Tracking of Crystal-Surface-Dependent CuO Nanoparticle Dissolution in an Aqueous Environment.

Metal-oxide-based nanoparticles (MONPs) such as CuO NPs have attracted growing attention, but the potential discharges of MONPs have raised considerable concern of their environmental fate including their dissolution behavior. The impacts of morphology on MONP dissolution are largely uncertain due to the lack of tracking techniques. In this study, we combined a series of technologies including liquid-cell transmission electron microscopy and fluorescence probes to reveal the dissolution process of CuO NPs in freshwater. Our results suggest that cubic CuO NPs exhibit a higher dissolution quantity compared with spherical NPs of the same surface area. The difference was mainly related to the crystal surface, while other factors such as particle size or aggregation status showed minor effects. Importantly, we demonstrated the simultaneous growth of new small NPs and the dissolution of pristine CuO NPs during the dissolution of CuO NPs. Cubic CuO NPs became much less soluble under O-limited conditions, suggesting that O concentration largely affected the dependence of dissolution on the NP morphology. Our findings highlight the potential application of techniques to track the environmental fates of MONPs, which would provide important information for assessing the ecological risks of engineered NPs.