I have read some papers stating that $\ce{SiO2}$ surfaces can bind phosphonates, but in water they hydrolyse. However, for $\ce{Si}$ surfaces, they are stable in water. In both cases, the reaction takes place through $\ce{OH}$ groups that are present on the surface.

  • What I think is that on $\ce{SiO2}$ surfaces, there could be some steric effects which make hydrolysis "more convenient".

  • Another answer which seems less reasonable is that maybe the phosphonate group is electron withdrawing, and as the Si in the oxide already lacks electron density, this makes $\ce{Si-O-P}$ less stable, which is not the case for pure Si.

Related to this, why is the $\ce{Al-O-P}$ bond more stable in water than $\ce{Si-O-P}$?

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