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- ItemInfluence of MoS2 on activity and stability of carbon nitride in photocatalytic hydrogen production(Basel : MDPI AG, 2019) Sivasankaran, R.P.; Rockstroh, N.; Kreyenschulte, C.R.; Bartling, S.; Lund, H.; Acharjya, A.; Junge, H.; Thomas, A.; Brückner, A.MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroyscopy, X-ray photoelectron spectroscopy, electron microscopy, photoluminescence, and in situ electron paramagnetic resonance spectroscopy. During photodeposition, the 2H MoS2 phase was formed upon reduction of [MoS4]2− by photogenerated conduction band electrons and then deposited on the surface of CN. A thin crystalline layer of 2H MoS2 formed an intimate interfacial contact with CN that favors charge separation and enhances the photocatalytic activity. The 2H MS-CN phase showed the highest photocatalytic H2 evolution rate (2342 µmol h−1 g−1, 25 mg catalyst/reaction) under UV-vis light irradiation in the presence of lactic acid as sacrificial reagent and Pt as cocatalyst.
- ItemTwo-step magnetization reversal FORC fingerprint of coupled bi-segmented Ni/Co magnetic nanowire arrays(Basel : MDPI AG, 2018) Fernández, J.G.; Martínez, V.V.; Thomas, A.; de la Prida Pidal, V.M.; Nielsch, K.First Order Reversal Curve (FORC) analysis has been established as an appropriate method to investigate the magnetic interactions among complex ferromagnetic nanostructures. In this work, the magnetization reversal mechanism of bi-segmented nanowires composed by long Co and Ni segments contacted at one side was investigated, as a model system to identify and understand the FORC fingerprint of a two-step magnetization reversal process. The resulting hysteresis loop of the bi-segmented nanowire array exhibits a completely different magnetic behavior than the one expected for the magnetization reversal process corresponding to each respective Co and Ni nanowire arrays, individually. Based on the FORC analysis, two possible magnetization reversal processes can be distinguished as a consequence of the ferromagnetic coupling at the interface between the Ni and Co segments. Depending on the relative difference between the magnetization switching fields of each segment, the softer magnetic phase induces the switching of the harder one through the injection and propagation of a magnetic domain wall when both switching fields are comparable. On the other hand, if the switching fields values differ enough, the antiparallel magnetic configuration of nanowires is also possible but energetically unfavorable, thus resulting in an unstable magnetic configuration. Making use of the different temperature dependence of the magnetic properties for each nanowire segment with different composition, one of the two types of magnetization reversal is favored, as demonstrated by FORC analyses.