An investigation on the aggregation phenomena of Titanium dioxide nanoparticles in natural waters: role of ionic strength, organic matter and natural colloidal particles

M. Romanello, V.A. Luppi, L. Bertini, M. Fidalgo de Cortalezzi
Instituto Tecnológico de Buenos Aires, AR

Keywords: TiO2, aggregation, natural water, microorganisms


The aggregation behavior of TiO2 nanoparticles under conditions normally encountered in natural waters was investigated. Aggregation kinetics and size distribution was determined by DLS using a Nanosizer ZS, Malvern, UK. SEM images were also collected. Conditions considered covered a pH range between 3 to 9. Different levels of ionic strength were studied, given by indifferent electrolytes (NaCl) as well as divalent, specifically adsorbing cations (CaCl2 and MgCl2). Tannic acid and humic acid were selected as model organic compounds for natural organic substances. The effect of kaolinite was also investigated as a model inorganic natural colloid; in this case, size distribution was determined by the flow field fractioning technique. The experiments conducted demonstrated that although nanomaterials are unstable and expected to form large particles even in low to moderate ionic strength conditions, the presence of adsorbent species can render them stable and therefore mobile in the natural environment. The experimental results were modeled by classic DLVO colloidal theory. Activated sludge from a wastewater treatment plant was used to test behavior of the nanoparticles in a biological setting. A standard inhibition test was applied to investigate the potential negative effects of the nanoparticles on biological activity.