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Using the sol-gel method a series of nonstoichiometric nanosilica doped with the rare earth element Ce (Ce x Si 1-x O 2-d , x = 0.0-0.14) were prepared in order to modify the physicochemical properties of the nanosilica surface and to enhance the strength of the Ce-nanosilica/polysulfone composite membranes. The Ce xSi 1-x O 2-d samples were characterized by Fourier transform infrared spectra, X-ray diffraction and X-ray photoelectron spectra. The observations from these characterizations suggest that most Ce atoms enter the silica framework to form a Ce-O-Si solid solution while the cubic CeO 2 phase is segregated when x >0.08. Transmission electron microscopy images show that Ce x Si 1-x O 2-d particles are spherical with a uniform size distribution in the range of 30-50 nm and contain some inner pores with sizes up to a few nanometers. Specifically, Ce 0.08 Si 0.92 O 2-d -700 calcined at 700°C shows the biggest surface area, the smallest pore size and the highest hydrophilicity, which makes the Ce 0.08 Si 0.92 O 2-d /polysulfone composite membranes (8.0 wt %) exhibit the strongest mechanical strength (3.223 MPa), which is enhanced by more than 100% in comparison with the pure polymer membrane.

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