1H MAS NMR spectra of hydroxyl species on diatomite surface
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High spinning speed1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR) was used to detect surface hydroxyl groups of diatomite, which include isolated hydroxyl groups and hydrogen-bonded hydroxyl groups, and water adsorbed on diatomite surface that include pore water and hydrogen-bonded water. The corresponding proton chemical shifts of above species are ca. 2.0, 6.0–7.1, 4.9 and 3.0 respectively. Accompanied by thermal treatment temperature ascending, the pore water and hydrogen-bonded water are desorbed successively. As a result, the relative intensities of the peaks assigned to protons of isolated hydroxyl groups and hydrogen-bonded hydroxyl groups increase gradually and reach their maxima at 1000°C. After 1100°C calcination, the hydroxyl groups that classified to strongly hydrogen-bonded ones and the isolated hydroxyl groups condense basically. But some weakly hydrogen-bonded hydroxyl groups may still persist in the micropores.
Keywordsdiatomite surface hydroxyl groups 1H MAS NMR thermal treatment
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