Gel Synthesis Route Research Articles

Inorganic–organic nanocomposites based on sol–gel derived magnesium fluoride

Monodispersed magnesium fluoride nanoparticles are utilized for the first time to prepare transparent inorganic-organic nanocomposite materials with improved mechanical properties. The fluorolytic sol-gel synthesis route has been modified for the preparation of monodispersed magnesium fluoride nanoparticles with a size of 2-3 nm. MgF(2) particles are effectively stabilised against agglomeration by phosphonic acids, which strongly bind to the particles and lead to an increased compatibility of the inorganic particles with the organic polymers. This way, highly transparent nanocomposite materials with up to 20 wt% magnesium fluoride in different acrylates are obtained, featuring high dispersion of MgF(2) particles in the polymer matrix and an increased hardness by the factor of 2. The nature of interaction between phosphonic acids and magnesium fluoride is thoroughly investigated by IR and NMR showing a monodentate coordination of phosphonates to the particle's surface.

Room-Temperature Ferromagnetism in Co-Doped In2O3 Nanocrystals

Co-doped In2O3 nanocrystals showing room-temperature ferromagnetism have been successfully prepared by a simple sol−gel synthesis route. The sample displays a clear ferromagnetism behavior above 300 K. Phase and structure analyses reveal that the nanocrystals are crystallized with Co ions substituted for In ions in the In2O3 matrix, and no trace of secondary phases or clusters is detected. The experimental results are explained theoretically by first-principles calculations based on density functional theory, which indicate that the native ferromagnetic behavior of Co-doped In2O3 could be mainly ascribed to the strong d−d coupling of the magnetic ions.

Effect of magnesia on the degradability and bioactivity of sol–gel derived SiO 2–CaO–MgO–P 2O 5 system glasses

Mesoporous 58SiO 2–(38 − x)CaO– xMgO–4P 2O 5 glasses (where x = 0, 5, 10 and 20 mol%) have been prepared by the sol–gel synthesis route. The effects of the substitution of MgO for CaO on glass degradation and bioactivity were studied in tris-(hydroxymethyl)-aminomethane and hydrochloric acid buffer solution (Tris–HCl) and simulated body fluid (SBF), respectively. It is observed that the synthesized glasses with various MgO contents possess the similar textural properties. The studies of in vitro degradability and bioactivity show that the rate of glass degradation gradually decreases with the increase of MgO and the formation of apatite layer on glass surface is retarded. The influences of the composition upon glass properties are explained in terms of their internal structures.

A novel sol–gel synthesis route to NaVPO 4F as cathode material for hybrid lithium ion batteries

Sodium vanadium fluorophosphate, NaVPO 4F, a cathode material for hybrid lithium ion batteries has been synthesized via a modified sol–gel method followed by heat treatment. The vanadium (Ш) gel precursor as the reaction intermediate phase can be facilely prepared in ethanol under ambient conditions, and this synthesis considerably simplifies the conventional high-temperature fabrication of VPO 4. X-ray diffraction (XRD) results indicate a phase transition of NaVPO 4F from the monoclinic crystal to the tetragonal symmetry structure. Meanwhile, the scanning electron microscope (SEM) images show the obvious spatial rearrangements on the morphology of samples. The hybrid lithium ion batteries based on the tetragonal NaVPO 4F exhibit an even discharge plateau at 3.6 V vs. Li in the limited voltage range of 3.0–4.2 V, and the discharge capacity retention is up to 98.7% after 100 cycles at C/4 rate. With voltage excursion to 3.0–4.5 V, the initial charge and discharge deliver the reversible storage capacity of 117.3 and 106.8 mAh g −1, respectively. Furthermore, the prepared NaVPO 4F has a capacity retention of 83% after 100th cycle at 2 C rate. The electrochemical properties reveal the reversible mixed alkali ion (Li +, Na +) insertion reactions for this fluorophosphate material.

