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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Construction of multi-shelled Bi2WO6 hollow microspheres with enhanced visible light photo-catalytic performance

Highlights: • Bi{sub 2}WO{sub 6} with multi-shelled hollow microstructure was successfully fabricated and the use of ethylene glycol is a key factor. • Bi{sub 2}O{sub 3}/Bi{sub 2}WO{sub 6} composite with multi-shelled hollow structure were also fabricated when concentration of solution was reduced. • Enhanced visible light photocatalytic performance was observed, which are believed due to the unique hollow microstructure. - Abstract: As a promising structure in enhancing the photo-catalytic performance of the materials, hollow-shell structure still faces the great challenge of constructing an effective architecture for catalytic application. Herein, multi-shelled hollow microspheres of the visible-light photo-catalyst Bi{sub 2}WO{sub 6} with shells up to the triple (BWO-MSH), have been synthesized by using a facile and effective carbonaceous template route. Intriguingly, the photo-catalytic reaction rate constant of BWO-MSH sample is nearly 16 times higher than the Bi{sub 2}WO{sub 6} prepared through solid-state reaction (BWO-SSR). The single-, double-shelled Bi{sub 2}WO{sub 6} microspheres (Broken) could only be synthesized with lower quality (synthesized with many broken species), and their photo-catalytic performance was nearly the same poor as the BWO-SSR sample. Furthermore, multi-shelled hollow microsphere of Bi{sub 2}O{sub 3}/Bi{sub 2}WO{sub 6} (BO/BWO-MSH) composite was also synthesized. The present work not only extends the scope of high-performance complex mixed metal oxides with multi-shelled microstructures, but also brings a good reference to engineer other impressive photo-catalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Visible Light-Driven H 2 Production over Highly Dispersed Ruthenia on Rutile TiO 2 Nanorods

The immobilization of miniscule quantities of RuO 2 (~0.1%) onto one-dimensional (1D) TiO 2 nanorods (NRs) allows H 2 evolution from water under visible light irradiation. Rod-like rutile TiO 2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO 2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO 2 (110) grown as 1D nanowires on rutile TiO 2 (110), which occurs only at extremely low loads of RuO 2 , leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects, band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Three-dimensional ruthenium-doped TiO 2 sea urchins for enhanced visible-light-responsive H 2 production

Here, three-dimensional (3D) monodispersed sea urchin-like Ru-doped rutile TiO 2 hierarchical architectures composed of radially aligned, densely-packed TiO 2 nanorods have been successfully synthesized via an acid-hydrothermal method at low temperature without the assistance of any structure-directing agent and post annealing treatment. The addition of a minuscule concentration of ruthenium dopants remarkably catalyzes the formation of the 3D urchin structure and drives the enhanced photocatalytic H 2 production under visible light irradiation, not possible on undoped and bulk rutile TiO 2 . Increasing ruthenium doping dosage not only increases the surface area up to 166 m 2 g –1 but also induces enhanced photoresponse in the regime of visible and near infrared light. The doping introduces defect impurity levels, i.e. oxygen vacancy and under-coordinated Ti 3+ , significantly below the conduction band of TiO 2 , and ruthenium species act as electron donors/acceptors that accelerate the photogenerated hole and electron transfer and efficiently suppress the rapid charge recombination, therefore improving the visible-light-driven activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Insulating titanium oxynitride for visible light photocatalysis

We propose insulating titanium oxynitrides Ti n N 2 O 2 n -3 as promising water-splitting photocatalytic materials in the visible light range. Using first-principles many-body perturbation theory based on the GW approximation, we show that corundum-type Ti 2 N 2 O (an example Ti n N 2 O 2 n -3 compound with n =2) has a smaller band gap of about 2.5 eV, which is more suitable to absorb visible light, compared to other Ti-based oxides such as TiO 2 and SrTiO 3 with a band gap of more than 3 eV. Band-gap reduction in Ti 2 N 2 O is caused by an upward shift of the valence band (negative shift to the oxidation potential of H 2 O to O 2 ) due to the presence of nitrogen 2 p states. The conduction band is dominated by Ti 3 d states and the conduction-band minimum is nearly unchanged. As a result, the band-edge potentials of Ti 2 N 2 O are better aligned to the water reduction and oxidation levels. Our theoretical predictions provide useful insights for the discovery of efficient visible-light-driven photocatalysts for water splitting.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Enhancement under UV–visible and visible light of the ZnO photocatalytic activity for the antibiotic removal from aqueous media using Ce-doped Lu3Al5O12 nanoparticles

