Showing papers in "Journal of Sol-Gel Science and Technology in 2011"

Sol–gel derived organic–inorganic hybrid materials: synthesis, characterizations and applications

Abstract: Organic/inorganic hybrid materials prepared by the sol–gel approach have rapidly become a fascinating new field of research in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental understanding of the sol–gel process and the development and applications of new organic/inorganic hybrid materials. Polymer-inorganic nanocomposite present an interesting approach to improve the separation properties of polymer material because they possess properties of both organic and inorganic such as good permeability, selectivity, mechanical strength, and thermal and chemical stability. Composite material derived by combining the sol–gel approach and organic polymers synthesis of hybrid material were the focus area of review It has also been demonstrated in this review that a more complete understanding of their structure–property behavior can be gained by employing many of the standard tools that are utilized for developing similar structure–property relationships of organic polymers. This review article is introductory in nature and gives introduction to composite materials/nanocomposite, their applications and the methods commonly employed for their synthesis and characterization. A brief literature survey on the polysaccharide templated and polysaccharide/protein dual templated synthesis of silica composite materials is also presented in this review article.

Synthesis of CeO2 or α–Mn2O3 nanoparticles via sol–gel process and their optical properties

Abstract: Nanocrystalline cubic fluorite/bixbyite CeO2 or α–Mn2O3 has been successfully synthesized by using methanol as a solvent via sol–gel method calcined at 400 °C. The obtained products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV–vis absorption and Photoluminescence (PL) spectroscopy. TEM reveals that the as-synthesized ultra-fine samples consist of elliptical/spherical and sheet-like morphology of crystalline particles of 8/30 nm, which are weakly aggregated. Optical absorbance spectra reveal that the absorption of ceria in the UV region originates from the charge- transfer transition between the O2− (2p) and Ce4+ (4f) orbit in CeO2. However, α–Mn2O3 nanostructures with nearly pure band gap emission should be of importance for their applications as UV emitters.

A simple template-free sol–gel synthesis of spherical nanosilica from agricultural biomass

Abstract: Mesoporous silica nanoparticles with a spherical morphology have been synthesized from rice husk (agricultural biomass) by a simple, template-free synthetic approach, which was carried out via sol–gel technique at ambient condition. Transmission electron micrographs revealed the formation of spherical silica nanoparticles with an average diameter of 50.9 nm. From the nitrogen adsorption–desorption analysis, the rice husk silica shows a high specific BET surface area of 245 m2 g−1. The silica nanoparticles have a narrow pore size distribution of 5.6–9.6 nm.

Microwave-assisted one-step hydrothermal synthesis of pure iron oxide nanoparticles: magnetite, maghemite and hematite

Abstract: A simple, rapid, one-step synthesis way of pure iron oxide nanoparticles: magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) was investigated. Nanoparticles were prepared by microwave synthesis, from ethanol/water solutions of chloride salts of iron (FeCl2 and FeCl3) in the presence of sodium hydroxide NaOH. X-ray powder diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize these nanoparticles.

Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol-gel process

Abstract: Combination of the surfactant-free nonaqueous sol–gel approach with the microwave technique makes it possible to synthesize Fe3O4, CoFe2O4, MnFe2O4, and NiFe2O4 nanoparticles of about 5–6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core–shell structures. These results extend the microwave-assisted nonaqueous sol–gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates.

Preparation of durable superhydrophobic surface by sol–gel method with water glass and citric acid

Abstract: Durable superhydrophobic surface on cotton fabrics has been successfully prepared by sol–gel method. Cellulose fabric was first coated with silica sol prepared with water glass and citric acid as the acidic catalyst. The silica coated fabric was then padded with hydrolyzed hexadecyltrimethoxysilane afterwards obtaining low surface energy. Water contact angle and hydrostatic pressure were used to characterize superhydrophobicity and washing durability. Scanning electron microscopy was used to characterize the surface morphology changes after certain washing times. All results showed good durable hydrophobicity on cellulose fabrics. In addition, the influence of citric acid and sodium hypophosphite (NaH2PO2) on the durability of hydrophobicity was also investigated. The durability of treated cotton improved with the increase of concentration of citric acid in the presence of NaH2PO2. It could be concluded that citric acid acted as multi-functional heterogeneous grafting chemicals to improve washing durability of hydrophobicity by forming the ester bonds between cotton fabric and silica sol and improved the durability of hydrophobicity.

