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.     

Infrared study of oxygen adsorption on impure zinc oxide

Absorption bands are observed in the 2200-1700 cm⁻¹ region when strongly electronegative gases such as oxygen and chlorine are adsorbed on zinc oxide powder. These bands are related to carbon and nitrogen present as impurities in the zinc oxide. Efforts have been made to determine whether the bands correspond to stretching vibrations or whether they are due to electronic transitions from impurity donors to discrete levels lying 0·2–0·3 eV above the impurity levels. Use of carbon-13 as an impurity has identified a strong band at 1990cm⁻¹ as a carbon-oxygen stretching vibration. It is presumed that other observed bands are also of vibrational rather than electronic origin. A suggested mechanism implies that adsorption of electron withdrawing gases brings about formation of bonds between impurity atoms and oxygen within the bulk of the zinc oxide. This phenomenon appears to be limited to a depletion layer 10–30 Å in depth.     

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.     

Pyroelectricity of zinc oxide

Wurtzite lattices show piezoelectricity as well as pyroelectric effects. The pyroelectric change of polarisation with temperature has not yet been studied on ZnO. The pyroelectric constant p^σ (constant stress) is reported here for the temperature range from 9.7 to 420°K. It is proportional to the specific heat at constant pressure for the whole temperature range. At low temperatures a T³ law holds. Furthermore the coefficients of thermal expansion are given for 300°K. This allows the determination of the pyroelectric constant p^ϵ(constant strain, 300°K) using piezoelectric constant observed by others. The data are compared with results for other crystals exhibiting wurtzite structure.     

Impedance spectroscopy study of zinc oxide incorporated iron borate glass-ceramic

Here, the effects of zinc oxide (ZnO) on impedance and dielectric properties of the ZnO incorporated iron borate (Fe₃BO₆) glass-ceramics were studied using impedance spectroscopy in a wide range of frequency (1 Hz – 1 MHz) and temperature (25 °C–250 °C). With ZnO addition, the ε′ and tanδ values were reduced significantly, the strength of the relaxation process also decreased, along with a decrease in conductivity. Activation energies associated with modulus and conductivity plots suggest that similar type of charge carriers was responsible for the relaxation and conduction processes. The analysis of both complex impedance and conductivity show the negative temperature coefficient of resistance (NTCR) behavior of the samples. The thermistor constant B-values of 5ZnO and 10ZnO were found to be 7223 and 7088 respectively. The study of the NTCR properties suggests a potential candidate for thermistor applications.     

The diffuse reflectance spectra of zinc oxide and zinc peroxide

Visible and near ultraviolet optical absorption spectra of mixtures of zinc oxide and zinc peroxide, obtained by the diffuse reflectance method, show that a strong absorption occurs in the peroxide at an energy at least 1.3 eV higher than a similar absorption in the oxide. The absence of any evidence of crystal field splitting denies the presence of Zn⁴⁺(3d⁸) ions in the peroxide as suggested by earlier X-ray absorption results.     

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.     

ZnO双晶纳米梳

以纯锌粉作为原料，用气相输运法在650℃合成了ZnO双晶纳米梳结构，并用高分辨透射电镜 及选区电子衍射等方法对其微观结构进行了研究.结果表明双晶纳米梳两侧的齿针呈一定角 度以孪晶方式对称生长，其孪晶面为(1 1-3)，两侧齿针都垂直于孪晶界，其直径均匀分布 在50—100nm，每一侧梳背和齿针的生长方向均分别为〈0 1-1 0〉和〈0 0 0 1〉.由于孪晶 造成了晶体取向的变化，基于镜像对称的特征，ZnO双晶纳米梳两侧梳背的外缘可以均为Zn 终结的(0 0 0 1)面，因此都可以发生自催化作用并形成分支结构，这种纳米结构的生长过 程与王中林等人提出的极性生长机理相符合. 关键词： 氧化锌 纳米梳 双晶 极性生长     

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     

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.