ABSTRACT
Experimental Details . . . . . . . . . . . . . . . . . . . . . . . . 388
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
Instrumental Analysis . . . . . . . . . . . . . . . . . . . . . . 388
Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
Data, Results and Discussion . . . . . . . . . . . . . . . . . . 389
Desorption Kinetics . . . . . . . . . . . . . . . . . . . . . . . 389
Effects of the Thermal Pretreatment
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . 395
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) is a convenient and useful tool to
decipher information regarding silanol (SiOH) site populations on porous silica surfaces. Studies that
employ probe base species that interact with accessible silanols, provide spectral evidence of distinct
silanol populations having differing affinity for, and strength of interaction with the base. Pyridine is a
weak base that was selected for use due to its ability to exhibit variable strengths of hydrogen bonding inter-
action with silanols. Desorption processes have been monitored in real-time via DRIFTS using the unasso-
ciated silanol site band near 3740 cm21and a ring vibration of hydrogen bonded pyridine at 1445 cm21. The
resultant kinetic data provides insight into the organization of silanols on the surface by virtue of the kinetic
order of the desorption process with respect to the base concentration. Pyridine desorption studies have
been applied to two porous silica gels having differing properties and intended applications; a general
purpose type A gel, and a high purity, chromatographic grade, type B silica. Both silicas were thermally
treated at different temperatures in the 200-4008C range and desorption studies conducted on the resultant surfaces. Major findings for the study include second order desorption kinetics with respect to pyridine con-
centration, evidence for three individual rate processes, increasing desorption rate constant thus diminished
acidity with increasing pretreatment temperature, and a greater general acidity for silanol sites on type A
versus type B silica. Data and results of the pyridine desorption studies followed by DRIFTS are presented
and discussed.
