Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions

We propose a simple method for the efficient and rapid synthesis of one-dimensional hematite (α-Fe₂O₃) nanostructures based on electrical resistive heating of iron wire under ambient conditions. Typically, 1–5 μm long α-Fe₂O₃ nanowires were synthesized on a time scale of seconds at temperatures of around 700 ° ⊂. The morphology, structure, and mechanism of formation of the nanowires were studied by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman techniques. A nanowire growth mechanism based on diffusion of iron ions to the surface through grain boundaries and to the growing wire tip through stacking fault defects and due to surface diffusion is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Shape-controlled synthesis of octahedral α-NaYF4 and its rare earth doped submicrometer particles in acetic acid

Submicrometer sized pure cubic phase, Eu³⁺ doped, and Yb³⁺/Er³⁺ co-doped α-NaYF₄ particles with octahedral morphology have been prepared in acetic acid. The acetate anion plays a critical role in the formation of such symmetric octahedral structures through its selective adsorption on the (111) faces of the products. The size of the as-prepared octahedra can be tuned by varying the amount of sodium acetate added to the acetic acid. A possible formation mechanism for these octahedra has been proposed. The doped α-NaYF₄ octahedral submicrometer particles show down-conversion and up-conversion photoluminescence typical of these materials. This article is published with open access at Springerlink.com     

Domain-engineered BiFeO<Subscript>3</Subscript> thin-film photoanodes for highly enhanced ferroelectric solar water splitting

In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO₃ thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001)_pc via (110)_pc to (111)_pc, the ferroelastic domains in epitaxial BiFeO₃ thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm². Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111)_pc BiFeO₃ thin-film photoanode leads to an approximate change of 8,000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes.

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CdSe quantum dot-sensitized Au/TiO2 hybrid mesoporous films and their enhanced photoelectrochemical performance

Novel CdSe quantum dot (QD)-sensitized Au/TiO₂ hybrid mesoporous films have been designed, fabricated, and evaluated for photoelectrochemical (PEC) applications. The Au/TiO₂ hybrid structures were made by assembly of Au and TiO₂ nanoparticles (NPs). A chemical bath deposition method was applied to deposit CdSe QDs on TiO₂ NP films with and without Au NPs embedded. We observed significant enhancements in photocurrent for the film with Au NPs, in the entire spectral region we studied (350–600 nm). Incident-photon-to-current efficiency (IPCE) data revealed an average enhancement of 50%, and the enhancement was more significant at short wavelength. This substantially improved PEC performance is tentatively attributed to the increased light absorption of CdSe QDs due to light scattering by Au NPs. Interestingly, without QD sensitization, the Au NPs quenched the photocurrent of TiO₂ films, due to the dominance of electron trapping over light scattering by Au NPs. The results suggest that metal NPs are potentially useful for improving the photoresponse in PEC cells and possibly in other devices such as solar cells based on QD-sensitized metal oxide nanostructured films. This work demonstrates that metal NPs can serve as light scattering centers, besides functioning as photo-sensitizers and electron traps. The function of metal NPs in a particular nanocomposite film is strongly dependent on their structure and morphology.      

Self-powered photoelectrochemical biosensing platform based on Au NPs@ZnO nanorods array

Photoanodes, which are used in photoelectrochemical (PEC) water splitting, have been shown to be applicable in the construction of a PEC biosensing platform. This was realized by replacing water oxidization with oxidation of an appropriate test molecule. Here, we have demonstrated the feasibility of adopting photoanodes consisting of zinc oxide nanorods arrays decorated with plasmonic gold nanoparticles (Au NPs@ZnO NRs) for the self-powered PEC bioanalysis of glutathione (GSH) in phosphate-buffered saline (PBS) at an applied bias potential of 0 V vs. Ag/AgCl. This heterostructure exhibited enhanced PEC properties because of the introduction of the Au/ZnO interface. Under visible light illumination, hot electrons from surface-plasmon resonance (SPR) at the Au NP surface were injected into the adjacent ZnO and subsequently driven to the photocathode. Under ultraviolet (UV) light illumination, the photogenerated electrons in ZnO tended to transfer to the fluorine-doped tin oxide due to the step-wise energy band structure and the upward energy band bending at the ZnO/ electrolyte interface. These results indicate that plasmonic metal/semiconductor heterostructure photoanodes have great potential for self-powered PEC bioanalysis applications and extended field of other photovoltaic beacons.

