The photodynamics of the [Ru(bpy)<Subscript>3</Subscript>]<Superscript>2+</Superscript> ion dopant in a solvent exposed silica sol–gel thin film

The [Ru(bpy)₃]²⁺ ion was encapsulated in a silica based sol–gel thin film, and the luminescence decay time constant of the photo-excited ³MLCT (metal-ligand-charge-transfer) was examined when this thin film was immersed in water, methanol, ethanol, 2-propanol, and glycerol. The luminescence decays of the films in the methanol, 2-propanol, and glycerol were better explained by a KWW model, while the luminescence decay of film immersed in water and ethanol were both well explained by a single exponential decay. Intriguingly, the dynamics of the dopants immersed in water, ethanol as well as in sol–gel bulk deviated from a single exponential fit and began to better explained by the the KWW model as temperature increased. The energy gap, ΔE(sol–gel film) and ΔE(solution), between the lowest ³MLCT state and atom localized ³ dd state for dopants under the presence of all solvents tested in this study were extracted from the temperature dependence study of the luminescence decay time constant. Generally, the ΔE(sol–gel film) values of ethanol and water were reduced from ΔE(solution), and ΔE(sol–gel film) value in all solvents matched the value of ΔE for sol–gel bulk. The effect on the dynamics in solvent over three weeks was investigated, and the films immersed in water presented the most remarkable monotonic increase in relaxation rates finally approaching the asymptotic value observed in the water solution. This phenomenon was considered to correspond to a trapping environment change due to a hydrophilic interaction through sequential intrusion of water or ethanol solvent into sol–gel pores.     

Luminescent characteristics and microstructures of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> phosphors prepared via sol–gel and solid-state reaction routes

Blue-light-emitting Sr₂CeO₄ phosphors were synthesized via a sol–gel process and the conventional solid-state method in this study. The developed sol–gel process lowered the synthesis temperature of monophasic Sr₂CeO₄ to as low as 900 °C. In comparison with the solid-state derived powders, the sol–gel derived powders had more uniform morphology and smaller particle sizes. In addition, sol–gel derived Sr₂CeO₄ displayed higher luminescent intensity than that prepared via the solid-state route under the same heating conditions. This is attributed to the improved compositional homogeneity and crystallinity in the sol–gel process. During the heating processes, Sr₂CeO₄ tended to thermally decompose at elevated temperatures. This decomposition reaction resulted in the formation of an impurity phase- SrCeO₃ and thereby a decrease in the luminescent intensity. For obtaining Sr₂CeO₄ phosphors with high luminescent intensity, the heating conditions in both processes need to be well modulated.     

Energy efficiency evaluation of lipid production by oleaginous yeast <Emphasis Type="Italic">Rhodosporidium toruloides</Emphasis>

The thermodynamics of aniline adsorption from aqueous solution on polyvinyl alcohol Sn(IV) tungstate nano composite cation-exchanger was studied. The nano composite cation-exchanger was prepared by surfactant assisted sol–gel precipitation method and characterized to elucidate the morphology, particle size, crystallinity and structure using SEM, TEM, X-RAY and FTIR. The nano composite cation-exchanger possessed flakes like morphology with particle size in the nano range. The analytical applicability and thermodynamic parameters like ΔH, ΔG and ΔS of this nano composite were also calculated. The thermodynamic parameters showed that the adsorption of aniline onto nano composite cation-exchanger is feasible, spontaneous and exothermic.     

