Effect of natural organic matter on the disagglomeration of manufactured TiO2 nanoparticles

Abstract

One major concern in the fate of nanomaterials in aquatic systems is the lack of data on nanomaterial transformations under relevant environmental conditions. The disagglomeration of aggregates composed of manufactured anatase titanium dioxide nanoparticles is investigated here in the presence of alginate and Suwannee River humic acids at varying concentrations using dynamic light scattering and electrophoretic measurements. Stability of TiO 2 nanoparticle agglomerates at typical environmental concentrations of natural organic matter is discussed at a pH value corresponding to the point of zero charge of TiO 2 nanoparticles. In this scenario, the surface charge of TiO 2 is neutralized, allowing the nanoparticles to form large agglomerates. Alginate and Suwannee River humic acids exhibit a negative structural charge under this pH condition and adsorption of both natural polyelectrolytes on the surface of nanoparticle agglomerates leads to disagglomeration and significant redispersion of TiO 2 nanoparticles into fragments. Results indicate that both electrostatic forces and steric interactions play key roles during the disagglomeration process and that the physicochemical properties of natural organic matter are found to influence the kinetics and importance of fragmentation in the disagglomeration process. Most importantly, our data indicate that the presence of natural organic matter at typical environmental concentrations induces significant disagglomeration of large submicron nanoparticle agglomerates. Such a result constitutes an important outcome with regards to the risk associated with manufactured nanoparticles by including the possible transformations of the micron size range structures they can form. Nano impactOne of the main problems in the ecological risk assessment of nanomaterials is the lack of important information on their environmental (bio)physicochemical transformations. The disagglomeration of manufactured titanium dioxide nanoparticles is investigated here in the presence of alginate and Suwannee River humic acids at realistic environmental concentrations. Under such concentration conditions, the adsorption of these compounds is found to induce disagglomeration and significant redispersion of TiO 2 nanoparticles into fragments. Such a result constitutes an important outcome with regards to the risk associated with manufactured nanoparticles by considering one important life-cycle transformation of micron size range structures composed of nanoparticles in aquatic systems.

Towards a better understanding on agglomeration mechanisms and thermodynamic properties of TiO2 nanoparticles interacting with natural organic matter

“…Indeed recent findings considering the effect of NOM have shown that electrostatic repulsions and steric interactions between NOM molecules adsorbed onto the ENPs surface enhance the stability and thus the ENPs dispersion state (Hyung et al 2007, Liu et al 2010, Loosli et al 2013, Louie et al 2013, Palomino and Stoll 2013, Zhang et al 2009). Moreover NOM complexation with ENPs is also found to induce the partial redispersion of already formed ENP agglomerates (Baalousha 2009, Loosli et al 2014, Mohd Omar et al 2014. All these studies are investigating the ENPs surface charge modification and give a special interest to the ENPs state of dispersion (resulting size, charge and stability of the ENPs) in presence of NOM.…”

Modelling the interaction processes between nanoparticles and biomacromolecules of variable hydrophobicity: Monte Carlo simulations

“…Due to their large specific surface area, nanoparticle reactivity is high which allows specific physico-chemical properties such as adsorption, catalysis, changes in mechanical and optical properties of materials, etc. [10][11][12][13][14] Nanoparticles can induce harmful biological behavior through a variety of mechanisms which are not fully understood or quantified. Their surrounding environment in natural or biological systems is also of main importance since nanoparticles have the tendency to form aggregates of larger dimensions.…”

Transformations of Metal Nanoparticles in the Aquatic Environment and Threat to Environmental Safety

“…shown that natural organic matter and the presence of microbes may lead to the transformation of nanocompounds and cause their mobilisation in the environment, which may have harmful effects on organisms [23][24][25][26][27].…”

“…The impact of nanoparticles on the environment has been studied not only in terms of interactions with NOM [19], [25], [32], [35], [40][41][42][43][44][45][46][47][48] but also in the context of the possibility of aggregation [23], [38], [40][41], [49][50], the impact of pH on nanoparticle transformation [19], [51][52][53][54][55] and the presence and concentration of various inorganic ions [25], [42], [56][57]. Liu et al [56] noticed that in the presence of CaCl�, the formation of ZnO NP aggregates was more effective than for NaCl and KCl [56].…”