Cobalt hexacyanoferrate in PAMAM-doped silica matrix: 1. Solid state electrochemistry and thermochromism

The solid-state electrochemistry and thermochromism of cobalt hexacyanoferrate (CoHCF) in a composite matrix comprising silica sol-gel and generation-4 poly(amidoamine) dendrimer was investigated and compared to analogous studies of CoHCF powders. The thermochromic behaviour over the range, 25-85 °C, of the reduced form in the sol-gel matrix differed from that of the powder. The results suggested that even in the presence of KCl in this matrix, the dominate form of the reduced CoHCF was Co₂^IIFe^II(CN)₆ rather than K₂Co^IIFe^II(CN)₆. In contrast, the thermochromic behaviour of the oxidized form of CoHCF was the same as that reported for the powders. The observed cyclic voltammetric behaviour of CoHCF in the sol-gel composite matrix was the same as that of powders in terms of the electrode processes, but the influence of scan rate on the current was dependent upon the cell configuration. With the CoHCF-doped composite contacted to a solution phase, this behaviour was consistent with anion intercalation/de-intercalation control, but in a solid-state cell, a transition from a surface-controlled to a mass-transport controlled current was observed.     

Electron rich porous carbon/silica matrix from rice husk and its characterization

Free electron rich porous carbon/silica matrix (ECS₈₀₀) was prepared from rice husk by carbonization at 400 °C and activation by phosphoric acid (H₃PO₄) at 800 °C. The ratio of H₃PO₄ to pre-carbonized carbon was fixed at 2.3. The surface area, pore volume, and pore size distribution of ECS₈₀₀ was measured, using nitrogen adsorption isotherms at 77 K. The unpaired electron density of ECS₈₀₀ was measured in electron spin resonance spectroscopy, using 4-hydroxy 2,2,6,6-tetramethyl piperidine-1-oxyl as the reference spin probe. ECS₈₀₀ was further characterized, using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscope, and ²⁹Si-nuclear magnetic resonance spectroscope to study crystallization, surface morphology, functional group and different types of silicon species.     

Gas permeation in poly(ether imide) nanocomposite membranes based on surface-treated silica. Part 2: With chemical coupling to matrix

Nanocomposite membranes based on nano-sized SiO₂ particles with chemical coupling to the polymer matrix are described with special emphasis on gas permeation properties. In this paper, poly(ether imide) with reactive imide rings in the backbone was used as the matrix to which the SiO₂ particles were chemically bonded via an amine-containing silane coupling agent. Four types of nanocomposite membranes were prepared by solution casting and melt processing and characterized in terms of morphology and void volume formed due to adding SiO₂ particles. The relative gas permeability of the nanocomposite with chemical coupling to matrix was decreased by the presence of SiO₂ particles. Diffusion coefficients computed from time lag data also decreased with SiO₂ content. However, solubility coefficients computed by dividing the experimental permeability by the diffusivity obtained from the observed time lag increased with SiO₂ content contrary to simple composite theory. These permeation properties are discussed in terms of the void volume fraction estimated by density observations. In addition, TEM and SEM were used to explore the morphology of these nanocomposite membranes.     

Enhancement of Sm3+ emission by SnO2 nanocrystals in the silica matrix

Silica xerogels containing Sm³⁺ ions and SnO₂ nanocrystals were prepared in a sol–gel process. The image of transmission electron microscopy (TEM) shows that the SnO₂ nanocrystals are dispersed in the silica matrix. The X-ray diffraction (XRD) of the sample confirms the tetragonal phase of SnO₂. The xerogels containing SnO₂ nanocrystals and Sm³⁺ ions display the characteristic emission of Sm³⁺ ions (⁴G_5/2 → ⁶H _J (J = 5/2, 7/2, 9/2)) at the excitation of 335 nm which energy corresponds to the energy gap of the SnO₂ nanocrystals, while no emission of Sm³⁺ ions can be observed for the samples containing Sm³⁺ ions. The enhancement of the Sm³⁺ emission is probably due to the energy transfer from SnO₂ nanocrystals to Sm³⁺ ions.     

