Nucleation effect of surface treated TiO2 on Poly(trimethylene terephthalate) (PTT) nanocomposites

A study of the nucleation effect of TiO₂ in poly(trimethylene terephthalate)/TiO₂ nanocomposite has been carried out using different theoretical models. The models were applied and developed with the aim to describe and better understand the influence of the TiO₂ dispersion on crystallization characteristics of PTT. The PTT/TiO₂ nanocomposites with untreated and surface‐treated TiO₂ were prepared by the melt mixing method. The nucleation efficiency of the TiO₂ nanoparticles has been analyzed with the use of the Avrami model and Mo's method. It was found that the PTT matrix incorporated with surface‐treated TiO₂ particles has a higher crystallization temperature and melting point than that incorporated with untreated TiO₂ particles. As per the models, unlike untreated TiO₂, surface‐treated TiO₂ particles had a lesser effect on the degree of crystallization of the PTT matrix. The TiO₂ nanoparticles act as a nucleating agent in the PTT matrix thereby reducing t_½ of the crystallization and leading to easier crystallization of the polymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication and photocatalytic properties of silicon nanowires by metal-assisted chemical etching: effect of H2O2 concentration

In the current study, monocrystalline silicon nanowire arrays (SiNWs) were prepared through a metal-assisted chemical etching method of silicon wafers in an etching solution composed of HF and H₂O₂. Photoelectric properties of the monocrystalline SiNWs are improved greatly with the formation of the nanostructure on the silicon wafers. By controlling the hydrogen peroxide concentration in the etching solution, SiNWs with different morphologies and surface characteristics are obtained. A reasonable mechanism of the etching process was proposed. Photocatalytic experiment shows that SiNWs prepared by 20% H₂O₂ etching solution exhibit the best activity in the decomposition of the target organic pollutant, Rhodamine B (RhB), under Xe arc lamp irradiation for its appropriate Si nanowire density with the effect of Si content and contact area of photocatalyst and RhB optimized.     

Yield enhancement for the surface of solar-cell silicon wafers with electromechanical micromachining

Effective yield enhancement for the surface of silicon wafers of solar cells was developed using electrochemical micromachining and a design disc-form tool as a precision recycling module for Si₃N₄ thin-film microstructures and epoxy film. The low yields of epoxy films and Si₃N₄ thin-film deposition are important issues in semiconductor production. The current approach uses strong acid and grinding and may cause both damage to the physical structure of silicon wafers and pollution. Electrochemical micromachining allows the removal of the surface Si₃N₄ layer and epoxy film from the silicon wafers and may lead to the development of a mass production system for recycling defective or discarded silicon wafers of solar cells. A high feed rate of the silicon wafers of solar cells combined with enough electric power produces fast machining performance during etching. High rotational speed of the disc-form tool leads to high dreg discharge mobility and a good etching effect. A small height or a small bitter end radius of the anode corresponds to a high removal rate of the Si₃N₄ and epoxy. A small surface area of the cathode also corresponds to a high removal rate.     

Photocatalytic activity of surface modified TiO2/RuO2/SiO2 nanoparticles for azo-dye degradation

SiO₂/RuO₂ modified high surface area titania dioxide nanoparticles prepared by hydrogen reduction were examined for their catalytic properties towards the photodegradation of methyl orange (MO), a common water pollutant in the textile industry. The modified materials present enhanced photocatalytic activity and can decompose the MO faster than the unmodified TiO₂. Results showed that doping with RuO₂ only offered a marginal benefit over TiO₂ alone. On the other hand, modification of TiO₂with RuO₂ and SiO₂ resulted in a marked increase in the rate constant and the photodegradation efficiency. These results are consistent with the unique structural, morphologoical and surface characteristics of the composite titania dioxide/ruthenium dioxide/silicon dioxide materials. The lower the average particle size and roughness of the materials, the higher the percentage of photodecomposition and the rate constant. The surface doping and modification effects thus appears synergetic to the charge separation process and the photocatalytic results are explained on the basis of the mechanism that involves efficient separation of electron–hole pairs induced by the silicon dioxide particles. This enhances the ability of the modified TiO₂ particles to effectively capture protons. Results also show that the modified nanoparticles can be used repeatedly over a long time without loss of efficiency.     

