Efficient electrochemical water splitting to hydrogen and oxygen is considered a promising technology to overcome our dependency on fossil fuels. Searching for novel catalytic materials for ...electrochemical oxygen generation is essential for improving the total efficiency of water splitting processes. We report the synthesis, structural characterization, and electrochemical performance in the oxygen evolution reaction of Fe-doped NiO nanocrystals. The facile solvothermal synthesis in tert-butanol leads to the formation of ultrasmall crystalline and highly dispersible Fe x Ni1–x O nanoparticles with dopant concentrations of up to 20%. The increase in Fe content is accompanied by a decrease in particle size, resulting in nonagglomerated nanocrystals of 1.5–3.8 nm in size. The Fe content and composition of the nanoparticles are determined by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy measurements, while Mössbauer and extended X-ray absorption fine structure analyses reveal a substitutional incorporation of Fe(III) into the NiO rock salt structure. The excellent dispersibility of the nanoparticles in ethanol allows for the preparation of homogeneous ca. 8 nm thin films with a smooth surface on various substrates. The turnover frequencies (TOF) of these films could be precisely calculated using a quartz crystal microbalance. Fe0.1Ni0.9O was found to have the highest electrocatalytic water oxidation activity in basic media with a TOF of 1.9 s–1 at the overpotential of 300 mV. The current density of 10 mA cm–2 is reached at an overpotential of 297 mV with a Tafel slope of 37 mV dec–1. The extremely high catalytic activity, facile preparation, and low cost of the single crystalline Fe x Ni1–x O nanoparticles make them very promising catalysts for the oxygen evolution reaction.
Zinc oxide nanoparticles were prepared by a solvothermal synthesis using various alcoholic reaction solvents including ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-octanol, at 170 °C. The ...nucleation and growth processes of the ZnO nanoparticles were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) characterization, and they were corroborated by means of quantum chemical calculations at the density functional theory level (DFT). On the basis of the results of joint microstructural and theoretical study, the nucleation and preferential growth mechanism of ZnO nanoparticles is proposed. The effect of various alcoholic solvent on the overall shape and growth rate along the preferential c-axis of ZnO nanoparticles were corroborated by means of theoretical simulations of interface-solvent interaction by using nanoclusters (ZnO) n (n = 12 and 36). The (ZnO)36–CH3(CH2) n OH (n ≤ 7) interaction has been found to be spontaneous exergonic process only in the presence of 1-butanol as reaction medium with ΔG*INT = −4.95 kcal mol–1, whereas endergonic in the presence of all remaining alcohols used (ΔG*INT > 0). The results of X-ray diffraction size-strain analysis reveal that solely the use of 1-butanol as solvent leads to rather isotropic crystallite shape (D v⊥c-ax ∼12 nm, D v∥c-ax ∼12 nm), whereas in the presence of all remaining alcohols used ZnO nanoparticles grew prevailing in the c-direction to form nanorods. The alcohols of different size and polarity acts as a solvent and reactant as well as controlling agents for crystal growth, providing different binding interactions involved in both the nucleation processes and preferential growth of ZnO nanoparticles. The calculated values of E O···H and E Zn–O of (ZnO)36–CH3(CH2)7OH (1-octanol) interaction indicate a weaker interaction of the nonpolar 1-octanol and polar a little positively charged Zn surface of ZnO crystal as well as a higher preferential growth rate along the c-axis in comparison to polar alcoholic media.
High-energy ball-milling in an oxidative atmosphere caused gradual transition of pure zincite into zinc ferrite due to the oxidation of steel contamination. The rate of contamination increased ...dramatically (>3×) in an inert atmosphere due to the abrasion of milling tools by the steel chips coming from it.
Conducting antimony-doped tin oxide (ATO) nanoparticles are prepared by a nonaqueous solution route, using benzyl alcohol as both the oxygen source and the solvent, and tin tetrachloride and various ...Sb(III) and Sb(V) compounds as tin and antimony sources, respectively. This reaction produces nonagglomerated crystalline particles 3−4 nm in size, which can be easily redispersed in high concentrations in a variety of solvents to form stable transparent colloidal solutions without any stabilizing agents. The synthesis temperature is the most important processing parameter largely governing the reaction course and the particle properties, while the nature of the antimony source has only a marginal influence. The cassiterite SnO2 lattice can accommodate up to 30 mol % antimony without significant changes in the structure. The incorporation of an increasing percentage of antimony causes a continuous decrease in particle size and a slight asymmetric lattice distortion. The introduction of an antimony dopant dramatically increases the particle conductivity, which reaches a maximum for 4% antimony, being more than 2 orders of magnitude higher than that of the pristine SnO2 nanoparticles. The obtained conductivity of 1 × 10−4 S/cm is the highest ever reported for the nonannealed nanosized ATO particles. Annealing in air at 500 °C further improves the conductivity to 2 × 102 S/cm, because of the particle sintering. Exceptionally high conductivity, small size, narrow size distribution, and dispersibility in various organic solvents make the ATO nanoparticles excellent primary building units for assembling nanostructured transparent conducting oxide materials with defined porous architectures.