Optimization in the immobilization of penicillin G acylase by entrapment in xerogel particles with magnetic properties

Biocatalysis presents a sound alternative to chemical synthesis in the field of drug production, given the highly selective nature of biological catalysts. Penicillin G Acylase (PGA) from E. coli is currently used to hydrolyze penicillin G (PG) and catalyzes the synthesis of β-lactam antibiotics. In this work, particular emphasis is given to recent developments in penicillin G acylase immobilization, by entrapment simultaneously with nano-magnetic particles in a silica matrix. The sol–gel biocatalytic particles were prepared either by a conventional method (crushed powder) or by a more recent approach, based in an emulsion system using 150 mM AOT/isooctane, which allowed for the formation of spherical micro- and nanobeads. The effects on PGA activity of different sol–gel precursors, additives, enzyme concentration, aging, drying conditions and mechanical stability were evaluated. After these optimization studies, a mechanically stable carrier based on porous xerogels silica matrixes, starting from tetramethoxysilane (TMOS) with 65–67% PGA activity yield in these carriers allowed an immobilization yield of 74 mg protein g_{dry sol–gel}⁻¹ and 930 Ug_{dry sol–gel}⁻¹ for specific activity were obtained.     

Synthesis,characterization and in vitro cytotoxicity of Pt-TiO<Subscript>2</Subscript> nanoparticles

The adverse toxicological profile of cisplatin (cis-dichlorodiammineplatinum (II)), characterized by nephrotoxicity and neurotoxicity is the main factor that limit the clinical usefulness of this antineoplastic drug, specifically the possibility of applying it in effective high-dose regimens. In order to overcome these disadvantages, many efforts in the search for new drugs have been made. Due to this particularity, we obtained via sol–gel process Pt(acac)₂–TiO₂ (NPt) nanostructured materials with antitumoral activity to be used as an alternative in the treatment of cancer tumors. The biocatalysts were prepared by the sol–gel route using the complex Pt(acac)₂. Sol–gel parameters were controlled in order to obtain high platinum dispersion and particles in the nano-size range. TEM, FTIR, N₂ adsorption and XPS characterization studies of the samples were carried out. In order to investigate interactions between the biocatalyst and DNA, agarose gel electrophoresis was performed, and we observed the formation of DNA adducts. 45 minutes after contact, NPt completely degraded the DNA (cisplatin 120 minutes). These results demonstrate that using a metal supported and dispersed over an inorganic biocompatible oxide, can be effectively used in the treatment of localized tumors.     

Comparison of different soft chemical routes synthesis of submicro-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and their influence on its electrochemical properties

A comparative study of submicro-crystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as hydrothermal and sol–gel methods is made. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammogram, charge–discharge test, and electrochemical impedance spectroscopy (EIS). The results show that the electrochemical performances of spinel LiMn₂O₄ depend strongly upon the synthesis method. The LiMn₂O₄ powder prepared by hydrothermal route has higher specific capacity and better cycling performance than the one synthesized from sol–gel method. The former has the max discharge capacity of 114.36 and 99.78 mAh g⁻¹ at the 100th cycle, while the latter has the max discharge capacity of 98.67 and 60.25 mAh g⁻¹ at the 100th cycle. The selected equivalent circuit can fit well the EIS results of synthesized LiMn₂O₄. For spinel LiMn₂O₄ from sol–gel method and hydrothermal route in the first charge process R _SEI remain almost invariable, R _e and R _ct first decreasing and then increasing with the increase of polarization potential.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Morphology and photoluminescence study of titania nanoparticles

Titania nanoparticles are prepared by sol–gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol–gel components—hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer—are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol–gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13–20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies.     

Surfactant assisted preparation and characterization of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger

Carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger with diameter in the range of 20–40 nm, length in the range of 100–150 μm and particle size in the range of 21–38 nm have been successfully prepared by surfactant assisted sol–gel method. Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, fourier transform infra red spectroscopy and thermogravimetric analysis-differential thermal analysis studies were carried out to study the structure and morphology of this composite nano-rod like cation exchanger. Freundlich adsorption isotherm is well fitted for the adsorption of pyridine on the surface of this composite nano-rod like cation exchanger. The thermodynamic parameters such as Freundlich constant, thermodynamic equilibrium constant (K ₀), standard free energy changes (ΔG ⁰), standard enthalpy changes (ΔH ⁰) and standard entropy changes (ΔS ⁰) have been evaluated. These parameters indicated that the adsorption of pyridine on the surface of composite nano-rod like cation exchanger was feasible, spontaneous and exothermic in nature which suggests for the potential application of pyridine removal from water.     

