2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

The crystal structure of Ho<Subscript>4</Subscript>Ni<Subscript>11</Subscript>In<Subscript>20</Subscript>

The polycrystalline Ho₄Ni₁₁In₂₀ was obtained by arc-melting of the elements. The subsequent high temperature procedure was used for single crystal growth. Crystal structure of the compound was investigated by X-ray single crystal method: U₄Ni₁₁Ga₂₀ type, C 2/m, a = 22.4528(17), b = 4.2947(3), c = 16.5587(13) Å, β = 124.591(5)°, R1 = 0.0276, wR2 = 0.0493 for 1989 independent reflections with [I>2σ(I)].The structure is composed of three-dimensional network from Ni and In atoms in which Ho atoms fill distorted pentagonal channels. Open image in new window     

Synthesis of dibromo ketones by the reaction of the environmentally benign H<Subscript>2</Subscript>O<Subscript>2</Subscript>-HBr system with oximes

It was found that oximes undergo deoximation in the presence of the H₂O_2aq-HBr_aq system to form ketones and bromo ketones. This reaction provided the basis for the synthesis of dibromo ketones in yields varying from 40% to 94%. This method is environmentally friendly, sustainable, and easy to perform. The results of this investigation extend the potential of the use of oximes for the protection of carbonyl group, thus offering the ability to perform not only conventional deoximation but also the subsequent bromination of ketones. The reaction is easily scaled up and dibromo ketones can be prepared in gram amounts.      

Calorimetric study of melts in the System KF - K<Subscript>2</Subscript>NbF<Subscript>7</Subscript>

The relative enthalpies of melts in the system KF - K₂NbF₇ were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing more complex fluoroniobate anions.      

Temperature effect over structure and photochemical properties of nanostructured SnO<Subscript>2</Subscript> powders

We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of V_O and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data.

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Methylcellulose/SiO<Subscript>2</Subscript> hybrids: sol-gel preparation and characterization by XRD,FTIR and AFM

Methylcellulose (MC) / SiO₂ organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO₂. AFM depicts surface roughness which depends on the silica precursor and MC content.      

Molecular dynamics simulation study of the diamond D<Subscript>5</Subscript> substructures

Diamond D₅ is the name proposed by Diudea for hyper-diamonds having their rings mostly pentagonal. Within D₅, in crystallographic terms: the mtn structure, known in clathrates of type II, several substructures can be defined. In the present work, the structural stability of such intermediates/fragments appearing in the construction/destruction of D₅ net was investigated using molecular dynamics simulation. Calculations were performed using an empirical many-body potential energy function for hydrocarbons. It has been found that, at normal temperature, the hexagonal hyper-rings are more stable while at higher temperature, the pentagonal ones are relatively more resistant against heat treatment.      

Influence of ThO<Subscript>2</Subscript> on the photocatalytic activity of TiO<Subscript>2</Subscript>

Microcomposites consisting of TiO₂ (or Ce-doped TiO₂) and ThO₂ (0.5–2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of ThO₂. X-ray diffraction study reveals the effects of ThO₂ (compared to the ThO₂-free TiO₂, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO₂ obtained at 550°C and containing 1% ThO₂. The composite exhibits activity in dark, also. The presence of Ce⁴⁺ ions is not an obligatory requirement for the realization of the ThO₂ effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO₂.      

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg<Subscript>2</Subscript>Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript> and graphite

Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.      

Preparation and characterization of high specific surface area Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> from electrolytic manganese residue

Mn₃O₄ powders have been produced from Electrolytic Manganese Residue (EMR). After leaching of EMR in sulfuric acid, MnSO₄ solution containing various ions was obtained. Purifying the solution obtained and then adding aqueous alkali to the purified MnSO₄ solution, Mn(OH)₂ was prepared. Two methods were employed to produce Mn₃O₄. One way was oxidation of Mn(OH)₂ in aqueous phase under atmosphere pressure to obtain Mn₃O₄. The other way was roasting Mn(OH)₂ precursors in the range of 500°C to 700°C. The prepared samples were investigated by using several techniques including X-ray powder diffraction (XRD), Fourier Transformation Infra-Red (FTIR) spectra, and Brunauer-Emmett-Teller (BET) specific surface area instrument. Particle distribution and magnetic measurements were carried out on laser particle size analyzer, vibrating sample magnetometer (VSM). Through XRD, FTIR and determination of total Mn content (TMC), the products prepared were confirmed to be a single phase Mn₃O₄. BET specific surface areas can reach to 32 m² g⁻¹. The results indicated that products synthesized by aqueous solution oxidation method had higher specific surface areas and smaller particle size than those prepared by means of roasting. However the products prepared using the above two methods showed no obvious differences in magnetic property.      

