The present invention discloses functionalized nanoparticles comprising on the surface a covalently bound radical of the formula (I) wherein the nanoparticles are SiO2, Al2O3 or mixed SiO2 and Al2O3 nanoparticles, and wherein the general symbols are as defined in claim 1. These functionalized nanoparticles are for example useful as stabilizers and/or compatibilizers in organic materials, or as photoinitiators in pre-polymeric or pre-crosslinking formulations, or as reinforcer of coatings and improver of scratch resistance in coating compositions for surfaces.