Optical properties of SiO2@TiO2core-shell nanoparticles

SARA ALDABE BILMES; SAJJAD ULLAH; ELIAS P. FERREIRA-NETO; MARTINEZ RICCI, MARIA LUZ; UBIRAJARA PEREIRA RODRIGUES-FILHO

Kyoto

Conferencia; Sol Gel 2015; 2015

International Sol Gel Chemistry

The use of SiO2@TiO2 core shell nanoparticles (CSNs) in aqueous suspensions allow to enhance the photocatalytic activity towards many photolytes. However, the description of optical processes leading to this enhancement is still poorly understood. In this work, we synthesized TiO2 nanoparticles (NPs) supported on the surface of 200 nm SiO2 particles and we correlate the contributions of scattering and absorption as a function of the shell thickness with the photocatalytic activity of these CSNs. TiO2 nanostructured shells of different thickness were grown by hydrolysis and condensation of titanium isopropoxyde (TiIP) on Stober SiO2 particles (Fig 1a). The layer formed on the silica surface grows with the amount of TiIP hydrolysed to a saturation value of 35nm. Attempts to develop thicker layers led to homogeneous nucleation of TiO2 NPs not attached to the silica surface. A mesoporous shell composed of around 5nm TiO2 anatase nanocrystals is obtained when using a low temperature (105°C) hydrothermal treatment. Photocatalytic activity tests were run either with the CSNs in suspension or deposited on a glass substrate. In all cases the photodegradation rate reaches a maximum when the silica particle is fully covered by TiO2[1] To relate the optical properties of CSNs with the photocatalytic activity a simple model was proposed taking into account absorption and scattering by mesoporous TiO2 shell. The model shows Rayleigh scattering is dominant in the measured extinction spectra and there is no significant band gap shift. The high contrast due to the differences in the core and shell refraction indexes[2] confines photons increasing the optical pathway, what leads to the observed photocatalytic enhancement.