Photocatalytic TiO 2 coatings on limestone

Abstract: The application of photocatalytic coatings on stone has been investigated for providing surface protection and self-cleaning properties. Sol–Gel and hydrothermal processes were used to synthesise TiO2 colloidal suspensions and coatings with enhanced photocatalytic activity without any thermal curing of the coated stone. The stone was a porous limestone (apulian sedimentary carbonatic, calcite stone). Films and powders prepared from TiO2 sols were studied using X-ray diffraction to evaluate the microstructure and identify rutile and anatase phases. A morphological and physical characterisation was carried out on coated and uncoated stone to establish the changes of appearance, colour, water absorption by capillarity and water vapour permeability. The photocatalytic activity of the coated surface was evaluated under UV irradiation through NO x and organics degradation tests. The performances of the synthesised TiO2 sols were compared with commercial TiO2 suspension. Since the coating doesn’t need temperature treatments for activating the photocatalytic properties, the nano-crystalline hydrothermal TiO2 sols seem good candidate for coating applications on stone that cannot be annealed after the coating application.

Redistribution of cations and enhancement in magnetic properties of sol–gel synthesized Cu0.7−xCoxZn0.3Fe2O4 (0 ≤ x ≤ 0.5)

Abstract: Cu0.7− x Co x Zn0.3Fe2O4 (0 ≤ x ≤ 0.5) nanoparticles are prepared by sol–gel auto combustion method, using copper nitrate, zinc nitrate, ferric nitrate, cobalt nitrate, and citric acid as the starting materials. The process takes only a few minutes to obtain as-received Co-substituted Cu–Zn ferrite powders. X-ray diffraction (XRD), vibrational sample magnetometer and thermo gravimetric analysis are utilized in order to study the effect of variation in the Co substitution and its impact on particle size, lattice constant, density, cation distribution and magnetic properties like magnetization, coercivity, remanent magnetization, ferritization temperature and associated water content. Lattice parameter found to increase with increasing Co content, whereas X-ray density, bulk density, particle size showed decreasing trend with the Co content. Cation distribution indicates that the Co and Cu ion show preference towards octahedral [B] site, Zn occupy tetrahedral (A) site whereas Fe occupy both tetrahedral (A) and octahedral [B] site. Redistribution of cations takes place for x > 0.3. Saturation magnetization (Ms) increases from 52.99 to 79.62 emu/g (x ≤ 0.3), for x > 0.3 Ms decreases with increase in Co content x. However, coercivity, magnetocrystalline anisotropy and remanent magnetization increases with the Co2+ substitution.

Next generation pseudocapacitor materials from sol―gel derived transition metal oxides

Abstract: Capacitive energy storage is distinguished from other types of electrochemical energy storage by short charging times and the ability to deliver significantly more power than batteries. A key limitation to this technology is its low energy density and for this reason there is considerable interest in exploring pseudocapacitive charge storage mechanisms which offer the prospect of increasing energy density without compromising the power density of electrochemical capacitors. In this paper we review our recent work on using sol–gel synthesis methods to prepare nanostructured transition metal oxides which exhibit increased levels of pseudocapacitance and enhanced energy storage properties. Our work with TiO2 nanoparticles and mesoporous films of TiO2 and CeO2 is highlighted as we use these studies to understand the role of crystallite size, nanoscale porosity and understanding the differences between pseudocapacitance and intercalation processes.

Sol–gel-derived photonic structures: fabrication, assessment, and application

Abstract: Sol–gel is a handy, very flexible, and cheap method to fabricate, study, and apply innovative photonic structures. The possibility of starting from molecular precursors and elementary building blocks permits to tailor structures at the molecular level and to create new materials with enhanced performances. Of specific interest for the study of important physical effects as well as for application in light management are confined structures on the nano-micro scale as photonic crystal and planar waveguides. Activation by luminescent species and in particular by rare earth ions allows results in the integrated optics area covering application in sensing, biomedical diagnostic, telecommunication, lightning, and photon management. The present review is focused on some recent results obtained by the authors in Sol–gel photonics. The first part presents colloidal structures including single nano-micro spheres and photonic crystal structures. The second part of the review deals with amorphous and transparent glass–ceramic employed for the fabrication of confined structures in planar format. Some specific application are also reported to highlight the role of sol gel photonics in the development of high performance optical sensors, waveguide lasers, and nanostructured materials.