Laser-transfer processing of functional ceramic films

Pulsed excimer laser irradiation through a UV-transparent fabrication substrate has been successfully employed to separate PZT thick films from their sapphire host substrates. Films of 20 μm in thickness were prepared by a hybrid particle sol–gel synthesis route. The microstructure, morphology and ferroelectric properties of the thick films after laser-transfer have been examined. Films were irradiated with a 248 nm, 15 ns pulse, and transferred to a platinised silicon substrate (Pt/Ti/SiO 2/Si). A laser fluence of 250 mJ/cm 2 was sufficient to delaminate the original PZT/sapphire interface. The pulsed energy density used here is lower than reported by other groups utilising a laser-transfer process for PZT. This is believed to be due to higher levels of porosity at the film/substrate interface in this study.

Effects of Sol−Gel Synthesis on 5Fe−15Mn−40Zn−40Ti−O Mixed Oxide Structure and its H2S Removal Efficiency from Industrial Gas Streams

A novel Fe-Mn-Zn-Ti-O mixed metal oxide has been developed for efficient low-temperature (25-50 degrees C) removal of H2S from a gas mixture containing 600 ppm H2S, 25 vol% H2, 7.5 vol % CO2, and 1-3 vol% H2O that simulates typical conditions experienced at the outlet of a bioreactor loaded with sulfate metal reducing bacteria (SMRB) that converts toxic Cr6+ and As5+ present in ground and surface waters and soils into nontoxic elements. During the latter conversion H2S gas is produced and has to be treated. In the present work it is demonstrated for the first time that by using the sol-gel synthesis route at given experimental conditions (e.g., metal precursor salts, solvent system, and solution pH), optimum structural properties for the Fe-Mn-Zn-Ti-O solid can be obtained for maximization of H2S uptake. In particular, at 25 degrees C an H2S uptake (0.085 g H2S/g solid) larger by at least a factor of 3 compared to a commercial Ni-based H2S absorbent material was obtained.

Novel Ternary Composite Electrolytes: Li Ion Conducting Ionic Liquids in Silica Glass

In this contribution, we report on a novel composite solid electrolyte material, SiO2/[BMIM]BF4/LiTf ([BMIM]BF4 = 1-butyl-3-methylimidazolium tetrafluoroborate, LiTf = lithium trifluoromethanesulfonate), prepared via a one-pot sol−gel synthesis route, in which the amorphous SiO2 glass network provides the mechanical stability and the ionic liquid/Li salt part the high ionic conductivity (0.5 × 10−2 S cm−1 at 298 K). The mobility of the ionic liquid and Li salt confined within the pores of the fully condensed SiO2 network is found to increase with the [BMIM]BF4/LiTf ratio, exhibiting an almost liquidlike mobility, as evidenced by multinuclear solid-state NMR, pulsed-field-gradient solid-state NMR, and impedance spectroscopy.

Synthesis of Hybrid Adsorbents Combining Sol−Gel Processing and Molecular Imprinting Applied to Lead Removal from Aqueous Streams

Two high-capacity thiol functionalized adsorbents are prepared, using sol−gel processing, and applied to the removal of lead(II) from aqueous streams. The first adsorbent (SN) is prepared by co-condensing oligomers of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPS); the second adsorbent (MI) is synthesized by a combined co-condensation/molecular imprinting route of TEOS and MPS. The resulting physicochemical properties of adsorbents are investigated by nitrogen sorption measurements, elemental analysis, Fourier transform infrared spectroscopy (FTIR), solid-state 13C and 29Si cross-polarization magic angle spinning nuclear magnetic resonance (13C and 29Si CPMAS NMR, respectively), and X-ray photoelectron spectroscopy (XPS). The adsorbents exhibit high ligand densities (1.19 mmol/g for SN and 1.03 mmol/g for MI), improved Brunauer−Emmett−Teller (BET) surface areas (SBET = 129 m2/g for SN and 464 m2/g for MI), and highly developed mesoporosity (Dp = 15.1 nm for SN and 8.3 nm for MI). 29Si CPMAS NMR measurements indicate that the silicon oxide solid structure of adsorbents is not modified by lead adsorption. XPS results indicate the presence of lead acetate species on the surface of adsorbents. Batch adsorption data are explained by a mechanism in which a hydrated species (Pb(OOCCH3)(H2O)5+) forms a monodentate complex with thiol surface groups. Further characterization of the adsorbents shows rapid adsorption kinetics and equilibrium lead(II) adsorption capacities of 1.13 and 0.715 mmol/g for SN and MI. Lead adsorption dynamics in a packed column indicates high lead uptakes (155 and 80 mg Pb/g-adsorbent for SN and MI, respectively). Combined and simple sol−gel synthesis routes for preparation of adsorbents with high ligand densities and mesoporous structures are demonstrated here.