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Rutile TiO2 microspheres with exposed nano-acicular single crystals for dye-sensitized solar cells

Uniquely structured rutile TiO₂ microspheres with exposed nano-acicular single crystals have been successfully synthesized via a facile hydrothermal method. After calcination at 450 °C for 2 h, the rutile TiO₂ microspheres with a high surface area of 132 m²/g have been utilized as a light harvesting enhancement material for dye-sensitized solar cells (DSSCs). The resultant DSSCs exhibit an overall light conversion efficiency of 8.41% for TiO₂ photoanodes made of rutile TiO₂ microspheres and anatase TiO₂ nanoparticles (mass ratio of 1:1), significantly higher than that of pure anatase TiO₂ nanoparticle photoanodes of similar thickness (6.74%). Such a significant improvement in performance can be attributed to the enhanced light harvesting capability and synergetic electron transfer effect. This is because the photoanodes made of rutile TiO₂ microsphere possess high refractive index which improves the light utilisation efficiency, suitable microsphere core sizes (450–800 nm) to effectively scatter visible light, high surface area for dye loading, and synergetic electron transfer effects between nanoparticulate anatase and nano-acicular rutile single crystals phases giving high electron collection efficiency.      

Metal–organic framework coated titanium dioxide nanorod array p–n heterojunction photoanode for solar water-splitting

This paper presents a p–n heterojunction photoanode based on a p-type porphyrin metal–organic framework (MOF) thin film and an n-type rutile titanium dioxide nanorod array for photoelectrochemical water splitting. The TiO₂@MOF core–shell nanorod array is formed by coating an 8 nm thick MOF layer on a vertically aligned TiO₂ nanorod array scaffold via a layer-by-layer self-assembly method. This vertically aligned core–shell nanorod array enables a long optical path length but a short path length for extraction of photogenerated minority charge carriers (holes) from TiO₂ to the electrolyte. A p–n junction is formed between TiO₂ and MOF, which improves the extraction of photogenerated electrons and holes out of the TiO₂ nanorods. In addition, the MOF coating significantly improves the efficiency of charge injection at the photoanode/electrolyte interface. Introduction of Co(III) into the MOF layer further enhances the charge extraction in the photoanode and improves the charge injection efficiency. As a result, the photoelectrochemical cell with the TiO₂@Co-MOF nanorod array photoanode exhibits a photocurrent density of 2.93 mA/cm² at 1.23 V (vs. RHE), which is ~ 2.7 times the photocurrent achieved with bare TiO₂ nanorod array under irradiation of an unfiltered 300 W Xe lamp with an output power density of 100 mW/cm².

     

Dopant-controlled synthesis of water-soluble hexagonal NaYF<Subscript>4</Subscript> nanorods with efficient upconversion fluorescence for multicolor bioimaging

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF₄ nanorods by doping rare-earth ions with large ionic radius (such as La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and Gd³⁺), and the dopantcontrolled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF₄:(Yb,Er)/La and NaYF₄:(Yb,Er)/Ce nanorods, which exhibited much brighter upconversion fluorescence than the corresponding cubic forms. The sizes of the nanorods can be adjusted over a broad range by changing the dopant concentration and reaction time. Furthermore, we successfully demonstrated a novel depth-sensitive multicolor bioimaging for in vivo use by employing the as-synthesized NaYF₄:(Yb,Er)/La nanorods as probes.      

