The goal here was to make titanium dioxide (TiO₂) ENMs that could be tracked in the environment against a high background of naturally abundant Ti.  NanoFASE partners EAWAG and UoB determined that to have sufficient resolution of the chemically labelled ENMs, at least 10% of the Ti atoms would have to be replaced by holmium (Ho). However, this would introduce too great a change in the lattice structure and properties of the Ti_xHo_1-xO₂ ENMs compared to those of the TiO₂ particles whose environmental fate and behaviour they were supposed to represent. To overcome this, an alternative strategy was developed, whereby all of the Ho was made as a core, and a layer of TiO₂ was grown around this, such that the TiO₂ layer would be representative of the unlabelled TiO₂ ENMs, while the Ho core would serve as a tracer for the ENMs. Core shell particles are represented notationally as Ho@TiO₂ core–shell ENMs.

This synthesis approach proved to be a lot harder than expected, and numerous routes were tried with varied degrees of success.  The outcome solution for producing the core-shell particles involved a templating method for the large-scale synthesis of NaHoF₄@TiO₂ core–shell ENMs, in which a sacrificial Al(OH)₃ layer was deposited onto the NaHoF₄ core ENM surface and then etched by HF or other fluorinated species via the hydrolysis of TiF₄, resulting in the outer TiO2 shell. The resulting ENMs consisted of a 60 nm NaHoF₄ core and a 5 nm anatase TiO₂ shell, as determined by TEM, STEM-EDX mapping, and spICP-MS.

Figure: A schematic illustration of the synthetic route to produce NaHoF₄@TiO₂ ENMs. From Cui et al., 2019.

Read more

Cui X, Fryer B, Zhou D, Lodge R, Khlobystov A, Valsami-Jones E, Lynch I. Core-shell NaHoF4@TiO2 NPs: A Labelling Method to Trace Engineered Nanomaterials of Ubiquitous Elements in The Environment. ACS Applied Materials & Interfaces, 2019, 11, 19452-19461. https://pubs.acs.org/doi/10.1021/acsami.9b03062

Contact

Xianjin Cui

 

 

 

 

Iseult Lynch

University of Birmingham

i.lynch@bham.ac.uk