Shrinkage and pore structure in preparation of carbon aerogels

Abstract: To aim at thermal insulator applications, the shrinkage and the pore structure of resorcinol–formaldehyde (RF) aerogels and carbon aerogels were investigated during the supercritical drying and the carbonization process. The water (W) molar ratio has small effects on the surface area or the particle size, but has significant effects on the density of the aerogel. Higher W/R ratio leads to lower density and larger pore size, and leads to less shrinkage during the carbonization process. The molar ratio of catalyst sodium carbonate (C) has significant effects on the shrinkage, pore size, and particle size of the aerogel. Lower R/C ratio leads to smaller particle size and smaller pore size, and thus induces more shrinkage both in the supercritical drying and in the carbonization, the obtained CA is much denser. The R/C ratio should be higher than 300 to prevent excessive shrinkage. In order to synthesize carbon aerogels combining with small shrinkage, low density (less than 0.1 g/cm3), and small pore size (less than 150 nm) for thermal insulators, the preferred W/R ratio is between 90 and 100, and the preferred R/C ratio is between 300 and 600.

FT-IR microscopy characterization of sol–gel layers prior and after glucose oxidase immobilization for biosensing applications

Abstract: Micro-Attenuated Total Reflection (ATR) Fourier Transform Infrared spectroscopy was used to investigate sol–gel layers for biosensing applications prior and after glucose oxidase (GOD) immobilization. The changes occurring in sol–gel infrared spectrum after GOD immobilization were clearly evidenced confirming the retaining of the enzyme activity. Moreover, micro-ATR experimental technique allowed us to investigate the spatial distribution of enzyme concentration. The non-destructive nature of our approach also enabled to monitor the time stability of sol–gel layers and of embedded GOD. The temporal evolution of some peaks in infrared spectra of these sol–gel layers was compared with absorption and steady-state fluorescence measurements. The results reported here confirm that micro-ATR infrared spectroscopy can be usefully employed for a non- or minimally invasive detailed characterization of supports for enzyme immobilization.

Room temperature ferromagnetism in sol–gel deposited un-doped ZnO films

Abstract: Dilute magnetic semiconductors are fast emerging spintronic materials where advantage of magnetic properties of semiconductor materials (usually doped with small quantities of magnetic ions) is being explored. Sol–gel technique, being low-cost simple and application oriented method, has been used in the present case. ZnO films of <150 nm thickness have been deposited by spin coating onto single crystal p-type Si substrates. The optimized sol is of paramagnetic nature, whereas, mixed para- dia-magnetic phase is observed for the as-prepared films. A complete ferromagnetic phase transition has been observed after heating the films in vacuum at a temperature of 300 °C. These sol–gel prepared films exhibit hexagonal wurtzite structure as observed by X-ray diffraction. After the magnetic field annealing in vacuum the films showed strengthened magnetic as well as structural properties. This work presents a clear evidence of ferromagnetic behavior of the un-doped ZnO films deposited by sol–gel at room temperature. It is also pointed out that Zn vacancies rather than oxygen deficiency are responsible for ferromagnetism in these sol–gel deposited ZnO thin films, whereas, the experimental evidence has been substantiated with the theoretical calculations using density functional theory.

The influence of titanium dioxide phase composition on dyes photocatalysis

Abstract: A comparative study of TiO2 powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes. The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification, for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples. It was found that the only TiO2 anatase phase of the synthesized TiO2 develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic properties. Different TiO2 doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO2 Aldrich with TiO2 Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene blue using TiO2 thin film were investigated.

