O3 Nanocrystals Research Articles

SnFe2 O4 Nanocrystals as Highly Efficient Catalysts for Hydrogen-Peroxide Sensing.

SnFe2 O4 nanocrystals (NC), prepared with a simple one-step carrier-solvent-assisted interfacial reaction process, were developed as highly efficient catalysts for hydrogen peroxide sensing. These NCs, with a size of around 7 nm, served as the sensing catalyst and were decorated onto the pore surfaces of a porous fluorine-doped tin oxide (PFTO) host electrode, prepared from commercial FTO glass with a simple anodic treatment, to form the sensing electrode for hydrogen peroxide. The SnFe2 O4 NCs-loaded PFTO electrode exhibited an ultra-high sensitivity of 1027 mA m(-1) cm(-2) toward hydrogen peroxide, outperforming Pt NCs-loaded PFTO electrodes. The SnFe2 O4 NCs-loaded PFTO electrode proved a promising relatively low cost, high performance sensing electrode for hydrogen peroxide.

Alternate current magnetic property characterization of nonstoichiometric zinc ferrite nanocrystals for inductor fabrication via a solution based process

We investigate the ac magnetic behavior of solution processable, non-stoichiometric zinc ferrite nanocrystals with a series of sizes and zinc concentrations. Nearly monodisperse ZnxFe3−xO4 nanocrystals (x = 0–0.25) with an average size ranging from 7.4 nm to 13.8 nm are synthesized by using a solvothermal method. All the nanocrystals are in a superparamagnetic state at 300 K, which is confirmed by Superconductive Quantum Interference Device magnetometry. Due to the doping of non-magnetic Zn2+ into A site of ferrite, the saturation magnetization of nanocrystals increases as the size and Zn concentration increases. The ac magnetic permeability measurements at radio frequencies reveal that the real part of the magnetic permeability of similarly sized ferrite nanocrystals can be enhanced by almost twofold as the Zn2+ doping level increases from 0 to 0.25. The integration of 12.3 nm Zn0.25Fe2.75O4 nanocrystals into a toroidal inductor and a solenoid inductor prepared via a simple solution cast process yields a higher quality factors than air core inductors with the same geometries up to 5 MHz and 9 MHz, respectively, which is in the regime of the switching frequencies for the advanced integrated power converters.

Electrical and Plasmonic Properties of Ligand-Free Sn(4+) -Doped In2 O3 (ITO) Nanocrystals.

Sn(4+) -doped In2 O3 (ITO) is a benchmark transparent conducting oxide material. We prepared ligand-free but colloidal ITO (8 nm, 10 % Sn(4+) ) nanocrystals (NCs) by using a post-synthesis surface-modification reaction. (CH3 )3 OBF4 removes the native oleylamine ligand from NC surfaces to give ligand-free, positively charged NCs that form a colloidal dispersion in polar solvents. Both oleylamine-capped and ligand-free ITO NCs exhibit intense absorption peaks, due to localized surface plasmon resonance (LSPR) at around λ=1950 nm. Compared with oleylamine-capped NCs, the electrical resistivity of ligand-free ITO NCs is lower by an order of magnitude (≈35 mΩ cm(-1) ). Resistivity over a wide range of temperatures can be consistently described as a composite of metallic ITO grains embedded in an insulating matrix by using a simple equivalent circuit, which provides an insight into the conduction mechanism in these systems.

Facile synthesis of high-performance Li1.2Ni0.13Co0.13Mn0.54O2 nanocrystals by a resorcinol formaldehyde gel route as lithium ion battery cathodes

In the paper, we report synthesis of Li1.2Ni0.13Co0.13Mn0.54O2 nanocrystals by a facile resorcinol formaldehyde gel route. The initial polymerization of precursor solution and subsequent high-temperature calcination results in the formation of Li1.2Ni0.13Co0.13Mn0.54O2 nanocrystals. The XRD, SEM, and electrochemical tests show the influence of calcination temperatures on the structures and electrochemical performances of obtained products. The XRD results reveal that the elevated temperature helps to improve the layered structure of the Li1.2Ni0.13Co0.13Mn0.54O2 nanocrystals, and the SEM results demonstrated that the elevated temperature helps to enlargement particle size. For lithium ion battery cathodes, the electrochemical performances can be well determined by corresponding structures. Among them, the 850 °C sample shows an initial discharge capacity of 259.9 mAh g−1 with Coulombic efficiency of 80.1 % at a current density of 40 mA g−1. After 50 cycles, the sample also can retain a capacity of 204.8 mAh g−1 at 200 mA g−1, which is 87.6 % of initial value. Even at a higher rate of 1000 mA g−1, the sample shows a stable discharge capacity of 130 mAh g−1. Maybe, the resorcinol formaldehyde gel route is suitable to prepare lithium ion battery cathode Li1.2Ni0.13Co0.13Mn0.54O2. The lithium rich layered oxides Li1.2Ni0.13Co0.13Mn0.54O2 have been prepared by a facile resorcinol formaldehyde gel route. The optimal sample with the size of 200–300 nm shows high discharge capacity, good cycling stability and rate capability as lithium ion battery cathode.

