Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Some studies on the phase formation and kinetics in TiO<Subscript>2</Subscript> containing lithium aluminum silicate glasses nucleated by P<Subscript>2</Subscript>O<Subscript>5</Subscript>

Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li₂O–71.7SiO₂–7.1Al₂O₃–4.9K₂O–3.2B₂O₃–1.25P₂O₅–1.25TiO₂ were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC) and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li₂SiO₃ is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest MH.     

Obtaining of Ni<Subscript>0.65</Subscript>Zn<Subscript>0.35</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites by thermal decomposition of complex compounds embedded in silica matrix

This article presents the results of our investigation on the obtaining of Ni_0.65Zn_0.35Fe₂O₄ ferrite nanoparticles embedded in a SiO₂ matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (Fe^III,Ni^II,Zn^II) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni_0.65Zn_0.35Fe₂O₄)_x–(SiO₂)_100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

Silica and core–shell structured titania/silica (TiO₂/SiO₂) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO₂ and TiO₂/SiO₂ nanoparticles were investigated.     

Effect of Er<Subscript>2</Subscript>O<Subscript>3</Subscript> on thermal stability of oxyfluoride glass

Glasses have been synthesized in the system SiO₂–Al₂O₃–Na₂O–AlF₃–LaF₃–Er₂O₃. A base glass (in mol% 67SiO₂–9Al₂O₃–20Na₂O–Al₂F₆–3La₂F₆) was modified by 0.5, 0.75, 1, 1.25, 1.5, 2 and 5 mol% Er₂O₃, respectively. Glasses were prepared by conventional fusion method from 20 g batches. The glass transition temperature (T _g), the jump-like changes of the specific heat (ΔC _p) accompanying the glass transition and the enthalpy of crystallization (ΔH) were calculated. DTA measurements clearly reveal that the increase of the Er₂O₃ content in the glass changes the effects of crystallization and diminishes the thermal stability of the glassy network. In the same time the changes in the transition temperature are observed. The formation of NaLaF₄ and Na_1.45La_9.31(SiO₄)₆(F_0.9O_1.1) as a main phase was confirmed. The diminishing of the thermal stability was connected with erbium which incorporated into Na_1.45La_9.31(SiO₄)₆(F_0.9O_1.1) structure.     

Quantitative study of hydration of C<Subscript>3</Subscript>S and C<Subscript>2</Subscript>S by thermal analysis

This research is part of a European project (namely, CODICE project), main objective of which is modelling, at a multi-scale, the evolution of the mechanical performance of non-degraded and degraded cementitious matrices. For that, a series of experiments were planned with pure synthetic tri-calcium silicate (C₃S) and bi-calcium silicate (C₂S) (main components of the Portland cement clinker) to obtain different calcium–silicate–hydrate (C–S–H) gel structures during their hydration. The characterization of those C–S–H gels and matrices will provide experimental parameters for the validation of the multi-scale modelling scheme proposed. In this article, a quantitative method, based on thermal analyses, has been used for the determination of the chemical composition of the C–S–H gel together with the degree of hydration and quantitative evolution of all the components of the pastes. Besides, the microstructure and type of silicate tetrahedron and mean chain length (MCL) were studied by scanning electron microscopy (SEM) and ²⁹Si magic-angle-spinning (MAS) NMR, respectively. The main results showed that the chemical compositions for the C–S–H gels have a CaO/SiO₂ M ratio almost constant of 1.7 for both C₃S and C₂S compounds. Small differences were found in the gel water content: the H₂O/SiO₂ M ratio ranged from 2.9 ± 0.2 to 2.6 ± 0.2 for the C₃S (decrease) and from 2.4 ± 0.2 to 3.2 ± 0.2 for the C₂S (increase). The MCL values of the C–S–H gels, determined from ²⁹Si MAS NMR, were 3.5 and 4 silicate tetrahedron, for the hydrated C₃S and C₂S, respectively, remaining almost constant at all hydration periods.     

The effect of PO<Subscript>2,5</Subscript> and AlO<Subscript>1,5</Subscript> additions on structural changes and crystallization behavior of SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> sol-gel derived glasses and thin films

SiO₂-TiO₂-PO_2,5 (STP) and SiO₂-TiO₂-AlO_1,5 (STA) glasses were prepared by sol-gel processing. Their infrared absorption spectra (IR), differential thermal analysis curves (DTA) and X-ray diffraction patterns (XRD) have been recorded. In the SiO₂-TiO₂ system, the chemical homogeneity of the sol-gel glass could be evaluated by the relative concentration of Si-O-Ti heterocondensation comparing to Si-O-Si homocondensation. For the STA system, a gradual decrease of the Si-O-Ti/Si-O-Si band ratio (based on IR spectra) with the addition of Al₂O₃ is observed, with the simultaneous formation of Si-O-Al and Ti-O-Al bounds, i.e Al₃ ⁺ ions are dissolved in the SiO₂-TiO₂ glass matrix and do not promote glass-in-glass phase-separation in the composition range of 0–15 mol% AlO_1.5. In the STP system, on the other hand, P=O bond IR stretch in the ternary glasses indicates that P=O free PO₂O_2/2 ⁻ tetrahedra are formed, rather than the double bonded POO_3/2 tetrahedra that usually occur in binary SiO₂-P₂O₅ glasses. It can be concluded that SiO₂-TiO₂-P₂O₅ glass separates into a SiO₂-rich phase and a TiO₂(P₂O₅)-rich phase. During heat-treatment in STA system only anatase precipitates, even at T ~ 1,000 °C, while in for STP, anatase (TiO₂) or (TiO)₂P₂O₇ (TOP) crystals precipitate at ~600 °C, depending on the P₂O₅ concentration. The major crystal phase, cristobalite, precipitated at ~1,000 °C and at ~1,200 °C, the P-containing phase melts.     