We report the first synthesis of Ce-doped Lu{sub 3}Al{sub 5}O{sub 12} Nanoparticles/ZnO Nanostructure (LuAG:Ce/ZnO NS) via a rapid hydrolysis/condensation of Zn(OAc){sub 2} on the surface of LuAG:Ce NPs. The structural, morphological and optical properties of LuAG:Ce/ZnO NS have been fully investigated using X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), diffuse reflectance UV–visible spectroscopy and N2 adsorption/desorption measurements. Results showed that ZnO Nanocrystals (ZnO NCs) of about 10 nm diameter are homogeneously grown on the surface of 100 nm LuAG:Ce NPs in a core/shell-like structure. The photocatalytic activity of the as-prepared nanostructure has been evaluated throught the photodegradation of sulfathiazole (STZ), a molecule widely used as antibiotic, under UV–vis and visible light irradiation. Results showed that STZ undergoes much higher photodegradation in the presence of LuAG:Ce/ZnO NS compared to the pure ZnO NCs under both UV–vis and visible light. This enhanced photocatalytic capability was found to result from higher specific surface area and visible light absorption in LuAG:Ce/ZnO NS, which allowed for more surface active sites and enhanced hydroxyl radicals (·OH) production from the nanostructured photocatalyst. The recyclability of LuAG:Ce/ZnO NS was also demonstrated.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Visible light carrier generation in co-doped epitaxial titanate films

Perovskite titanates such as SrTiO{sub 3} (STO) exhibit a wide range of important functional properties, including ferroelectricity and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications; however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr, we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr{sup 3+} dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to 2.4–2.7 eV depending on doping levels. Transient reflectance spectroscopy measurements are in agreement with the observations from ellipsometry and confirm that optically generated carriers are present for longer than 2 ns. Finally, through photoelectrochemical methylene blue degradation measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

A Donor–Acceptor [2]Catenane for Visible Light Photocatalysis

Colored charge-transfer complexes can be formed by the association between electron-rich donor and electron-deficient acceptor molecules, bringing about the narrowing of HOMO–LUMO energy gaps so that they become capable of harnessing visible light. In an effort to facilitate the use of these widespread, but nonetheless weak, interactions for visible light photocatalysis, it is important to render the interactions strong and robust. Furthermore, we employ a well-known donor–acceptor [2]catenane—formed by the mechanical interlocking of cyclobis(paraquat-p-phenylene) and 1,5-dinaphtho[38]crown-10—in which the charge-transfer interactions between two 4,4'-bipyridinium and two 1,5-dioxynaphthalene units are enhanced by mechanical bonding, leading to increased absorption of visible light, even at low concentrations in solution. As a result, since this [2]catenane can generate persistent bipyridinium radical cations under continuous visible-light irradiation without the need for additional photosensitizers, it can display good catalytic activity in both photo-reductions and -oxidations, as demonstrated by hydrogen production—in the presence of platinum nanoparticles—and aerobic oxidation of organic sulfides, such as l-methionine, respectively. This research, which highlights the usefulness of nanoconfinement present in mechanically interlocked molecules for the reinforcement of weak interactions, can not only expand the potential of charge-transfer interactions in solar energy conversion and synthetic photocatalysis but also open up new possibilities for the development of active artificial molecular shuttles, switches, and machines.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

Helium line-ratios for electron temperature (T{sub e}) and density (n{sub e}) plasma diagnostic in the Scrape-Off-Layer (SOL) and edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet, 667.8 and 728.1 nm, and triplet, 706.5 nm, visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of this powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. The analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer or by other conflicting lines from different ions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Visible-telecom tunable dual-band optical isolator based on dynamic modulation in thin-film lithium niobate

