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Regarding catalytic and plasmonic properties of gold nanoparticles (NPs), the novel area of research on photocatalytic gold properties has been recently started. In contrast with catalytically active gold NPs, where nano-sized gold is recommended, our results showed that polydispersity of deposited gold NPs on semiconducting support was beneficial for photocatalytic activity under visible light irradiation. It is thought that wide size/shape distribution of gold NPs, and thus the ability of absorption of light in a wide wavelengths range is responsible for the high level of photoactivity. Though desirable absorption properties of plasmonic photocatalysts can be easily obtained by preparation of nanoparticles of different sizes and shapes, their photocatalytic activities under visible light irradiation are still low and should be enanced. The improvement of photocatalytic activities under visible light irradiation was achieved by enlargement of interfacial contact between titania and NPs of noble metals, extension of photoabsorption ranges (by preparation of NPs of various sizes and shapes or composed of two kinds of noble metals), and by deposition of noble metals NPs on faceted titania, i.e., octahedral (OAPs) and decahedral (DAPs). Plasmonic photocatalysts composed of titania and NPs of silver, gold or copper showed also high antiseptic properties under visible light irradiation, due to possible synergism of antiseptic properties of noble metals and photodisinfection properties of photocatalyst, since reactive oxygen species or photogenerated holes are formed on the surface of irradiated semiconductor.
A co-catalyst was synthesized by photochemically depositing Pd nanoparticles onto TiO2 nanopowder support in a one-pot synthesis procedure. The Pd nanoparticles exhibited localised surface plasmon resonance observed using UV-VIS which increased the absorption cross-section of the co-catalyst system into the visible as well as UV regions of the spectrum. This was found to have a significant contribution to the photocatalytic activity of the catalyst in dye degradation experiments. The size, morphology and distribution of the Pd nanoparticles were determined by TEM, while the chemical state and amount of Pd deposited were analysed via XPS and ICP respectively.
We use BaTiO3 as a model photocatalyst to investigate the effect of ferroelectricity on catalytic activity against photocatalytic decolourisation of Acid Black 1. We find that there is a strong relationship between the degree of ferroelectric nature of the BaTiO3 and the catalytic activity. When Ag is photodeposited onto BaTiO3 to produce a modified BaTiO3, the higher tetragonal material content shows the highest photocatalytic efficiency even though there is a reduced surface area due to heat treatment. This change in the performance of the catalyst is associated with improvements in charge carrier separation due to the internal space charge layer formed in a ferroelectric due to the internal dipole.
We show that we have developed a hydrothermal process that produces a high surface area TiO2 on glass fibre supports. The as produced titania shows good photocatalytic activity against a standard commercial dye – Rhodamine B– giving full decolourisation within 3 hours under UV and visible light irradiation. The samples are mechanically robust and can act as a photocatalytic filter for waste streams and pollutants. In addition to testing the standard titania we also photochemically deposit nanostructures of Pd. These hybrid catalysts show enhanced decolourisation by an order of magnitude over the native titania systems. This enhanced performance is due to the increased energy harvesting of the hybrid system through a visible light plasmon interaction and the direct injection of electrons from the noble metal into the adsorbed dye molecules. There is a clear relationship between the absorbed light and photochemical reactivity of the system which is further explained in terms of electron hole generation and separation and plasmonic interaction. In summary, we have generated a high performance catalyst that is produced on a bulk commodity substrate with enhanced activity due to control of the surface plasmon and direct band gap transition of electron hole pairs in the semi-conductor.
The influence of super high frequency (SHF) circular magnetic field on magnetization reversal in the Co-rich glass covered microwire has been investigated. The study has been performed by magneto-optical Kerr effect (MOKE) technique. It was found that the presence of the SHF field causes the change of the re-magnetization mechanism – the rotation of the magnetization is observed instead of domain walls motion. Also the hysteresis loop has an asymmetric shape that confirms the co-existence of the stable and meta-stable helical magnetic states in the surface of microwires.