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•Pt(acac)2 precursor ensured even PtNP dispersion on α-MnO2 nanorods.•Surprisingly, increasing the Pt loading induced a transition from α-MnO2 to Mn5O8.•XPS showed a decrease in ...Pt(IV) and Pt(II) with Pt loading, while Pt(0) increased.•Pt/MnO2 nanorods displayed excellent catalytic activity for 4-NP to 4-AP reduction.•The presence of Pt(IV) is not a limiting factor for the catalytic conversion of 4-NP to 4-AP.
α-MnO2 nanorods (NRs) were synthesized by microwave irradiation and used as supports for platinum nanoparticles by wet impregnation with Pt(acac)2 as precursor. XRD analysis revealed that the samples without platinum (sample MP0) and with 1 % platinum (sample MP1) contained tetragonal α-MnO2. Samples with 3 % (sample MP3) and 5 % (sample MP5) of platinum contained monoclinic Mn5O8 in addition to α-MnO2, with Mn5O8 dominating in sample MP5. Rietveld analysis showed that the lattice parameters of α-MnO2 increased slightly with Pt loading. SEM and STEM showed that higher Pt loadings resulted in shorter nanorods and different sizes and dispersions of PtNPs on their surface. XPS results showed a decrease in Pt(IV) and Pt(II) concentration with Pt loading, while Pt(0) increased. NEXAFS results showed the presence of Mn(II) in MP3 and MP5, which is consistent with XRD results detecting Mn5O8. The catalytic activity of the Pt/α-MnO2 nanorods was tested in the catalytic reduction of 4-nitrophenol to 4-aminophenol. MP1, with the lowest platinum content, exhibited the highest mass normalized rate constant kapp/mPt of 1.8 × 104 s−1 g−1. The study suggests that the presence of Pt(IV) is not a limiting factor for the catalytic reduction of 4-NP to 4-AP.
δ-FeOOH is a synthetic analogue of a relatively uncommon mineral feroxyhyte (δ′-FeOOH). The conventional syntheses of δ-FeOOH start from the Fe(II) salt and proceed by a rapid oxidation of iron(II) ...hydroxide with H2O2. The new synthesis route to δ-FeOOH nanodiscs reported in this work is based on the γ-irradiation of a deoxygenated iron(III) chloride alkaline aqueous colloidal solution in the presence of 2-propanol and diethylaminoethyl-dextran hydrochloride (DEAE-dextran). γ-irradiation of the colloidal solution enabled the strong reducing conditions thus favouring the reduction of Fe(III) to Fe(II). Under such strong reducing conditions the white suspension characteristic of Fe(OH)2 was formed. When the white suspension came into contact with oxygen from air it rapidly oxidized into stable green-gray suspension characteristic of Fe(II)-Fe(III) hydrochloride known as Green Rust I. In the conventional process of sample isolation the green-gray stable suspension transformed to δ-FeOOH reddish powder that consists of rather uniform regular nanodiscs. The synthesized δ-FeOOH nanodiscs are magnetic and contain a magnetically ordered component in the Mössbauer spectrum at room temperature. It is expected that the results of this work will have a strong impact on finding new synthetic routes to the δ-FeOOH.
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•The new synthesis route to δ-FeOOH (feroxyhyte) was reported.•γ-irradiation of Fe(III) precursor in the presence of amino-dextran produced δ-FeOOH.•In highly reducing and alkaline conditions the Fe(III) reduced to Fe(II).•The rather uniform δ-FeOOH disc-like regular magnetic nanoparticles were formed.
Zinc oxide particles were synthesized from zinc acetylacetonate in the presence of triethanolamine (TEA) and various alcoholic solvent, ethanol or octanol, at 170 °C. The structural, optical and ...morphological characteristics of ZnO particles were monitored using X-ray powder diffraction (XRD), UV–Vis and FT-IR spectroscopies and field emission scanning electron microscopy (FE-SEM). The experimental findings were confirmed by means of DFT calculations which were obtained in nonpolar alcohol 1-octanol, as a follow up to our previous study in polar ethanol 9. The nucleation and formation mechanism of ZnO nanoparticles is proposed considering the results obtained from a computational study of Gibbs free energies of ZnO−TEA molecular interactions (ΔG*INT) in various solvent system. The calculations revealed different binding affinities which initiated the nucleation processes of ZnO nanoparticles in the presence of alcohols of different size and polarity. The high chelating efficiency of TEA towards zinc with tetrahedral geometry is observed. The results of X-ray diffraction size-strain analysis indicate the presence of size anisotropy as well as a reduction in the ZnO crystallite size with the change of solvent from ethanol to 1-octanol (<10 nm).
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•ZnO particles were synthesized in the presence of alcohols of different polarity.•The high chelating efficiency of triethanolamine towards zinc is observed.•The experimental findings are confirmed by means of DFT calculations.•Changing the solvent from ethanol to octanol caused reduction of crystallite size.•The nucleation and formation mechanism of ZnO nanoparticles is proposed.