On the nature of the processes occurring in silver doped SiO<Subscript>2</Subscript> films under heat treatment

The processes taking place on air-heating of SiO₂−Ag⁺ films and xerogels produced from the SiO₂ sols of different pH (3.7 or 9.5) were investigated. Silver nanoparticles 10–40 nm in size tolerant to oxidation at temperatures above 600 °C were found to be formed in the systems whatever the pH value of the starting sol. SiO₂ crystallization giving the cristobalite phase in the temperature range from 500 to 800 °C was shown to proceed only in the films produced from the acidic sol, while in those formed from the alkali one SiO₂ remained amorphous. A mechanism by which the formation of Ag nanoparticles and the cristobalite phase occurs in the films at the oxidative conditions is suggested.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

XAFS investigation of [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][AuCl<Subscript>4</Subscript>]<Subscript>2</Subscript> and its thermolysis products

Thermolysis of double complex salt [Pd(NH₃)₄][AuCl₄]₂ has been studied in helium atmosphere from ambient to 350 °C. The XAFS of Pd K and Au L₃ edges and thermogravimetry measurements have been carried out to characterize the intermediates and the final product. In the temperature range 115–160 °C the complex is decomposed to form Pd(NH₃)₂Cl₂ and AuCl_4−x N _x species with x ranging from 2 to 3. Subsequent heating of the intermediate up to 300 °C leads to the total loss of NH₃. The Au–Cl and Au–Au bonds form the local environment of Au at the stage of decomposition while only four chlorine atoms are around Pd. At the temperature of 330 °C the Au and Pd nanoparticles as well as residues of palladium chloride are detected. The final product consists of separated Au and Pd nanoparticles.     

Sintering behavior and ionic conductivity of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> with a small amount of MnO<Subscript>2</Subscript> doping

A 20% GdO_1.5 doped ceria solid solution with a small amount of MnO₂ doping (≤5% molar ratio) was prepared via the mixed oxide method from high-purity commercial powders with grain size around 0.2–0.5 μm. X-ray diffraction analysis indicated that all the samples exhibited the fluorite structure, and no new phase was found. The data from dilatometeric measurements and scanning electron microscopy observations revealed that 1% Mn doping reduced the sintering temperature by over 150 °C, and enhanced the densification and grain growth. Mn doping has little effect on grain interior conductivity, but a marked deterioration in grain boundary behavior is observed. This leads to a lower total conductivity in comparison with the undoped Ce_0.8Gd_0.2O_2–δ. Therefore, for solid oxide fuel cells (SOFCs) with Mn-containing compounds as electrodes, optimization of electrode fabrication conditions is needed to prevent the formation of a lower conductivity layer at the electrode/electrolyte interface since Mn will diffuse from the electrode side to the electrolyte during fabrication and operation of SOFCs. Electronic Publication     

Synthesis,Characterization and Structure of [Fe(2,2′-bipy)<Subscript>3</Subscript>]<Subscript>2</Subscript>[α-Mo<Subscript>8</Subscript>O<Subscript>26</Subscript>]: An α-Octamolybdate-Supported Compound Formed During the Diffuse Process

The α-octamolybdate-supported compound: [Fe(2,2′-bipy)₃]₂[α-Mo₈O₂₆] has been unexpectedly synthesized during a diffuse process and characterized by the IR spectroscopy, UV–Vis diffuse reflectance spectroscopy and the single crystal X-ray diffraction. The title compound exhibits an interesting 3D honeycomb ‘host’ supramolecular network with 1D channels, in which only α-octamolybdate anions ‘guests’ reside. The title compound shows the anisotropic property and probably will be applied as a novel semiconductor in the future.     

Influence of B<Subscript>2</Subscript>O<Subscript>3</Subscript> on the structure and crystallization of soil active glasses

Glasses of the SiO₂–P₂O₅–K₂O–MgO–CaO–B₂O₃ system acting as nutrients carriers in the soil environment were synthesised by the melt-quenching technique. Thermal properties were studied using DTA/DSC methods and the influence of B₂O₃ and P₂O₅ content on thermal stability and crystallization process of these glasses was examined. The structure of the glass network was characterized by FTIR, ³¹P, and ¹¹B MAS NMR. The chemical activity of the glasses in the 2 mass% citric acid solution was measured by the ICP-AES method. The analysis indicated that the formation of P–O–B units with chemically stable tetrahedral borate groups decreases the glass solubility in conditions simulating the soil environment.     

