Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm)=" for=" the=" samples=" prepared=" with=">₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.     

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm) for the samples prepared with FeCl₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.This revised version was published online in August 2005 with a corrected issue number.     

A zinc oxide microwire laser

In this paper, we report stimulated emission from a zinc oxide (ZnO) microcrystal grown by carbothermal evaporation observed by spatially resolved photoluminescence (PL) and high excitation spectroscopy (HES).     

First principle study of unzipped zinc oxide nanotubes

First principle calculations have been employed in order to explain the dangling bonds behavior in the rolling up of a zinc oxide nanoribbon (ZnONR) to construct a single-walled zinc oxide nanotube (SWZnONT). Our results show in armchair ZnONR two degenerative dangling bonds split and moved up to higher energies due to symmetry breaking of the system. By more rolling up (increasing the curvature), the energy gap is increased by increasing of curvature.     

Direct fabrication of graphene/zinc oxide composite film and its characterizations

Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer for enhancing properties. In this work, a new mixed dispersion approach for graphene-based composite has taken on. Graphene flakes (<4 layers) and a well-known semiconductor zinc oxide (ZnO) (<50 nm particle size) have dispersed in N-methyl-pyrrolidone. We deposited graphene/ZnO composite thin film by a simple, low-cost, environmentally friendly and non-vacuum electrohydrodynamic atomization process on silicone substrate. Experiments have been carried out by changing flow rate and applied potential while keeping stand-off distance and substrate velocity constant, to discover the optimum conditions for obtaining a high-quality thin film. It has been explored that high-quality thin composite film is obtained at optimum flow rate of 300 μl/h at 6.3 kV applied potential after curing for 2 h at 300 °C. Graphene/ZnO thin composite film has been characterized using Field emission scanning electron microscopy, Ultra-violet Visible near Infra Red spectroscopy, X-ray diffraction, Raman Spectroscopy and 3D-Nanomap. For electrical behavior analysis, a simple diode Indium tin oxide/(poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/polydioctylfluorene-benzothiadiazole(F8BT)/(Graphene/ZnO) has fabricated. It is observed that at voltage of 0.3 V, the current in organic structure is at low value of 1.20 × 10^?3 Amp/cm² and after that as further voltage was applied, the device current increased by the order of 110 and reaches up to 1.32 × 10^?1 Amp/cm² at voltage 2 V.     

Rational doping for zinc oxide and its influences on morphology and optical properties

Zinc oxide(ZnO) nanopowders doped with different metal ions(Me, Me = Sn4+, In3+, Mn2+, and Co2+) are prepared by a simple sol–gel method. Influences of the ion doping on morphology and optical properties of the resulting ZnxMeyO are investigated by scanning electron microscopy, X-ray diffraction, UV-vis absorption spectrum, and photoluminescence. The morphology of ZnO can be tailored by ion doping, which is closely related not only to the ionic radii and electronegativities of the doped ions, but also to their oxidation states and electron configurations. The optical band gap and photoluminescence of ZnO can also be modulated by ion doping, which results from a combination of different effects, Burstein–Moss, band tail, charge compensation, sp–d exchange, non-radiative recombination, and blocking barrier. This may offer us a viable approach to tuning the(optical) properties of ZnO-based materials via rational ion doping.     

Impact of zinc substitution on the structural and magnetic properties of chemically derived nanosized manganese zinc mixed ferrites

Mn_1−xZn_xFe₂O₄ nanoparticles (x=0-1) were synthesized by wet chemical co-precipitation techniques. X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The elemental analysis was conducted using energy-dispersive spectrum and inductively coupled plasma analysis. The magnetic properties such as magnetization and coercivity were measured using vibrating sample magnetometer. The observed magnetization values of the nanoparticles were found to be lower compared to the bulk counterpart. The magnetization showed a gradual decrease with zinc substitution except for a small increase from x=0.2 to 0.3. The Curie temperature was found to be enhanced in the case of ferrites in the nanoregime. The variation in lattice constant, reduced magnetization values, variation of magnetization with zinc substitution, the presence of a net magnetic moment for the zinc ferrite and the enhancement in Curie temperature in Mn_1−xZn_xFe₂O₄ all provide evidence to the existence of a metastable cation distribution together with possible surface effects at the nanoregime.     

Theoretical study of structural, optical and electrical properties of zirconium-doped zinc oxide

The structural, optical and electrical properties of zirconium-doped zinc oxide have been investigated by first principle calculations. Three possible structures including substitutional Zr for Zn (Zr_Zn), interstitial Zr (Zr_i) and substitutional Zr for O (Zr_O) are considered. The results show that the formation energy of Zr_Zn defect is the lowest, which indicates that Zr_Zn defect forms easier and its concentration may be the highest in the samples. It is also found that as the proportion of Zr increases, the lattice constants increase while the optical band gap first becomes larger and then smaller, which are consistent with our recently experimental results. The electronic structure calculations display that as Zr_Zn defect is introduced into ZnO, the Fermi-level shifts to the conduction band, and there are excess electrons in the conduction band, which may be a possible reason of the good conductivity of Zr doped ZnO film.     