Convectional hydrothermal synthesis of high-purity pesudo-cubic BaTi0.09Nb0.01O3 nanocrystals in rotary autoclave

Nano-sized BaTiO3 powders with particular Nb concentrations were prepared by Rotary- Hydrothermal (RH) method. Hydrothermal method was used at 180 °C for 5 hours with new Ti pressure and the teflon vessel was rotated at a speed of 160 rpm during the hydrothermal reaction. New hydrothermal method was used instead of previous solid state reaction for the system BaTiO3±Nb2O3 in high temperature to achieve nano sized particles in lower time and temperature. Synthesis with Rotary-hydrothermal has the advantages of faster crystallization, decreased crystal size, more homogenous distribution of dopants at lower temperature and time in comparison with the solid state method. In case of the phase evolution studies the X-ray diffraction patterns (XRD) measurements and Raman spectroscopy were performed. The Transmission Electron Microscope (TEM) and the Field Emission Scanning Electron Microscopy (FE-SEM) images were taken for the detailed analysis of the grain size, surface and morphology. Synthesis of Nb doped BaTiO3 with the Rotary- hydrothermal provided advantages of fast crystallization and decreased crystal size.

Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy.

Epitaxial core-shell CoO-CoFe2 O4 nanocrystals are fabricated by using pulsed laser deposition with the aid of melted material (Bi2 O3 ) addition and suitable lattice mismatch provided by substrates (SrTiO3 ). Well aligned orientations among nanocrystals and reversible core-shell sequence reveal tunable magnetic anisotropy. The interfacial coupling between core and shell further engineers the nanocrystal functionality.

Highly ordered mesoporous few-layer graphene frameworks enabled by fe3 o4 nanocrystal superlattices.

While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self-assembled superlattices of Fe3 O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face-centered-cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium-ion batteries, thus retaining a specific capacity of 520 mAh g(-1) at a current density of 300 mA g(-1) after 400 cycles.

Complex perovskite oxide nanocrystals: low-temperature synthesis and crystal structure.

This Perspective reviews our recent efforts towards the low-temperature synthesis of complex perovskite oxide ABO3 (A = Sr, Ba; B = Ti, Zr) nanocrystals using the vapor diffusion sol-gel method and the determination of their room-temperature crystal structure. From a synthetic standpoint, emphasis is placed on demonstrating the ability of the vapor diffusion sol-gel approach to yield compositionally complex nanocrystals at low temperatures and atmospheric pressure without the need for postsynthetic heat treatment to achieve a crystalline and phase-pure oxide product. The ability to successfully achieve this is illustrated using Ba1-xSrxTi1-yZryO3 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) and Eu(3+)-doped Ba(Ti,Zr)O3 nanocrystals as examples. From the standpoint of the structural analysis, emphasis is placed on highlighting how multiple and complementary spectroscopic techniques that probe atomic correlations in short (≤1 nm), intermediate (∼1-3 nm), and long (≥3 nm) length scales can be employed to gain insight into the atomic structure of the resulting nanocrystals. Examples that clearly illustrate this strategy of structural characterization are the investigation of the size- and composition-dependence of the structure of polar nanoregions in sub-10 nm BaTiO3 and sub-20 nm Ba1-xSrxTiO3 and BaTi1-yZryO3 nanocrystals, and the investigation of the distribution of rare earth dopants in sub-15 nm Eu(3+):BaTiO3 nanocrystals.