Metastable solid solutions of ZrO2-YO1.5 system (from 0 to 100 mol%) were prepared by crystallization of the amorphous precursors, coprecipitated from aqueous solutions of nitrate salts, using two ...synthesis routes: hydrothermal treatment at 150 °C for 24 h and annealing in the air atmosphere for 2 h at temperatures between 400 and 1200 °C. Thermal behavior of the amorphous precursors were followed by differential scanning calorimetry (DSC), structural analysis of the crystallization product was performed by X-ray powder diffraction (XRPD) and Raman spectroscopy, and the morphology of the crystalline grains was determined by the scanning electron microscope (FE-SEM). It was found that the crystallization temperature of ZrO2-type solid solutions increase with an increase in the YO1.5 content, from 487 °C (0 mol% of YO1.5) to 516 °C (20 mol% of YO1.5). Comparison of the obtained results with the results obtained for mixed oxides of zirconium with different trivalent dopants indicates that the crystallization temperature rises with the increase of dopand content and the difference between the ionic radius of the zirconium and the doped cation. The results of Rietveld refinements show that, regardless of the significant differences in the crystallite size and the morphology of the products obtained by two different synthesis routes, the phase composition and the unit cell parameters of the solid solutions obtained are very similar and depend mostly on the Zr/Y ratio. Crystallization products with YO1.5 content ≥5 mol% contain only one type of solid solution structurally closely related to tetragonal ZrO2 (from 5 to 15 mol% of YO1.5), cubic ZrO2 (from 15 to more than 60 mol% of YO1.5) and cubic Y2O3 (from 70 to 100 mol% of YO1.5). The unit-cell volume of the ZrO2- and Y2O3-type solid solutions increases linearly with the increase in the fraction of the yttrium. This linear dependence continued even after the transitions from ZrO2-type to Y2O3-type lattice.
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•Metastable ZrO2-YO1.5 solid solutions synthetize within entire concentration range.•Examined impact of dopants ionic radius on the crystallization temperature.•Only one type of solid solution in products with YO1.5 content ≥5 mol%.•Linear change of the unit cell volume within the entire concentration range.•Maximum solubility of Y3+ ions in metastable ZrO2 solid solution ∼70 mol%.
The solvothermal synthesis of ZnO particles from zinc acetylacetonate Zn(acac)2 in the presence of triethanolamine (TEA) and various solvent systems at 170 °C is reported. The structural, optical and ...morphological characteristics of ZnO particles were investigated. It was found that the size and shape of ZnO nanoparticles and the way of their aggregation depend on the mole ratio TEA/Zn(acac)2 and the type of alcohol used as a solvent. Doubling the molar ratio of TEA to Zn(acac)2 in the presence of ethanol favoured the formation of huge spherical aggregates (>3 μm) assembled from fine and uniform ZnO nanoparticles (∼20 nm). The results of present investigation show a strong impact of surface interactions between the formed ZnO nanoparticles and the molecules of solvent and TEA on the way of growth and aggregation, which enables the control of their morphological properties. The results show that TEA serves as a link between primary ZnO nanoparticles to form spherical aggregates with a controllable diameter. The results of X-ray diffraction size-strain analysis indicate the presence of size anisotropy with bigger crystallites in the direction of the c-ax of the zincite lattice compared with the direction perpendicular to the c-ax. The red shift of the absorption edge and reduced band gap energies are clearly visible with the increased sample microsphere size.
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•ZnO microspheres were solvothermally prepared in the presence of triethanolamine.•The morphology of ZnO microspheres depends on the polarity of the solvent used.•The dense and regular ZnO microspheres were obtained in the presence of ethanol.•The results of size-strain analysis indicate the presence of size anisotropy.•The relationship between ZnO particle size and optical properties was determined.
Commercial micrometer silicon (Si) powder was investigated as a potential anode material for lithium ion (Li-ion) batteries. The characterization of this powder showed the mean particle size of ...approx.75.2 nm, BET surface area of 10.6 m
g and average pore size of 0.56 nm. Its band gap was estimated to 1.35 eV as determined using UV-Vis diffuse reflectance spectra. In order to increase the surface area and porosity which is important for Li-ion batteries, the starting Si powder was ball-milled and threatened by metal-assisted chemical etching. The mechanochemical treatment resulted in decrease of the particle size from 75 nm to 29 nm, an increase of the BET surface area and average pore size to 16.7 m
/g and 1.26 nm, respectively, and broadening of the X-ray powder diffraction (XRD) lines. The XRD patterns of silver metal-assisted chemical etching (MACE) sample showed strong and narrow diffraction lines typical for powder silicon and low-intensity diffraction lines typical for silver. The metal-assisted chemical etching of starting Si material resulted in a decrease of surface area to 7.3 m
/g and an increase of the average pore size to 3.44 nm. These three materials were used as the anode material in lithium-ion cells, and their electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge-discharge cycles. The enhanced electrochemical performance of the sample prepared by MACE is attributed to increase in pore size, which are large enough for easy lithiation. These are the positive aspects of the application of MACE in the development of an anode material for Li-ion batteries.
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