Variation in the strength of base sites in the system La<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> in the range 25-200°C

Based on electronic diffuse reflectance spectra of indicators adsorbed on La₂O₃–ZrO₂, obtained at 25-200 °C, we have shown that the strength of its basic sites sharply increases from H_–S ≤ +17.2 to H_–S ≤ +33.0 in the range 25-140 °C. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 112-114, March-April, 2009.     

X-ray,SEM, and DSC studies of ferroelectric Pb<Subscript>1−<Emphasis Type="Italic">X</Emphasis></Subscript>Ba<Subscript><Emphasis Type="Italic">X</Emphasis></Subscript>TiO<Subscript>3</Subscript> ceramics

The polycrystalline ferroelectric compounds of general formula Pb_1−X Ba _X TiO₃ with X = 0.00, 0.1, 0.2 and 0.5 were prepared by high temperature solid-state reaction technique using high purity oxides and carbonates. The compounds formation was confirmed by X-ray diffraction and all the X-ray peaks were indexed with tetragonal structure of space group P4mm. Morphology and particle size of the compounds were obtained using scanning electron microscopy. Ferroelectric phase transition, enthalpy change, and specific heat of the compounds were obtained using modulated differential scanning calorimetry. It was observed that the phase transition temperature decreased linearly with the increase of substitution concentration.     

LaNi<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based sensor for sensitive determination of paracetamol

A novel electrochemical sensor based on LaNi_0.5Ti_0.5O₃/CoFe₂O₄ nanoparticle-modified electrode (LNT–CFO/GCE) for sensitive determination of paracetamol (PAR) was presented. Experimental conditions such as the concentration of LNT–CFO, pH value, and applied potential were investigated. Under the optimum conditions, the electrochemical performances of LNT–CFO/GCE have been researched on the oxidation of PAR. The electrochemical behaviors of PAR on LNT–CFO/GCE were investigated by cyclic voltammetry. The results showed that LNT–CFO/GCE exhibited excellent promotion to the oxidation of PAR. The over-potential of PAR decreased significantly on the modified electrode compared with that on bare GCE. Furthermore, the sensor exhibits good reproducibility, stability, and selectivity in PAR determination. Linear response was obtained in the range of 0.5 to 901 μM with a detection limit of 0.19 μM for PAR.     

Catalytic activity and physicochemical properties of Ni-Au/Al<Subscript>3</Subscript>CrO<Subscript>6</Subscript> system for partial oxidation of methane to synthesis gas

This work is focused on the role of gold and Al₃CrO₆ support for physicochemical properties, and catalytic activity of supported nickel catalysts in partial oxidation of methane (POM). Catalysts, containing 5% Ni and 5% Ni-2% Au active phases dispersed on mono- (Al₂O₃, Cr₂O₃) and bi-oxide Al₃CrO₆ support, were investigated by TPR, BET and XRD methods, and the activity tests in POM reaction were carried out. Bimetallic Ni-Au catalysts dispersed on Al₃CrO₆ support remained highly stable and active. The amorphous binary oxide Al₃CrO₆ can stabilize considerable amount of Cr⁴⁺, Cr⁵⁺, and Cr⁶⁺ species in Ni-Au/Al₃CrO₆ catalyst network during its calcination in the air. Nickel supported on binary oxide Ni/Al₃CrO₆ can form Ni(III)CrO₃ bi-oxide phase in reductive conditions. During TPR H2 reduction of Ni-Au/Al₃CrO₆ catalyst chromium(II) oxide Cr(II)O phase is observed. After POM reaction the existence of bimetallic Au-Ni alloy was experimentally confirmed on mono-oxide Al₂O₃ support surface, but its formation was not identified on bioxide Al₃CrO₆ support. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 149–156. The article is published in the original. Based on a report at the VII Russ. Conf. on Mechanisms of Catalytic Reactions (with international participation), St. Petersburg, July 2–8, 2006.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

Phase equilibria in the PbSe-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Se system and thermodynamic properties of intermediate phases

The Pb-Bi-Se system in the PbSe-Bi₂Se₃-Se-Se composition region was studied by measurement of concentration circuits of the type (−) PbSe(solid) liquid electrolyte, Pb²⁺(Pb-Bi-Se)(solid) (+) in the temperature range 300–430 K and by X-ray powder diffraction. A solid-phase equilibrium diagram was constructed, and the formation was confirmed for the ternary compounds Pb₅Bi₆Se₁₄, Pb₅Bi₁₂Se₂₃, and Pb₅Bi₁₈Se₃₂, which belong to the homologous series [(PbSe)₅] _m · [(Bi₂Se₃)₃] _n . From the emf versus temperature equations, the partial thermodynamic functions [`(DG)]\overline {\Delta G}, [`(DH)]\overline {\Delta H}, [`(DS)]\overline {\Delta S} of PbSe in alloys were calculated. Based on the solid-phase equilibrium diagram from these partial molar quantities using the corresponding data for PbSe and Bi₂Se₃, the standard thermodynamic functions of formation and standard entropies of the above ternary compounds were calculated.