Monodisperse, monocrystalline magnesium ferrite (MgFe2O4) nanoparticles were synthesized phase purely by fast nonaqueous microwave-assisted solution-phase synthesis. Colloidal stabilization of the nanocrystals in nonaqueous media was realized either in-situ during synthesis or postsynthetically by surface capping with oleylamine and oleic acid. Phase transfer to aqueous media was performed employing citric acid and betaine hydrochloride, resulting in agglomerate-free dispersions of citrate- or betaine-functionalized MgFe2O4 nanocrystals. Furthermore, a one-step synthesis of highly stable, water-dispersible colloids of MgFe2O4 was achieved using polyvinylpyrrolidone as stabilizer. Characterization of the as-synthesized and functionalized nanoparticles was performed employing X-ray diffraction, UV–vis and infrared spectroscopy, thermogravimetry, dynamic light scattering, and transmission electron microscopy. Special focus was laid on phase purity, which was thoroughly monitored using Raman microscopy/spectroscopy. Photocatalytic reactions were performed to evaluate the use of such highly stable ferrite colloids for solar energy conversion.

Phase-pure magnesium ferrite (MgFe2O4) spinel nanocrystals are synthesized by a fast microwave-assisted route. The elemental composition is optimized via the ratio of the precursor mixture and controlled by energy-dispersive X-ray spectroscopy. Fine-tuning of the magnetic properties without changing the overall elemental composition is demonstrated by superconducting quantum interference device (SQUID) magnetometry and Mössbauer spectroscopy. Together with X-ray absorption spectroscopy and X-ray emission spectroscopy, we confirm that the degree of cation inversion is altered by thermal annealing. We can correlate the magnetic properties with both the nanosize influence and the degree of inversion. The resulting nonlinear course of saturation magnetization (M s) in correlation with the particle diameter allows to decouple crystallite size and saturation magnetization, by this providing a parameter for the production of very small nanoparticles with high M s with great potential for magnetic applications like ferrofluids or targeted drug delivery. Our results also suggest that the optical band gap of MgFe2O4 is considerably larger than the fundamental electronic band gap because of the d5 electronic configuration of the iron centers. The presented different electronic transitions contributing to the absorption of visible light are the explanation for the large dissent among the band gaps and band potentials found in the literature.

Electrospun layered perovskite Ba5Ta4O15 nanofibers are varied in their diameter for the first time by the identification of electrospinning setup parameters controlling the resulting nanofiber diameter. The influence of fiber diameter on photocatalytic water splitting activity is revealed.

Earth-abundant visible light-absorbing photoelectrodes of the spinel ferrites ZnFe 2 O 4 and MgFe 2 O 4 have been prepared as dense and crackfree thin films using pulsed laser deposition, to investigate the basic electronic properties of these two emerging absorber materials. X-ray diffraction and Raman spectroscopy confirm the phase purity of the prepared thin films, whereas magnetotransport and Hall measurements in combination with Mott− Schottky and photoelectrochemical measurements were performed to reveal the performance-limiting factors of those absorbers for photoelectrochemical water oxidation. Our results provide new insights to improve the performance of ferrite-based photoelectrodes in the future.