Submicron-sized anatase, TiO2 with high photocatalytic activity, and (Ti, Sn)O2 nanocrystals formed via hydrothermal technique

The compositional dependence of the crystalline phase and properties of precipitates (TixSn1−xO2) in the TiO2–SnO2 system, which were hydrothermally formed at 100–200 °C from the precursor solutions of TiCl4 and SnCl4 under weakly basic conditions in the presence of tetramethylammonium hydroxide (TMAH) was investigated. Rutile-type (Ti, Sn)O2 solid solutions with nano-sized crystallite were directly formed at 180 °C in the composition range of x = 0–0.8. Nanoparticles with anatase crystallite around 10 nm as a main crystalline phase of precipitates that were formed in the compositions x = 0.9 and 1.0 showed similar photocatalytic activity. As the hydrothermal treatment temperature rose from 100 to 200 °C, the crystallite size of rutile solid solution, Ti0.5Sn0.5O2, increased from 2.5 to 8.0 nm. The optical band gap of the samples changed in the range of 2.93–3.25 eV depending on their composition in the system. At the composition of x = 1.0, submicron-sized anatase-type pure TiO2 particles (sizes of cuboid sides are around 100–120 nm) with pretty high crystallinity and superior photocatalytic activity were formed from the aqueous solution of TiCl4 under basic hydrothermal condition at 180 °C in the presence of TMAH with concentration as 1.3 times high as the condition in the case of the nano-sized anatase.

Structural, optical and morphological properties of La, Cu co-doped SnO2 nanocrystals by co-precipitation method

Sn0.96−xLa0.04CuxO2 (0⩽x⩽0.03) nanocrystals have been successfully synthesized by employing a simple co-precipitation method. The crystal structure of the synthesized nanocrystals was found to be tetragonal rutile of tin oxide by using X-ray diffraction technique and was not affected by doping. The change in lattice parameters was discussed based on the secondary phase formation and presence of Cu2+/Cu3+ in LaSnO2 lattice. The variation in size and shape of the nanocrystals by Cu-doping was discussed using scanning electron microscope. The chemical stoichiometry of Sn, Cu, La and O was confirmed by energy dispersive X-ray spectra. The best optical transparency and lower absorption observed at Sn0.97La0.02Cu0.01O2 nanocrystals seems to be optimal for industrial applications especially as transparent electrode. The initial blue shift of energy gap from 3.65eV (Cu=0%) to 3.78eV (Cu=1%) (ΔEg≈0.13eV) is due to the distortion in the crystal structure of the host compound and generation of defects. The red shift of energy gap after Cu=1% is due to the charge-transfer transitions between the metal ions d-electrons and the SnO2 conduction or valence band. Lattice mode of SnO2 at 686cm−1 in Sn0.98La0.02O2 nanocrystals and anti-symmetric SnOSn stretching mode of the surface bridging oxide around 634–642cm−1 in Cu doped Sn0.98La0.02O2 nanocrystals was confirmed by Fourier transform infrared spectra.

Solvothermal‐Induced Self‐Assembly of Fe2O3/GS Aerogels for High Li‐Storage and Excellent Stability

A novel solvothermal-induced self-assembly approach, using colloid sol as precursor, is developed to construct monolithic 3D metal oxide/GS (graphene sheets) aerogels. During the solvothermal process, graphene oxide (GO) is highly reduced to GS and self-assembles into 3D macroscopic hydrogels, accompanying with in situ transformation of colloid sol to metal oxides. As a proof of concept, Fe2 O3 /GS aerogels are synthesized based on Fe(OH)3 sol, in which GS self-assemble into an interconnected macroporous framework and Fe2 O3 nanocrystals (20-50 nm) uniformly deposit on GS. Benefitting from the integration of macroporous structures, large surface area, high electrical conductivity, and good electrode homogeneity, the hybrid electrode manifests a superior rate capability (930, 660 and 520 mAh g(-1) at 500, 2000 and 4000 mA g(-1), respectively) and excellent prolonged cycling stability at high rates (733 mAh g(-1) during 1000 charge/discharge cycles at 2000 mA g(-1)), demonstrating its great potential for application in high performance lithium ion batteries. The work described here provides a versatile pathway to construct various graphene-based hybrid aerogels.

