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Evolution mechanism of surface hydroxyl groups of silica during heat treatment
- Source :
- Applied Surface Science. 513:145766
- Publication Year :
- 2020
- Publisher :
- Elsevier BV, 2020.
-
Abstract
- The surface hydroxyl groups of nano-silica have a great influence on its application properties. In this paper, the changes of the number of various hydroxyl groups after dehydroxylation and rehydration progress of silica were quantitatively analyzed by thermogravimetric (TG) analysis and 29Si Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) measurements. According to the different stability of Si-O-Si bond formed after dehydroxylation, we propose two types of hydroxyl groups depending on the relative positions of them: chain adjacent hydroxyl groups (C-OHs) and spatially adjacent hydroxyl groups (S-OHs). DFT calculations indicate that two C-OHs dehydroxylation form a four-atoms ring structure, and the resulting O Si O bond angle deviation from optimal value is up to 19.56°, and the average bond length of the Si O bond increase more than 4.66%. Further more, its rehydration reaction activation energy (Ear) is very low, even only 0.21 kJ/mol, so it is easy to re-open and return to hydroxyl groups under environmental conditions. Conversely, the S-OHs dehydroxylation form a stable multi-atoms ring. The DFT calculations are a good illustration of the phenomenon in which some unstable siloxane bonds in a dehydroxylated sample are restored to hydroxyl groups in TG analysis and 29Si MAS NMR measurements.
- Subjects :
- Thermogravimetric analysis
Chemistry
General Physics and Astronomy
02 engineering and technology
Surfaces and Interfaces
General Chemistry
Activation energy
010402 general chemistry
021001 nanoscience & nanotechnology
Condensed Matter Physics
Ring (chemistry)
01 natural sciences
0104 chemical sciences
Surfaces, Coatings and Films
Bond length
Crystallography
chemistry.chemical_compound
Molecular geometry
Siloxane
Magic angle spinning
0210 nano-technology
Subjects
Details
- ISSN :
- 01694332
- Volume :
- 513
- Database :
- OpenAIRE
- Journal :
- Applied Surface Science
- Accession number :
- edsair.doi...........9fad0239b07f8911dd1a98d7ca288f88