Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

Preparation of Cu/SiO2 Catalyst by Solution Exchange of Wet Silica Gel

Structural formation process of Ni/SiO₂ and Cu/SiO₂ catalysts prepared by solution exchange of wet silica gel was investigated. Microstructures of Cu/SiO₂ and Ni/SiO₂ were quite different from each other. In the case of Cu/SiO₂, Cu particles with diameter of ca. 3–5 nm dispersed homogeneously at less Cu content, and the particle size of Cu as well as pore size of silica gel support increased with increasing Cu content. In the Ni/SiO₂, the Ni particles with diameter of ca. 6–10 nm gathered densely to form aggregates in silica matrix resulting in sea-island structure, whereas the size of Ni particle slightly increased with increasing Ni content. The difference in the structure of the metal-silica composites is probably caused by the difference in interaction between silica gel network and metal ions during drying and heating processes.     

Studies on Acrylic Emulsion Polymerization Containing Hydrophilic Hydroxyl Monomer in the Presence of Nano‐SiO2 Particles

Emulsion polymerization with nano‐scale SiO₂ particles as seeds composed of methyl methacrylate (MMA), butyl acrylate (BA), hydroxyethyl methacrylate (HEMA), and acrylic acid (AA) was studied from varying reaction temperatures, level of SiO₂ particle, HEMA, and emulsifier. The morphology of the emulsion particle was examined with a transmission electron microscope (TEM). The results showed that the addition of nano‐SiO₂ particles decreased the coagulum greatly when its level was lower than 7%. The coagulum also decreased with the increasing of temperature from 65°C to 75°C. The level of HEMA and emulsifier had little influence on the coagulum in the presence of nano‐SiO₂. The particle size of the emulsion increased with the increase of level of nano‐SiO₂ and HEMA. Part of the emulsion particles connected together due to the existence of HEMA, and yet some of the nano‐SiO₂ particles were not covered with polymer.     

Synthesis and electromagnetic properties of polyaniline-coated silica/maghemite nanoparticles

Polyaniline coated silica/maghemite nanoparticles (PANI/SiO₂/γ-Fe₂O₃ composites) were synthesized by the combination of a sol-gel process and an in-situ polymerization method, in which ferrous and ferric salts as well as tetraethyl orthosilica (TEOS) acted as the precursor for γ-Fe₂O₃ and silica, respectively. As a result, the SiO₂/γ-Fe₂O₃ particle showed a core-shell structure, with γ-Fe₂O₃ as the magnetic core and silica as the shell of the particle. The shell thickness can be controlled by changing the TEOS concentration. The PANI/SiO₂/γ-Fe₂O₃ composites revealed a multilayer core-shell structure, where PANI is the outer shell of the composite. The doping level and the conductivity of PANI/SiO₂/γ-Fe₂O₃ composites decreased with increasing the TEOS content due to the presence of the less coated PANI on the SiO₂/γ-Fe₂O₃ core at higher TEOS content. For a SQUID analysis at room temperature, all γ-Fe₂O₃ containing composites showed a typical superparamagnetic behavior. The saturation magnetization of SiO₂/γ-Fe₂O₃ nanoparticles decreased with increasing the TEOS content due to the increase in silica shell thickness, while the saturation magnetization of PANI/SiO₂/γ-Fe₂O₃ composites also decreased with increasing the TEOS content, which is attributed to the lower conductivity of PANI in the composites at higher TEOS content.     

Sol-Gel Derived TiO2-SiO2 Fibres

TiO₂−SiO₂ fibres with 0, 5, 10 and 20 volume % SiO₂ have been prepared by drawing from a gel followed by sintering at different temperatures. Nearly one meter long fibres can be drawn easily in conditions of about 50% relative humidity. Addition of SiO₂ inhibits the crystallisation of TiO₂ and also the anatase → rutile transformation and improves the strength of the fibres. While the pure TiO₂ fibres are brittle, those with 5, 10 and 20 volume % SiO₂ are flexible and strong. Tensile strength values as high as 3 GPa have been achieved in the 10 volume % SiO₂−TiO₂ fibres. Fibres heated above 900°C are brittle. The shape of the cross section of the fibres is found to depend on their diameters.     

