Titania (TiO2) nanoparticles are used in a great number of consumer products and therefore the quantity of nanoparticles and their transformation products reaching the environment is increasing. The question is, when they reach the aquatic environment, what happens to their stability?
Nanoparticles in aquatic environments are subject to different types of forces which can lead to aggregation, stabilization or deposition of the particles.
The aggregation of nanoparticles has a strong influence in determining their final fate in the environment. Julián A. Gallego-Urrea and colleagues from the University of Gothenburg have conducted a study to evaluate the effects of natural organic matter (NOM) on the aggregation kinetics of titania nanoparticles.
It is important to be able to predict nanoparticles transformation products in a physically meaningful way for near source emissions, spill situations and ecotoxicity tests, where other particles are less significant for determining ENP fate. When nanoparticles interact with NOM transformation processes can occur. For example, sorption of NOM onto the surface of engineered nanoparticles (ENP) can lead to aggregation via bridging mechanisms or stabilization.
The stability of titania nanoparticles in natural water is influenced not only by their concentration, but also by the physico-chemical characteristics of the receiving water.
In this study the stabilization of synthesized titania nanoparticles obtained at various pH levels, with a variety of electrolytes, was evaluated.
The titania nanoparticles were rapidly mixed with NOM, Sodium Alginate, Fulvic acid or Humic acid and three different electrolytes, NaCl, CaCl2 and Na2SO4
The change in particle size was then monitored with time-resolved dynamic light scattering (TR-DLS) at different concentrations of three different electrolytes and different solutions of pH. By measuring the particle size it could be determined what effects the different systems actually had on the stability of the nanoparticles.
The results showed that:
- The addition of NOM increased the stability of the systems with NaCl and Na2SO4.
- NOM had little influence on the CaCl2 system, suggesting that there is bridging coagulation between the NOM and calcium.
In general, it was demonstrated that a low coverage of NOM on top of bare titania particles can induce aggregation, but further coverage can protect them from aggregation – even at high ionic strengths. The degree of coverage is governed by the concentration ratio between nanoparticles and NOM.
The study showed that the ionic strength, pH, quality and quantity of NOM all have a significant influence on the aggregation behaviour of titania.
To read more about the full experiment, download a copy for free by clicking the link below.
Julian Alberto Gallego-Urrea, Jenny Perez-Holmberg and Martin Hasselloev
DOI: 10.1039/C3EN00106G
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