Evaluation of hybrid silica sols for stable microporous membranes using high-throughput screening

Abstract: Microporous membranes are a promising option for energy-efficient molecular separations. Long-term hydrothermal stability of the membrane material is of prime importance for several industrial processes. Here, a short overview of silica-based membrane materials and their hydrothermal stability is presented. Following this, the development of a series of organic–inorganic hybrid silica sols is described, based on α,ω-bis(triethoxysilyl)-precursors with bridging methane, ethane, propane, and benzene groups. High-throughput screening was used to scan a range of sol parameters, followed by membrane preparation from the most promising sols. These organic–inorganic hybrid silica (HybSi®) membranes were used in dewatering of lower alcohols by pervaporation. Separation factors up to 200 were found for ethanol/water mixtures, and up to 23 for methanol/water mixtures. Modest permselectivity values for hydrogen over nitrogen were found, ranging up to 20.7 for the shortest bridging group. It was concluded that the length of the organic bridge has a clear effect on the pore size distribution and the selectivity of the membrane.

Mesoporous hybrid and nanocomposite thin films. A sol–gel toolbox to create nanoconfined systems with localized chemical properties

Abstract: Mesoporous Thin Films (MTF) can be created by combining sol–gel synthesis, template self-assembly and chemical surface modification. A wide palette of inorganic (oxides, phosphates, carbon-based, etc.) and hybrid organic–inorganic frameworks with a variety of composition, pore sizes, and nanoscale, organic or biological functions located in the inorganic skeleton, pore surface or pore interior can be obtained. The properties of the functional pore systems are tuned by the pore size and geometry, wall composition and surface features. These MTF with interesting electronic and optical controlled features are indeed a “nanofacility”. Well-defined monodisperse sized pores also act as nanoreactors, or nanocavities with controlled environment and behaviour. In the last years, the production of accessible MTF, in which either the pore surface or pore volume can be modified by organic functional groups or nanoparticles has been thoroughly explored. Each highly controlled MTF originated from a reproducible and modular synthesis is in itself a building block for more complex structures, presenting order at different length scales (molecular, mesoscopic, macroscopic), and novel properties derived thereof. Selected examples of optical and chemical behaviour of these multiscale materials are presented to illustrate these points.

Synthesis of hierarchical macro/mesoporous dicalcium phosphate monolith via epoxide-mediated sol–gel reaction from ionic precursors

Abstract: Starting from calcium chloride dihydrate (CaCl2·2H2O), phosphoric acid (H3PO4), and poly(acrylic acid) (PAA) dissolved in a mixture of water and methanol (MeOH), dicalcium phosphate anhydrous (DCPA, CaHPO4) monoliths with co-continuous macropores and mesopores have been synthesized by the addition of propylene oxide. Macropores are formed as a result of phase separation, while mesopores as interstices between primary particles with the size of ca. 30 nm. Propylene oxide acts as a proton scavenger and leads to moderate pH increase in a reaction solution, which brings about gelation in several minutes. On the other hand, PAA acts as a crystal growth inhibitor as well as a phase separation inducer. The extensive crystal growth of DCPA is hindered by the addition of PAA which allows morphological control of the structure in micrometer range. Fourier transform infrared spectroscopy indicates that PAA and DCPA form composite via interaction between the carboxyl groups and the surface of crystals, and together form gel phase. The solvent phase, which is converted to macropores after evaporative drying, is mainly comprised of solvent. The degree of supersaturation in a reaction solution considerably influence on the crystallization process, and thereby, influences on the porous structure in nano- and micrometer ranges.

Preparation and characterization of a new sol–gel hybrid based tetraethoxysilane-polydimethylsiloxane as a stir bar extraction sorbent materials

Abstract: A new tetraethoxysilane-polydimethylsiloxane (TEOS-PDMS) for use as sorbent of stir bar sorptive extraction (SBSE) towards two selected organophosphorus pesticides (OPPs) namely chlorpyrifos and malathion was successfully synthesized through sol–gel technology. Four different molar ratios of TEOS:PDMS (1:1, 2:1, 3:1 and 4:1) sol solutions were prepared and dipped coated onto the surface of a glass-encased stir bar. Extraction efficiency of the prepared coatings towards the two selected OPPs were compared. A number of factors have been found to greatly affect the characteristics and properties of a particular sol–gel coating. Hence, in this study, several sol–gel coating conditions have been optimized using the optimized molar ratio 3:1 TEOS:PDMS to obtain the best coating as the stationary phase for SBSE. The raw OH-TPDMS and TEOS were characterized using Fourier Transform Infrared Spectroscopy (FT-IR) and compared with spectra of the four different molar ratios of TEOS:PDMS. The FT-IR spectrum of TEOS:PDMS showed the co-polymerization between PDMS and hydrolyzed TEOS molecules demonstrating the formation of the hybrid network in the sol–gel hybrid material. Surface morphology of hybrid sol–gel TEOS-PDMS with optimized molar ratio of 3:1 TEOS:PDMS were examined using FE-SEM. The surface of the sol–gel coating seems to be rough and homogeneous. The more rough structure formed by the 3:1 molar ratio TEOS:PDMS provides enhanced surface area which in turn improved sample capacity or adsorption process.

