Properties of NiO thin films deposited by chemical spray pyrolysis using different precursor solutions

NiO thin films have been deposited by chemical spray pyrolysis using a perfume atomizer to grow the aerosol. The influence of the precursor, nickel chloride hexahydrate (NiCl₂·6H₂O), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel hydroxide hexahydrate (Ni(OH)₂·6H₂O), nickel sulfate tetrahydrate (NiSO₄·4H₂O), on the thin films properties has been studied. In the experimental conditions used (substrate temperature 350 °C, precursor concentration 0.2-0.3 M, etc.), pure NiO thin films crystallized in the cubic phase can be achieved only with NiCl₂ and Ni(NO₃)₂ precursors. These films have been post-annealed at 425 °C for 3 h either in room atmosphere or under vacuum. If all the films are p-type, it is shown that the NiO films conductivity and optical transmittance depend on annealing process. The properties of the NiO thin films annealed under room atmosphere are not significantly modified, which is attributed to the fact that the temperature and the environment of this annealing is not very different from the experimental conditions during spray deposition. The annealing under vacuum is more efficient. This annealing being proceeded in a vacuum no better than 10⁻² Pa, it is supposed that the modifications of the NiO thin film properties, mainly the conductivity and optical transmission, are related to some interaction between residual oxygen and the films.     

Study on the adhesion mechanism of electrodeposited nickel clusters on carbon substrates

Growth and adhesion mechanisms of Ni clusters electrodeposited on three different carbon-based substrates have been studied. Glassy carbon, carbon paper and PAN-based fibres have been used as working electrodes and Ni clusters have been electrodeposited from a NiCl₂·6H₂O. Ni reduction on carbon substrates has been studied by cyclic voltammetry, chronocoulometry and in situ SERS, whereas the morphological and structural characterization of the interface between Ni clusters and carbon-based substrates has been performed by High Resolution TEM.From our results we can conclude that the precipitation of Ni hydroxides and basic salts in the unbuffered catholyte promotes the adhesion of Ni clusters on the carbon-based substrates considered in this study. This feature of the investigated Ni clusters electrodeposition suggests that it may be a suitable fabrication route for applications in catalytic processes, such as metal-particle catalysed growth of carbon nanotubes.     

A chemical strategy to control the shape of oxide nanoparticles

A new strategy, epoxide-assisted precipitation route presented in this work, allows the shape control synthesis of Co₃O₄ nanoparticles. The shape of the nanoparticles is determined by the nature of the precursor cobalt salts (Co(NO₃)₂ · 6H₂O, CoCl₂ · 6H₂O) used for the preparation of the particles. The different reaction dynamics of the two salts in ethanolic and aqueous solutions with propylene oxide result in precursor particles with different structures, which lead to the formation of oxide nanoparticles with different shapes during the heat treatment. Spherical particles of about 20 nm are obtained from the ethanolic solution of Co(NO₃)₂ · 6H₂O; cubic-shaped particles of about 30 nm can be prepared from the ethanolic solution of CoCl₂ · 6H₂O; whereas platelet-like particles of more than 100 nm are synthesized from the aqueous solution of the mixture of Co(NO₃)₂ · 6H₂O and CoCl₂ · 6H₂O.     

Synthesis of NiCo2S4 nanospheres/reduced graphene oxide composite as electrode material for supercapacitor

The NiCo₂S₄ nanospheres arrayed on the surface of reduced graphene oxide (rGO) was fabricated via one-step hydrothermal method. The effect of initial feeding mass of Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O to rGO on the microstructure and electrochemical performance of the as-prepared composites was studied. The results indicated that the specific capacitances of the composites were first increased and then reduced due to the aggregation of NiCo₂S₄ nanospheres. NiCo₂S₄ nanospheres/rGO composites exhibited a remarkable specific capacitance of 1406 F/g and excellent cyclic stability of 82.36% at the current density of 1 A/g, which were better than those of individual NiCo₂S₄ (792 F/g and 64.77%) counterpart. These results showed that the as-prepared NiCo₂S₄ nanospheres/rGO composites were outstanding candidate for electrode material of supercapacitors.     