Two-dimensional zinc oxide nanostructure

Transparent two-dimensional ultralong and ultrabroad single crystal zinc oxide (ZnO) nanosheets were directly synthesized by a simple solid vapor deposition process under lead oxide (PbO) atmosphere. The nanosheets are well grown single crystals with thickness of about 50-70 nm, breadth of 50-100 μm and length of 4-6 mm. The growth mode of the ultrabroad nanosheets displays a unique aspect that (001) planes form the narrowest facets of the nanosheets, which is completely different from other belt-like nanostructures of ZnO. Control experiments show that PbO play an important role in the vapor-solid growth process of ZnO nanosheets.     

Structural,morphological, optical and antibacterial activity of rod-shaped zinc oxide and manganese-doped zinc oxide nanoparticles

Pure ZnO and Mn-doped ZnO nanoparticles were synthesized by Co-precipitate method. The structural characterizations of the nanoparticles were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. UV–Vis, FTIR and photoluminescence (PL) spectroscopy were used for analysing the optical properties of the nanoparticles. XRD results revealed the formation of ZnO and Mn-doped ZnO nanoparticles with wurtzite crystal structure having average crystalline size of 39 and 20 nm. From UV–Vis studies, the optical band-gap energy of 3.20 and 3.25 eV was obtained for ZnO and Mn-doped ZnO nanoparticles, respectively. FTIR spectra confirm the presence of ZnO and Mn-doped ZnO nanoparticles. Photoluminescence analysis of all samples showed four main emission bands: a strong UV emission band, a weak blue band, a weak blue–green band and a weak green band indicating their high structural and optical qualities. The antibacterial efficiency of ZnO and Mn-doped ZnO nanoparticles were studied using disc diffusion method. The Mn-doped ZnO nanoparticles show better antibacterial activity when higher doping level is 10 at% and has longer duration of time.     

Nanotubular structures of zinc oxide

ZnO nanotubes with a regular polyhedral shape, hollow core, and wall thickness as small as 4 nm, have been prepared in large-area substrate by vapor phase growth. The nanotubes can be classified into two groups consisting of either polycrystalline or straight single crystal. The formation of the ZnO nanotubes was found closely related to the hexagonal structure of the ZnO crystal and the peculiar growth conditions used.     

Growth of zinc oxide nanostructures

Zinc oxide (ZnO) nanowhiskers have been prepared using a multilayer ZnO(50 nm)/Zn(20 nm)/ZnO(2μm) structure on a polished stainless steel (SS) substrate by high rate magnetron sputtering. The formation of uniformly distributed ZnO nanowhiskers with about 20 nm dia. and 2 to 5 μm length was observed after a postdeposition annealing of the prepared structure at 300–400° C. An array of highlyc-axis oriented ZnO columns (70–300 nm in dia. and up to 10 μm long) were grown on Si substrates by pulsed laser deposition (PLD) at a high pressure (1 Torr), and Raman studies showed the activation of surface phonon modes. The nanosized powder (15–20 nm) and nanoparticle ZnO films on glass substrate were also prepared by a chemical route. Nanowhiskers showed enhanced UV light detection characteristics, and the chemically prepared ZnO nanoparticle films exhibited good sensing properties for alcohol     

Surface modification of zinc oxide nanoparticle by PMAA and its dispersion in aqueous system

Commercial zinc oxide nanoparticles were modified by polymethacrylic acid (PMAA) in aqueous system. The hydroxyl groups of nano-ZnO particle surface can interact with carboxyl groups (COO-) of PMAA and form poly(zinc methacrylate) complex on the surface of nano-ZnO. The formation of poly(zinc methacrylate) complex was testified by Fourier-transform infrared spectra (FT-IR). Thermogravimetric analysis (TGA) indicated that PMAA molecules were absorbed or anchored on the surface of nano-ZnO particle, which facilitated to hinder the aggregation of nano-ZnO particles. Through particle size analysis and transmission electron micrograph (TEM) observation, it was found that PMAA enhanced the dispersibility of nano-ZnO particles in water. The dispersion stabilization of modified ZnO nanoparticles in aqueous system was significantly improved due to the introduction of grafted polymer on the surface of nanoparticles. The modification did not alter the crystalline structure of the ZnO nanoparticles according to the X-ray diffraction patterns.     

