Optical properties of SiO2@TiO2 core-shell nanoparticles

SAJJAD ULLAH; ELIAS P FERREIRA-NETO; MARÍA LUZ MARTÍNEZ RICCI; UBIRAJARA PEREIRA RODRIGUES-FILHO,; ALDABE BILMES, SARA

kyoto

Congreso; XVIII International Sol-Gel Conference; 2015

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 synthesize TiO2 nanoparticles (NPs) on the surface of 200 nm SiO2 and we correlate the contributions of scattering and absorption as a function of the shell thickness with the photocatalytic activity.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 by increasing the TiIP addition led to homogeneous nucleation of TiO2 NPs not attached to the silica surface. A mesoporous shell composed by 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]For modelling optical properties a simple model was proposed to consider absorption and scattering by mesoporous TiO2 shell. The model shows that 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] produces a confinement of photons that increase their optical pathway what leads to the observed photocatalytic enhancement.