Indium tin oxide (ITO) is the largest industrial product containing indium and among the most widely produced engineered nanomaterials globally owing to widespread use in the electronics industry, namely in flat-panel displays. Numerous studies have demonstrated toxicity of ITO nanoparticles in various organisms, including humans. However, scientific research into the transport, transformation, and eventual fate of ITO in the environment is lacking. This study advances the fundamental understanding of the behavior of ITO, both physical and chemical, in aqueous systems as a function of the relative amount of tin within the ITO nanoparticle. Specifically, we investigated dissolution and aggregation phenomena as a function of tin content. Commercial ITO nanopowders with SnO2:I2O3 ratios of 0, 5, and 10% by mass were used as-received. Each nanopowder was ultrasonically dispersed in reagent water adjusted to various pH values between 3 and 11. Dissolution rates of well-mixed ITO nanopowder dispersions were monitored by filtering aliquots and determining ionic indium and tin concentrations by ICP-OES. Equilibrium concentrations of indium and tin were used to determine the solubility constants of ITO. It was found that at environmentally-relevant concentrations of ITO (less than 1 mg L-1) and near neutral pH, a significant amount of indium leaches from the nanocrystal, resulting in an ITO/SnO2 core-shell nanoparticle. Aqueous stability and aggregation kinetics of these nanoparticles in electrolyte solutions at multiple pH values were monitored with time-resolved dynamic light scattering. Zeta-potential was determined as a function of ionic strength and pH using electrophoretic mobility measurements. These data were used to determine aggregation stability constants (1/W) for each level of tin dopant at each pH and electrolyte type. The experimental stability constants were fit to theoretical models, both classic DLVO and a Maxwell-Boltzmann distribution-modified DLVO, to determine which model best described homoaggregation behavior of ITO nanoparticles in model aqueous solutions.

Transformation and aggregation of indium tin oxide (ITO) nanoparticles: Influence of surface chemistry on environmental fate of globally important engineered nanomaterial

255th National Meeting (2018)

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