Abstract
Mesoporous titanium dioxide sub-microspheres were prepared using aerosol techniques with a size distribution from 80 nm to 3 mu m. Both theoretical and experimental results showed that non-equilibrium sucrose density gradient centrifugation is an effective way to size-partition these titanium dioxide nanoparticles from a continuous and broad particle size range. The sucrose serves as a multifunctional solution and plays three significant roles during the metal oxide fractionation. First, the high viscosity and density make the sedimentation rate of nanomaterials sensitive to particle size, which leads to particle fractionation in solution. Second, sucrose greatly decreases aggregation among nanoparticles during the separation by acting as a non-ionic capping agent. No other capping agent or surfactant is required. Finally, the density gradient stratifies the nanoparticles with a similar size into well-defined layers, so that the size-selected particles are relatively easy to collect. In addition, the unique biocompatibility of sucrose makes this fractionation method an ideal candidate for biological applications of nanoparticles. Post-aerosol synthesis separation of mesoporous metal oxide nanoparticles using a non-equilibrium density gradient has proven to be an effective, scalable way to access a large fraction of TiO2 sub-microspheres within a narrow size range and a low polydispersity index.