly hydrogen-bonded silanols, while the weaker site appears to be primarily
surface-bound water. Adsorbed pyridine is partially protonated at the surfa
ce, a 13% fraction at the stronger adsorption site and smaller fraction at
the weaker site. Derivatizing the sol-gel surface with 3-cyanopropyidimethy
l-chlorosilane decreases the total number of adsorption sites by 43%. Two d
istinct adsorption sites are still observed with the cyanopropyl-derivatize
d surface, but the stronger adsorption site is almost exclusively weakly hy
drogen bonding silanols. The signal due to protonated pyridine is the same
as was observed on the underivatized surface, but the percentage of pyridin
e that is protonated at the stronger site has increased to 22%. This result
suggests that weakly hydrogen-bonded silanols are the sites of protonation
.