Dynamic nanocrystal response and high temperature growth of carbon nanotube–ferroelectric hybrid nanostructure

A long standing problem related to the capping of carbon nanotubes (CNT) by inorganic materials at high temperature has been solved. In situ dynamic response of Pb(Zr0.52Ti0.48)O3 (PZT) nanocrystals attached to the wings of the outer surface of PZT/CNT hybrid-nanostructure has been demonstrated under a constant-energy high-resolution transmission electron microscopy (HRTEM) e-beam. PZT nanocrystals revealed that the crystal orientations, positions, faces, and hopping states change with time. HRTEM study has been performed to investigate the microstructure of hybrid nanostructures and nanosize polycrystal trapped across the wings. Raman spectroscopy was utilized to investigate the local structures, defects, crystal qualities and temperature dependent growth and degradation of hybrid nanostructures. Raman spectra indicate that MWCNT and PZT/MWCNT/n-Si possess good quality of CNT before and after PZT deposition until 650 °C. The monoclinic Cc/Cm phase of PZT which is optimum in piezoelectric properties was prominent in the hybrid structure and should be useful for device applications. An unusual hexagonal faceting oscillation of the nano-crystal perimeter on a 10-30 s period is also observed.

Origin of Tunable Photocatalytic Selectivity of Well‐Defined α‐Fe2O3 Nanocrystals

Visible-light induced degradation of an aqueous mixture containing MO and RhB on well-defined α-Fe2 O3 nanocrystals shows that MO degradation is more favorable and such selectivity on the {012} facet is greater than that on {001}. The origin of selectivity is rationalized as the inherent surface structural difference and preferential molecular adsorption.

Facile Size-Controllable Synthesis of Colorful Quasi-Cubic α-Fe2 O3 Materials from Nanoscale to Microscale and Their Properties Related to the Size Effect.

A facile and environmentally friendly hydrothermal approach has been employed to synthesize size-controllable quasi-cubic α-Fe2 O3 nanocrystals by using an aqueous solution of FeCl3 without any alkaline materials and stabilizing agent. The as-prepared products were carefully characterized and the growth mechanism is also discussed. This hydrothermal synthesis of such quasi-cubic structures implies a simple and low-cost route to prepare monodisperse nanomaterials on a large scale. The size-controllable synthesis of α-Fe2 O3 is the first achieved successfully from 80 nm to 2 μm with constant structures. The synthesized α-Fe2 O3 materials have different optical properties and stabilities in water, which are caused by the change of their band-gap energy and specific surface areas. Finally, the dielectric properties of synthesized α-Fe2 O3 cubes were also investigated, and the differences caused by the particle sizes are discussed.

Photoluminescence properties of Ca0.99Eu0.01(Mo1−xSix)O4 nanocrystals red-phosphors obtained by the hydrothermal method

Abstract In this paper, we report the obtention of a novel red-emitting Ca 0.99 Eu 0.01 (Mo 1− x Si x )O 4 nanocrystals phosphor synthesized by the hydrothermal method for the first time, and its photoluminescence (PL) properties were investigated for application to white-light-emitting diodes (W-LEDs). The as-synthesized phosphors were characterized by means of X-ray powder diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microcopy (HR-TEM), photoluminescence excitation (PLE) and PL emission spectra. XRD patterns, TEM images and PL emission indicated that the introduction of Si 4+ ions promotes the distortion and slight shrinking of the unit cell, narrow size distribution and the blue-shift of the charge transfer bands of Ca 0.99 Eu 0.01 MoO 4 red-phosphors. PL properties revealed that the optical brightness as well as the intensity ratio of 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 was highly dependent on the Si 4+ ions concentration. The morphological evolution was explained via a crystal growth mechanism. Introduction of 5 mol% Si 4+ ions into the crystal structure enhanced the PL emission brightness, and the nanocrystals Ca 0.99 Eu 0.01 (Mo 0.95 Si 0.05 )O 4 red-phosphors showed the relatively most promising PL performance with the most intense emission. The CIE chromaticity coordinates for nanocrystals Ca 0.99 Eu 0.01 (Mo 1− x Si x )O 4 red-phosphors were simulated and located in the red region. All the results imply that the studied Ca 0.99 Eu 0.01 (Mo 1− x Si x )O 4 nanophosphors could be potentially used as W-LEDs.

Synthesis of Single‐Crystalline LiMn2O4 and LiMn1.5Ni0.5O4 Nanocrystals and Their Lithium Storage Properties

Yolk–shell spheres as nanoreactors: Single-crystalline LiMn2O4 and LiMn1.5Ni0.5O4 nanocrystals have been prepared by using yolk–shell spheres as nanoreactors to confine the size of the nanocrystals to a range of 14–19 nm (see scheme). These nanocrystals were subsequently employed as cathode materials and showed high lithium-ion storage capacities and stable charge–discharge cycling, especially at high current densities.

