In situ formation of Mn-doped ZnO aligned structures by rapid heating method

ZnO tetrapods and Mn doped multipods have been prepared by a rapid thermal oxidation at 1220 °C during 6 min. Moreover, Mn doped ZnO nearly aligned nanostructures forming carpets over sintered pellets have been produced by the same method without the use of catalyst or gas flow. These rods show two different diameters, one of 500 nm and the other one of 300 nm, with lengths of 5 µm. XRD and Raman spectra demonstrate a good crystalline quality of the doped nanostructures. The room temperature photoluminescence shows a quenching of the intrinsic UV emission band on the ZnO tetrapods, due to an increase of material defects.     

Novel synthesis and electrochemical investigations of ZnO/C composites for lithium-ion batteries

For the first time, ZnO/C composites were synthesized using zinc glycerolate as a precursor through one-step calcination under a nitrogen atmosphere. The effect of the heat treatment conditions on the structure, composition, morphology as well as on the electrochemical properties regarding application in lithium-ion batteries are investigated. The products obtained by calcination of the precursor in nitrogen at 400—800 °C consist of zinc oxide nanoparticles and amorphous carbon that is in-situ generated from organic components of the glycerolate precursor. When used as anode material for lithium-ion batteries, the as-prepared ZnO/C composite synthesized at a calcination temperature of 700 °C delivers initial discharge and charge capacities of 1061 and 671 mAh g^?1 at a current rate of 100 mA g^?1 and hence 1.5 times more than bare ZnO, which reaches only 749/439 mAh g^?1. The native carbon improves the conductivity, allowing efficient electronic conductivity and Li-ion diffusion. By means of ex-situ XRD studies a two-step storage mechanism is proven.

     

Starch-stabilized synthesis of ZnO nanopowders at low temperature and optical properties study

Zinc oxide nanoparticles (ZnO–NPs) were synthesized via the sol–gel method in starch media. Starch was used as a stabilizer to control of the mobility of zinc cations and then control growth of the ZnO–NPs. Because of the special structure of the starch, it permits termination of the particle growth. Thermogravimetry analysis (TGA) was applied on dried gel to obtain the certain calcination temperature(s) of the ZnO–NPs. The dried gel was calcined at different temperatures of 400, 500, and 600 °C. Several techniques such as X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and high-magnification transmission electron microscopy (TEM) were used to characterize the ZnO–NPs. The ZnO–NPs calcined at different temperatures exhibited a hexagonal (wurtzite) structure with sizes from 30 to 50 nm. The optical properties of the prepared samples were investigated using UV–vis spectroscopy. The results showed that starch is a suitable stabilizer in the sol–gel technique, and this method is a reasonable and facile method to prepare ZnO–NPs for large-scale production.     

Growth and properties of ZnO nanowires synthesized by a simple hydrothermal method

Hexagonal ZnO nanowires were synthesized on pre-seeded silicon (100) substrates by a simple hydrothermal method at a relatively low temperature of 95 °C without any catalyst or template. The pre-seeded layer was produced using the sol–gel spin coating technique with 1 M zinc acetate in ethanol and ethanolamine. The structural properties of the nanowires were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern indicated that the as-grown ZnO nanowires had the single-phase wurtzite structure, formed along the c-axis. SEM revealed that the nanostructure thin film had wire textures and the synthesis processes importantly influence the final size and shape of the ZnO nanowires. High-resolution transmission electron microscopy (HRTEM) provided further insight into the structure of ZnO nanostructures. The obtained HRTEM image was of the tip of an individual nanowire. The ZnO nanowires highly preferentially grew in the (002) crystal plane. The lattice spacing between adjacent (002) lattice planes was calculated to be 0.52 nm. The optical characteristics of the nanowires were determined from cathodoluminescence (CL) spectra. The CL revealed a fairly high surface state density of ZnO nanowires that grew at reaction concentrations of 0.01–0.25 M.     

Optimizing conditions for preparation of MnOx/RHA catalyst particle for the catalytic oxidation of NO

Rice husk ash (RHA) was utilized as support to synthesize MnOx/RHA catalyst by incipient wetness impregnation. In order to detailedly investigate the influence of preparation variables on the catalytic activity of MnOx/RHA for NO oxidation, the quadratic regression orthogonal rotation design (QRROD) was employed. An empirical model was developed to correlate preparation variables with the conversion of NO to NO₂. The surface species and morphology of the catalyst were also analyzed by SEM and XRD, respectively. It was found that most of MnOx supported on RHA were granular with micron-size and in the form of amorphous phase. The preparation variables except for calcination time (x₂) had significant effect on the catalytic activity of MnOx/RHA. The model could accurately describe the relationship between the preparation variables and NO conversion through the analysis of variance (ANOVA) and the comparison of experimental results and predicted results. The particles size of MnOx was increased from 0.1 to 1.0 μm, as the calcination temperature was raised from 200 to 800 °C, and the fraction of crystal MnOx also increased. The surface structure of RHA was markedly affected by incineration temperature. With incineration temperature increasing, the surface structure becomes compacter.     

Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation

Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed.     

Comparison between synthesis techniques to obtain ZnO nanorods and its effect on dye sensitized solar cells

This paper reports additive-free, reproducible, low-temperature solution-based process for the preparation of crystalline ZnO nanorods by homogeneous precipitation from zinc acetate. Also, ZnO nanorod structured dye sensitized solar cells using ruthenium dye (Z907) have been fabricated and characterized. The formation and growth of zinc oxide nanorods are successfully achieved. We analyzed three different synthesis method using solution phase, autoclave and microwave. The calcination effects on the morphology of ZnO nanorods are also investigated. Analysis of ZnO nanorods shows that calcination at lower temperature is resulted in a nanorod growth. Additive-free, well-aligned ZnO nanorods are obtained with the length of 330–558 nm and diameters of 14–36 nm. The XRD, SEM, and PL spectra have been provided for the characterization of ZnO nanorods. Microwave-assisted ZnO nanostructured dye sensitized solar cell devices yielded a short-circuit photocurrent density of 6.60 mA/cm², an open-circuit voltage of 600 mV, and a fill factor of 0.59, corresponding to an overall conversion efficiency of 2.35% under standard AM 1.5 sun light.     

Preparation and gas sensing properties of the nutlike ZnO microcrystals via a simple hydrothermal route

Large-scale uniform nutlike ZnO microcrystals are successfully synthesized via a facile hydrothermal process at low temperature (95 °C). The structure and morphology of the ZnO products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results reveal that the as-prepared ZnO products have average length of 2.2 µm and diameter of 1.8 µm, possessing a single crystal wurtzite structure. The possible formation mechanism of nutlike microcrystals is proposed. The samples exhibit excellent ethanol sensing properties at the operating temperature of 250 °C detecting ethanol as low as 1 ppm.     

Synthesis of minimal-size ZnO nanoparticles through sol–gel method: Taguchi design optimisation

Zinc oxide (ZnO) has excellent potential to be used in water and wastewater treatment, either as a photocatalyst or in membrane incorporation. In this work, the synthesis of smaller ZnO NPs through a sol–gel approach was enhanced by applying Taguchi design. Recent work on the synthesis of ZnO NPs was optimised to ensure relatively smaller sized particles were obtained. Several parameters of the synthesis process, such as molar ratio of starting materials, molar concentration and calcination temperature, were selected as they have the dominant effects on the particle size of ZnO NPs. Each of these factors was studied at three levels. Various analyses such as ANOVA, model adequacy check and numerical optimisation were performed to validate the predicted optimal model. As a result, the optimum conditions were estimated at a molar ratio of 50:50, an oxalic acid molar concentration of 0.1 M and a calcination temperature of 400 °C. Experiments were performed to validate the model at the selected conditions and the particle size was around 20 ± 2 nm according to XRD analysis, which was in good agreement with the predicted size of 19.8 nm. In addition, the actual size of the synthesised NPs was confirmed by TEM analysis, with the average size of 13 ± 5 nm. Hence, the Taguchi design was an essential tool in the optimisation of ZnO NP synthesis process with fewer experimental runs and relatively low cost approach.     

Preparations of nano-particles,nano-composites and fibers of ZnO from an amide precursor: Photocatalytic decomposition of (CH3)2S2 in a continuous flow reactor

High surface area hexagonal ZnO nano-particles were obtained at room temperature from hydrolysis of the amide derivative Zn[N(SiMe₃)₂]₂. The same procedure applied on silica or cellulose substrates led to homogeneous crack-free hybrid materials for which micro- down to nano-meter replication into ZnO cloth was achieved by calcination at 700 °C. These materials were characterized by FT-IR, UV–vis, photoluminescence, X-ray diffraction (XRD) and transmission electron microscopy (TEM). They demonstrated enhanced photocatalytic degradation of a tough pollutant such as CH₃SSCH₃ compared with commercial ZnO powder.     

Synthesis of deer horn-like and spherical ZnO nanoparticles by microwave decomposition of bis(2-pyridinethiol <Emphasis Type="Italic">N</Emphasis>-oxide)zinc using factorial and Taguchi experimental designs

Deer horn-like and spherical nanoparticles of ZnO have been prepared via microwave heating (MWH) of Bis (2-pyridinethiol N-oxide) Zinc (II) [BPTZ] complex. The product was characterized by XRD, SEM, LLS, BET, FTIR and chemical analysis. The 2³ factorial and the Taguchi L ₄ designs were used for factors effect estimation and determination of optimum conditions for spherical ZnO nanoparticle synthesis. The three main factors considered were power of microwave, temperature of pyrolysis and time of thermal decomposition. The time of pyrolysis had the most influence on the average particle size and the size distribution of product. The average particle size for the spherical ZnO at optimum conditions was found to be 16 nm and the particle range was 16 ± 13 nm.     

Orientation enhancement of polycrystalline ZnO thin films through thermal oxidation of electrodeposited zinc metal

The polycrystalline ZnO thin films with (002) orientation enhancement were prepared by annealing of electrodeposited metallic Zn films from the ethylene glycol solution of zinc acetate without using any catalyst and template. The morphologies of the thin films were evolved from the nanoplate to the nanocolumn structures with increasing of annealing temperature from 100 °C to 500 °C. SEM and XRD studies indicated that the ZnO nanocolumns were enhanced in the (002) orientation along their length direction. The UV-vis absorption spectra of the ZnO films obtained by annealing at 300 °C and 500 °C were carried out and their band gaps were 3.18 eV and 3.20 eV, respectively. A possible growth mechanism of the ZnO nanostructures responsible for the morphologies and orientation evolution was discussed.     

Catalyst-free synthesis of ZnO nanowire arrays on zinc substrate by low temperature thermal oxidation

High density ZnO nanowire arrays were successfully synthesized without catalyst by direct oxidation of zinc substrate in air below 400 °C, lower than the melting point of zinc metal. The as-grown ZnO nanowires are single crystalline with a Wurzite structure extending in <110> direction. The diameters of the ZnO nanowires range from 20 to 150 nm and the lengths from several to over ten micrometers. Room temperature photoluminescence measurements reveal an intense ultraviolet emission at 397 nm. The present work highlights the promise of the low temperature, direct oxidation process in the high-yield synthesis of high quality semiconductor nanowire arrays for nano-devices.     

Nanostructured ZnO hexagons and optical properties

We report the solvothermal synthesis of nanostructured ZnO hexagons by hydrothermal method via intermediate zinc adipate. The intermediate zinc adipate was obtained using precursors zinc acetate and adipic acid in aqueous and organic medium. Detailed XRD analysis of the zinc adipate was studied for the first time. Thermal study of intermediate showed the formation of ZnO at 400 °C. XRD study demonstrated the existence of wrutzite ZnO of high degree of crystallinity with crystallite size in the range of 20–25 nm. Scanning Electron Microscopy (SEM) showed distinguished morphology in different medium. Transmission Electron Microscopy (TEM) demonstrated nanostructured ZnO hexagons with average size 25–50 nm. The band gap for aqueous and organic mediated ZnO was found to be 3.24 and 3.26 eV, respectively. The band gap obtained is higher than the bulk ZnO, which implies nanocrystalline nature of the material.     

Comparative photocatalytic performance and therapeutic applications of zinc oxide (ZnO) and neodymium-doped zinc oxide (Nd–ZnO) nanocatalysts against Acid Yellow-3 dye: kinetic and thermodynamic study of the reaction and effect of various parameters

Zinc oxide (ZnO) nanoparticles (NPs) were synthesized hydrothermally and doped with 4% Neodymium (Nd). The produced NPs were characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Photoluminescence (PL) spectroscopy. With the addition of 4% Nd, the bandgap reduced from 3.20 to 3.00 eV which confirmed successful doping with Nd which also evident from FTIR study. The XRD study showed hexagonal structure of the synthesized material, while SEM study confirmed that Nd-doped ZnO (Nd–ZnO) NPs are well dispersed as compare to ZnO. TGA study revealed that synthesized NPs were much stable to temperature and only 11.3% and 7.2% the total loss occurred during heating range (40–600 °C) in case of ZnO and Nd–ZnO NPs, respectively. The PL intensity of the visible peaks of ZnO reduced after doping with Nd. The degradation of Acid yellow-3 over both the catalysts followed first-order kinetics. The activation energy calculated for the photodegradation reaction was 43.8 and 33.7 kJ/mol using pure ZnO and Nd–ZnO NPs, respectively. About 91% and 80% dye was degraded at the time interval of 160 min using Nd–ZnO and ZnO NPs, respectively. High percent degradation of dye was found at low concentration (10 ppm) and at optimal dosage (0.035 g) of the catalyst. The rate of Acid yellow-3 dye degradation was found to increase with increase in temperature (up to 50 °C) and pH(8) of the medium. The recyclability study showed that both pure ZnO and Nd–ZnO NPs could be reused for the degradation of the given dye. With the addition of H₂O₂ up to 5 µL, the rate of reaction increased clearly indicating the effect of OH^· generation during photocatalysis. When compared with Nd–ZnO NPs at low concentrations, ZnO NPs at higher concentrations were found to be less hazardous. Both the NPs showed best antibacterial activities against Staphylococcus aureus. The hemolytic study indicated that at low concentration, pure ZnO was non-hemolytic as compared to Nd–ZnO.

     

A facile and green approach for the fabrication of ZnO nanorods using bamboo charcoal as the template

A green synthetic approach was presented for the fabrication of ZnO nanorods via the bamboo charcoal-assisted impregnation route with ZnC₂O₄ colloid in ethanol as the inorganic precursor, followed by calcination at 800 °C for 7 h in air. These ZnO samples were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is shown that wurtzite hexagonal structured ZnO nanorods were fabricated, with an average diameter of about 300 nm and a length up to several micrometers. Bamboo charcoal played a key role in the formation of ZnO nanorods. The possible formation mechanism for ZnO nanorods was proposed.     

Photocatalytic oxidation of nitric oxide with immobilized titanium dioxide films synthesized by hydrothermal method

Gas-phase photocatalytic oxidation (PCO) of nitric oxide (NO) with immobilized TiO2 films was studied in this paper. The immobilized TiO2 films were synthesized by hydrothermal method. The characterization for the physicochemical properties of catalysts prepared under different hydrothermal conditions were carried out by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), Brunauer-Emmett-Teller measurements (BET) and scanning electron micrograph (SEM). It was found that the PCO efficiency of the catalyst was mainly depended on the hydrothermal conditions. The optimal values of hydrothermal temperature and hydrothermal time were 200 degrees C and 24 h, respectively. Furthermore, it was also known that the photocatalytic efficiency would decrease remarkably when the calcination temperature was over than 450 degrees C. Under the optimal conditions (hydrothermal condition: 200 degrees C for 24 h; calcination temperature: 450 degrees C), the photocatalytic efficiency of catalyst could reach 60% higher than that of Degussa P25.     

TiO_2/AC复合光催化剂制备及性能研究

以TiCl4乙醇溶液为前驱物、煤质活性炭为载体,通过溶胶-凝胶法制备活性炭(AC)/TiO2复合光催化剂。利用扫描电子显微镜(SEM)、X-射线衍射仪(XRD)和BET比表面积孔径测定仪等对制备的样品进行表征。以光催化降解甲基橙溶液为模型反应,表征其光催化活性,考察了TiCl4/乙醇体积比、煅烧温度和煅烧时间等制备条件对光催化活性的影响。结果表明:在TiCl4/乙醇体积比为1∶20,500℃煅烧2h时,光催化降解甲基橙的活性最高,降解率达到95%;TiCl4/乙醇体积比和煅烧温度对光催化活性影响较大,煅烧时间对光催化活性影响甚小。含少量金红石相的TiO2有利于光催化降解甲基橙。     

Synthesis of γ-alumina via precipitation in ethanol

Nanosized γ-alumina powder was prepared via sol-gel precipitation in ethanol followed by a washing-drying treatment and calcination. The reactant concentration, the molar ratio of reactants and the calcination temperature were inspected by homogenous design. BET, TEM, XRD and IR were used to characterize the products. The experimental results showed that ethanol can avoid hard agglomerate during precipitation and that calcination temperature was the major factor to determine the surface area, the diameter and the phase composition of the final product. When the calcination temperatures were controlled between 686-1029 °C, the agglomerate-free nano-sized γ-alumina particles with a size range of 5-9 nm were obtained.     

Preparation and microwave absorption of porous hollow ZnO by CO2 soft-template

The porous hollow ZnO samples were prepared by calcination of ZnCO₃ precursor at 450 °C. The structural properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis and differential thermal analysis (TG-DTA). A possible mechanism for the formation of porous hollow microstructure was proposed. The microwave absorption properties of the porous hollow structural ZnO have been investigated. The reflection loss (RL) of the ZnO was calculated based on the relative complex permeability and permittivity. A minimum reflection loss of the wax-composite with 25 wt% porous hollow ZnO is −36.3 dB at 12.8 GHz with a thickness of 4.0 mm. The results indicate that porous hollow structural ZnO can be used as a desirable material for the microwave absorption.