Cobalt species in promoted cobalt alumina-supported Fischer–Tropsch catalysts

The structure of cobalt species at different stages of the genesis of monometallic and Pt-promoted cobalt alumina-supported Fischer–Tropsch catalysts was studied using X-ray diffraction, UV–visible spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, and DSC–TGA thermal analysis. The catalysts were prepared by incipient wetness impregnation using solutions of cobalt nitrate and dihydrogen hexachloroplatinate. Both variation of catalyst calcination temperature between 473 and 773 K and promotion with 0.1 wt% of Pt had no significant affect on the size of supported Co₃O₄ crystallites. The size of cobalt oxide particles in the calcined catalysts seems to be influenced primarily by the pore diameter of the support. Cobalt reducibility was relatively low in monometallic cobalt alumina-supported catalysts and decreased as a function of catalyst calcination temperature. The effect was probably due to the formation of mixed surface compounds between Co₃O₄ and Al₂O₃ at higher calcination temperatures, which hinder cobalt reduction. Promotion with platinum spectacularly increased the rate of cobalt reduction; the promotion seemed to reduce the activation energy of the formation of cobalt metallic phases. Analysis of the magnetization data suggests that the presence of Pt led to the reduction of smaller cobalt oxide particles, which could not be reduced at the same conditions in the cobalt monometallic catalysts. Promotion of cobalt alumina-supported catalysts with small amounts of Pt resulted in a significant increase in Fischer–Tropsch cobalt time yield. The efficient control of cobalt reducibility through catalyst calcination and promotion seems to be one of the key issues in the design of efficient cobalt alumina-supported Fischer–Tropsch catalysts.     

Effects of In2O3 nanoparticles doping on the photoluminescent properties of Eu2+/Eu3+ ions in silica glasses

Eu²⁺/Eu³⁺ ions doped silica glasses contained In₂O₃ nanoparticles (NPs) have been fabricated by using nanoporous silica glasses. Interestingly, efficient energy transfer from In₂O₃ NPs to Eu²⁺/Eu³⁺ ions enhanced the photoluminescence (PL) emission of Eu²⁺/Eu³⁺ ions, which derives from lattice defects in In₂O₃ NPs. Our work has not only demonstrated a facile way to fabricate NPs and rare earth ions co-doped silica glasses, but also extended the applications of semiconductor oxide NPs such as In₂O₃ NPs.     

Gas permeation in poly(ether imide) nanocomposite membranes based on surface-treated silica. Part 1: Without chemical coupling to matrix

The long range objective of this research is to understand to what extent the presence of nanosized particles may change the local properties, and specifically permselectivity characteristics, of a glassy polymer matrix or whether conventional composite theory can be applied to such composites, i.e., the matrix properties are not changed by the filler. In this work, nanocomposite membranes based on an amorphous, glassy poly(ether imide) were formed by incorporating three kinds of hydrophobically treated fumed silica by solution casting and melt processing techniques. However, there is considerable evidence that these nanocomposites contain voids or defects, probably at the polymer-particle interface or within aggregates, that increase gas permeability and decrease selectivity. Thus, the primary focus of this paper is the relation between the extent of voids formed in the nanocomposite and the permeation properties. In addition, this paper deals with techniques for dispersing nanosized particles, fumed silica, in the polymer matrix, characterization of morphology of this mixture using TEM and SEM, and evaluation of local properties based on gas permeation.     

XAFS study of Ti-silicalite: structure of framework Ti(IV) in presence and in absence of reactive molecules (H2O,NH3)

X-ray absorption at the Ti K edge (both XANES and EXAFS) of a very pure Ti-silicalite containing a small fraction of Ti(IV) substituting Si(IV), has been performed in order to study the effect of the presence or absence of ligands such as H₂O and NH₃ on the Ti(IV) coordination sphere. In particular, the effect of an outgassing treatment at 400 K and of the interaction with NH₃ has been studied and described in detail. It has been found that the Ti(FV) is fourfold coordinated in the samples outgassed at 400 K and expands its coordination sphere number under the action of adsorbates.     

Poly(methylene blue) doped silica nanocomposites with crosslinked cage structure: Electropolymerization, characterization and catalytic activity for reduction of dissolved oxygen

The poly(methylene blue) (PMB) modified glassy carbon electrode (GCE) exhibiting different electrochemical behavior was prepared via two methods, respectively. The PMB polymer, derived from the two-step electropolymerization, suffered structure conversion between Poly(leuco-MB) and Poly(MB) during cyclic voltammetric measurement and exhibited electrocatalytic activity for reduction of dissolved oxygen (DO). The monodispersed hollow methylene blue doped SiO₂ nanoparticles were synthesized in the W/O microemulsion. A new material, PMB doped SiO₂ nanocomposites, presenting monolayer sheets with crosslinked cage structure, were electrochemically polymerized on GCE surface. Compared with PMB film, the nanocomposite material provided a significantly improved sensitivity for reduction of DO and an excellent ability to resist interference from macromolecule contaminants. The detection of DO was performed using the nanocomposite material modified electrode. The calibration curve was linear over a DO concentration range of 0.112–5.78 mg L⁻¹ with a correlation coefficient of 0.998 and a detection limit (3σ) of 0.037 mg L⁻¹.     