Local Structural Changes in Aluminum Isopropoxide Fluoride Xerogels and Solids as a Consequence of the Progressive Fluorination Degree

Different solid aluminum isopropoxide fluorides AlFx(OiPr)3−x with varying Al/F molar ratios (from 4:1 to 1:3) were synthesized following the fluorolytic sol−gel synthesis route. The subsequent characterization by multinuclear (27A1, 19F, 1H, and 13C) and multidimensional solid-state MAS NMR techniques enables the characterization of local structural features in these solids. The mechanism of the fluorolytic sol−gel process deduced earlier was strongly supported by following changes of the local structures in these compounds in dependence on their composition. For the first time, the existence of four-fold fluorine-coordinated Al species (AlF4) was proven as intermediates in the case of low fluorine supply. Additionally, a plausible pathway for the formation of monofluorinated Al3(OiPr)8F·D (DMSO, pyridine) is given, which was isolated as single crystals recently. The appropriate spectra point out that similar species exist also in powders of pyridine- and DMSO-free reaction mixtures.

The influence of HS-AlF 3 on the decomposition reaction of MgH 2

The influence of nanoscopic aluminium fluoride prepared via a sol–gel-synthesis route developed by our group on the thermal decomposition of MgH 2 used as hydrogen storage material has been comprehensively investigated. Combined XRD and MAS NMR experiments have been performed to follow structural changes in ball milled MgH 2/ HS-AlF 3 mixtures at thermal decomposition. Although the behaviour of Lewis acidic metal fluorides is discussed being catalytic, our results with HS-AlF 3 clearly give a different picture. We found strong evidence for a decrease of the decomposition temperature in combination with a significant acceleration of the decomposition rate; however, the action of at least AlF 3 is not catalytic in nature. As shown, a fluoride against hydride exchange is taking place, thus transforming AlF 3 irreversibly into AlH 3, which is followed by decomposition into metallic Al (MgAl alloy).

Photocatalytic Segmented Nanowires and Single-step Iron Oxide Nanotube Synthesis: Templated Electrodeposition as all-round Tool

AbstractTemplated electrodeposition was used to synthesize silver-zinc oxide nanowires and iron oxide (Fe2O3) nanotubes in polycarbonate track etched (PCTE) membranes. Metal/oxide segmented nanowires were made to produce hydrogen gas from a water/methanol mixture under ultraviolet irradiation. It was observed that gas production increased during irradiation. Iron oxide nanotubes were synthesized via a gel synthesis route, avoiding clogging of the membrane pores during growth. The nanotubes formed without thermal after-treatment. Transmission electron microscopy (TEM) analysis and selected area electron diffraction (SAED) revealed a completely amorphous iron oxide structure. By demonstrating the synthesis of photocatalytically active segmented nanowire and nanotubes without post-treatment steps, templated electrodeposition can be a versatile and low cost tool for nanowires with designed functionality or fast nanotube synthesis.