Nano‐pits: supports for heterogeneous model catalysts prepared by interference lithograpy

Nanostructured 4 inch Si wafers were prepared as new supports for model catalysts. A single wafer exhibits 10⁹–10¹⁰ pits on an otherwise flat silicon oxide surface. To produce these nanostructures, oxidized wafers were covered with photoresist material and exposed to laser interference patterns. Using hydrofluoric acid, wet‐chemical etching of the SiO₂ through the structured resist resulted in a pitted surface. The etched pits with diameters of 200–400 nm and depths between 50 and 70 nm were loaded with metal particles by evaporation (palladium, silver) or by means of spin‐coating (copper). Optimizing the methods enabled exact deposition of single metal clusters in the pits. The resulting model catalysts are remarkably stable against sintering, a major problem of conventional model catalysts when exposed to elevated temperatures and oxidizing gas atmosphere. The topography and chemical composition as well as their changes, induced by the reaction conditions applied, including stability and chemical behavior of the nanostructured systems, were investigated by means of AFM, SEM, temperature‐programmed methods and XPS. To determine their usefulness in catalysis, specially designed reactors were developed for catalytic investigations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preparation of nano - coating powder CaF2@Al(OH)3 and its application in Al2O3/Ti(C,N) self-lubricating ceramic tool materials

Nano CaF₂ particles of different sizes were prepared by direct precipitation. The diameters of nano CaF₂ particles prepared in mixed solvent can reach 5–7 nm, and can be effectively dispersed. The surface of nano CaF₂ was modified and coated by heterogeneous nucleation method. A shell layer of Al(OH)₃ was coated on the surface of nano CaF₂, and the structure and coating mechanism of the coated powder were analyzed. Under varying preparation conditions, the surface morphology of CaF₂@Al(OH)₃ was analyzed using TEM and SEM. The results showed that the coating powder showed good dispersion in mixed solvents, and the particle size of the composite powder was about 20 nm. Self-lubricating ceramic tool materials were prepared by adding coating particles to the Al₂O₃/Ti(C,N) matrix. The coating powder shell and the matrix material melt during sintering, so that CaF₂ forms nanostructures in the particles. thereby improving the mechanical properties of the material. Cutting experiments show that the addition of coating particles can effectively reduce the temperature, cutting force and friction coefficient in the cutting process of the tool, thus improving the cutting performance of the tool material.     

Enhancement of catalytic activity of Au/TiO2 by thermal and plasma treatment

A significant enhancement in the catalytic activity of Au/TiO₂ in CO oxidation and preferential oxidation reaction by creating the active sites on the catalyst surface by thermal treatment as well as by producing small gold particles by plasma treatment has been studied. Au/TiO₂ catalyst (Au (1 wt%) supported on TiO₂) was prepared by conventional deposition-precipitation method with NaOH (DP NaOH) followed by washing, drying and calcination in air at 400 °C for 4 h. Thermal treatment of Au/TiO₂ was carried out at 550 °C under 0.05 mTorr. A small amount of Au/TiO₂ catalyst was taken from the untreated and thermally treated Au/TiO₂ and both kinds of catalysts were treated with plasma sputtering at room temperature. The activity of the catalysts has been examined in the reaction of CO oxidation and preferential oxidation (PROX) at 25–250 °C. Thermally treated Au/TiO₂ showed better catalytic activity as compared to the untreated catalyst. There is also an additional enhancement in the catalytic activity due to plasma sputtering on the both kinds of catalysts. Thermally treated Au/TiO₂ followed by plasma sputtering Au/TiO₂ showed higher conversion rates for CO oxidation reaction compared with untreated, thermally treated and plasma sputtered Au/TiO₂ catalysts. It may be concluded that the enhancement of catalytic activity of thermally treated Au/TiO₂ followed by plasma sputtering is owing to the generation of active sites such as oxygen vacancies/defects in TiO₂ support using thermal treatment as well as by producing small gold particles using plasma treatment.     

