| Abstract
| - Surprisingly, SBA-15 mesoporous silicas are not as stable as expected in water, even at room temperature,despite their thick walls. The microporosity of SBA-15, synthesized at a temperature below 110 °C, is lostduring water treatment, leading to a strong decrease in specific surface area and an increase in mesopore size.Only SBA-15s without microporosity, such as the ones synthesized at 130 °C, are stable under water treatment.Investigations by nitrogen adsorption isotherms and hyperpolarized 129Xe NMR spectroscopy have beenperformed in an effort to understand the silica dissolution/redeposition processes occurring during watertreatment at room temperature and at the boiling point for three SBA-15s synthesized at different temperaturelevels: 60, 100, and 130 °C. The differences between the local curvatures of silica in the different structuresexplain the difference of behavior in water with respect to silica dissolution/redeposition. Similar experimentson MCM-41 lead to a totally different dissolution/redeposition process because of its thinner walls: decreaseof pore size, surface area and pore volume.
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