Optical and thermal insulation properties of silica aerogel under a 7 kW·cm-2 power laser irradiation

Laser technology has made great progress over the past decades. However, corresponding defense systems have lagged slightly behind. Therefore, there is significant room for research with respect to the principles and bases of existing laser protective materials. In this paper, a kind of silica aerogel material is prepared with the acid-base sol-gel process. Considering the influence of thermal conductivity and the porosity of the aerogel materials on the laser irradiation results, the best laser resistance times of the materials were obtained. The concept of the maximum energy transfer radius is proposed to build a preliminary laser irradiation model for porous materials. It indicates that under the irradiation of a continuous wave laser with a power of 7 kW·cm^?2, the silica aerogel materials with the thickness of 3, 6, and 9 mm can withstand the laser for maximum times of 26, 61, and 100 s, respectively. After 7 s of irradiation, the surface temperature of 3 mm from the laser incident point is 226.9 °C. Aerogels, especially silica aerogels, should be considered as future laser protection materials. The extremely low thermal conductivity and the strong scattered ability for laser of these materials will provide a good defensive effect against large-energy laser weapons.     

Structural and magnetic properties of Co/Al2O3 cermet synthesized by mechanical ball milling

Cobalt nanoparticles in the alumina matrix were synthesized using high energy mechanical ball milling of Co₃O₄ and Al powders mixture. The effect of ball mill time of 1 up to 12 h on the phase formation and crystalline lattice of the samples was investigated by the fitting of the X-ray diffraction patterns with Fullprof software and Rietveld method. The results show that 6 h milling of the primary powders yields a nanocomposite of Co/Al₂O₃ cermet. The formation of Co/Al₂O₃ nanocomposite was confirmed by a morphological study using scanning electron microscopy and transmission electron microscopy. The prepared nanocomposite by 12 h ball mill time has ferromagnetic properties with a high saturation magnetization value of 118 emu/g. Also, using Henkel plot analysis, it was shown that there are strong dipole-dipole magnetic interactions between the prepared cobalt nanoparticles in the Al₂O₃ matrix.     

Cobalt and iron oxide modified mesoporous zirconia: Preparation, characterization and catalytic behaviour in methanol conversion

Mesoporous zirconia materials with different textural characteristics and degrees of crystallinity were obtained by various procedures and modified with cobalt and iron oxide nanoparticles. The obtained materials were characterized by N₂-physisorption, XRD, TEM, FTIR, Mössbauer spectroscopy, TPR-TG and methanol conversion as a catalytic test. Formation of finely dispersed iron and cobalt oxide species, hosted in the zirconia matrix, was observed after the modification. The obtained composites possess higher catalytic activity and different in comparison with the corresponding zirconia supports dehydration and dehydrogenation ability. It was demonstrated that the variations in the textural and surface features of zirconia support and the deposition of different metal oxides on it provided a great opportunity for the preparation of catalysts with tunable bi-functional acidic and redox properties.     

Stability-enhanced indium hexacyanoferrate electrodes: Morphological characterization, in situ EQCM analysis in nonaqueous electrolytes and application to a WO3 electrochromic device

This paper presents a promising transparent counterelectrode system for a WO₃ electrochromic device (ECD) on the basis of a stability-enhanced indium hexacyanoferrate (InHCF) electrode and a NaClO₄/propylene carbonate (PC) electrolyte. Through SEM characterization it was found that clusters of granular InHCF nanoparticles (ca. 80-140 nm) were deposited on ITO substrates in HCl and KCl-stabilized plating solutions, and uniform micrometer thick films with high charge capacity could be obtained. From in situ electrochemical quartz crystal microbalance study, it was discovered that Na⁺ would enter or move out from the InHCF film in the “desolvated” form during the redox process in a PC electrolyte. Besides, NaClO₄/PC resulted in higher electrochemical activity and reversibility than LiClO₄/PC. With these discoveries, a durable WO₃-InHCF ECD featuring blue-to-colorless electrochromism was fabricated successfully. The device remained 73.6 and 88.7% of its initial ΔT values at 600 and 800 nm after 40,000 rapid and successive coloring/bleaching cycles, respectively. Moreover, the cycling-induced loss of electrochromic performance almost completely restored after 1-month rest and kept unchanged for another month. Thus, the applicability of this nonaqueous InHCF counterelectrode system to ECDs was verified.     

