Determination of the flat band potential of doped and non-doped nanoparticles in aqueous environment using a novel electrode preparation method
Final Report Abstract
In this project, a novel three-step electrode preparation was established that enabled the characterization of porous metal oxide nanoparticle electrodes through electrochemical impedance spectroscopy. The three-steps are (A) dry printing, (B) monomer imbibition and polymerization and either (C1) plasma-treatment or (C2) dry polishing. The electrode preparation aimed to block the substrate-electrolyte contact, which would otherwise interfere in the electrochemical characterization. The electrode characterization indicated the complete filling of the pore structure with polymer and the successful blocking of the substrate-electrolyte contact. Mott-Schottky analyses were performed using the impedance spectra of plasma-treated electrodes and the flat band potentials for TiO2, WO3, Co3O4, CuO and ZnO were determined, in agreement with literature values for bulk materials and even measurements from ultraviolet photoelectron spectroscopy (UPS). The theory of amorphous semiconductors (a-SC) was implemented to account for the presence of defect states using density of states distribution functions that provide a more realistic view of the impedance behavior of porous nanoparticle layers. Based on the Mott-Schottky analyses, the estimation of energy levels in relation to the biological redox potential was possible enabling the prediction of the potential toxicity of nanoparticles. The more homogeneous layer thicknesses and the possibility to implement the method with common lab equipment makes dry polishing a promising alternative to the limiting plasma-treatment step. Using the dry polishing technique, the systematic investigation of the electrode structure was possible for the exposed surface area, indicating that the high frequency region reflects the nanoparticle-electrolyte interface required for Mott- Schottky analyses. The successful implementation of the electrode preparation enabled the systematic investigation of the influence of doping on the flat band potential for pure and iron-doped CuO. The difference in the flat band potentials between pure and 10% Fe-doped CuO is about 0.3 V. The measurement of the dissolution kinetics of pure 1, 6 and 10 % Fe-doped CuO and the development of the kinetic model enabled the quantification dissolution rate constants. The dissolution rate constant decreased and the flat band potential shifted to more positive values vs. Ag/AgCl, with increasing iron-content, following a relationship as described by the Tafel equation. We demonstrated that the potential toxicity of nanoparticles is predictable, based on the Mott-Schottky analyses, and we exemplarily showed the correlation of the flat band potential with the application relevant dissolution rate constant. The gained knowledge about the dissolution kinetics was successfully transferred to the field of nanomedicine. These are only a few examples for the relevance of reliable flat band potential measurements for the characterization of nanoparticles. The full potential is far from reach.
Publications
- Determination of the Flat Band Potential of Nanoparticles in Porous Electrodes by Blocking the Substrate–Electrolyte Contact. The Journal of Physical Chemistry C, 2018. 122(5): pp. 2796-2805
Naatz, H., Hoffmann, R., Hartwig, A., La Mantia, F., Pokhrel, S., Mädler, L.
(See online at https://doi.org/10.1021/acs.jpcc.7b11423) - Verfahren zur Bestimmung des Flachbandpotenzials von Nanopartikeln in porösen Elektroden. Chemie Ingenieur Technik, 2018. 90 (9): pp. 1212-1212
Naatz, H., Hoffmann, R., Hartwig, A., La Mantia, F., Pokhrel, S., Mädler, L.
(See online at https://doi.org/10.1002/cite.201855178) - Inside Back Cover: Model-Based Nanoengineered Pharmacokinetics of Iron-Doped Copper Oxide for Nanomedical Applications. Angewandte Chemie International Edition, 2020. 59(5): pp. 2123-2123
Naatz, H., Manshian, B. B., Rios Luci, C., Tsikourkitoudi, V., Deligiannakis, Y., Birkenstock, J., Pokhrel, S., Mädler, L., Soenen, S. J.
(See online at https://doi.org/10.1002/anie.201916183) - Iron-Doping of Copper Oxide Nanoparticles Lowers Their Toxic Potential on C6 Glioma Cells. Neurochemical Research, 2020. 45: pp. 809-824
Joshi, A., Naatz, H., Faber, K., Pokhrel, S., Dringen, R.
(See online at https://doi.org/10.1007/s11064-020-02954-y) - Model-Based Nanoengineered Pharmacokinetics of Iron-Doped Copper Oxide for Nanomedical Applications. Angewandte Chemie International Edition, 2020. 59 (5): pp. 1844-1852
Naatz, H., Manshian, B. B., Rios Luci, C., Tsikourkitoudi, V., Deligiannakis, Y., Birkenstock, J., Pokhrel, S., Mädler, L., Soenen, S. J.
(See online at https://doi.org/10.1002/anie.201912312)