Synthesis of hierarchical flower-like NiO and the influence of surfactant

The NiO nanoflowers were prepared by a facile surfactant assisted hydrothermal method using Ni(NO₃)₂–6H₂O or NiCl₂–6H₂O as precursor compound. The microstructure of the samples was characterized by SEM and XRD. The gas sensing properties of the NiO nanoflowers toward ethanol was also investigated. The results show that surfactant plays a key role in the synthesis of flower-like NiO. The NiO nanoflowers show excellent sensing performances to ethanol gas. This morphology holds substantial promise for applying NiO as a potential gas sensing material for future sensor application.     

Effective atomic numbers of some vanadium and nickel compounds for total photon interactions using transmission experiments

Effective atomic numbers of V₂O₃,VO₂,VF₃,NH₄VO₃,VF₄,NiF₂,NiCl₂,NiF₂4H₂O,NiCl₂6H₂O,Ni(ClO₄)₂6H₂O were measured in the X-ray energy range 15.746- using an Si(Li) detector. The measured values are compared with the theoretical ones calculated using WinXcom.     

Nickel coated on beech wood by electroless nickel coating: effects of complexing agent concentrations on nickel film properties

In order to obtain beech wood substrates with new functions as conductive materials and to develop their utilities in industrial fields, the technique of electroless nickel coating on the beech wood substrate was employed. The influence of complexing agent concentration [Na₂EDTA·2H₂O] on the nickel surface resistivity was studied. The process conditions were Ni(CH₃COO)₂·4H₂O 0.103?mol/L, CH₃CHOCOOH 18.18?mL/L, N₂H₅OH 54.54?mL/L, NaOH 0.193?mol/L, pH value of 9.5, temperature of 75?°C, and the complexing agent concentration varied between 0.012 and 0.061?mol/L. By means of XRD, EDXRF, and SEM, the chemical composition and morphology of the prepared films were investigated. The results showed that when the complexing agent concentration increased from 0.012 to 0.061?mol/L in the electroless nickel coating baths, the gained nickel mass on the beech wood substrate decreased from 17.04 to 9.03?mg/cm², the nickel crystallite sizes reduced from 16.1 to 1.41?nm and the electric measurements demonstrated that the nickel surface resistivity rose from 0.004 to 192.16?kΩ/cm².     

Electro-oxidation of ethanol using PtRuBi/C electrocatalyst prepared by borohydride reduction

Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H₂PtCl₆·6H₂O, RuCl₃·xH₂O, and Bi(NO₃)₃·5H₂O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques.     

Correlation between the mesoporous carbon sphere with Ni(OH)<Subscript>2</Subscript> nanoparticle contents for high-performance supercapacitor electrode

Ni(OH)₂ nanoparticles were decorated on mesoporous carbon spheres (MPCS) using a simple hard template method. The MPCS were derived from sodium carboxymethyl cellulose. As-prepared MPCS/Ni(OH)₂ nanocomposites were used as electrode materials for supercapacitors. These composites exhibited better electrochemical properties than a pristine mesoporous carbon sphere owing to the synergistic effect. However, the increase in Ni(OH)₂ is not proportional to the electrochemical performance improvement. The addition of an optimal amount of Ni(OH)₂, typically 1:20 by weight (MPCS:NiCl₂·6H₂O), showed an excellent specific capacitance of 1338.296 F g^?1 at a scan rate of 5 mV s^?1. These encouraging results indicate excellent potential for the development of highly capacitive energy storage devices for practical applications.     

A simple route to the synthesis of high-quality NiO nanoparticles

Dispersed nickel oxide nanoparticles were obtained by a simple and low-cost method using a mixture of gelatin as organic precursor and NiCl₂ · 6H₂O as Ni source. The average particle size was estimated from X-ray powder diffraction (XRPD) peaks using the Rietveld refinement. The values ranged from 3.2 to 79 nm. We observed that the particle size changes as a function of synthesis time, with a notable decrease after the addition of NaOH to the solution. Field emission scanning electron microscopy (FE-SEM) measurements show that particles have well defined shapes and are dispersed in an organic matrix. X-ray absorption near edge spectroscopy (XANES) shows also the formation of fcc NiO nanoparticles structures.     