Retracted: Effect of surface‐treated TiO2 on non‐isothermal crystallization behavior of poly trimethylene terephthalate nanocomposites

The study of the non‐isothermal crystallization behavior of poly(trimethylene terephthalate) (PTT)/TiO₂ nanocomposites using untreated and surface‐treated TiO₂ has been carried out with different theoretical models. The PTT/untreated TiO₂ and surface‐treated TiO₂ nanocomposites were prepared employing batch mixing technique with an aim to investigate the influence of the TiO₂ dispersion on the crystallization behavior. The nucleation efficiency of the TiO₂ nanoparticles has been demonstrated with the use of Avrami and Jeziorny models. Test results indicated that the PTT matrix with surface‐treated TiO₂ particles has higher crystallization temperature and melting point than those with untreated PTT/TiO₂ nanocomposites. Unlike untreated TiO₂, surface‐treated TiO₂ particles also showed less effect on the degree of crystallization of the PTT matrix. The TiO₂ nanoparticles act as a nucleating agent in the PTT matrix by reducing the t_½ of the crystallization time, thus making it easy to form crystals. © 2012 Society of Plastics Engineers     

Anionic nylon 6/TiO2 composite materials: Effects of TiO2 filler on the thermal and mechanical behavior of the composites

The nylon 6‐based composite materials containing untreated and surface‐treated TiO₂ particles with 3‐aminopropyltriethoxysilane (APTEOS), as coupling agent were prepared by in situ anionic polymerization of ε‐caprolactam in the presence TiO₂ as a filler using the rotational molding technique. The thermal behavior and mechanical properties of the neat nylon 6 and its composites were investigated using various techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), a tensile and flexural test and impact strength. Experimental results revealed that both untreated and surface‐modified TiO₂ had distinct influence on the melting temperature (T_m), crystallization temperature (T_c), and degree of crystallinity (α_DSC), thermal stability, storage modulus (E′), and loss factor (tan δ), and mechanical properties of nylon 6 matrix. Dynamical mechanical analysis indicated that addition of TiO₂ particles into nylon 6 matrix increased both the storage modulus and the glass transition temperature. The corresponding values of nylon 6 composites with modified filler were higher than that of nylon 6 composite with untreated TiO₂ particles. Tensile and flexural characteristics of the nylon 6 composites were found to increase while the elongation at break and impact strength with increase in TiO₂ concentration relative to neat nylon 6. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

SnO2 and CeO2-doped SnO2 materials obtained by sol–gel alkoxide route

Tin dioxide-based materials have interesting electrical and optical properties being used as gas sensor, catalysts and inorganic ion-exchanger. In this paper a study on the preparation of the SnO₂ and CeO₂-doped SnO₂ powders and films by a sol–gel method, starting from the corresponding metal alkoxides, has been performed. The stabilized tin and tin with cerium organic sols were used for deposition of the thin films on glass and silicon single crystal. Powders were obtained after thermal treatment of the gels formed by the gelation of the solutions in air, at room temperature. The films have been deposited by dip coating on glass and silicon wafers and were characterized by X-ray diffraction and atomic force microscopy and the powders by DTA/TG analysis, X-ray diffraction, IR spectroscopy and specific surface area analysis.     

Effects of SDBS and ZrO2 additives on the microstructure and properties of silicon-bonded SiC porous ceramics

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO₂ as sintering additives, the effects of SDBS and ZrO₂ on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO₂ could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na₂O which reacted with ZrO₂ and impurity SiO₂, which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO₂ would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO₂ were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m³/m²·h·kPa and 28.2 MPa, respectively.     

Electrochemical and XPS studies of the surface oxidation of synthetic heazlewoodite (Ni3S2)

X-ray photoelectron spectroscopic (XPS) and electrochemical techniques have been applied to the investigation of the surface oxidation of synthetic heazlewoodite (Ni₃S₂). The XPS data showed that exposure of the sulphide to air resulted in nickel atoms migrating to the surface to form an overlayer of a hydrated nickel oxide and leave a sulphur-rich heazlewoodite. A hydrated nickel oxide was also produced on immersion of heazlewoodite in acetic acid solution in equilibrium with air, despite nickel being soluble under these conditions. After the acetic acid treatment, the S(2p) spectrum had a component at the binding energy of NiS and a small contribution due to sulphur-oxygen species. Voltammetry with bulk heazlewoodite electrodes, and the ground sulphide in a carbon paste electrode, indicated that, at pH 4.6, the initial anodic product was a sulphur-rich heazlewoodite and that oxidation was inhibited when NiS was formed on the surface. Further oxidation to higher nickel sulphides and elemental sulphur occurred at high potentials. In basic solutions, oxidation was restricted due to the formation of nickel oxide.     