The paper considers the effects of compacting pressure and the working parameters (maximum flux density, excitation frequency) on power loss dissipated in a soft magnetic composite core. The effects may be efficiently described with simple power laws . The description has been verified using commercial SMC cores. The proposed dependencies are in a good agreement with experiment.
Magnetocaloric materials with a Curie temperature near room temperature are of interest for application in high-efficiency solid state cooling. There are several promising families of materials including the LaFe13-xSix system which offers large magnetocaloric entropy change, low magnetic and thermal hysteresis, and tunability of the metamagnetic transition by introduction of interstitial hydrogen or partial substitution on the La or Fe sites. There is a large amount of literature on the properties and mechanism of the magnetocaloric effect in this material system, and more recently our group and several other groups have discussed the origins of the dynamics of the metamagnetic transition and its relation to magnetic hysteresis. Nevertheless, although extremely informative in other systems, there has been little spatially resolved information concerning the nature of the magnetic transition in this system. Here we use scanning Hall probe imaging to study LaFe13-xSix polycrystalline samples with x=1.2 prepared by induction melting to resolved the local static and dynamic magnetic properties. We find that the local properties of the magnetic transition are governed by chemical inhomogeneity rather that demagnetization effects associated with sample geometry.
One of the most surprising and significant advances in the study of the photosynthetic light- harvesting process is the discovery that the electronic energy transfer (ET) might involve long-lived electronic coherences, also at physiologically relevant conditions. This means that the transfer of energy among different chromophores does not follow the expected classical incoherent hopping mechanism, but that quantum-mechanical laws can steer the migration of energy. The implications of such quantum transport regime, although currently under debate, might have a tremendous impact in our way to think about natural and artificial light-harvesting and suggest new directions for the development of artificial devices for the efficient capture and re-use of solar energy. Central to these discoveries has been the development of new ultrafast spectroscopic techniques, in particular two-dimensional electronic spectroscopy, which is now the primary tool to obtain clear and definitive experimental proof of such effects.
Different nanocomposite materials consisting of semiconducting CdSe nanocrystals (NCs) and a low band gap copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4- b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) were prepared, morphologically characterized, and tested in hybrid solar cells. In addition, a PCPDTBT-based rod-coil diblock copolymer was synthesized through a grafting-onto approach and a preliminary evaluation of the morphology of the hybrid nanocomposites with CdSe NCs was performed.
In this work we present some results of an extensive investigation aimed to find suitable conditions to grow CuZnSnSe (CZTSe) nanostructures through single-step electrodeposition into the channels of polycarbonate membranes. After the optimization of several electrodeposition parameters, we have found that pulsed current deposition, between 0 and -1 mA cm-2, is the best way to obtain CZTSe nanostructures mechanically attached to the support. An interesting result concerns the effect of supporting electrolyte in the deposition bath. In fact, changing its concentration it is possible to vary morphology of nanostructures from nanotubes to nanowires. In both case uniform arrays of ordered nanostructures were obtained on a Ni current collector that are very stable also after thermal treatment at 550°C.
Ni-Co thin films were prepared on glass substrate by RF magnetron sputtering technique. Post-deposition annealing of Ni-Co film in oxygen atmosphere was found to improve film structure and electrical characteristics. The correlation between annealing conditions and the physical structure of the films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis-NIR spectrophotometer. The lowest resistivity was observed after annealing a sputter-deposited Ni-Co film at 600 °C for 5h. The transmittance showed more than 85% in the infrared range. The preferred annealing condition has been found to improve Ni-Co film characteristics for transparent conducting material applications.
We report on advances in the fabrication of high quality bipolar heterodiodes with oxide electrodes. The highest rectification above 1010 is obtained for a structure from a-ZCO/ZnO/ZnO:Al on Al2O3 (a-ZCO: amorphous ZnCo2O4). Rectification better than 106, a value larger than reported for all previous attempts, is obtained for our a-ZCO/a-ZTO (a-ZTO: amorphous zinc tin oxide), a-NiO/ZnO and CuI/ZnO diodes. The ZCO/ZnO has been used as gate in JFETs with ZnO as channel. The bipolar diodes open the field of oxide semiconductor electronics to applications in photovoltaics.
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