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At least 1,639 records · Page 91

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DOE OSTI2013

Uniformly dispersed CdS nanoparticles sensitized TiO{sub 2} nanotube arrays with enhanced visible-light photocatalytic activity and stability

In this study, TiO{sub 2} nanotube arrays (TiO{sub 2}-NTs) with various intertube spaces were fabricated in the electrolyte with different water contents and the CdS nanoparticles (CdS NPs) were further deposited onto the TiO{sub 2}-NTs as a sensitizer via a sequential chemical bath deposition (S-CBD) method. The FE-SEM, TEM, XRD and XPS results demonstrated that the CdS NPs were uniformly deposited onto the surface of TiO{sub 2}-NTs. It was found that higher water content in electrolyte was in favor of large intertube space and pore size and the uniform deposition of CdS NPs. The photocatalytic degradation of methyl orange was tested with the as-prepared CdS/TiO{sub 2}-NTs under visible light (λ>400 nm). It was found that the photodegradation rate reached as high as 96.7% under visible irradiation for 180 min. In addition, a reasonable degradation rate of 75.8% was achieved even after 5 cycles, suggesting a good photocatalytic stability of the as-prepared CdS/TiO{sub 2}-NTs. - Graphical abstract: The whole sheet of CdS NPs sensitized TiO{sub 2}-NTs with the Ti subtract was used for degradation of methyl orange under visible light (λ>400 nm) on a XPA-7 photochemical reactor. - Highlights: • Intertube space, pore size were controlled by changing water content in electrolyte. • CdS nanoparticles were uniformly deposited onto the surface of TiO{sub 2} nanotubes. • The catalyst with Ti substrate used as a whole was very convenient for recycling. • Visible-light photocatalytic activity and stability were highly enhanced.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites

Highlights: ► Topochemical reactions involving intercalation allow construction of metal chalcogenide arrays within perovskite hosts. ► Gaseous chalcogen hydrides serve as effect reactants for intercalation of sulfur and selenium. ► New compounds prepared by a two-step intercalation strategy are presented. -- Abstract: A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb{sub 2}O{sub 7}, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb{sub 2}LaNb{sub 2}O{sub 7}. This compound is then reacted at room-temperature with in situ generated H{sub 2}S gas to create Rb-S layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) Å, c = 15.256(1) Å; space group P4/mmm) shows the compound to be isostructural with (Rb{sub 2}Cl)LaNb{sub 2}O{sub 7} where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (∼0.8) of the product indicate a higher sulfur content than expected for S{sup 2−} alone. This combined with the Raman studies, which show evidence for an H-S stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H{sub 2}Se{sub (g)} were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.

36 MATERIALS SCIENCE↗

DOE OSTI2015

UV light-assisted fabrication of Cu{sub 0.91}In{sub 0.09}S microspheres sensitized TiO{sub 2} nanotube arrays and their photoelectrochemical properties

Highlights: • Cu{sub 0.91}In{sub 0.09}S microspheres were deposited on TiO{sub 2} NTs by a photodeposition method. • The average diameter of Cu{sub 0.91}In{sub 0.09}S microspheres is 600 nm. • The TiO{sub 2} NTs/CIS shows high photocurrents and visible photocatalytic activity. - Abstract: TiO{sub 2} nanotube arrays sensitized with Cu{sub 0.91}In{sub 0.09}S microspheres (TiO{sub 2} NTs/CIS) were successfully fabricated by a two-step process of anodization and followed by an in situ photodeposition method. The structural investigation by scanning electron microscopy and transmission electron microscopy indicated that the Cu{sub 0.91}In{sub 0.09}S microspheres with average diameter of 600 nm grew on the surface of the TiO{sub 2} nanotubes. The TiO{sub 2} NTs/CIS exhibited more excellent photoelectrochemical properties and photocatalytic activities than those of TiO{sub 2} NTs under visible light irradiation, and the corresponding electron transformation was proposed in detail.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2015

Remarkably improved field emission of TiO{sub 2} nanotube arrays by annealing atmosphere engineering

