An innovative filtration based Raman mapping technique for the size characterization of anatase titanium dioxide...

Characterization of titanium dioxide nanoparticles (TiO₂-NPs) is of significant importance in the production quality control, applications and study of their toxicological effects. In this study, we developed a filtration-based Raman mapping technique as a rapid approach for the analysis of different sizes and concentrations of anatase TiO₂-NPs. Four different sizes of TiO₂ standards: 173, 93, 41, and 8 nm measured by electron microscopy techniques were dispersed using a probe sonicator with sodium pyrophosphate as a dispersing agent. The resulting hydrodynamic diameter measured by dynamic light scattering (DLS) was stabilized at 192, 289, 325, and 360 nm respectively as a negative correlation with the ones by TEM. These NPs were then collected on a 0.1 μm (pore size) filter membrane with a vacuum pump and scanned using a Raman imaging microscope. The result shows that the 100 × objective lens was more capable of detecting the smallest size particles (8 nm) and lowest concentration (0.0004 g L^-1) evaluated than the 20 × objective lens. Moreover, at low concentrations (i.e. 0.0004 and 0.004 g L^-1), we established a linear correlation between the map area covered by the particles and the particle size measured by TEM. While at higher concentration (i.e. 0.04 g L^-1), a positive correlation was established between the particle size and its corresponding Raman intensity. These results demonstrated a successful application of Raman mapping technique in rapid characterization of the size of anatase TiO₂-NPs as small as 8 nm, which will facilaite the TiO₂-NPs research, production, and applications.