Determination of europium by using the chemical oscillating system of Ce(IV)-KBrO<Subscript>3</Subscript>-acetone-oxalic acid-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

A sensitive and convenient method for the determination of trace europium ions using an oscillating chemical reaction involving Ce(IV) - KBrO₃ - acetone - oxalic acid - H₂SO₄ was proposed. The results indicated that the changes in oscillating period (T) was linearly proportional to the negative logarithmic concentration of Eu³⁺ (-log C) in the range of 1.41 × 10⁻⁸ ˜ 1.41 × 10⁻⁴ mol L⁻¹ (r = 0.9982) with a detection limit of 1.04 × 10⁻⁹ mol L⁻¹. The recoveries were limited to the range of 99.5% to 100.8%. Under the same conditions, other rare earth ions did not interfere with the determination of Eu³⁺. In addition, a perturbation mechanism was also discussed briefly.      

The role of Mg<Subscript>2</Subscript>FeH<Subscript>6</Subscript> formation on the hydrogenation properties of MgH<Subscript>2</Subscript>-FeF<Subscript>x</Subscript> composites

The hydrogenation properties of magnesium hydride mechanically milled with iron fluorides (FeF₂ and FeF₃), were investigated by Temperature Programmed Desorption (TPD) and volumetric methods using a Sieverts-type apparatus, as prepared upon dehydrogenation and finally upon subsequent hydrogenation. The activation energy of hydrogen desorption (E_a), calculated from the Kissinger formula using TPD measurements obtained with different heating rates, showed significant decreases of Ea in comparison to that of milled MgH₂ without any dopants. Moreover, the influence of these metal fluorides on the thermodynamics of the decomposition process was also examined. In the case of the FeF₂ dopant, rehydrogenation following desorption caused the complete decomposition of the iron fluoride to BCC iron and the formation of a predominant MgH₂ phase. In contrast to FeF₂, the addition of FeF₃ led to the formation of β-MgH₂ as a major phase coexisting with Mg₂FeH₆ and MgF₂ compounds. The presence of pure Fe in the MgH₂+FeF₂ composite, as opposed to MgH₂+FeF₃ containing Mg₂FeH₆ and MgF₂, did not cause any significant influence on the sorption properties of MgH₂. Moreover, the original material doped with FeF₃ predominantly showed iron in the Mg₂FeH₆ compound, while the FeF₂ dopant iron mostly showed the nearly pure BCC metallic phase      

Determination of ultra-trace amounts of inorganic selenium species in natural water by ion chromatography-inductively coupled plasma-mass spectrometry coupled with nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid phase extraction

This work presents a nano-Al₂O₃ solid phase extraction technique for the determination of ultra-trace amounts of inorganic selenium species in aqueous systems using ion chromatography inductively coupled plasma-mass spectrometry (IC-ICP-MS). In this experiment, the inorganic selenium species were successfully extracted on a nano-Al₂O₃ solid phase column and then quantitative eluted with a 100 mmol L⁻¹ NaOH solution. Extraction conditions such as solvent identity, solvent concentration, solvent volume, solvent pH and salt addition were optimized. Under the optimum extraction conditions (elute solvent: 100 mmol L⁻¹ NaOH, solvent volume: 4 mL, pH: 7.0), low detection limits (Se (IV): 6 ng L⁻¹, Se (VI): 11 ng L⁻¹; RSD<5.0%) and good linear range (0.5–100 ng mL⁻¹, R² > 0.999) were obtained for all of the analytes. Good spiked recoveries over the range of 80–98% were obtained by applying the proposed method on real environmental water samples. These results indicated that this method is very sensitive and reliable when monitoring trace levels of inorganic selenium species in aqueous samples.      

Supported H4SiW12O40 catalysts for α-pinene isomerization

The heterogeneous isomerization of α-pinene was studied at 100, 130 and 160°C using 10% supported H₄SiW₁₂O₄0 (SiW) on SiO₂, TiO₂ and HZSM-5. The effect of the reaction temperature and the concentration of the catalyst over the conversion of α-pinene and the selectivity of camphene, limonene and terpinolene had been monitored. The recovery, reuse and leaching effect of the catalysts were studied. Simple, environmentally friendly and economic methods for the synthesis of camphene and limonene were developed and optimized.      