Thermoanalytical and spectroscopic studies of the synthesis of suppokted palladium catalyst in A H2/PdCl2/SiO2 parent system

A 5 wt% Pd/SiO₂ catalyst was synthesized by heating PdCl₂-impregnated SiO₂ in H₂ at 300°C for 2 h. It was found that the metal particle dispersion is improved when the reduction step is preceded by calcination at 300°C for 2h. Thermogravimetry of the impregnated support in air, N₂ and H₂ atmospheres was used to monitor the interactions occurring during the various preparative steps (i.e. drying, calcination and reduction) of the catalyst. The solid prduct of each preparative step was characterized by X-ray diffractometry and UV/Vis diffuse reflectance spectroscopy. The results indicate that following the drying step (at 110°C in air) the palladium occurs in two detectable forms: PdCl₂ particles and Si?O?Pdⁿ⁺ surface species. The calcination appears to transform the PdCl₂ particles into the latter surface species. The H₂-reduction eventually converts the surface species into finely-dispersed Pd° metal particles (average size=8–14 nm). No other reduction products, such as Pd_ySi_x, were detected.     

Rheology and phase structure of PP/EPDM/SiO2 ternary composites

In this article, the rheological properties of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/silicon dioxide (SiO₂) ternary composites were systematically investigated. Two kinds of nano-SiO₂ particles (with hydrophobic (denoted as A-SiO₂) or hydrophilic (denoted as B-SiO₂)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO₂ ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO₂ binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO₂ ternary systems, depending on the SiO₂ surface property, processing method and EPDM content. It seemed that SiO₂ with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO₂ ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].     

Synthesis of Gels in the System Na2O-ZrO2-SiO2

Gels have been synthesized in the SiO₂-Na₂O-ZrO₂ system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO₄ unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses.     

Investigation of Solid-Solid Interactions between Pure and Li2O-Doped Magnesium and Ferric Oxides

The results obtained showed that the addition of small amounts of LiNO₃ to the reacting mixed solids, consisting of equimolar proportion of Fe₂O₃ and basic MgCO₃ much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO₃ (6 mol% Li₂O) decreased the decomposition temperature of MgCO₃ from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe₂O₄. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li₂O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe₂O₄ phase at temperatures starting from 700°C. The addition of 6 mol% Li₂O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe₂O₄ structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61 kJ mol⁻¹ for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li₂O, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pickering emulsion polymerization kinetics of styrene: Comparison of bare and surface modified SiO2 nanoparticles

A step towards the understanding of some mechanistic events occurring in the styrene Pickering emulsions, using a SiO₂ dispersion, is presented. Polymerizations at 80°C with different levels of a water soluble initiator were performed. The emulsion polymer content was ca. 15% with conversions close to 90%. With conversion and particle size measurements, the particle density was estimated for bare and surface modified SiO₂ particles. Then, the average number of radicals per particle was inferred, yielding a pseudo-bulk type polymerization. It was found that bare SiO₂ nanoparticles do not participate in the nucleation mechanism; however, they, along with the initiator, promote an enhanced oligomer coagulation. On the other hand, the hexadecyltrimethylammonium bromide modified SiO₂ nanoparticles do participate in the nucleation and coagulation mechanisms, yielding more stable and smaller poorly-covered polymer particles. This approach allowed untangling some events such as: particle nucleation, radical entry to particles, particle density, coagulation and vitreous and Trommsdorff effects.     

Formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber blends: Effects of preparation method,composition, and thermal condition

The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007     

Direct formation of SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> composite nanoparticles with high surface area and high thermal stability by sol–gel-hydrothermal process

SnO₂/SiO₂ composite nanoparticles were prepared by sol–gel-hydrothermal process and their physico-chemical structure and photocatalytic property were investigated. The results of XRD, TEM and FT-IR indicated that SnO₂ crystallites with the tetragonal rutile structure were well-developed directly during hydrothermal process. The SnO₂/SiO₂ composite nanoparticles owned narrow size distribution, large specific surface area, and good thermal stability. As the presence of 25.0 wt% SiO₂, the SnO₂ nanoparticles were about 4.0 nm in diameter and the specific surface area was 259.0 m²/g. After calcination at 800 °C, the crystalline grain size maintained 16.2 nm and the surface area still remained 132.6 m²/g. The SnO₂/SiO₂ composite nanoparticles showed better photocatalytic activity than pure SnO₂ nanoparticles.     

Planar ZrO2 Waveguides Prepared by the Sol-Gel Process: Structural and Optical Properties

ZrO₂ waveguides are prepared by the sol-gel process from a solution containing zirconiumn-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300°C and the pure ZrO₂ tetragonal crystalline phase appears beyond 400°C. Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38 Å at 400°C to 53 Å at 600°C. Waveguides are at least monomode TE₀ at 632.8 nm. At this wavelength, optical losses are about, 0.8±0.2dB/cm for amorphous layers and increase up to 2.5±0.4 dB/cm for 600°C heat-treated waveguides.     