Ni(NO3)2·6H2O/I2/water: A new,mild and efficient system for the selective oxidation of alcohols into aldehydes and ketones under sonic condition

A new, simple, efficient and rapid method for the oxidation of alcohols into respective aldehydes and ketones by Ni(NO₃)₂·6H₂O/I₂/water system under ultrasonic irradiation is reported. The process is mild and inexpensive; the yields are high and the reactions go to completion within 2–7 min.     

A possible tricritical line in Ni(NO3)2 · 2H2O

We obtain the behaviour of the critical (possibly tricritical) point for metamagnetic Ni(NO₃)₂·2H₂O as a function of several applied hydrostatic pressures up to 11 kbar. The obtained line of possible tricritical points greatly suggests a pressure induced metamagnetic transition in a 0.8 kbar range.     

An ESR study of phase transitions in crystals of M(BF4)2·6H2O (M = Fe,Co, Ni,Zn)

From a temperature dependent ESR study of Mn²⁺-doped crystals of M(BF₄)₂·6H₂O, M Zn, Co and Ni, new structural phase transitions have been detected and studied. First order structural phase transitions occur in Co(BF₄)₂·6H₂O at T₁ ~ 281K, T₂~189 K and T₃~172K (during cooling), in Zn(BF₄)₂·6H₂O at T₁ ~ 286 K and in Ni(BF₄)₂·6H₂O at T₁ ~ 301 K. A continuous phase transition occurs in Co(BF₄)₂·6H₂O at T_p ~ 257 K, in Zn(BF₄)₂·6H₂O at T_p ~ 277 K and in Ni(BF₄)₂·6H₂O at T_p ~ 294 K. The ESR spectral characteristics suggest similarities in the structures of these fluoroborate compounds in the phase above T₁ with the room temperature structure of Mg(ClO₄)₂·6H₂O. All these compounds are found to have a tendency to crystallise in a triply-twinned pseudo-hexagonal form, although the unit cell above T₁ is found to be orthorhombic. The structural changes related to the water octahedron around the metal at T₁ were found to be very small and basically the same for these three compounds. Although the unit cell structure of Fe(BF₄)₂·6H₂O above the first order phase transition temperature T₁ was found to be similar to that of the other fluoroborate compounds, the structural changes occurring at T₁ appeared to be quite different. The low temperature thermal behaviour differs considerably in the Co, Fe and Zn compounds.     

Synthesis and Raman spectroscopy of indium‐based hydrotalcites of formula Mg6In2(CO3)(OH)16· 4H2O

Insight into the unique structure of layered double hydroxides has been obtained using a combination of X‐ray diffraction and Raman spectroscopy. Indium‐containing hydrotalcites of formula Mg₄In₂(CO₃)(OH)₁₂· 4H₂O [2:1 In‐LDH (layered double hydroxides)] through to Mg₈In₂(CO₃)(OH)₁₈· 4H₂O (4:1 In‐LDH) with variation in the Mg : In ratio have been successfully synthesized. The d(003) spacing varied from 7.83 Å for the 2:1 LDH to 8.15 Å for the 3:1 indium‐containing layered double hydroxide. Raman spectroscopy complemented with selected infrared data has been used to characterize the synthesized indium‐containing layered double hydroxides of formula Mg₆In₂(CO₃)(OH)₁₆· 4H₂O. Raman bands observed at around 1058, 1075 and 1115 cm⁻¹ are attributed to the symmetric stretching modes of the CO₃²⁻ units. Multiple ν₃ CO₃²⁻ antisymmetric stretching modes are found at around 1348, 1373, 1429 and 1488 cm⁻¹ in the infrared spectra. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands observed at 690 and 700 cm⁻¹ assigned to the ν₄ CO₃²⁻ modes support the concept of multiple carbonate species in the interlayer. Copyright © 2010 John Wiley & Sons, Ltd.     