Hollow 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 microspheres as a high-performance cathode material for lithium–ion batteries

Hollow 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) microspheres are synthesized on a large scale through a simple in situ template-sacrificial route. Starting from porous MnO(2) microspheres, the hollow microspheres assembled with 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) nanocrystals are formed by a nanoscale Kirkendall effect. The nanocrystal-assembled hollow 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) microspheres exhibit a highly reversible capacity as high as 295 mAh g(-1) over 100 cycles and excellent rate capability (125 mAh g(-1) at 1000 mA g(-1)). Benefitting from a unique hollow and nanocrystalline architecture, the as-formed hollow microspheres show much enhanced high-temperature (55 °C) electrochemical performances, compared with the products obtained by conventional sol-gel/solid-state reaction methods. This work demonstrates that a fabrication strategy based on the present in situ template-sacrificial approach offers a new method for the design of high-performance cathode materials with hollow interiors for Li-ion battery applications.

Effect of Transition Metal Ion Doping on the Photocatalytic Activities of TiO<sub>2</sub> Synthesized by Sol-Gel Method

Pure TiO2 , Ti 0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were prepared by low temperature sol-gel method. The samples were characterized by using transmission electron microscope, X-ray diffractometer and ultraviolet-visible spectrophotometer to study the effect of transition metal ions on the photocatalytic properties of TiO2 nanocrystals. The results show that the pure TiO2 and Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were granular and the size of which is 3.5, 2.9, 3.6, 3.9 nm, respectively. The titania anatase phases appear in the pure TiO2 , the Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2. The absorption edge of Ti0.75 Fe0.25 O2occur red shift comparing with that of pure TiO2 and the absorption edge of Ti0.75 Fe0.25 O2and Ti0.75 Fe0.25 O2occur blue shift comparing with that of pure TiO2. The photocatalytic properties of pure TiO2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2nanocrystals synthesized at low temperature by sol-gel method were investigated by degrading the methyl orange solution under ultraviolet irradiation. The degradation rate of Ti0.75 Fe0.25 O2is the highest (60%) and that of Ti0.75Co0.25O2 (10%) is the lowest among these catalysts after degradation for 120min.The result shows that the photocatalytic property ofTi0.75 Fe0.25 O2nanocrystals synthesized at low temperature is obviously better than that of pure TiO2 and Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2.

Synthesis of monodisperse Ce x Zr1−x O2 nanocrystals and the size-dependent enhancement of their properties

Monodisperse Ce1−x Zr x O2 nanocrystals have been synthesized using a simple two-phase approach; adjusting the ratio of precursors used, amount of capping agent used, reaction time and temperature affords precise control over their composition, structure and size. Size-dependent enhancement of oxygen-storage capacity and kinetics of oxygen storage and release were observed. Systematic studies were conducted in order to understand the size-dependent enhancement of these properties. This work provides important insights into the synthesis and fundamental understanding of multi-component nanocrystals with a large variety of applications.

Effect of Ni Doping on the Structure and Magnetic Property in Chemically Synthesized (In1−x Ni x )2 O3 (x = 0.03, 0.05, and 0.07) Nanocrystals

In order to experimentally check the Ni doped In2O3 as a potential spintronic material and to search for high temperature ferromagnetic material, a series of (In1−x Ni x )2O3 (x = 0.03, 0.05, and 0.07) nanoparticles were prepared by sol–gel method. Lattice parameter measurement shows distinct shrinkage of the lattice constant indicating the actual incorporation of Ni ions into the In2O3 lattice. X-ray diffraction (XRD) data show that all the samples exhibit single-phase polycrystalline behavior. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that the particle size of the calcined powder is in the range of 10–14 nm and 8–9 nm, respectively. SEM energy dispersive x-ray spectrometer (EDS) mapping shows the presence of Ni ions in the Ni doped In2O3 sample. High resolution transmission electron microscopy (HRTEM) micrographs show lattice fringes of 0.290 and 0.322 nm corresponding to the crystallographic plane (222) and (310) of cubic In2O3. Magnetization study indicated that the Ni doped In2O3 samples exhibit diamagnetic behavior.