Surface modification of metal oxide nanoparticles by capillary condensation and its application

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Titania nanoparticles were modified using tetraethyl orthosilicate in a capillary condensation process and nanoparticles interconnected by silica layers were obtained. The amount of the silica layer was tunable by adjusting saturation conditions and the thickness of the layer generally increased as the saturation ratio increased up to a saturation ratio of 1.0. However, layer thickness was significantly affected by the geometric dimensions of the space between nanoparticles.

Grand canonical Monte Carlo simulation was utilized in order to study the role of particle surface curvature and gap space between particles in capillary condensation. The curvature of the particle surface and the gap space played a crucial role in the meniscus formation. Simulation results suggested that the effect of gap space becomes significant at the saturation ratios less than 0.8 and the effect of the particle curvature is important near the saturation ratio of 1.0. From these results, these effects need to be considered for the formation of silica layers with a specific thickness.

In order to further investigate the effect of addition of a silica layer, photocatalytic activity of surface-modified bi-phase titania nanoparticles was characterized on the basis of a pseudo-first order kinetic model. The results indicate that surface modification can enhance the photoactivity of original titania nanoparticles when an optimal amount of silica layer is present on the surface of nanoparticles.