Core-shell Au-Ag nanoparticles in dielectric nanocomposites with plasmon-enhanced fluorescence: A new paradigm in antimony glasses

The nano era demands the synthesis of new nanostructured materials, if possible by simplified techniques, with remarkable properties and versatile applications. Here, we demonstrate a new single-step reproducible melt-quench methodology to fabricate core-shell bimetallic (Au⁰-Ag⁰) nanoparticles (28–89 nm) embedded glasses (dielectrics) by the use of a new reducing glass matrix, K₂O-B₂O₃-Sb₂O₃ (KBS) without applying any external reducing agent or multiple processing steps. The surface plasmon resonance (SPR) band of these nanocomposites embedded in KBS glass is tunable in the range 554–681 nm. More remarkably, taking advantage of the selective reduction capability of Sb₂O₃, this single-step methodology is used to fabricate inter-metallic: rare-earth ions co-embedded (Au-Ag:Sm³⁺) dielectric (glass)-based-dnanocomposites and study the effect of enhanced local field on the red upconversion fluorescence of Sm³⁺ ions at 636 nm. The enhancement is found to be about 2 folds. This single-step in-situ selective reduction approach can be used to fabricate a variety of hybrid-nanocomposite devices for laser based applications (see supplementary information). Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Activating ZnO nanorod photoanodes in visible light by Cu ion implantation

Utilization of visible light is of crucial importance for exploiting efficient semiconductor catalysts for solar water splitting. In this study, an advanced ion implantation method was utilized to dope Cu ions into ZnO nanorod arrays for photoelectrochemical water splitting in visible light. X-ray diffraction （XRD） and X-ray photo-electron spectroscopy （XPS） results revealed that Cu^＋ together with a small amount of Cu^2＋ were highly dispersed within the ZnO nanorod arrays. The Cu ion doped ZnO nanorod arrays displayed extended optical absorption and enhanced photoelectrochemical performance under visible light illumination （A 〉 420 nm）. A considerable photocurrent density of 18 μA/cm^2 at 0.8 V （vs. a saturated calomel electrode） was achieved, which was about 11 times higher than that of undoped ZnO nanorod arrays. This study proposes that ion implantation could be an effective approach for developing novel visible-light-driven photocatalytic materials for water splitting.     

A novel Sn<Subscript>2</Subscript>Sb<Subscript>2</Subscript>O<Subscript>7</Subscript> nanophotocatalyst for visible-light-driven H<Subscript>2</Subscript> evolution

A novel pure cubic-phase pyrochlore structure tin(II) antimonate nanophotocatalyst, stoichiometric Sn₂Sb₂O₇, has been prepared by a modified ion-exchange process using an antimonic acid precursor, and employed in visible-light-driven photocatalytic H₂ evolution for the first time. The physicochemical properties (crystal phase, chemical composition and state, textural properties, and optical properties) of the material were investigated by different instrumental techniques. Compared with the antimonic acid precursor, the as-prepared Sn₂Sb₂O₇ had a narrower bandgap, smaller crystal size, and larger BET surface area. The as-prepared Sn₂Sb₂O₇ was validated as a promising candidate for visible-light-driven photocatalytic H2 evolution with a constant rate of 40.10 μmol·h⁻¹·g_cat ⁻¹.      

Interfacial activation of catalytically inert Au (6.7 nm)-Fe3O4 dumbbell nanoparticles for CO oxidation

Au nanoparticles epitaxially grown on Fe₃O₄ in Au (6.7 nm)-Fe₃O₄ dumbbell nanoparticles exhibit excellent stability against sintering, but display negligible catalytic activity in CO oxidation. Starting from various supported Au (6.7 nm)-Fe₃O₄ catalysts prepared by the colloidal deposition method, we have unambiguously identified the significance of the Au-TiO₂ interface in CO oxidation, without any possible size effect of Au. In situ thermal decomposition of TiO₂ precursors on Au-Fe₃O₄ was found to be an effective way to increase the Au-TiO₂ interface and thereby optimize the catalytic performance of TiO₂-supported Au-Fe₃O₄ dumbbell nanoparticles. By reducing the size of Fe₃O₄ from 15.2 to 4.9 nm, the Au-TiO₂ contact was further increased so that the resulting TiO₂-supported Au (6.7 nm)-Fe₃O₄ (4.9 nm) dumbbell particles become highly efficient catalysts for CO oxidation at room temperature.      

