Effect of Aluminum Doping on the Performance and Microstructure of Methyl-Modified SiO2 Sol

Abstract

With methyltriethoxysilane as hydrophobic precursors and aluminum isopropoxide as the aluminum source, the Al₂O₃/SiO₂ sols and their gel materials were prepared. The effects of aluminum content (n_Al) on the viscosity (η), density (ρ), reaction rate constant (k), Gibbs energies of activation for viscous flow (ΔG*), particle size of Al₂O₃/SiO₂ sols were studied. And the high temperature calcined materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results show that, with the increase of n_Al, the η, n and ΔG* values of the Al₂O₃/SiO₂ sols decrease while the k and ρ values and average particle sizes increase. There is strong intermolecular interaction between the Al₂O₃ and SiO₂ sol molecules. The Al-O-Si bond exists in the Al₂O₃/SiO₂ materials before and after calcination at 350?°C. Calcination at 350?°C in N₂ atmosphere can change the phase structure of Al₂O₃/SiO₂ sample greatly, which can make the γ-AlOOH in the Al₂O₃/SiO₂ gel material convert to γ-Al₂O₃ through dehydration.     

Probing hydroxyl radical generation from H<Subscript>2</Subscript>O<Subscript>2</Subscript> upon plasmon excitation of gold nanorods using electron spin resonance: Molecular oxygen-mediated activation

Gold nanostructures are among the noble metal nanomaterials being intensely studied due to their good biocompatibility, tunable localized surface plasmon resonance (SPR), and ease of modification. These properties give gold nanostructures many potential chemical and biomedical applications. Herein, we demonstrate the critical role of oxygen activation during the decomposition of hydrogen peroxide (H₂O₂) in the presence of photoexcited gold nanorods (AuNRs) by using electron spin resonance (ESR) techniques. Upon SPR excitation, O₂ is activated first, and the resulting reactive intermediates further activate H₂O₂ to produce ?OH. The reactive intermediates exhibit singlet oxygen-like (¹O₂-like) reactivity, indicated by ¹O₂-specific oxidation reaction, quenching behaviors, and the lack of the typical ¹O₂ ESR signal. In addition, by using the antioxidant sodium ascorbate (NaA) as an example, we show that hydroxyl radicals from H₂O₂ activation can induce much stronger NaA oxidation than that in the absence of H₂O₂. These results may have significant biomedical implications. For example, as oxidative stress levels are known to influence tumorigenesis and cancer progression, the ability to control redox status inside tumor microenvironments using noble metal nanostructures may provide new strategies for regulating the metabolism of reactive oxygen species and new approaches for cancer treatment.

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RECENT ADVANCES AND FUTURE ASPECTS IN THE LOW-TEMPERATURE CONVERSION OF SATURATED HYDROCARBONS

A brief review on the advances and future aspects in the low-temperature activation of carbon–hydrogen and carbon–carbon bonds in hydrocarbons is presented. Particular attention is given to a catalyst formulation for low-temperature conversion of hydrocarbons. An efficient catalyst design method for low-temperature activation of saturated hydrocarbons has been worked out using metal evaporation techniques. The characteristic property of such catalysts is the presence of metal particles on the surface in an atomically dispersed state. Some of the prepared catalysts cause complete hydrocracking of alkanes and cycloalkanes at 423–463K.     

Decolorization of Methyl Orange Dye at IrO2‐SnO2‐Sb2O5 Coated Titanium Anodes

A film of iridium and tin dioxides doped with antimony oxide (IrO₂‐SnO₂‐Sb₂O₅) was deposited onto Ti mesh and plate substrates by the Pechini method. The electrode surface morphology and composition were characterized by SEM‐EDS. The ternary oxide coating was used for the anodic oxidation of methyl orange (MO) azo dye. Linear sweep voltammetry was used to identify the electrode potentials that favour MO degradation. Batch electrolyses were then carried out at a constant electrode potential of 1.5, 1.75 and 2.0 V vs. SHE using either a three‐electrode batch cell or a flow reactor. The dye solutions were totally decolorized via reactive oxygen species, such as ^?OH, H₂O₂ and O₃ formed in situ from water oxidation at the Ti/IrO₂‐SnO₂‐Sb₂O₅ surface.     

Oxide formation and conversion on carbon steel in mildly basic solutions

Surface oxide film growth and conversion processes on carbon steel were studied using a range of electrochemical techniques and ex situ surface analyses. The electrochemical study included (i) cyclic voltammetry as a function of various scan conditions and (ii) 7-day potentiostatic oxidation at a range of potentials while periodically performing Electrochemical Impedance Spectroscopy. Carbon steel surfaces at various stages of electrochemical oxidation were examined by SEM, Raman and X-ray photoelectron spectroscopy (XPS). These studies yield a consistent picture of film formation/conversion processes on carbon steel at pH 10.6, which is different to that reported for basic solutions (pH > 13). Oxide film formation/conversion mechanisms for three potential regions are proposed. In region I (≤−0.6 V vs SCE), the main oxide formed is Fe₃O₄ which grows via a solid-state process; in region II (−0.5 V ≤ E (vs SCE) ≤ −0.2 V), continuous growth of the Fe₃O₄ layer is accompanied by its anodic conversion to a more maghemite (γ-Fe₂O₃)-like phase near, or at, the oxide/solution interface by a similar solid-state mechanism to that described for region I; in region III (0.0 V < E (vs SCE) < 0.4 V), the anodic conversion of this Fe₃O₄/γ-Fe₂O₃ oxide to γ-FeOOH leads to a significant structural change, which can lead to film fracture and the introduction of enhanced transport pathways in the film.     