A study on sol–gel synthesis and characterization of SiC nano powder

Abstract: Nano sized β-SiC particles were synthesized from sol–gel process. Mono dispersed β-SiC nano particles with semi spherical morphology were obtained by employing APC as a dispersant agent and adjusting pH in the range of 2.5–4. Phenolic resin and TEOS were employed as precursors and heat treatment was conducted up to 1500 °C. Different techniques such as XRD, DTA, FTIR, PSA, SEM and TEM were used to characterize the formation of β-SiC. The (Si–O-C) bonds were formed by hydrolysis and condensation reactions in the gel while the nucleation of crystalline β-SiC was found to be initiated at 1400 °C. The primary particles in the sol were found to be (< 10 nm) while the size distribution in the final product was recorded in the range of 30–50 nm.

Size-controlled synthesis of BiFeO3 nanoparticles by a soft-chemistry route

Abstract: In this work we report the size-controlled synthesis of BiFeO3 nanoparticles via a soft-chemistry route. In this route, the aqueous solution of inorganic Bi and Fe salt is gelled by using acrylamide and bisacrylamide. It is demonstrated that the grain size of resulted BiFeO3 powders can be tailored by varying the ratio of acrylamide to bisacrylamide. With increase in the bisacrylamide content, the grain size decreases monotonously. By using this method, a series of BiFeO3 samples with average grain size ranging from 110 to 52 nm have been prepared. The thermal decomposition process of precursor xerogels and the formation of BiFeO3 phase are investigated by means of X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry analysis, and fourier transform infrared spectroscopy (FTIR). SEM observations reveal that the prepared BiFeO3 nanoparticles are nearly spherical in shape with a narrow diameter distribution. Magnetic hysteresis loop measurement shows that the BiFeO3 nanoparticles exhibit weak ferromagnetic behavior at room temperature, and a saturation magnetization of ~1.56 emu/g is achieved for the 52 nm sample.

Structural, dielectric and electrical properties of zinc doped nickel nanoferrites prepared by simplified sol–gel method

Abstract: Zinc doped nickel ferrite nanoparticles having the general formula Ni1−xZnxFe2O4 (x = 0.1, 0.2, 0.3, 0.4, 0.5) were prepared with simplified sol–gel method. The structural and dielectric properties of these samples sintered at 750 ± 5 °C were studied. X-ray diffraction patterns confirm the single phase spinel structure for prepared samples. The scanning electron microscope images indicated that the particle size of the samples lies in the nanometer regime. The dielectric constant (er) and dielectric loss tangent (tan δ) of nanocrystalline nickel ferrites were investigated as a function of frequency and Zn concentration. The dependence of er and tan δ on the frequency of the alternating applied electric field is in accordance with the Maxwell–Wagner model. The prepared samples have a lowest dielectric constant compared to the already reported samples of the same composition to the best of our knowledge. The effect of Zn doping on the dielectric properties of nickel ferrites is explained on the basis of cations distribution in the crystal structure.

TiO2/SiO2 hybrid nanomaterials : synthesis and variable UV-blocking properties

Abstract: 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.