X‐ray absorption spectroscopy at the Ni?K edge in Stackhousia tryonii Bailey hyperaccumulator

Young plants of Stackhousia tryonii Bailey were exposed to 34 mM Ni kg^?1 in the form of NiSO₄· 6H₂O solution and grown under controlled glasshouse conditions for a period of 20 days. Fresh leaf, stem and root samples were analysed in vivo by micro x‐ray absorption spectroscopy (XAS) at the Ni? K edge. Both x‐ray absorption near edge structure and extended x‐ray absorption fine structure spectra were analysed, and the resulting spectra were compared with spectra obtained from nine biologically important Ni‐containing model compounds. The results revealed that the majority of leaf, stem and root Ni in the hyperaccumulator was chelated by citrate. Our results also suggest that in leaves Ni is complexed by phosphate and histidine, and in stems and roots, phytate and histidine. The XAS results provide an important physiological insight into transport, detoxification and storage of Ni in S. tryonii plants. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of hexagonal nano-sized nickel selenide by simple hydrothermal method assisted by CTAB

Nano-sized nickel selenide powders have been successfully synthesized via an improved hydrothermal route based on the reaction between NiCl₂·6H₂O, SeCl₄ and hydrazine (N₂H₄·H₂O) in water, in present of cetyltrimethyl ammonium bromide (CTAB) as surfactant, at various conditions. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray energy dispersive spectroscopy analysis. Effects of temperature, reaction time and reductant agent on the morphology, the particle sizes and the phase of the final products have been investigated. It was found that the phase and morphology of the products could be greatly influenced by these parameters. The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. Photoluminescence (PL) was used to study the optical properties of NiSe samples.     

Optical absorption spectrum of diammonium nickel bis(tetrafluoroberyllate) hexahydrate

The optical absorption spectrum of diammonium nickel bis (tetrafluoroberyllate) hexahydrate (NH₄)₂Ni(BeF₄)₂.6H₂O has been investigated at the laboratory and liquid nitrogen temperatures. The spectrum is characteristic of the Ni²⁺ ion in an octahedral crystal field. Splitting of one of the bands at the liquid nitrogen temperature are attributed to the spin-orbit interaction.     

The mass attenuation coefficients in some vanadium and nickel compounds

The mass attenuation coefficients for V₂O₃, VO₂, VF₃, NH₄VO₃, VF₄, NiF₂, NiCl₂, NiCl₂H₂O, NiF₂4H₂O, NiCl₂6H₂O, Ni(ClO₄)₂6H₂O were measured in the X-ray energy range from 15.746 to using a Si(Li) detector. The measured values are compared with the theoretical ones calculated using WinXcom.     

Complexation between variable-valency uranium and organic ligands in solutions,their photostability and spectral identification

We discuss possible directions for searching for prospective materials based on low-valency uranium (III–V) as detection media for hard electromagnetic radiation. We have studied the processes of formation of tetravalent and pentavalent uranium complexes from UO₂(NO₃)₃·6H₂O and UO₂Cl₂·H₂O in DMF and with addition of CCl₄, including when the systems are exposed to radiation in the visible range (400–450 nm). In the first case (UO₂(NO₃)₃·6H₂O solutions in DMF), upon irradiation we observe stable complexes of pentavalent uranium, and when CCl₄ is added to the solution we observe complexes of tetravalent uranium. In the system UO₂Cl₂·3H₂O in DMF, we do not observe the appearance of new forms of uranium; but when CCl₄ is added, then complexes of tetravalent uranium are formed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 184–187, March–April, 2007.     

Raman spectra of crystalline double sulphates

Raman spectra of single crystals of K₂M(SO₄)₂ · 6 H₂O where M=Mg, Zn, Ni or Co have been recorded for the first time usingλ 2537 as the exciting radiation. The corresponding five single sulphates have also been studied. Interesting results concerning the substitution of magnesium, zinc, nickel or cobalt in the double sulphate lattice on the sulphate frequencies are observed. The lattice spectra of these double sulphates are analysed group theoretically and discussed in relation to the lattice spectra of the corresponding individual sulphates. Certain new results concerning the Raman spectra of the individual sulphates have also been obtained and in the case of CoSO₄ · 7 H₂O the spectrum has been recorded for the first time.