Sol–gel synthesis and photoluminescence of RE 3BO 6: Eu 3+/Tb 3+ (RE = Y, Gd) microcrystalline phosphors from hybrid precursors

Novel phosphors of Eu 3+/Tb 3+ doped RE 3BO 6 (RE = Y, Gd) have been prepared using an original modified in situ sol–gel synthesis route. Different optimized organic media were mixed with rare earth coordination polymers, and tri- n-butyl borate was added to assemble inorganic/organic multi-component hybrid precursors. After calcinations of the resulting precursors at 1000 °C, target phosphors were obtained. The microstructure and morphology information of the phosphors were investigated via the technique of X-ray powder diffraction (XRD) and scanning electronic microscopy, and it has been shown that these phosphors present symmetrical distribution and high packing density, whose grain sizes were around 200 nm. Analyzed by luminescent spectra, these phosphor particles show narrow lines of emissions respectively originating from their characteristic transitions, and the dominating emission peak is due to the hypersensitive transition. The RE 3BO 6: Eu 3+/Tb 3+ (RE = Y, Gd) phosphors can be expected to gain more practical applications in commercial phosphors and other luminescent materials used in advanced devices.

Preparation of optical axial GRIN components through migration of charged amorphous ZrO2 nanoparticles inside an organic–inorganic hybrid matrix by electrophoresis

A novel sol–gel synthesis route for the preparation of a transparent organic–inorganic nanocomposite was developed by combining methacrylic acid (MA) stabilized, amorphous ZrO2 nanoparticles, which were synthesized by the sol–gel process, with an organic–inorganic dodecandioldimethacrylate (DDDMA)/3-methacryloxypropyl trimethoxysilane (MPTS) hybrid matrix. The average hydrodynamic particle size was determined to be approximately 6nm by photon correlation spectroscopy. HR-TEM micrographs present irregular shaped zirconia particles with diameters up to 3nm. Nearly solvent-free nanocomposites with zirconium (Zr) contents up to 15.2mol% were synthesized and photochemically cured to transparent crack-free bulks. The surface charged nanoparticles in 1-propanol had an electrophoretic mobility of 0.017 (μmcm)/(Vs), measured by Laser Doppler Anemometry (LDA) and a refractive index ne of ⩾1.648±0.007 determined by spectroscopic ellipsometry. After filling the nanocomposite into a linear electrophoresis cell (1×1.6×0.8cm3), positively charged high refractive nanoparticles migrated through the low refractive hybrid matrix toward the cathode by the application of an electric potential difference of 2kV/cm for 96h. A 67% increase in Zr over a distance of 8mm between the cathode and anode was observed by high-resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDXS).

A micro-structured 5kW complete fuel processor for iso-octane as hydrogen supply system for mobile auxiliary power unitsPart I. Development of autothermal reforming catalyst and reactor

A micro-structured autothermal reformer was developed for a fuel processing/fuel cell system running on iso-octane and designed for an electrical power output of 5 kWel. The target application was an automotive auxiliary power unit (APU). The work covered both catalyst and reactor development. In fixed bed screening, nickel and rhodium were identified as the best candidates for autothermal reforming of gasoline. Under higher feed flow rates applied in microchannel testing, a catalyst formulation containing 1 wt.% Rh on alumina prepared by the sol–gel synthesis route proved to be stable at least in the medium term. This catalyst was introduced into the final prototype reactor designed to supply a 5 kW fuel cell, which was based upon micro-structured stainless steel foils. The reactor was optimised for equipartition of flows by numerical simulation. Testing in a pilot scale test rig, which was limited to a specified power equivalent of 3.5 kWel, revealed more than 97% conversion of gasoline at 124 Ndm3/min total flow-rate of reformate, which corresponded to a WHSV of 316.5 Ndm3/(h gcat).

Characterization of PbZrO 3 prepared using an alkoxide-based sol–gel synthesis route with different hydrolysis conditions

PbZrO 3 precursor powders were prepared from lead acetate and zirconium n-butoxide in n-butanol and hydrolysed with R w (molar ratio of water/lead acetate) = 2 and 15 at different pH values. Upon heating the organic groups were removed in two steps for the precursor prepared at R w = 2, and in one step at R w = 15. The perovskite phase crystallizes at approximately 700 °C, irrespective of the hydrolysis conditions.