Evolution mechanism of alumina nanofilms on rutile TiO2 starting from sodium metaaluminate and the pigmentary properties

Alumina-coated rutile TiO₂ samples were prepared starting from NaAlO₂ by the chemical liquid deposition method. The alumina nanofilms existed in amorphous hydrated alumina phase and anchored at the surfaces of TiO₂ particles via Ti-O-Al bonding. The formation of continuous and dense alumina nanofilms on the TiO₂ surface depended on the pH value of the reaction solution and the alumina loading. After coated by alumina nanofilms, the whiteness and brightness of the alumina-coated TiO₂ samples increased with the increase of the alumina loading while the relative light scattering index was found to depend upon the alumina loading.     

Exposed crystal surface-controlled rutile TiO2 nanorods prepared by hydrothermal treatment in the presence of poly(vinyl pyrrolidone)

Rutile TiO₂ particles with specific exposed crystal faces were prepared by hydrothermal treatment of titanium trichloride (TiCl₃) solution with poly(vinyl pyrrolidone) (PVP) as a shape-control reagent. Crystal phase, shape, and size of TiO₂ particles were found to be greatly dependent on the concentration of PVP in the solution. The exposed crystal surface of TiO₂ was controlled by changing the concentration of PVP in TiCl₃ and NaCl solutions. The prepared TiO₂ particles were characterized by TEM, SEM, XRD, and specific surface area measurements. The photocatalytic activity of the synthesized TiO₂ particles was evaluated by decomposition of acetaldehyde and toluene in gas phase. The synthesized TiO₂ particles showed higher photocatalytic activity for degradation of acetaldehyde and toluene than did commercial TiO₂ particles (MT-600B). However, the tendency of photocatalytic activities of the synthesized TiO₂ particles for degradation of acetaldehyde in gas phase was different from that for degradation of toluene. From the photodeposition of Pt and PbO₂, we propose that the (1 1 0) face provides reductive sites and that the (1 1 1) face provides oxidative sites. The results suggest that the crystal faces facilitate the separation of electrons and holes, resulting in improvement in photocatalytic activity.     

Multi-target reactive sputtering—A promising technology for large-area Pb(Zr,Ti)O3 thin film deposition

Beyond target diameters of 100 mm, multi-target reactive sputtering becomes a promising technology for ferroelectric thin film deposition. The main advantages of multi-target sputtering technology are: (i) thin films with precise composition control, (ii) stoichiometric variations on the target surface during repeated use are prevented by target preconditioning and operation in the metallic mode, and (iii) higher deposition rate due to sputtering from metals in the metallic mode. The latter requires a much greater precision in control of the partial pressure of oxygen, e.g., by a plasma emission monitor. In this work, Pb(Zr,Ti)O₃ thin film deposition on 150 mm silicon wafers by an industrial system is demonstrated. This technology can be easily scaled-up for larger silicon wafers and is compatible with standard semiconductor technology. Films deposited onto ZrO₂ buffer layers were polarized in-plane and they are suitable for piezoelectric MEMS application.     

Growth of magnetic thin films using CO2 RESS expansions

A continuous-flow rapid expansion of supercritical solution (RESS) apparatus is used to grow thin iron oxide thin films under ambient and vacuum conditions. The magnetic thin films are produced by expanding a supercritical solution of ferric acetylacetonate (Fe(acac)₃) and CO₂ and directing the resulting supersonic jet onto both hot and cold silicon wafers. The concentration of the expanding solution is monitored in-line with a UV–vis high pressure view cell which is also used to perform solubility measurements. The resulting films contain nano- and sub-micronic particles in the 13–700 nm size range and show magnetic order. Structural and magnetic data for these thin particle films have been obtained by SQUID and SEM measurements and compared as a function of substrate surface temperature, growth times, and initial solute concentrations. Experimental and theoretical analysis of the thermodynamics and fluid mechanics appropriate for this RESS process is discussed.     