Optical properties of zinc peroxide and zinc oxide multilayer nanohybrid films

Zinc peroxide and zinc oxide nanoparticles were prepared and self-assembled hybrid nanolayers were built up using layer-by-layer (LbL) technique on the surface of glass substrate using the layer silicate hectorite and an anionic polyelectrolyte, sodium polystyrene sulfonate (PSS). Light absorption, interference and morphological properties of the hybrid films were studied to determine their thickness and refractive index. The influence of layer silicates and polymers on the self-organizing properties of ZnO₂ and ZnO nanoparticles was examined. X-ray diffraction revealed that ZnO₂ powders decomposed to ZnO (zincite phase) at relatively low temperatures (less than 200 °C). The optical thickness of the films ranged from 190 to 750 nm and increased linearly with the number of layers. Band gap energies of the ZnO₂/hectorite films were independent from the layer thickness and were larger than that of pure ZnO₂ nanodispersion. Decomposition of ZnO₂ to ZnO and O₂ at 400 °C resulted in the decrease of the band gap energy from 3.75 to 3.3 eV. Concomitantly, the refractive index increased in correlation with the formation of the zincite ZnO phase. In contrast, the band gap energies of the ZnO₂/PSS hybrid films decreased with the thickness of the nanohybrid layers. We ascribe this phenomenon to the steric stabilization of primary ZnO₂ particles present in the confined space between adjacent layers of hectorite sheets.     

Synthesis and characterization of copper doped zinc oxide nanoparticles and its application in energy conversion

Solar cells, in general, perform under light source of solar influx, while the heat energy of solar radiation remains unutilized. Using an aqueous suspension of copper doped zinc oxide nanoparticles in specially-designed electrochemical cells we have observed significant voltage (maximum 632.0 mV) and storage duration (∼47 h) upon thermal excitation. The cells exhibit reasonable energy conversion efficiency (maximum 1.36%). These cells generate voltage even at room temperature (∼30 °C) and the voltage increases gradually with increasing temperature. When the platinum foil separating the two compartments of the electrochemical cell is replaced by a planar lipid membrane, all the parameters e.g., thermovoltage, storage capacity and the energy conversion efficiency increase significantly.     

Fabrication and characterization of graphene oxide/zinc oxide nanorods hybrid

This work presented a hybrid architecture of graphene oxide (GO)/ZnO nanorods (ZNs) with ZNs attached parallel onto GO sheets. ZNs were synthesized by refluxing zinc acetate dehydrate in methanol solution under basic conditions followed by surface modification of 3-aminopropyl triethoxysilane (ATS), and then the preformed ZNs were attached onto GO sheets by reaction of the amino groups on the outer wall of ZNs with the carboxyl groups on the GO surface. Transmission electron microscopy (TEM) image of the as-prepared hybrid reveals the morphology of the architecture of GO/ZNs hybrid. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and fluorescence spectroscopy were also performed to characterize the structure and properties of the GO/ZNs hybrid. It was shown that ZNs maintained their initial morphology and crystallinity in the hybrid and the luminescence quenching of yellow-green emission of ZNs confirmed the electron transfer from excited ZnO to GO sheets.     

Electrochemical synthesis of nanocrystalline zinc oxide and phase transformations of zinc hydroxides

Nanoscaled ZnO was synthesized by an electrochemical process using zinc or Al-alloyed zinc electrodes in an aqueous system with acetic acid as a conductive salt. Depending on the synthetical parameters, the precipitated precursor solids were found to consist of various compounds such as zincite, presumably δ-Zn(OH)₂, β₁-Zn(OH)₂, ε-Zn(OH)₂, Zn₅(CO₃)₂(OH)₆ and, in case an Al-alloyed electrode was used for the synthesis, Zn_0.71Al_0.29(OH)₂ (CO₃)_0.145·xH₂O. The intermediate solids served as precursors for the subsequent thermal treatment resulting in zincite powders with various morphologies. Depending on the processing conditions, zincite was formed between 100 and 260 °C with a mean crystallite size between 6 and 25 nm. Selected zincite powders were pressed to pellets, sintered at temperatures between 900 and 1,100 °C and characterized by measurements of the electrical bulk conductivities, yielding values up to 1.69 S cm⁻¹ in samples with 1.24 wt% Al. Comparison with samples prepared by precipitation methods showed that the latter had values of up to 44 S cm⁻¹.     

Synthesis and study of electrical and magnetic properties of vanadium oxide micro and nanosized rods grown using pulsed laser deposition technique

Vanadium oxide micro and nanosized rods were grown using pulsed laser deposition technique under different oxygen pressures. X-ray diffractogram shows a predominant mixture of vanadium dioxide, VO₂ and Magneli phase, V₃O₇. The diameters of the rods were found to increase from 300 nm to 2.3 μm with increase in oxygen pressure from 0.1 mbar to 0.5 mbar as seen from high resolution scanning electron microscope images. Raman spectra of the rods show peaks at all the characteristic vibrations corresponding to that of V O_x phase. The 0.5 mbar oxygen deposited sample shows a semiconducting behavior from 300 to 77 K and is paramagnetic down to 5 K. Using versatile pulsed laser deposition we have established the tunability of the dimensions of V O_x nanorods which can find numerous potential applications in electrochemistry, catalysis, etc.