Characterization of Titanium Dioxide Nano Particle in Aqueous Solution: pH and Humic Acid Interaction

Recent reports revealed that titanium dioxide-nano particle (TiO₂-NP) is one of the major engineered nano sized materials available in the market. Considering the wide range of industrial applications of TiO₂-NPs, their release into the soil and environment would be inevitable and in near future soil will act as a sink of TiO₂-NPs. Furthermore, the state of aggregation of the nano particles in the natural environment depends on natural organic matter (humic substances) or environmentally relevant conditions of pH. The size of the TiO₂-NP (<10 nm) was measured by the transmission electron microscopy (TEM). In the present investigation, results revealed that the colloidal behaviour of TiO₂-NP was significantly influenced by the solution pH. The aggregation of TiO₂-NP in aqueous solution was occurred near its isoelectric point (pH: 5.8). The addition of humic acid (HA) (10 and 25 mg L⁻¹) in TiO₂-NP suspension increased the stability of colloidal suspension. Humic acid was characterized by using FTIR analysis. The TiO₂-NP surface was identified by atomic force microscope (AFM) height-contrast imaging, because AFM can distinguish the difference in material properties.