3-Aminopropyltriethoxysilane-Assisted Si@SiO2/CNTs Hybrid Microspheres as Superior Anode Materials for Li-ion Batteries

A silicon based composite (Si@SiO₂/CNTs) with outstanding electrochemistry performance has been easily synthesized using a spray drying method; The composite microsphere is mainly made up of carbon nanotubes and the prepared nano silicon particles. With the help of a silane coupling agent, carbon nanotubes tightly intertwined with nano silicon particles and formed microspheres together. On the surface of the prepared nano silicon particles, a layer of oxide film plays a role as a barrier to reduce the rupture of the particles during the lithium intercalation/extraction process. In addition, the added twisted carbon nanotubes can help to maintain the conductive network, thus stabilizing the electrode working environment during the lithium intercalation/extraction process. As a superior anode material, an initial specific discharge capacity of approximately 2846.9 mAh g^?1 with a coulombic efficiency of 86 % and a reversible specific capacity of 2035.9 mAh g^?1 after 100 cycles at a constant density of 500 mA g^?1 are obtained.     

Molecular dynamics study of TiO2/poly(acrylic acid‐co‐methyl methacrylate) and Fe3O4/polystyrene composite latex particles prepared by heterocoagulation

All‐atom molecular dynamics simulations were used to study the morphology of polymer/inorganic composite particles prepared by heterocoagulation. The results were also compared to those of our previous study of the preparation of TiO₂/poly(acrylic acid‐co‐methyl methacrylate) and Fe₃O₄/polystyrene composite particles. In the simulation system, polymer or inorganic particles were simulated by surface‐charge‐modified C₆₀ or Na atoms. Through a combination of analysis of the radial distribution functions of charged atoms and snapshots of the equilibrated structure, three kinds of particle distributions were observed under different conditions. When the polymer and inorganic particles had opposite surface charges and their sizes were very different, the composite morphology showed a core–shell structure with small particles adsorbed onto the surfaces of large particles. Furthermore, when the polymer and inorganic particles had opposite surface charges but comparable sizes, the polymer and inorganic particles aggregated domain by domain. Finally, when the polymer and inorganic particles were endowed with the same surface charge, the distribution of these two types of particles was homogeneous, regardless of their size difference. The simulation results were in agreement with the experimental results. The electrostatic interaction and the size of the particles dominated the final morphology of the composite particles when the heterocoagulation method was used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Photocatalytic decomposition of 2-propanol and acetone in air by nanocomposites of pre-formed TiO2 particles and mesoporous silica

The photocatalytic efficiency in the degradations of gaseous 2-propanol and acetone has been studied on nanocomposite materials prepared by embedding well-crystallized titanium dioxide (TiO₂) particles (Degussa P25) into surfactant-templated mesoporous silica. The composite materials adsorbed the organic substances considerably in dark conditions and decomposed them completely to CO₂ under photoirradiation. The efficiency was influenced remarkably by the surface modification of TiO₂ particles. According to the transmission electron microscope observations, using carbon-coated TiO₂ particles gave a composite MCT-C with well-ordered channels of the mesoporous silica, but not all the TiO₂ particles were embedded in silica. MCT-C showed a high CO₂ production rate comparable to that of pristine TiO₂ (P25) when the concentrations of gaseous 2-propanol and acetone were as low as several ppm. On the other hand, using n-octadecyl-grafted TiO₂ particles resulted in a composite MCT-S in which most of the TiO₂ particles were well embedded in mesoporous silica, but the degree of channel-ordering was comparatively lower than that in MCT-C. The CO₂ production rate for MCT-S was lower than that for P25. This is probably due to the deactivation of TiO₂ surface by the silane-coupling reagent and/or the disorder of the mesopore channels. These composite photocatalysts could suppress the emission of unhealthy degradation products by adsorptive capacity of mesoporous silica.     

The preparation and characterisation of nanometre platinum colloids on silicon wafers as model catalysts

Platinum particles of 2 nm diameter have been immobilised on oxidised silicon wafers by spin coating with colloidal solutions and characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The coverage and dispersion of the Pt colloids on the Si wafer are controlled by varying the concentration and the spin speed. Under optimal conditions mono-dispersed Pt colloids on silicon wafers are prepared. For the Pt colloids immobilised on the Si wafer, the majority of the stabilising ligands are removed through a reduction (with H₂ at 200°C) or an oxidation (in air at 300°C) procedure. AFM showed that particle sizes are retained after the reduction procedure, while significant sintering occurs after oxidation. The mechanism of ligand removal was studied using an in situ XPS reaction cell. This revised version was published online in July 2006 with corrections to the Cover Date.