Effect of cobalt-60 γ radiation on the physical and chemical properties of poly(ethylene terephthalate) polymer

The structural, optical, and morphological properties of Co⁶⁰ γ irradiation on poly(ethylene terephthalate) polymer samples were studied with X-ray diffraction (XRD), ultraviolet–visible spectroscopy, scanning electron microscopy (SEM), and Raman spectroscopy. The diffraction pattern of virgin sample showed that the polymer was semicrystalline in nature. However, because of irradiation, the crystallinity decreased up to a dose level of 110 kGy and increased up to 300 kGy. The crystallite size, strain, and dislocation were calculated from the XRD data, and the crystallite size decreased from 291.07 to 346.90 Å. The absorption edge shifted from 315 to 330 nm, and the band gap of the samples decreased from 3.79 to 3.66 eV. The SEM micrographs showed radial bulging along with inhomogeneous liner exfoliation, and also, a rocky shape pattern with different sizes was observed. A significant change was found in the Raman spectra of the γ-irradiated polymer at the highest dose. The results of the structural, optical, and morphological studies show recovery characteristics at the highest dose level of 300 kGy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Graft copolymerization of poly(methyl methacrylate) with some alkyl methacrylates by atom transfer radical polymerization method and thermal properties

The preparation of graft copolymers of poly(methyl methacrylate) with some alkyl methacrylates were carried out via atom transfer radical polymerization method catalyzed by CuCl/2,2′-bipyridine and using a macroinitiator, poly[(methyl methacrylate)-co-(3,5-bis(chloroacetoxy)phenyl methacrylate)], including an amount of 1 mol % having α-halogeno carbonyl group in the side groups. Although the number-average molecular weights of a graft copolymer series of n-butyl methacrylate (n-ButMA) ended at different times increased from 55,700 to 99,500, the polydispersities decreased from 1.85 to 1.39 with time. The thermal degradation kinetics of macroinitiator and a two-armed graft copolymer of n-ButMA with this macroinitiator, PMMA-g-PnButMA: 4% (by mol), were carried out at different heating rates by thermogravimetric analysis and the results were compared. Using both the Flynn–Wall–Ozawa and Kissinger methods, the decomposition activation energies for macroinitiator were determined as 168 and 162 kJ/mol, respectively; they were also calculated as 233 and 239 kJ/mol for PMMA-g-PnButMA: 4%. The solid state thermodegradation mechanisms of both macroinitiator and PMMA-g-PnButMA: 4% are R₁-type mechanism, a phase boundary-controlled reaction, and F₁-type mechanism, a random nucleation with one nucleus on the individual particle, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Microstructure,strength, and moisture stability of alkali activated glass powder-based binders

Thermally assisted alkali activation of silica-rich glass powder to produce sustainable binders is investigated. Glass powder activated using NaOH provides higher compressive strengths than NaOH activated fly ash binders at lower heat curing temperatures. Sodium silicate gel is the reaction product when glass powder alone is used as the source material, while a combination of sodium silicate and sodium aluminosilicate (N–A–S–H) gels form in activated glass powder–fly ash blends. The activated glass powder-containing binders are found to disintegrate and lose strength when exposed to moisture or an alkaline solution, with the pure glass powder binders suffering the highest strength loss. Structural changes to the reaction product on exposure to moisture are explained using microstructural and FTIR spectroscopic observations. Doping the systems with Al containing (metakaolin) and Ca containing (slag) source materials, while retaining glass powder as the major component (50% or more), result in the formation of moisture-stable reaction products thereby mitigating the strength loss to a large extent.     

Reliable synthesis of bismuth nanoparticles for heavy metal detection

A reliable and facile pathway is described here for preparing high-quality bismuth nanoparticles. Combined with hydrothermal method and confined growing effect of polymer, bismuth nanoparticles with uniform size and shape were obtained with remarkable productivity. The nanoparticles is proved to be pure Rhombohedral structure Bi crystals with R-3m space group and the diameter of the nanoparticles is about 80 nm with a quite narrow particle size distribution. Those bismuth nanoparticles were predicted to grow from a rolling process by sheet-like Bi nanocrystal intermediates. The obtained bismuth nanoparticles were used to prepare modified electrode for the detection of Cd²⁺ and Pb²⁺ in water solution by stripping analysis. Compared with naked glassy carbon electrodes, the modified electrode showed two obvious responses at −0.85 V and −0.62 V, corresponding to the reduction process of Pb²⁺ and Cd²⁺ and this well-resolved stripping response can be observed when the concentration is as low as 10 μg/L, indicating potential application in electroanalysis for environmental inspection.     

L—半胱氨酸盐酸盐电化学生产工艺的工业化研究

就Ｌ－半胱氨酸盐酸电化学生产工艺的工业化进行了讨论，并分布了工业化实验一些研究成果。