Effects of material properties on sedimentation and aggregation of titanium dioxide nanoparticles of anatase and rutile in the aqueous phase

This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO2) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO2 nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10 × 40 and 30 × 40 nm). The 50 nm anatase and 10 × 40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10 × 40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl2 solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin–Landau–Verwey–Overbeek (DLVO) equations for the TiO2 nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO2 nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO2 nanoparticles in the aqueous phase.

The experimental attachment efficiencies for the 50 nm anatase were quantitatively in accordance with the DLVO prediction at greater than 0.015 M NaCl, under which condition the Derjaguin Approximation was satisfied.Figure optionsDownload high-quality image (60 K)Download as PowerPoint slideHighlights
► Crystallinity and morphology are not influential factors in determining the stability of TiO2 suspensions.
► The stability of TiO2 suspensions was determined by the surface charge via nanoparticle chemical compositions.
► PZC of the TiO2 nanoparticles correlated with the extractable impurities, i.e., Si and P.
► The aggregation kinetics can be fit reasonably well with the DLVO equations for the TiO2 nanoparticles.