Synthesis of monodisperse CoPt3 nanocrystals and their catalytic behavior for growth of boron nanowires

Monodisperse CoPt₃ nanocrystals (NCs) have been synthesized in oleylamine solution by an organic solvothermal method. The NCs were ellipsoidal particles with a diameter around 6.6 nm and length around 10 nm with a good single crystal structure. Using CoPt₃ NCs as catalysts, large-area boron nanowires with diameters ranging from 30 to 50 nm were successfully prepared by chemical vapor deposition using a C/B/B₂O₃ mixture as the precursor. Structural analysis indicated that these nanowires were single crystalline with a β-rhombohedral structure. Measurement of the field emission properties of boron nanowire films showed that the boron nanowires have good field emission characteristics.      

Electrodeposited nanostructured α-Fe2O3 thin films for solar water splitting: Influence of Pt doping on photoelectrochemical performance

Electrochemically deposited α-Fe₂O₃ thin films, whose composition was tuned by Pt doping, were investigated as photoanode for photoelectrochemical water splitting. Morphological and structural characteristics of the nanostructured α-Fe₂O₃ thin films were studied by scanning electron microscopy and X-ray diffraction techniques. The films were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy to determine the effect of Pt doping on the α-Fe₂O₃ structure. The photoelectrochemical performance of the films was examined by linear sweep voltammetry and electrochemical impedance spectroscopy. Results of these studies showed that Pt doping increased the density of small-sized nanoparticles in α-Fe₂O₃ thin films. The Pt doped films exhibited higher photoelectrochemical activity by a factor of 1.4 over un-doped α-Fe₂O₃ films. The highest photocurrent density of 0.56 mA cm⁻² was registered for 3% pt doped film at 0.4 V versus Ag/AgCl in 1 M NaOH electrolyte and under standard illumination conditions (AM 1.5 G, 100 mW cm⁻²). This high photoactivity can be attributed to the high active surface area and increased donor density caused by Pt doping in the film. Electrochemical impedance analysis also revealed significantly low charge transfer resistance of Pt doped films, indicating its superior electrocatalytic activity for water splitting reaction compared to un-doped α-Fe₂O₃ thin films.     

Perpendicularly self-oriented and shape-controlled L10-FePt nanorods directly synthesized by a temperature-modulated process

The synthesis and self-assembly of tetragonal phase-containing L1₀-Fe₅₅Pt₄₅ nanorods with high coercive field is described. The experimental procedure resulted in a tetragonal/cubic phase ratio close to 1:1 for the as-synthesized nanoparticles. Using different surfactant/solvent proportions in the process allowed control of particle morphology from nanospheres to nanowires. Monodisperse nanorods with lengths of 60 ± 5 nm and diameters of 2–3 nm were self-assembled in a perpendicular oriented array onto a substrate surface using hexadecylamine as organic spacer. Magnetic alignment and properties assigned, respectively, to the shape anisotropy and the tetragonal phase suggest that the self-assembled materials are a strong candidate to solve the problem of random magnetic alignment observed in FePt nanospheres leading to applications in ultrahigh magnetic recording (UHMR) systems capable of achieving a performance of the order of terabits/in².      

Myoglobin/gold nanoparticles/carbon spheres 3-D architecture for the fabrication of a novel biosensor

A novel biosensor based on a myoglobin/gold nanoparticles/carbon spheres (Mb-AuNPs-CNs) 3-D architecture bioconjunction has been fabricated for the determination of hydrogen peroxide (H₂O₂). Cyclic voltammetry (CV), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were used to characterize the bioconjunction of the AuNPs-CNs with Mb. Experimental results demonstrate that the AuNPs-CNs hybrid material is more effective in facilitating electron transfer of the immobilized enzyme than CNs alone, which can be attributed to the unique nanostructure and larger surface area of the bioconjunction. The biosensor displayed good performance for the detection of H₂O₂ with a wide linear range from 0.28 μmol/L to 116.5 μmol/L and a detection limit of 0.12 μmol/L. The Michaelis-Menten constant K _M^app value was estimated to be 0.3 mmol/L. The resulting biosensor exhibited fast amperometric response, and good stability, reproducibility, and selectivity to H₂O₂. This article is published with open access at Springerlink.com     

