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Complex Formation and Dissociation Dynamics on Amorphous Silica Surfaces
- Source :
- The journal of physical chemistry. B. 125(17)
- Publication Year :
- 2021
-
Abstract
- Benzene complex formation and dissociation dynamics with silanols on the amorphous silica surfaces of nanoporous SiO2, from a benzene/carbon tetrachloride solution, were measured by the growth of off-diagonal peaks in the two-dimensional infrared (2D IR) chemical exchange spectrum of the isolated Si-OD stretch. The presence of two types of isolated silanols, termed type I and II, was revealed, with dissociation time constants of 82 and 4.0 ps, respectively. The type I silanols are associated with the main IR absorption feature in the Si-OD stretching region, while the type II silanols give rise to a broader shoulder to lower frequency. Polarization selective pump-probe (PSPP) measurements provided the vibrational lifetimes and orientational relaxation rates of the two silanols in the CCl4 (free) and benzene (complex) environments. The type II silanols constitute roughly 30% of the isolated silanol population and exhibit a substantially faster rate of vibrational relaxation, making the type I dynamics the dominant contribution to the PSPP and 2D IR signals. From the measured dissociation times, the enthalpies of formation for the two surface complexes were obtained, with the formation of the type I complex being significantly more exothermic. As the type II site is preferentially removed from the amorphous silica surface with increasing activation temperature, the results provide a reasonable explanation for the increased exothermicity of benzene adsorption on silica with increasing activation temperature in previous calorimetry experiments.
- Subjects :
- education.field_of_study
010304 chemical physics
Relaxation (NMR)
Population
010402 general chemistry
01 natural sciences
Dissociation (chemistry)
Standard enthalpy of formation
0104 chemical sciences
Surfaces, Coatings and Films
Silanol
chemistry.chemical_compound
Adsorption
chemistry
0103 physical sciences
Materials Chemistry
Vibrational energy relaxation
Physical chemistry
Physical and Theoretical Chemistry
education
Benzene
Subjects
Details
- ISSN :
- 15205207
- Volume :
- 125
- Issue :
- 17
- Database :
- OpenAIRE
- Journal :
- The journal of physical chemistry. B
- Accession number :
- edsair.doi.dedup.....dabb64c41735e35c44febd599937f903