Browsing by Subject "Charge transfer process"

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Open Access
Nanograined surface shell wall controlled ZnO–ZnS core–shell nanofibers and their shell wall thickness dependent visible photocatalytic properties
(Royal Society of Chemistry, 2017) Ranjith, K. S.; Senthamizhan A.; Balusamy, B.; Uyar, Tamer
The core-shell form of ZnO-ZnS based heterostructural nanofibers (NF) has received increased attention for use as a photocatalyst owing to its potential for outstanding performance under visible irradiation. One viable strategy to realize the efficient separation of photoinduced charge carriers in order to improve catalytic efficiency is to design core-shell nanostructures. But the shell wall thickness plays a vital role in effective carrier separation and lowering the recombination rate. A one dimensional (1D) form of shell wall controlled ZnO-ZnS core-shell nanofibers has been successfully prepared via electrospinning followed by a sulfidation process. The ZnS shell wall thickness can be adjusted from 5 to 50 nm with a variation in the sulfidation reaction time between 30 min and 540 min. The results indicate that the surfaces of the ZnO nanofibers were converted to a ZnS shell layer via the sulfidation process, inducing visible absorption behavior. Photoluminescence (PL) spectral analysis indicated that the introduction of a ZnS shell layer improved electron and hole separation efficiency. A strong correlation between effective charge separation and the shell wall thickness aids the catalytic behavior of the nanofiber network and improves its visible responsive nature. The comparative degradation efficiency toward methylene blue (MB) has been studied and the results showed that the ZnO-ZnS nanofibers with a shell wall thickness of ∼20 nm have 9 times higher efficiency than pristine ZnO nanofibers, which was attributed to effective charge separation and the visible response of the heterostructural nanofibers. In addition, they have been shown to have a strong effect on the degradation of Rhodamine B (Rh B) and 4-nitrophenol (4-NP), with promising reusable catalytic efficiency. The shell layer upgraded the nanofiber by acting as a protective layer, thus avoiding the photo-corrosion of ZnO during the catalytic process. A credible mechanism for the charge transfer process and a mechanism for photocatalysis supported by trapping experiments in the ZnO-ZnS heterostructural system for the degradation of an aqueous solution of MB are also explicated. Trapping experiments indicate that h+ and OH are the main active species in the ZnO-ZnS heterostructural catalyst, which do not effectively contribute in a bare ZnO catalytic system. Our work also highlights the stability and recyclability of the core-shell nanostructure photocatalyst and supports its potential for environmental applications. We thus anticipate that our results show broad potential in the photocatalysis domain for the design of a visible light functional and reusable core-shell nanostructured photocatalyst.
Open Access
Probing the interfacial molecular structure of a Co-Prussian blue in situ
(Wiley-VCH Verlag GmbH & Co. KGaA, 2024-04-29) Bera, A.; De, R.; Schmidt, H.; Leistenschneider, D.; Ulusoy Ghobadi, Türkan Gamze; Oschatz, M.; Karadaş, Ferdi; Dietzek-Ivansic, B.
Molecular-level insight into the interfacial composition of electrodes at thesolid-electrolyte and the solid-electrode interface is essential to understanding the charge transfer processes, which are vital for electrochemical (EC) and photoelectrochemical (PEC) applications. However, spectroscopic access toboth interfaces, particularly upon application of an external bias, remains achallenge. Here, in situ surface sensitive vibrational sum-frequency generation (VSFG) spectroscopy is used for the ﬁrst time to directly access the interfacial structure of a cobalt-containing Prussian blue analog (Co-PBA) incontact with the electrolyte and TiO₂/Au surface. Structural and compositional changes of the Prussian blue layer during electrochemicaloxidation are studied by monitoring the stretching vibration of the CN group. At open circuit potential, VSFG reveals a non-homogeneous distribution ofoxidation states of metal sites: Feᴵᴵᴵ–CN–Coᴵᴵ and Feᴵᴵ –CN–Co coordinationmotifs are dominantly observed at the Co-PBA|TiO₂ interface, while it is onlythe Feᴵᴵ–CN–Coᴵᴵ unit at the electrolyte interface. Upon increasing the potential applied to the electrode, the partial oxidation of Feᴵᴵ–CN–Coᴵᴵ to Feᴵᴵᴵ–CN–Coᴵᴵ is observed followed by its transformation to Feᴵᴵ–CN–Coᴵᴵᴵ via charge transfer and, ﬁnally, the formation of Feᴵᴵᴵ–CN–Coᴵᴵᴵ species at the interface with TiO2 and the electrolyte.