Facile synthesis of LiCoO2 nanowires with high electrochemical performance

Cobalt precursor Co(CO₃)_0.35Cl_0.2(OH)_1.1 nanowire bunches have been synthesized by a hydrothermal method and transformed into Co₃O₄ nanowires by calcination at 500 °C for 3 h. The Co₃O₄ nanowires were then mixed with LiOH and formed the LiCoO₂ nanowires by calcination at 750 °C. High resolution transmission electron microscopy revealed that the LiCoO₂ nanowires were composed of nanoparticles with most of the nanoparticles having exposed (010) planes. The electrochemical performance of the LiCoO₂ nanowires was thoroughly investigated by galvanostatic tests. The as-prepared LiCoO₂ nanowires exhibited excellent rate capability and satisfactory cycle stability, where the charge and discharge capacity still stabilized at 100 mA·h/g at a rate of 1000 mA/g after 100 cycles. The favorable electrochemical performance of the LiCoO₂ nanowires may result from their one-dimensional nanostructure and the exposure of (010) planes, since the (010) plane is electrochemically active for layered LiCoO₂ with the α-NaFeO₂ structure and favors fast Li⁺ transportation.      

One-pot synthesis of highly luminescent CdTe quantum dots by microwave irradiation reduction and their Hg2+-sensitive properties

A facile one-pot microwave irradiation reduction route has been developed for the synthesis of highly luminescent CdTe quantum dots using Na₂TeO₃ as the Te source in an aqueous environment. The synthesis parameters of this simple and rapid approach, including the reaction temperature and time, the pH of the reaction solution and the molar ratio of the 3-mercaptopropionic acid (MPA) stabilizer to Cd²⁺, have considerable influence on the particle size and photoluminescence quantum yield of the CdTe quantum dots. The photoluminescence quantum yield of CdTe quantum dots prepared using relatively short reaction times (10–40 min) reached 40%–60% (emission peaks at 550–640 nm). Furthermore, the resulting products could be used as fluorescent probes to detect Hg²⁺ ions in aqueous media. The response was linearly proportional to the concentration of Hg²⁺ ion in the range 8.0×10⁻⁹ mol/L to 2.0×10⁻⁶ mol/L with a detection limit of 2.7×10⁻⁹ mol/L. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Hierarchical growth of a novel Mn-Bi coupled BiVO4 arrays for enhanced photoelectrochemical water splitting

Oxygen evolving catalyst (OEC) is a critical determinant for the efficiency of photoelectrochemical (PEC) water splitting. Here we report an approach to depositing a novel manganese borate (Mn-Bi) OER catalyst on BiVO₄ nanocone photoanode by photodeposition in sodium borate buffer solution containing Mn(II) ions. Due to the spontaneous photo-electric-field-enhancement effect at the vertically oriented BiVO₄ nanocone structure, spherical Mn-Bi nanoparticle was selectively photodeposited at the apex of BiVO₄ nanocone. Significant improvement of photocurrent was observed for the obtained hierarchical Mn-Bi/BiVO₄ photoanode which could be ascribed to enhanced hole injection efficiency, especially in low bias region. It was observed that the injection efficiency of Mn-Bi/BiVO₄ is 98% which gave a photocurrent of 0.94 mA/cm² at 1.5 V vs. RHE.

     

NiaSi2O5（OH）4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries

Highly crystalline and thermally stable pure multi-walled Ni₃Si₂O₅(OH)₄ nanotubes with a layered structure have been synthesized in water at a relatively low temperature of 200–210 °C using a facile and simple method. The nickel ions between the layers could be reduced in situ to form size-tunable Ni nanocrystals, which endowed these nanotubes with tunable magnetic properties. Additionally, when used as the anode material in a lithium ion battery, the layered structure of the Ni₃Si₂O₅(OH)₄ nanotubes provided favorable transport kinetics for lithium ions and the discharge capacity reached 226.7 mA·h·g⁻¹ after 21 cycles at a rate of 20 mA·g⁻¹. Furthermore, after the nanotubes were calcined (600 °C, 4 h) or reduced (180 °C, 10 h), the corresponding discharge capacities increased to 277.2 mA·h·g⁻¹ and 308.5 mA·h·g⁻¹, respectively.