Kinetic analysis of the thermal stability of lithium silicates (Li4SiO4 and Li2SiO3)

The kinetics describing the thermal decomposition of Li₄SiO₄ and Li₂SiO₃ have been analysed. While Li₄SiO₄ decomposed on Li₂SiO₃ by lithium sublimation, Li₂SiO₃ was highly stable at the temperatures studied. Li₄SiO₄ began to decompose between 900 and 1000 °C. However, at 1100 °C or higher temperatures, Li₄SiO₄ melted, and the kinetic data of its decomposition varied. The activation energy of both processes was estimated according to the Arrhenius kinetic theory. The energy values obtained were −408 and −250 kJ mol⁻¹ for the solid and liquid phases, respectively. At the same time, the Li₄SiO₄ decomposition process was described mathematically as a function of a diffusion-controlled reaction into a spherical system. The activation energy for this process was estimated to be −331 kJ mol⁻¹. On the other hand, Li₂SiO₃ was not decomposed at high temperatures, but it presented a very high preferential orientation after the heat treatments.     

The influence of film thickness and process temperature on <Emphasis Type="Italic">c</Emphasis>-axis orientation of Bi<Subscript>3</Subscript>TiTaO<Subscript>9</Subscript> thin films

Bi-layered ferroelectric Bi₃TiTaO₉ (BTT) thin films with different thickness (ranging from 100 to 400 nm) were successfully fabricated on Pt(111)/TiO₂/SiO₂/(100)Si substrates using chemical solution deposition (CSD) technique at different annealing temperatures. The c-axis orientation of the films was affected by film thickness and process temperature. The thinner the film and the higher the process temperature, the higher the c-axis orientation. With the increase of film thickness, the stress decreased but the film roughness increased, which led to the decrease of c-axis orientation of films. BTT films annealed at 800°C were found to have much improved remament polarization (P _r ) than that of films annealed at 650 and 750°C. The P _r and coercive field (E _c ) values were measured to be 2 μC/cm² and 100 kV/cm, respectively. BTT films showed well-defined ferroelectric properties with grain size larger than 100 nm.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

Preparation and characterization of monodisperse solvent-free silica nanofluids

A series of solvent-free ionic silica (SiO₂) nanofluids of 12.3–17.3 nm in diameter were synthesized by surface functionalizing nanoscale SiO₂ with a charged corona and ionically tethering with oligomeric chains as canopy. The structure and properties of the nanofluids were systematically characterized by Fourier transform infrared (FTIR), differential scanning calorimeter (DSC), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and rheology tests. The resultant nanofluids with low-molecular-weight oligomeric as canopy are homogeneous, stable yellow-like fluids with no evidence of phase separation at room temperature, while other nanofluids containing high-molecular-weight as canopy behave like a soft glassy, and they exhibit fluidity with still high modulus and viscosity above 60°C. For deeper understanding of the nature of SiO₂ nanofluids, the rheological behavior, thermal stability, as well as morphology of SiO₂ nanofluids were investigated in details. The flow properties of nanofluids could be easily regulated from soft glassy to free flowing liquids by varying the molecule weight of canopy. Most importantly, the thermal stability, rheological behavior, as well as morphology can be also regulated through varying molecule weight and thickness of canopy, which will guide our future work on synthesis of nanofluids with controllable physical properties.     

Interaction of Co nanoparticles with SiO2: silicide formation

The interaction of 1 and 4 nm thick Co films with SiO₂ support in vacuum at high temperature has been investigated by TEM, SAED and HRTEM methods. It was found that annealing in vacuum at 800 °C caused the transformation of the smallest Co particles into Co₂Si silicide.     

Hydrogenolysis of hexane on supported rhodium catalysts

Hexane was reacted in mixtures with excess hydrogen on 5% Rh on different supports: Al₂O₃ and SiO₂, the latter catalyst in two states: after reduction at 603 K (LT) and after a prereduction at 1253 K (HT). The main reaction was hydrogenolysis. The catalysts were characterized with the fragment composition at different temperatures and hydrogen pressures. Two surface states could be distinguished: one with more hydrogen favored single rupture, the other with less hydrogen preferred multiple fragmentation. The transition between these states could be rather abrupt, as the surface hydrogen availability changed. The tendency to produce multiple fragments increased in the order Rh/Al₂O₃< Rh/SiO₂-LT < Rh/SiO₂-HT.