Structural study of VO x doped aluminium fluoride and aluminium oxide catalysts

The structural properties of vanadium doped aluminium oxyfluorides and aluminium oxides, prepared by a modified sol–gel synthesis route, were thoroughly investigated. The influence of the preparation technique and the calcination temperature on the coordination of vanadium, aluminium and fluorine was analysed by different spectroscopic methods such as Raman, MAS NMR and ESR spectroscopy. In all samples calcined at low temperatures (350 °C), vanadium coexists in two oxidation states V IV and V V, with V IV as dominating species in the vanadium doped aluminium oxyfluorides. In the fluoride containing solids aluminium as well as vanadium are coordinated by fluorine and oxygen. Thermal annealing of 800 °C leads to an extensive reorganisation of the original matrices and to the oxidation of V IV to V V in both systems.

Mesoporous ZSM-5 catalysts: Preparation, characterisation and catalytic properties. Part I: Comparison of different synthesis routes

In an attempt to improve mass-transport limitations, mesopores were created in a series of ZSM-5 catalysts by the carbon-templating procedure. A successful low-cost dry gel synthesis route was developed which almost entirely removed the need for the organic structure-directing agent (TPA/SiO 2 = 0.0033). Both an aqueous colloidal graphite sol and a pyrogenic (carbon black) material were investigated, at addition levels of 16.5–100 wt.%. No major differences were observed between the two carbon sources. The addition of carbon to the synthesis composition retarded the crystallisation rate and modified the crystal morphology. The products were characterised by a variety of physical techniques. Additional post-synthesis treatment (alkaline leaching) extended the mesopore system but also tended to reduce crystallinity and micropore volume.

Ethane–silica hybrid material with ordered hexagonal mesoporous structure

An ordered mesoporous hybrid material, with ethane–silica framework, has been prepared by a sol–gel synthesis route involving the condensation of 1,2-bis(triethoxysilyl)ethane (BTEE) under basic conditions, in the presence of octadecyltrimethylammonium bromide (ODTMABr) as a structure directing agent. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and N 2 adsorption measurements show a hybrid material highly ordered at the mesoscale, uniform pore-size distribution and high surface area. 13C and 29Si MAS NMR analyses reveal that the ethylene group bridging two silicon nuclei remains intact both in prepared material and after solvent extraction of the surfactant template. The synthesis conditions have been studied, showing that the preparation conditions should accurately be defined to avoid the decomposition of BTEE and to obtain the ordered mesoporous hybrid material. The presence of TEOS as silica source together with BTEE has also been considered.

A fluoride-catalyzed sol–gel route to catalytically active non-ordered mesoporous silica materials in the absence of surfactants

A fluoride catalyzed route for the synthesis of catalytically active non-ordered mesoporous silica based materials in the absence of surfactants is presented and discussed. This synthesis procedure has allowed the introduction of different organic and inorganic functionalities with specific chemical activities within silica networks with well-tailored mesoporous distributions. Particularly, this sol–gel synthesis route has permitted the synthesis of Al- and Ti-containing mesoporous silica materials that have been found to be catalytically active for acid and redox processes, respectively. This synthetic approach has also allowed the preparation of hybrid organic–inorganic mesoporous materials.

A versatile sol–gel synthesis route to metal–silicon mixed oxide nanocomposites that contain metal oxides as the major phase

The general synthesis of metal–silicon mixed-oxide nanocomposite materials, including a variety of both main group and transition metals, in which the metal oxide is the major component is described. In a typical synthesis, the metal-oxide precursor, MClx·yH2O(x=2–6,y=0–7), was mixed with the silica precursor, tetramethoxysilane (TMOS), in ethanol and gelled using an organic epoxide. The successful preparation of homogeneous, monolithic materials depended on the oxidation state of the metal as well as the epoxide chosen for gelation. The composition of the resulting materials was varied from M/Si=1–5 (mol/mol) by adjusting the amount of TMOS added to the initial metal-oxide precursor solution. Supercritical processing of the gels in CO2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 100–800m2g−1. The bulk materials are composed of metal oxide/silica particles that vary in size from 5–20nm depending on the epoxide used for gelation. Metal oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The versatility and control of the synthesis method will be discussed as well as the properties of the resulting metal–silicon mixed oxide nanocomposite materials.