Synthesis of functional magnetic porous SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/P(St-DVB-MAA) microspheres by a novel suspension polymerization

In this study, a novel and effective suspension polymerization has been employed to prepare functional magnetic porous SrFe₁₂O₁₉/P(St-DVB-MAA) microspheres in the presence of bilayer surfactants (sodium dodecyl benzene sulfonate (SDBS) and oleic acid (OA)) coated on micro-size magnetic SrFe₁₂O₁₉. This was achieved by pre-polymerizing the organic phase, which contained co-monomers, porogens and treated magnetic particles, at 65°C for 0.5 h under ultrasound conditions. Aqueous solutions containing a dispersion agent were then added to effect suspension polymerization. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and magnetic property measurement system (MPMS) were used to characterize the functional magnetic porous microspheres. The results show that the microparticles are well shaped with a uniform size distribution of about 0.5 ∼ 0.7 mm and the surfaces of the microspheres have many micro-pores with an average diameter of 0.533 μm. There are carboxyl groups (−COOH) on the surface of the microspheres to the extent of 0.65 mmol g⁻¹, as determined by conductometric titration. According to the XRD spectra, iron oxide consists mainly of SrFe₁₂O₁₉ which reveals hexahedral structure. The content of magnetic SrFe₁₂O₁₉ reaches 17.81% (by mass), and the microspheres have good heat resistance. The magnetic porous microspheres are ferromagnetic with high residual magnetization and coercivity, 21.59 emu g⁻¹ and 4.13 kOe, respectively. The saturation magnetisation is around 42.85 emu g⁻¹.      

Synthesis of novel mesoporous Al2O3 microspheres with flower-like structure

Using glucose as a structuring additive and aluminium nitrate as the Al precursor, a novel kind of mesoporous Al₂O₃ microspheres with flower-like structure were synthesized hydrothermally at 180°C for 20 h. When the synthesis temperature was lowered to 140°C, the carambola-like Al₂O₃ can be synthesized. This approach is convenient and simple, and flower-like Ce-Al₂O₃ and La-Al₂O₃ spheres have also been prepared in this way. It may be applied to synthesize other metal oxides when suitable precursor salts are used. From an analysis of the experimental results, a mechanism for the formation of the flower-like Al₂O₃ spheres has been proposed and discussed.      

The effect of anatase crystal morphology on the photocatalytic conversion of NO by TiO<Subscript>2</Subscript>-based nanomaterials

Hydrogen titanate nanotubes (H-TTNT) were synthesized by the alkali hydrothermal method followed by proton exchange and then submitted either to thermal treatment or to acid hydrothermal reaction to generate TiO₂-anatase nanocrystals of different morphologies. The samples were characterized by XRPD, TGA, sulfur analysis, N₂ physisorption, UV-Vis spectroscopy and TEM. Their photocatalytic activities were determined by measuring the NO conversion in inert gas stream passed through the powder catalyst bed under UV radiation. Incomplete transformation into anatase resulted in nanomaterials with low activity due to coexistence with H-TTNT or TiO₂-B precursors. Anatase specimens derived from H-TTNT aged in strong sulfuric acid media contained equidimensional nanoparticles, but retention of sulfate negatively affected their photocatalytic activity. Combining milder acidic pH with higher aging temperature, allowed synthesis of a sulfate free anatase with the same optical properties and specific surface area as the counterpart produced by calcination of H-TTNT at 550°C; however, the former exhibited truncated bi-pyramid nanocrystals and the other adopted the form of nanorods. This latter showed the highest photocatalytic activity for NO abatement, outperforming the benchmark photocatatyst TiO₂-P25; this improved activity was tentatively ascribed to the maximization of high energy {001} facets in anatase nanorods formed during calcination of H-TTNT.

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Synthesis of SnO<Subscript>2</Subscript> nanopowders by a sol-gel process using propanol-isopropanol mixture

A simple sol-gel process is proposed for synthesizing SnO₂ nanopowders utilizing normal propanol and isopropanol mixture instead of just using normal alcohols such as ethanol, propanol or butanol for Sol preparation. No surfactant was used in this Sol preparation process. The structure of sol is studied by FT-IR-ATR technique. On altering propanol to isopropanol ratio, three different nanopowders were obtained. X-ray powder diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and BET techniques were used to characterize prepared powders. Results show that smaller grain size was obtained via altering alcohols ratio. In addition, Merck commercial SnO₂ powder was also used as a reference material for comparing purposes; because it has nanometer scale (ca. 60 nm). HRTEM images show that obtained nanopowders were polycrystalline and their average diameters fall into the range of 6–80 nm. Finally, the effect of alkoxide ligand size through sol-gel synthesis on product particle size is discussed.      

The binary system PbO - BiVO4

Phase equilibria established in the PbO - BiVO₄ system over the whole component concentration range up to 1000°C have been investigated. A phase diagram has been constructed using DTA and XRD.