Optical isolators are an essential component of photonic systems. Current integrated optical isolators have limited bandwidths due to stringent phase-matching conditions, resonant structures, or material absorption. Here, we demonstrate a wideband integrated optical isolator in thin-film lithium niobate photonics. We use dynamic standing-wave modulation in a tandem configuration to break Lorentz reciprocity and achieve isolation. We measure an isolation ratio of 15 dB and insertion loss below 0.5 dB for a continuous wave laser input at 1550 nm. In addition, we experimentally show that this isolator can simultaneously operate at visible and telecom wavelengths with comparable performance. Isolation bandwidths up to ∼100 nm can be achieved simultaneously at both visible and telecom wavelengths, limited only by the modulation bandwidth. Our device’s dual-band isolation, high flexibility, and real-time tunability can enable novel non-reciprocal functionality on integrated photonic platforms.

Shah, Manav↗
DOE OSTI2017

Visible-light-driven ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalysts with enhanced photocatalytic activity under visible light irradiation

Highlights: • The ZnFe2O4/Ag/Ag3VO4 composites were successfully synthesized by a hydrothermal method. • ZnFe2O4/Ag/Ag3VO4 composites showed better photocatalytic activity for MO and TC degradation under visible light. • The ZnFe2O4/Ag/Ag3VO4 photocatalyst is promising for designing an environmental purification material. - Abstract: A novel visible-light driven ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalyst was successfully fabricated through a two-step hydrothermal method. The structure, morphology and composition of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photo-electron spectroscopy (XPS). The as-prepared ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composites possessed an excellent performance in the photocatalytic degradation of methyl orange and tetracycline under visible-light irradiation. The results of electrochemical impedance spectroscopy (EIS) indicated that the ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composite could facilitate the separation of photo-generated carriers, as well as accelerated charge transfer. The 5% ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composite exhibited the upmost photocatalytic activity, the degradation constant of 5% ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} is as high as 1.49 times to that of Ag/Ag{sub 3}VO{sub 4}. Also, according to the trapping experiments, it’s found that the superoxide radicals (·O{sub 2}{sup −}) and hole (h{sup +}) were the predominant reactive species in this system. The ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalyst is promising for designing as an environmental purification material in treatment of antibiotic pollutant.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Visible light absorbance enhanced by nitrogen embedded in the surface layer of Mn-doped sodium niobate crystals, detected by ultra violet - visible spectroscopy, x-ray photoelectron spectroscopy, and electric conductivity tests

Sodium niobate crystals doped with manganese ions, Na(NbMn)O{sub 3}, were annealed in a nitrogen N{sub 2} flow at 600, 670, and 930 K. It was verified that simultaneous doping with Mn ions and annealing in nitrogen enhanced the photocatalytic features of sodium niobate. The transmission in the ultraviolet-visible range was measured at room temperature. The absorbance edge is in the range from 3.4 to 2.3 eV. The optical band gap E{sub gap} = 1.2–1.3 eV was evaluated using the Tauc relation. Crystals annealed at 670 K and 930 K exhibited an additional shift of the absorption edge of ∼20–40 nm toward longer wavelengths. The optical energy gap narrowed as a result of the superimposed effect of Mn and N co-doping. The x-ray photoelectron spectroscopy test showed that N ions incorporated into the surface layer. The valence band consisted of O 2p states hybridized with Nb 4d, Mn 3d, and N 2s states. The disorder detected in the surroundings of Nb and O ions decreased due to annealing. The binding energy of oxygen ions situated within the surface layer was E{sub B} ≈ 531 eV. The other contributions were assigned to molecular contamination. The contribution centered at 535.5 eV vanished after annealing at 600 K and 670 K. The contribution centered at 534 eV vanished after annealing at 930 K. The N{sub 2} annealing partly removed carbonates from the surfaces of the samples. In the 480–950 K range, the electric conductivity activation energy, E{sub a} = 0.7–1.2 eV, was comparable with the optical E{sub gap}. The electric permittivity showed dispersion in the 0.1–800 kHz range that corresponds to the occurrence of defects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