Highlights: • TNAs were prepared by anodization and annealed in different atmospheres. • The crystal structure and electronic properties of the prepared TNAs were investigated. • The field emission of TNAs was highly dependent on annealing atmosphere. • A low turn-on of 2.44 V/μm was obtained for TNAs annealed in H{sub 2} atmosphere. - Abstract: Highly ordered TiO{sub 2} nanotube arrays (TNAs) were prepared by anodization, and followed by annealing in the atmospheres of Air, Vacuum, Ar, and H{sub 2}. The effect of annealing atmosphere on the crystal structure, composition, and electronic properties of TNAs were systematically investigated. Raman and EDS results indicated that the TNAs annealed in anaerobic atmospheres contained more oxygen vacancies, which result in the substantially improved electron transport properties and reduced work function. Moreover, it was found that the FE properties of TNAs were highly dependent on the annealing atmosphere. By engineering the annealing atmosphere, the turn-on field as low as 2.44 V/μm can be obtained from TNAs annealed in H{sub 2}, which was much lower than the value of 18.23 V/μm from the TNAs annealed in the commonly used atmosphere of Air. Our work suggests an instructive and attractive way to fabricate high performance TNAs field emitters.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Titania nanotube arrays surface-modified with ZnO for enhanced photocatalytic applications

Highlights: • Heterostructures of TNA/ZnO synthesised through potentiostatic anodisation followed by hydrothermal method. • Evaluation of morphological features of the heterostructure with hydrothermal processing time. • Correlation of photocatalytic activity of the hetrostructure with its morphology and surface texture. - Abstract: Well ordered titanium dioxide nanotube arrays (TNA) of average diameter 129 nm and wall thickness of 25 nm were fabricated through potentiostatic anodisation of titanium (Ti) metal substrates. Such TNA were subsequently surface-modified with various amounts of zinc oxide (ZnO) nanopowders using hydrothermal technique to obtain heterogeneous TNA/ZnO nanostructures. The crystalline phase and surface microstructure of the heterostructures were determined by X-ray diffraction, Raman spectroscopy and scanning electron microscopy respectively. The morphology of the heterostructures strongly depended on the hydrothermal conditions employed. The photocatalytic activity of the heterostructures have also been investigated and correlated with their surface morphology and texture.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Wettability, structural and optical properties investigation of TiO{sub 2} nanotubular arrays

Graphical abstract: FESEM images of the TiO 2 nanotube layers formed at 0.5 wt% NH4F/ glycerol. - Highlights: • Structural property investigation of TiO{sub 2} nanotube. • Evaluation of wettability of TiO{sub 2} nanotube. • Study on optical properties of TiO{sub 2} nanotube. • The effect of anatase phase on optical and wettability properties of TiO{sub 2.} - Abstract: In this study, the effect of microstructural evolution of TiO{sub 2} nanotubular arrays on wettability and optical properties was investigated. Pure titanium was deposited on silica glass by PVD magnetron sputtering technique. The Ti coated substrates were anodized in an electrolyte containing NH{sub 4}F/glycerol. The structures of the ordered anodic TiO{sub 2} nanotubes (ATNs) as long as 175 nm were studied using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The result shows a sharp peak in the optical absorbance spectra around the band gap energy, 3.49–3.42 eV for annealed and non-annealed respectively. The thermal process induced growth of the grain size, which influence on the density of particles and the index of refraction. Furthermore, the wettability tests' result displays that the contact angle of intact substrate (θ = 74.7°) was decreased to 31.4° and 17.4° after anodization for amorphous and heat treated (450 °C) ANTs coated substrate, respectively.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Enhanced field emission properties of tilted graphene nanoribbons on aggregated TiO{sub 2} nanotube arrays