Water dynamics in bulk and dispersed in silica CaCl2 hydrates studied by neutron scattering methods

Quasi-elastic and inelastic neutron scattering techniques have been used to study the dynamics of water in CaCl₂ · nH₂O (n = 1/3,2,4,6,9) hydrates dispersed in silica, in comparison with the bulk hydrates. Inelastic scattering shows that the water molecules in dispersed hydrates are in an amorphous state. Quasi-elastic scattering indicates a higher mobility of water in the hydrates dispersed in silica, compared to bulk hydrates. The self-diffusivity of water in the dispersed hydrates increases with water concentration, while remaining below the one of pure water. The neutron and pulsed-field gradient NMR diffusivities are similar, which indicates that the hydrates form a thin and continuous layer on the pore walls of silica.     

Preparation and characterization of CO2-selective Pebax/NaY mixed matrix membranes

CO₂-selective Pebax/NaY mixed matrix membranes (MMMs) were prepared by incorporating NaY zeolite into Pebax matrix. The morphology, chemical groups, thermal stability, and microstructure of the MMMs were investigated by scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction, respectively. The effects of zeolite loading amount, permeation temperature and pressure on the CO₂/N₂ separation performance of the resultant membranes were studied. The as-prepared MMMs are much superior to the pristine Pebax membranes in terms of permeability and selectivity. The CO₂ permeability and CO₂/N₂ selectivity can respectively reach to 131.8 Barrer and 130.8 for MMMs made by the starting materials containing 40 wt % NaY. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48398.     

Structural and electrochemical characterization of a cobalt phthalocyanine bulk-modified SiO2/SnO2 carbon ceramic electrode

A cobalt phthalocyanine bulk-modified carbon ceramic composite has been prepared by using sol-gel processing, and characterized by BET surface area, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. A water-soluble 3-n-propylpyridinium chloride silsesquioxane (SiPyCl), an ion exchanger polymer, was employed to attach cobalt(II) tetrasulfophthalocyanine (CoTsPc) and prevent its leakage, as well as, to ensure adequate dispersion in the sol-gel network. The modified electrode built in a rigid disk-format displayed good electrocatalytic behavior towards the oxidation of oxalic acid at 0.84 V (SCE), as evidenced by the enhancement of the anodic current peak intensity when the concentration of oxalic acid was increased. A linear response was found in the range of 1.6 × 10⁻⁵ to 1.5 × 10⁻³ mol l⁻¹ with a detection limit of 7.1 × 10⁻⁶ mol l⁻¹.     

Structural characterization,defect evolution and luminescence properties of natural CaF2 under 10 MeV electron irradiation

Present study investigates the response of various coloured variants of natural fluorite (CaF₂) to 10 MeV electron beam irradiation at accumulated dose of 5–10 MGy. The fluorite specimens did not show any post irradiation radioactivity. However, after irradiation the specimens developed purple colouration of different shades depending on the dose. In-depth characterization of the as-received and irradiated specimens using XPS and Raman spectroscopy confirm the relocation of fluorine (F) anions at interstitial sites and formation of metallic calcium (Ca). The calculated displacement cross sections for F and Ca indicate that it is easier to form fluorine anion interstitials within lattice structure. However, the estimated lower fraction of interstitial fluorine (∼14%) as compared to metallic Ca (>50%) is attributed to their surface diffusion and desorption. Electron irradiation was found to cause photoluminescence quenching in all the CaF₂ specimens that is likely caused by a radiation-induced formation of competing recombination channels.     

Biochar as a filler in mixed matrix materials: Synthesis,characterization, and applications

The use of mixed-matrix materials (MMM) has become a major topic of research in recent years, due to unique properties achieved in these composites. In this work, biochar from sunflower seed hull pyrolysis and biochar/polysulfone (PSF) MMMs were produced and characterized. The optimal pyrolysis temperature for biochar production was determined to be 500 °C. The resulting biochar properties were an iodine number of 203 mg/g and a pore volume of 0.595 mL/g. In MMM fabrication, the use 4% ethanol as nonsolvent in the wet phase inversion process increased the glass transition temperature by 8 °C, indicating improved biochar/PSF interaction. The presence of biochar was shown to create pores in otherwise dense surfaces. The critical surface energy was also increased by the addition of biochar from 28.6 mN/m in pristine PSF to 35.7 mN/m in biochar/PSF MMMs. We identified and discussed several potential applications based on the determined properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48027.     

Approach of phase transformations and densification in nanostructured and (Bi2O3, ZnO,TiO2) doped silica ceramics

The low temperature sintering of silica is studied under the influence of sintering aids and nanosized powders using X-Ray Diffractometry (XRD) and high-temperature environmental scanning electron microscopy analyses (HT-ESEM). Two particular aids were chosen to conduct this study, [Bi₂O₃–ZnO]_eutectic and titania. We report a lowering of the crystallization temperature when the former compound is introduced in the silica while a raise is observed when the latter is used. Moreover, the amorphous silica crystallization into cristobalite inhibits drastically the kinetics of densification of silica-based materials.