Study on synthesis and evolution of sodium potassium niobate ceramic powders by an oxalic acid-based sol–gel method

Abstract: Potassium sodium niobate (KNN) ceramic powders by a variation of sol–gel method is synthesized. The metal precursors used for the KNN synthesis are potassium carbonate, sodium carbonate and niobium hydroxide, ethylene glycol are used as chelating and esterification agent, respectively. The effects of amount of oxalic acid (OA) and ethylene glycol (EG), pH value on the stability of the precursor sol were investigated. The evolution of (K0.5Na0.5)NbO3 crystal phase was also investigated by XRD, IR, SEM and TG-DTA. The results showed that stable precursor sol was formed when n(OA):n(Mn+) = 3:1, n(OA):n(EG) = 1:2 and pH value was in the range of 2.5–3.5. Xerogel was sintered in the range of 500–650 °C to prepare K6Nb10.88O30 and Na2Nb4O11 powder. Then the compound was sintered at 750 °C to produce perovskite (K0.5Na0.5)NbO3 ceramic powders. The grain size is about 100–200 nm.

An innovative CaSiO3 dielectric material from eggshells by sol–gel process

Abstract: Calcium silicate (CaSiO3), wollastonite, with a molar ratio of CaO:SiO2 of 1:1, was synthesized by a sol–gel process and sintered at 1,100°C for 1 h. The synthesis of calcium silicate was carried out using chicken eggshells as the starting material possessing several advantages such as low cost, high purity, and less moisture sensitivity, when compared with those obtained from metal alkoxide precursors via the sol–gel process. The CaSiO3 samples have the triclinic or anorthic phase formations and good electrical properties. The dielectric constant and electrical conductivity are 62.59 ± 0.44 and 8.0052 × 10−4 (Ω.m)−1, respectively, at 25°C and 1 MHz. The transmission electron microscopy (TEM) images of the samples show a good dispersion and uniform particles with an average diameter of about 0.5 nm. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and Simultaneous thermal analysis (STA) were used to verify the synthesis.

The role sol–gel process for nuclear fuels-an overview

Abstract: The paper reviews the sol–gel methods used for the preparation of nuclear fuel materials in the form of microspheres. It also discusses how these microspheres can be fabricated into nuclear fuels for reactors such as High Temperature Gas Cooled Reactors and Fast Reactors. The performance of these microsphere-based fuels is reviewed. More recent applications, such as the transmutation of minor actinides, (Np, Am and Cm) and hydrogen production, are also briefly covered.

Chemical synthesis of Ni/TiO2 nanophotocatalyst for UV/visible light assisted degradation of organic dye in aqueous solution

Abstract: The Ni/TiO2 nanoparticles with different Ni dopant content were prepared by a modified sol–gel method. The structure and photoinduced charge properties of the as-prepared catalysts were determined using X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy techniques, and the photocatalytic efficiency of these catalysts was tested using an organic dye. It was shown that Ni modification could greatly enhance the photocatalytic efficiency of these nanocomposite catalysts by taking the photodegradation of methyl orange as a model reaction. With appropriate ratio of Ni and TiO2, Ni/TiO2 nanocomposites showed the superior photocatalytic activity than the single TiO2 nanoparticles. Surface photovoltage spectra demonstrated that Ni modification could effectively inhibit the recombination of the photoinduced electron and holes of TiO2. This electron–hole pair separation conditions are responsible for the higher photocatalytic performance of Ni/TiO2 nanocomposites in the visible region of electromagnetic spectrum.

Preparation of nanostructure Ni doped CdO thin films by sol gel spin coating method

Abstract: The nanostructure Ni-doped CdO films have been prepared by sol gel spin coating method Atomic force microscopy results indicate that the CdO films are formed from the nanoparticles and the grain size is changed with nickel content X-ray diffraction patterns of the films indicate that the undoped and Ni-doped CdO films have polycrystalline structure with a cubic sodium chloride structure, showing two main characteristic peaks assigned to the (111) and (200) planes The optical band gap values of undoped and Ni-doped CdO films were determined by optical absorption method The Eg values of the CdO films were found to be in the range of 226–260 eV The Eg values of the CdO films increase with the content of Ni dopant (up to 6% Ni) It is evaluated that the optical band gap and grain size of the CdO film can be controlled by doping with nickel atoms

Synthesis and characterization of polydimethylsiloxane-cyanopropyltriethoxysilane-derived hybrid coating for stir bar sorptive extraction