Highlights: • Graphene nanoribbons (GNBs) slanted on aggregate TiO{sub 2} nanotube (A-TNTs) as field-emitters. • Turn-on electric field and field enhancement factor β are dependent on the substrate morphology. • Various quantities of GNRs are deposited on top of A-TNTs (GNRs/A-TNTs) with different morphologies. • With an increase of GNBs compositions, the specimens' turn-on electric field is reduced to 2.8 V/μm. • The field enhancement factor increased rapidly to about 1964 with the addition of GNRs. - Abstract: Graphene nanoribbons (GNRs) slanted on aggregate TiO{sub 2} nanotube arrays (A-TNTs) with various compositions as field-emitters are reported. The morphology, crystalline structure, and composition of the as-obtained specimens were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectrometry. The dependence of the turn-on electric field and the field enhancement factor β on substrate morphology was studied. An increase of GNRs reduces the specimens’ turn-on electric field to 2.8 V/μm and the field enhancement factor increased rapidly to about 1964 with the addition of GNRs. Results show a strong dependence of the field emission on GNR composition aligned with the gradient on the top of the A-TNT substrate. Enhanced FE properties of the modified TNTs can be mainly attributed to their improved electrical properties and rougher surface morphology.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Fabrication of In2O3/TiO2 nanotube arrays hybrids with homogeneously developed nanostructure for photocatalytic degradation of Rhodamine B

Highlights: • A new class of plate-like In{sub 2}O{sub 3}/TNAs photocatalyst is successfully fabricated. • The obtained In{sub 2}O{sub 3}/TNAs hybrid presents a well-aligned nanotubular structure. • In{sub 2}O{sub 3} particles are dispersed homogeneously on TNAs without blocking the nozzles. • In{sub 2}O{sub 3}/TNAs hybrid shows a much enhanced Rhodamine B degradation efficiency. • In{sub 2}O{sub 3}/TNAs hybrid demonstrates an excellent recycling capability. - Abstract: To enhance the photocatalytic recycling capability of the TiO{sub 2}-based photocatalysts, a new kind of plate-like In{sub 2}O{sub 3}/TiO{sub 2} nanotube array (TNA) hybrids is fabricated herein by constructing TNAs via an anodization method followed by doping In{sub 2}O{sub 3} via a solvothermal method. The obtained In{sub 2}O{sub 3}/TNA hybrid demonstrates a well-aligned nanotubular structure with homogeneous dispersion of In{sub 2}O{sub 3} nanoparticles. It shows a much higher degradation rate of 77% after 2 h compared to TNA (37%). In addition, the plate-like feature endows the photocatalysts with an excellent recycling capability. These superior photocatalytic degradation performances can be ascribed to the following factors: (1) the enhanced light absorption ability and efficient separation of photoexcited electron-hole pairs derived from the formation of the heterostructure between the interface of TiO{sub 2} and In{sub 2}O{sub 3}; (2) the efficient transport of reactant molecules provided by the well-defined TNAs and the homogeneous distribution of the In{sub 2}O{sub 3} nanoparticles without blocking the nanotubes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Upconversion Er-doped TiO2 nanorod arrays for perovskite solar cells and the performance improvement

Highlights: • Er-doped TiO{sub 2} nanorod absorbs IR and converts into visible light. • The introduction of Er could make a positive shift in flat-band potential. • Er-doped TiO{sub 2} solar cells show a 20% increment in the current density. - Abstract: Upconversion erbium-doped rutile TiO{sub 2} nanorod arrays were synthesized by a facile process and applied in perovskite solar cells (PSCs). The structure was characterized by X-ray powder diffraction (XRD). Energy dispersive spectrometer (EDS) and Tauc plot indicated that Er was successfully introduced and changed TiO{sub 2} band gap from 3.00 eV to 3.07 eV. The incorporation of Er shifts the flat band potential positively and enhances the electron density. The Er-doped TiO{sub 2} nanorods have a broad absorption in the infrared light and up-convert it into visible light, which provides a possibility for PSCs to use NIR light for higher performance. A higher photocurrent density (J{sub sc}) of 22.97 mA/cm{sup 2} and a power conversion efficiency (PCE) of 10.6% were obtained, showing 20% and 16.5% increment in J{sub sc} and PCE, respectively, when compared with the un-doped device. The performance improvement was ascribed to the upconversion performance, enhanced electron-injection efficiency and reduced charge recombination.

14 SOLAR ENERGY↗

DOE OSTI2014

A new time calibration method for switched-capacitor-array-based waveform samplers

Here we have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibration is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. Ultimately, the new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.