Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.079
Publication date: 18th July 2019
We have developed a straightforward microwave synthesis protocol to produce nanocrystals of the earth-abundant cubic spinel ferrites MgFe2O4, NiFe2O4 and ZnFe2O4,[1,2] which are promising materials for both photoelectrochemical and photocatalytic water splitting under visible light irradiation due to their narrow band gaps (~ 2.0 eV) and matching band positions. The crystallite size can be tailored by post-synthetic heat treatment, however the materials are already partly crystalline as-prepared. Samples were characterized employing transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and N2 physisorption, indicating highly-crystalline, single phase nanoparticles with specific surface areas of around 200 m²/g and good colloidal stability in non-polar solvents. Phase transfer into aqueous medium has been performed using different organic capping ligands, resulting in stable dispersions with a narrow size distribution. First results of photocatalytic experiments will be presented.
In addition, well-ordered mesoporous ZnFe2O4 and a-LiFe5O8 thin film photoanodes were fabricated by sol-gel synthesis,[3,4] using a polymer-templating approach previously reported by Haetge et al..[5] Ordered mesopores are obtained after dip-coating by evaporation-induced self-assembly followed by heat treatment. Scanning electron microscopy (SEM) confirms the porous morphology with average pore diameters of 12-15 nm. Raman spectroscopy and XRD Rietveld analysis revealed phase pure mesoporous thin films with a crystallite size of 15 nm. Furthermore, photocurrent and Mott-Schottky measurements were performed at different pH values to determine the flat band potential and photocurrent density of the thin film electrodes calcined at various temperatures.
Finally, mesoporous CaFe2O4 photocathodes will be presented showing p-type behavior.[6] For the first time, this material can be prepared at temperatures as low as 700 °C.
Sincere thanks go to Dr C. Suchomski and Prof. B. M. Smarsly for their support in the beginning of this project. R. M. acknowledges funding by the German Research Foundation DFG under the priority program SPP 1613, Project MA 5392/5-1, and the Emmy-Noether program, project MA 5392/3-1
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