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- ItemLong-Living Holes in Grey Anatase TiO2 Enable Noble-Metal-Free and Sacrificial-Agent-Free Water Splitting(Weinheim : Wiley-VCH, 2020) Liu, Ning; Mohajernia, Shiva; Nguyen, Nhat Truong; Hejazi, Seyedsina; Plass, Fabian; Kahnt, Axel; Yokosawa, Tadahiro; Osvet, Andres; Spiecker, Erdmann; Guldi, Dirk M.; Schmuki, PatrikTitanium dioxide has been the benchmark semiconductor in photocatalysis for more than 40 years. Full water splitting, that is, decomposing water into H2 and O2 in stoichiometric amounts and with an acceptable activity, still remains a challenge, even when TiO2-based photocatalysts are used in combination with noble-metal co-catalysts. The bottleneck of anatase-type TiO2 remains the water oxidation, that is, the hole transfer reaction from pristine anatase to the aqueous environment. In this work, we report that “grey” (defect engineered) anatase can provide a drastically enhanced lifetime of photogenerated holes, which, in turn, enables an efficient oxidation reaction of water to peroxide via a two-electron pathway. As a result, a Ni@grey anatase TiO2 catalyst can be constructed with an impressive performance in terms of photocatalytic splitting of neutral water into H2 and a stoichiometric amount of H2O2 without the need of any noble metals or sacrificial agents. The finding of long hole lifetimes in grey anatase opens up a wide spectrum of further photocatalytic applications of this material. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemHighly selective visible light-induced Ti–O bond splitting in an ansa-titanocene dihydroxido complex(Cambridge : Soc., 2015) Godemann, Christian; Dura, Laura; Hollmann, Dirk; Grabow, Kathleen; Bentrup, Ursula; Jiao, Haijun; Schulz, Axel; Brückner, Angelika; Beweries, TorstenIrradiation of a substituted ansa-titanocene(IV) dihydroxido complex with visible light induces Ti–O bond dissociation. In contrast to previous studies on structurally similar unbridged complexes, no side reactions are observed and formation of the Ti(III) species is highly selective. The formation of OH radicals was proved using a biradicaloid species.
- ItemTernary CNTs@TiO2/CoO nanotube composites: Improved anode materials for high performance lithium ion batteries(Basel : MDPI, 2017) Madian, Mahmoud; Ummethala, Raghunandan; El Naga, Ahmed Osama Abo; Ismail, Nahla; Rümmeli, Mark Hermann; Eychmüller, Alexander; Giebeler, LarsTiO2 nanotubes (NTs) synthesized by electrochemical anodization are discussed as very promising anodes for lithium ion batteries, owing to their high structural stability, high surface area, safety, and low production cost. However, their poor electronic conductivity and low Li+ ion diffusivity are the main drawbacks that prevent them from achieving high electrochemical performance. Herein, we report the fabrication of a novel ternary carbon nanotubes (CNTs)@TiO2/CoO nanotubes composite by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2/CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2/CoO NTs, without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity, promoting a strongly favored lithium insertion into the TiO2/CoO NT framework, and hence resulting in high capacity and an extremely reproducible high rate capability.
- ItemCrystallization behavior of poly(lactic acid)/titanium dioxide nanocomposites(Bangkok : King Mongkut’s University of Technology, 2015) Nomai, Jiraporn; Suksut, Buncha; Schlarb, Alois KIn this study, a poly(lactic acid) (PLA) with various titanium dioxide (TiO2) nanoparticles loading were prepared by a manual laboratory mixing method. The effect of TiO2 nanoparticles on the non-isothermal and the isothermal crystallization behavior of PLA was investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The presence of TiO2 nanoparticles decreased the spherulite growth rate of PLA, whereas it initiated faster crystallization through the heterogeneous nucleation process as observed by optical microscopy. The results of DSC analyzes confirmed that the TiO2 nanoparticles act as an efficient nucleating agent for PLA crystallization. The cold crystallization temperature and crystallization half-time of PLA decreased, while the degree of crystallinity of PLA increased in relation to increases of TiO2 nanoparticles.