Abstract: New inorganic–organic hybrid materials were synthesized by hydrolysis and condensation of cyanopropyltriethoxysilane (CNPrTEOS) and polydimethylsiloxane (PDMS) in the presence of hydrochloric acid, HCl catalyst and methyl trimethylmethoxysilane as precursor via sol–gel method and coated on glass encased stir bar for use in stir bar sorptive extraction (SBSE). The cyano part provides polar moiety, which may improve the extraction of polar analytes. The physico-chemical properties and extraction ability of PDMS-CNPrTEOS-derived hybrid coatings can be fine tuned via manipulation of solvents (tetrahydrofuran (THF)-based and dichloromethane (DCM)-based) and PDMS-CNPrTEOS molar concentrations during the sol synthesis. Clear, homogeneous PDMS-CNPrTEOS-derived hybrid sols were obtained using THF and DCM at optimized molar ratios. The optimized molar ratios of THF:CNPrTEOS and THF:PDMS were 5:1 and 25:1, respectively. The optimized molar ratios of DCM:CNPrTEOS and DCM:PDMS were 10:1 and 70:1, respectively. FTIR spectrum showed that the intensity of the CN peak increased with increasing content of CNPrTEOS in the PDMS;CNPrTEOS-derived hybrid. The Field Emission Scanning Electron micrographs of prepared coatings revealed smooth, homogenous surfaces and crack-free coatings with film thickness of 200 nm to 2.5 μm attributing to different solvent types. All coatings prepared were thermally stable at temperature higher than 200 °C. The DCM-based PDMS-CNPrTEOS-derived coating shows more advantages in terms of physical characteristics and extraction ability compared to THF-based PDMS-CNPrTEOS-derived coatings due to higher cyano part content and its thicker coating. The PDMS-CNPrTEOS-derived hybrid coatings can be used as extraction sorbent for analysis of non steroidal anti-inflammatory drugs namely ketoprofen and diclofenac sodium in SBSE.

Effects of Fe-doping of ceria-based materials on their microstructural and dynamic oxygen storage and release properties

Abstract: The structural/textual characteristics and dynamic oxygen storage capacity (DOSC) of Fe0.1Ce0.9Ox and Fe0.1Ce0.6Zr0.3Ox samples prepared by sol–gel method are investigated by X-ray powder diffraction (XRD), Raman, Hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and mass spectrometry with CO/O2 transient pulses. The dynamic oxygen storage capacity and rate are largely promoted by Fe doping, and their thermal stability is enhanced by Fe and Zr co-doping. The DOSC (at 673 K) are ordered as: Fresh: Fe0.1Ce0.6Zr0.3Ox (566.6 μmol/g) > Fe0.1Ce0.9Ox (551.8 μmol/g) > Ce0.67Zr0.33O2 (287.5 μmol/g) > CeO2 (140.3 μmol/g); Annealed1,173K: Fe0.1Ce0.6Zr0.3Ox (101.6 μmol/g) > Ce0.67Zr0.33O2 (45.3 μmol/g) > Fe0.1Ce0.9Ox (44.9 μmol/g) > CeO2 (43.3 μmol/g). The H2-TPR results showed that Fe-incorporation improve the total oxygen storage capacity (TOSC) of mixed oxide and low temperature activity. The TOSC are ordered as: Fe0.1Ce0.9Ox (1.53 mmol/g) > Fe0.1Ce0.6Zr0.3Ox (1.42 mmol/g) > Ce0.67Zr0.33O2 (1.16 mmol/g) > CeO2 (0.88 mmol/g). XRD and Raman results indicate that Fe0.1Ce0.9Ox and Fe0.1Ce0.6Zr0.3Ox are characterized with the fluorite-type cubic structure similar to CeO2. TPR and XPS analyses reveal that the introduction of Fe into ceria and ceria-zirconia mixed oxides strongly modified the structural and textural properties, which influenced the kinetics of bulk oxygen diffusion.

The “benzyl alcohol route”: An elegant approach towards doped and multimetal oxide nanocrystals

Abstract: In this article, the versatility and the potential of the “benzyl alcohol route” for the synthesis of multimetal and doped metal oxides are highlighted in the first part of the manuscript. Among the presented examples, some materials have not been accessible by other solution syntheses and could so far only be obtained through solid state reactions. The second part describes the synthesis and characterization of 5–6 nm ZnAl2O4 nanoparticles which form flower-like aggregates through the oriented attachment crystallization mechanism.