How many types of surface hydroxyl on the surface of silica?

The silica surface can adsorb some water, which is very common in the silica gel manufacturing process, because the silica synthesis process is the orthosilicic acid dehydration process, and this dehydration process cannot be completely complete. Different silica treatment processes can control the hydroxyl group content on the surface.

There are 3 types of surface hydroxyl on the surface of silica gel, you will find it in the below pictures.

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