- ItemStrain-stabilized superconductivity([London] : Nature Publishing Group UK, 2021) Ruf, J.P.; Paik, H.; Schreiber, N.J.; Nair, H.P.; Miao, L.; Kawasaki, J.K.; Nelson, J.N.; Faeth, B.D.; Lee, Y.; Goodge, B.H.; Pamuk, B.; Fennie, C.J.; Kourkoutis, L.F.; Schlom, D.G.; Shen, K.M.Superconductivity is among the most fascinating and well-studied quantum states of matter. Despite over 100 years of research, a detailed understanding of how features of the normal-state electronic structure determine superconducting properties has remained elusive. For instance, the ability to deterministically enhance the superconducting transition temperature by design, rather than by serendipity, has been a long sought-after goal in condensed matter physics and materials science, but achieving this objective may require new tools, techniques and approaches. Here, we report the transmutation of a normal metal into a superconductor through the application of epitaxial strain. We demonstrate that synthesizing RuO2 thin films on (110)-oriented TiO2 substrates enhances the density of states near the Fermi level, which stabilizes superconductivity under strain, and suggests that a promising strategy to create new transition-metal superconductors is to apply judiciously chosen anisotropic strains that redistribute carriers within the low-energy manifold of d orbitals.
- ItemDielectric Properties and Spectral Characteristics of Photocatalytic Constant of TiO2 Nanoparticles Doped with Cobalt(Basel : MDPI, 2021) Bessergenev, V.G.; Mariano, J.F.; Mateus, M.C.; Lourenço, J.P.; Ahmed, A.; Hantusch, M.; Burkel, E.; Botelho do Rego, A.M.Dielectric properties and spectral dependence of the photocatalytic constant of Co doped P25 Degussa powder were studied. Doping of TiO2 matrix with cobalt was achieved by precipitation method using of Tris(diethylditiocarbamate)Co(III) precursor (CoDtc–Co[(C2H5)2NCS2]3). Five different Co contents with nominal Co/Ti atomic ratios of 0.005, 0.01, 0.02, 0.05 and 0.10 were chosen. Along with TiO2:Co samples, a few samples of nanopowders prepared by Sol-Gel method were also studied. As it follows from XPS and NMR studies, there is a concentration limit (TiO2:0.1Co) where cobalt atoms can be uniformly distributed across the TiO2 matrix before metallic clusters start to form. It was also shown that CoTiO3 phases are formed during annealing at high temperatures. From the temperature dependence of the dielectric constant it can be concluded that the relaxation processes still take place even at temperatures below 400 °C and that oxygen defect Ti–O octahedron reorientation take place at higher temperatures. The spectral dependency of the photocatalytic constant reveals the presence of some electronic states inside the energy gap of TiO2 for all nanopowdered samples.
- ItemOrdered Mesoporous TiO2 Gyroids: Effects of Pore Architecture and Nb-Doping on Photocatalytic Hydrogen Evolution under UV and Visible Irradiation(Weinheim : Wiley-VCH, 2018) Dörr, Tobias Sebastian; Deilmann, Leonie; Haselmann, Greta; Cherevan, Alexey; Zhang, Peng; Blaha, Peter; de Oliveira, Peter William; Kraus, Tobias; Eder, DominikPure and Nb-doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well-controllable mesopore size of 15 nm via co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X-ray scattering, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter-bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25-TiO2 more than fivefold. Under UV light, the Nb-doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter-bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial-like behavior, which will stimulate further studies focusing on novel light–matter interactions.
- ItemCompositional Patterning in Carbon Implanted Titania Nanotubes(Weinheim : Wiley-VCH, 2021) Kupferer, Astrid; Holm, Alexander; Lotnyk, Andriy; Mändl, Stephan; Mayr, Stefan G.Ranging from novel solar cells to smart biosensors, titania nanotube arrays constitute a highly functional material for various applications. A promising route to modify material characteristics while preserving the amorphous nanotube structure is present when applying low-energy ion implantation. In this study, the interplay of phenomenological effects observed upon implantation of low fluences in the unique 3D structure is reported: sputtering versus readsorption and plastic flow, amorphization versus crystallization and compositional patterning. Patterning within the oxygen and carbon subsystem is revealed using transmission electron microscopy. By applying a Cahn–Hilliard approach within the framework of driven alloys, characteristic length scales are derived and it is demonstrated that compositional patterning is expected on free enthalpy grounds, as predicted by density functional theory based ab initio calculations. Hence, an attractive material with increased conductivity for advanced devices is provided. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH