Electrochemical impedance spectroscopy of ZnO nanostructures

The paper reports on the use of electrochemical impedance spectroscopy to determine the doping character and carrier density of freshly prepared and annealed ZnO nanostructures. The ZnO nanostructures were obtained by chemical oxidation of metallic Zn in a 5% N,N-dimethylformamide (DMF) aqueous solution at 95 °C for 24 h. The as-grown nanostructured ZnO samples display a high donor density of 3.71 ± 0.88 × 10²¹ cm^?3. Annealing at 100 and 200 °C did not have any effect on the donor density while thermal annealing at 300 °C in air for 1 h induced a decrease in the doping concentration without affecting the surface morphology.     

Solution decomposition of the layered double hydroxide (LDH) of Zn with Al

The layered double hydroxides (LDH) of Zn with Al containing intercalated CO₃²⁻ and NO₃⁻ ions undergo solution decomposition to yield a highly crystalline oxide mixture comprising ZnO and ZnAl₂O₄ at temperatures as low as 150–180 °C under hydrothermal conditions. In contrast solid-state decomposition takes place at a much higher temperature (240–315 °C) in air. Solution decomposition is not only guided by the low octahedral crystal field stabilization energy of Zn²⁺ ions, a factor that also affects solid-state decomposition, but also by solubility considerations. The LDHs of Mg and Ni with Al do not undergo solution decomposition.     

Reduction of carbonyl compounds by Raney Ni–Al alloy and Al powder in the presence of noble metal catalysts in water

Raney Ni–Al alloy was found to be capable of reducing benzophenones to the corresponding diphenylmethanes (2) in water in good to excellent yields within 3 h at 60 °C in a sealed tube. The complete reduction process of both aromatic rings required 18 h at 80 °C with Raney Ni–Al and Al powder in the presence of Pt/C. The nature of the hydrogenated products was also found to greatly depend on temperature, reaction time, volume of water, and amount of Raney Ni–Al alloy being used.     

Surface structures and electrochemical characteristics of surface-modified carbon anodes for lithium ion battery

Petroleum coke and those heat-treated at 1860 °C, 2100 °C, 2300 °C 2600 °C and 2800 °C (abbreviated as PC, PC1860, PC2100, PC2300, PC2600 and PC2800) were fluorinated by elemental fluorine of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Natural graphite powder samples with average particle sizes of 5 μm, 10 μm and 15 μm (abbreviated as NG5μm, NG10μm and NG15μm) were also fluorinated by ClF₃ of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Transmission electron microscopic (TEM) observation revealed that closed edge of PC2800 was destroyed and opened by surface fluorination, which increased the first coulombic efficiencies of PC2300, PC2600 and PC2800 by 12.1–18.2% at 60 mA/g and by 13.3–25.8% at 150 mA/g in 1 mol/dm³ LiClO₄–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 in volume). Light fluorination of NG10μm and NG15μm increased the first coulombic efficiencies by 22.1–28.4% at 150 mA/g in 1 mol/dm³ LiClO₄–EC/DEC/PC (PC: propylene carbonate, 1:1:1 in volume).     

Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn, Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid at a temperature of 90 °C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M_s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid with current density of 0.5 mA/cm² was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods.     

Optical and Raman studies of Zn1-xMgxO ceramic pellets

The undoped and Mg-doped ZnO ceramics have been successfully synthesized using the conventional solid state sintering method. The doping effect of MgO content on the structural properties of ZnO/MgO composites has been investigated by X-ray diffraction (XRD) and Raman spectroscopy. The XRD patterns reveal that all the samples are polycrystalline and have a prominent hexagonal crystalline structure with (002) and (101) as preferred growth directions. The formation of the hexagonal ZnMgO alloy phase and the segregation of MgO-cubic phase took place for an MgO composition x ≥ 20 wt%. This finding is in good agreement with the Raman spectroscopy measurements which prove the existence of multiple-order Raman peaks originating from ZnO-like and MgO phonons. The band gap energy and the carrier concentration of ZnO pellets were found to be dependent upon the Mg doping whose values vary from 3.287 to 3.827 eV and from 1.6 × 10¹⁷ to 5.2 × 10²⁰ cm⁻³, respectively.     

Microstructural,magnetic and crystal field investigations of nanocrystalline Dy3+ doped zinc oxide

Dy³⁺ doped zinc oxide was prepared by co-precipitation method. The as-prepared samples were annealed at different temperatures to obtain the samples with different particle sizes. The crystallographic phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. Rietveld analysis of the XRD pattern of the sample annealed at 80 °C showed that most of the Dy³⁺ ions were substituted in the Zn²⁺ site of the hexagonal ZnO lattice. But in case of samples annealed at higher temperatures, a fraction of Dy³⁺ ions comes out from the ZnO lattice and this fraction increases with the increase of annealing temperature. The sizes of nanoparticles and the lattice strains of all the samples were obtained from the Hall–Williamson plot. High resolution transmission electron microscopy showed that ZnO nanoparticles are more or less spherical. Magnetic susceptibilities (χ) of some selected samples measured in the temperature range of 300–14 K indicate that the samples are paramagnetic. Values of χ were successfully fitted by Curie–Weiss law. A good theoretical simulation of χ of the sample annealed at 80 °C has been achieved using the one-electron crystal field interaction of the Dy³⁺ ions with its diamagnetic neighbors in the hexagonal single crystal.     

Low-temperature chemical bath deposition of crystalline ZnO

ZnO crystals can be grown from alkaline aqueous solution not only by the standard hydrothermal technique at temperatures between 350 °C and 400 °C, but also by chemical bath deposition (CBD) at temperatures below 100 °C. In the presence of ZnO and ScAlMgO₄ (SCAM) substrates almost all ZnO deposits on the substrate, with different habits, however. Under optimized conditions even homoepitaxial layers can be obtained, while rod-like structures are obtained on SCAM substrates. The chemistry and the driving forces behind the two processes are considered in detail and the temperature dependence of the solution composition has been calculated. The driving force for the ZnO crystal growth in the standard hydrothermal technique is the difference in the ZnO solubility in alkaline solutions at different temperatures. In contrast, the driving force for the chemical bath deposition of ZnO at low temperatures is the decay of zinc ion complex molecules with increasing temperature.     

Low temperature heat capacity of bulk and nanophase ZnO and Zn1−xCoxO wurtzite phases

The low temperature heat capacity of the ZnO–CoO solid solution system was measured from 2 to 300 K using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). The thermodynamic functions in this temperature range were derived by curve fitting. The standard entropies of bulk ZnO and bulk ZnO–CoO (wurtzite, 18 mol% CoO) at T = 298.15 K were calculated to be (43.1 ± 0.4) J · mol⁻¹ · K⁻¹ and (45.2 ± 0.5) J · mol⁻¹ · K⁻¹, respectively. The surface entropy of ZnO was evaluated to be (0.02 ± 0.01) mJ · K⁻¹ · m⁻², which is essentially zero. No sharp magnetic transitions were observed in the solid solution samples. The nanophase solid solution, 12 mol% CoO, appears to bind H₂O on its surface more strongly than ZnO.     

Low temperature synthesis and characterization of rosette-like nanostructures of ZnO using solution process

Rosette-like structures of ZnO were synthesized at low temperature (60 °C) using solution process over 20 min of time. Hydroxylamine hydrochloride was used as capping agent with zinc nitrate hexahydrate and sodium hydroxide. Transition from triangular shaped plate like particles to rosette-like structure and to individual nanorods is observed with increasing refluxing temperature. Single-crystalline nature with wurtzite hexagonal phase is confirmed from transmission electron microscopic observations. Photoelectron spectroscopic measurement presented spectra close to the standard bulk ZnO, with an O 1s peak composed of surface adsorbed O–H group, O^2? in the oxygen vacancies on ZnO structure and ZnO.     

Kinetics of thermal and photolytic degradation of decabromodiphenyl ether (BDE 209) in backcoated textile samples

Kinetics of the thermal and photolytic degradation of decabromodiphenyl ether (DBE 209) was studied using HPLC. Samples lost an amount of ∼8.4% (w/w), 24% (w/w), 39.4% (w/w) and 28.5% of the amount of DBE 209 originally present in the samples due to ageing at 25, 60, 90 °C and UV exposure, respectively. The thermal and photolytic release was found to follow the first order kinetics with rate constants estimated to be 3.6 × 10⁻³, 1.03 × 10⁻², 3.6 × 10⁻² and 3.94 × 10⁻² day⁻¹, respectively. Ageing of the textile samples enhanced the release of the DBE 209 from the backcoated textile. Photodegradation of BDE 209 into lower congeners of brominated flame retardants was also observed for the UV-aged samples.Migration of DBE 209 from the backcoated textile into biological fluids was studied using Head-over-Heels and contact-Blotting test for unaged, thermally and UV aged samples. The presence of biological fluids (sweat, saliva and juice) was found to enhance the migration of DBE 209 compared to water. Migration of BDE 209 into artificial biological fluids is significantly increased for samples previously exposed to UV radiation or thermally aged. An increase from 0.6% (w/w) to a maximum of 2% (w/w) of the amount of BDE 209 migrated into artificial biological fluids due to ageing conditions in the presence of biological fluid was recorded.     

Synthesis and characterization of layered zinc hydroxychlorides

Layered material of zinc hydroxychlorides (Zn₅(OH)₈Cl₂·nH₂O: ZHC), which is one of the basic zinc salts (BZS), was synthesized from ZnO nano-particles aged with aqueous ZnCl₂ solutions at different temperatures ranging from 6 to 140 °C for 48 h. X-ray diffraction (XRD) results indicated that the diffraction peaks of ZnO completely disappeared by aging at 6 °C and the ZHC peaks were developed. By increasing the aging temperature, crystallinity of the layered structure was improved. At 6 °C, the ZHC particles were thin hexagonal plate particles with sizes ranging from 1 to 3 μm. The particle size of ZHC was independent of aging temperature. The atomic Cl/Zn ratios of all the ZHC materials were almost 0.2 less than 0.4 of the theoretical ratio, indicating that the synthetic ZHC is Cl-deficient. It seemed that half of Cl atoms in the layer were replaced with HCO₃⁻ and/or OH⁻. The specific surface areas of ZHC estimated from N₂ adsorption isotherms were ca. 10 m² g⁻¹ and were independent of the aging temperature. However, the H₂O monolayer adsorption capacity per unit surface area (n_w) for all the samples was higher than that of ZnO particles, revealing the high affinity of ZHC to H₂O molecules. The n_w values were increased by reducing the crystallinity of ZHC. This enhancement of H₂O adsorption selectivity was thought to be related with less-crystallized parts of the particles.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.     

Effects of H3PO4 and KOH in carbonization of lignocellulosic material

Samples of lignocellulosic material, stem of date palm (Phoenix dactylifera), were carbonized at different temperatures (400–600 °C) to investigate the effects of their impregnation with aqueous solution of either phosphoric acid (85 wt%) or potassium hydroxide (3 wt%). The products were characterized using BET nitrogen adsorption, helium pycnometry, Scanning Electron Microscopy (SEM) and oil adsorption from oil–water emulsion (oil viscosity, 60 mPa s at 25 °C). True densities of the products generally increased with increase in carbonization temperature. Impregnated samples (acid/base) showed wider differences in densities at 400 (1.978/1.375 g/cm³) than at 600 °C (1.955/2.010 g/cm³). Without impregnation, the sample carbonized at 600 °C showed higher density of 2.190 g/cm³. This sample has impervious surface with BET surface area of 124 m²/g. Acid-impregnated sample carbonized at 500 °C has the highest surface area of 1100 m²/g and most regular pores as evidenced by SEM micrographs. The amounts of oil adsorbed decreased with increase in carbonization temperature. Without impregnation, sample carbonized at 400 °C exhibited equilibrium adsorption of 4 g/g which decreases to about a half for sample carbonized at 600 °C. Impregnation led to different adsorptive capacities. There are respective increase (48 wt%) and decrease (5 wt%) by the acid- or base-impregnated samples carbonized at 600 °C. This suggests higher occurrence of oil adsorption-enhancing surface functional groups such as carbonyl, carboxyl and phenolic in the former sample.     

Reduction of aromatic compounds with Al powder using noble metal catalysts in water under mild reaction conditions

In water, Al powder becomes a powerful reducing agent, transforming in cyclohexyl either one or both benzene rings of aromatic compounds such as biphenyl, fluorene and 9,10-dihydroanthracene under mild reaction conditions in the presence of noble metal catalysts, such as Pd/C, Rh/C, Pt/C, or Ru/C. The reaction is carried out in a sealed tube, without the use of any organic solvent, at low temperature. Partial aromatic ring reduction was observed when using Pd/C, the reaction conditions being 24 h and 60 °C. The complete reduction process of both aromatic rings required 12 h and 80 °C with Al powder in the presence of Pt/C.     

Structure and oxygen storage capacity of Pr/Nd doped CeO2–ZrO2 mixed oxides

Binary Ce–Zr (CZ), trinary Ce–Zr–Pr (CZP), Ce–Zr–Nd (CZN) mixed oxides were prepared by coprecipitation. The structural and textural properties were characterized by the X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) method, Raman and X-ray absorption near-edge spectra (XANES) techniques, while the oxygen storage capacity (OSC) was evaluated under both dynamic and static conditions at 500 °C. The doping of Pr or Nd cations causes the lattice deformation of the tetragonal Zr-rich mixed oxides to form a pseudocubic structure and prevents the phase demixing after calcination in flowing steam/air at 1050 °C for 5 h. After the hydrothermal ageing treatment, the doped samples show higher BET surface areas and better oxygen mobility. Pr exists mainly in the form of trivalent cations in the aged CZP and functions primarily as the doping element with large ionic radius instead of redox couple Pr³⁺/Pr⁴⁺, which may introduce more Ce³⁺ species and hereby more lattice defects. Among the aged samples, CZP shows the best oxygen storage capacity and the fastest oxygen release rate.     

A composite of layered double hydroxides obtained through random costacking of layers from Mg–Al and Co–Al LDHs by delamination–restacking: Thermal decomposition and reconstruction behavior

A composite of dodecylsulfate intercalated Mg–Al and Co–Al LDHs in which the layers of the two LDHs are randomly costacked was prepared starting from the monolayer colloidal dispersions of the individual surfactant intercalated LDHs obtained through delamination in 1-butanol. The surfactant ion of the composite could be exchanged for acetate ions. The thermal decomposition and reconstruction behavior of the acetate-intercalated composite was found to be different from those of an LDH in which each layer contains Mg, Co and Al and a physical mixture of Mg–Al and Co–Al LDHs. While the composite shows partial reconstruction to LDH phase even after heating up to 1000 °C the other samples do not show reconstruction beyond 800 °C.     

Thermoluminescence analyses of irradiated dried sea foods using different methods of mineral separation

This research was conducted to find the most suitable parameters to separate minerals from irradiated dried shrimps and mussels (0 and 5 kGy) for thermoluminescence analysis using density separation and modified acid hydrolysis (at 50 °C with continuous agitation) methods. Nonirradiated samples gave TL glow curve of low intensity with peak after 300 °C except dried mussel sample, which gave false positive result. This problem was absent in minerals separated by acid hydrolysis. TL ratios of all nonirradiated samples were <0.1 irrespective of method used for mineral separation. Minerals separated from irradiated samples by density separation showed very high intensity of TL glow peak before 200 °C, where results from irradiated dried shrimp samples were better because of good availability of minerals. The minerals separated from irradiated samples by acid hydrolysis showed slightly low TL intensity and glow curve peak was found at about 200 °C. However, acid hydrolysis method was less laborious and required less sample weight as compared to density separation method. TL ratios of all irradiated samples were >0.1 confirming the quality of minerals on TL discs.     

Variable temperature diffuse reflectance infrared Fourier transform spectroscopic investigation of the effect of ball milling on the water sorbed to kaolin

Variable temperature DRIFTS has been used to investigate temperature variation of the number and population of the different environments occupied by water on unmilled kaolin and samples ball milled for 3, 10 and 30 min. Increasing the milling time resulted in structural damage of the kaolin and an increase in the amount of hydrogen bonded water indicated by bands in the OH stretching and bending regions. Curve fitting of the spectra, collected at 50 °C intervals in the temperature range 25–500 °C, established that the intensity of the bands diminished as the temperature was increased but also revealed bands that were more stable to high temperatures or were generated as the sample temperature was increased. Bands at 3750, 3386 and 3200 cm⁻¹ and 1680, 1650, 1634 and 1600–1580 cm⁻¹ were identified in the OH-stretching and bending regions, respectively. In particular a band at 1670 cm⁻¹ has been attributed to strongly hydrogen bonded water which acts to hold the deformed kaolin sheets together. Upon aging the samples the intensity of this band decreased and was replaced by a band at 1630 cm⁻¹. Boehmite was tentatively identified as a product of the milled kaolin.     

Comparison of two digestion procedures for the determination of lead in lichens by electrothermal atomic absorption spectrometry

The efficiency of two procedures for the digestion of lichen was investigated using a heating block and a microwave oven. In the open vessels, concentrated nitric acid was added to the samples, left for 1 h, and the addition of 30% (v / v) hydrogen peroxide completed the digestion. In the closed system, the complete digestion was performed using concentrated nitric acid and hydrogen peroxide, reducing the amount of chemicals, time and contamination risk. Both digestion methods gave comparable results, and recoveries were statistically not different. For a lichen sample spiked with 10 μg Pb, the recovery was 111% and 110% using microwave and heating block digestion, respectively, while it was 100% and 103% for a 100 μg Pb spike. For the determination by electrothermal atomic absorption spectrometry samples were diluted 20 times with water and a volume of 20 μL was injected into the graphite furnace without chemical modifier. Pyrolysis and atomization temperatures of 700 °C and 1500 °C, respectively, were used. The characteristic mass was 8.4 ± 0.6 pg for aqueous calibration solutions and 8.9 ± 0.8 pg for samples. Calibration was against matrix matched standards. The recovery test showed some contamination problem with the lowest concentrations in both procedures. The detection limits were 4.4 μg L^− 1 with microwave oven and 5.4 μg L^− 1 with the heating block in the undiluted blank.