UV/Vis Spectroscopic Properties of <Emphasis Type="Italic">N</Emphasis>-(2′-Hydroxy-4′-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

Summary.  N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift. Corresponding author. E-mail: stefan.spange@chemie.tu-chemnitz.de Received July 8, 2002; accepted (revised) September 30, 2002     

Micro structural investigations on TNT and PETN incorporated silica xerogels

Silica xerogels incorporated with trinitrotoluene (TNT) and pentaerythritoltetranitrate (PETN) were synthesized using sol–gel method. Tetramethoxysilane was used as precursor for silica. TNT and PETN content in the resulted explosive/silica xerogel was varied ranging from 50 to 90%. Infra red spectra showed that explosives were retained in the silica xerogel matrix. Transmission electron microscopy (TEM) reveal that explosives particles were uniformly distributed in xerogel matrix and the size of the PETN and TNT particles are in the range 15–18 nm. Small angle x-ray scattering showed that the sizes of the pores in the silica matrix are in the range 25–13 nm. The particles of TNT and PETN occupy the pores in the matrix resulting in gradual reduction of pore-size affecting the surface characteristics of the pore-matrix interface. Understanding of the structure of aggregates of small particles thus produced could be useful to explain the properties shown by the fine explosives. Our study suggests that particle size of explosives in the nanometer range can be achieved using the sol–gel method.     

CAM sol–gel synthesized LiMPO<Subscript>4</Subscript> (M=Co,Ni) cathodes for rechargeable lithium batteries

The emerging category cathode candidates such as LiCoPO₄ and LiNiPO₄ were synthesized at 800 °C using Citric acid assisted modified sol–gel (CAM sol–gel) method and examined for possible lithium intercalation behavior. Compound formation temperature is confirmed from thermogravimetry and differential thermal analysis (TG/DTA). Powder X-ray diffraction (PXRD) pattern evidenced the absence of undesirable peaks and confirmed the formation of phase pure LiMPO₄ (M=Co, Ni) compounds with an orthorhombic structure and finer crystallite size. Presence of nanosized particles as observed from TEM image of LiCoPO₄ and the presence of preferred local cation environment as understood from FT–IR studies are the added advantages of CAM sol–gel synthesis. Further, Cyclic voltametry (CV) and Impedance spectroscopy (EIS) studies performed on the synthesized LiCoPO₄ and LiNiPO₄ cathodes revealed excellent reversibility and structural stability of CAM sol–gel synthesized cathodes, especially upon storage as well as during cycling.     

Microstructure and Photocatalytic Property of SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> Under Various Process Condition

Nanophase silica-titania particles were prepared by two different synthetic routes, namely, sol–gel and hydrothermal processing. The crystallinity and crystallographic phases, particle size and surface area of the materials were controlled by varying the calcination temperature, and/or the ratio of Si to Ti. It was determined by XRD that the crystallite sizes of SiO₂-TiO₂ prepared by sol–gel and hydrothermal processing decreased from 11 to 6 nm and 12 to 9 nm, respectively, as the mole fraction of silica was increased from 0.1 to 0.4. It is proposed that the presence of the amorphous silica suppresses the growth of anatase TiO₂ grains and their phase transformation to rutile. The photocatalytic decomposition rate of 1,4-dichlorobenzene (DCB) in aqueous solution with the sol–gel derived SiO₂-TiO₂ powder prepared at 750 °C was about 10 ± 5% higher than that observed with Degussa P25, whereas the SiO₂-TiO₂ samples prepared by hydrothermal processing at 250 °C showed a slightly lower decomposition rate than P25.     

Alumina cryogels with superior thermal stability for catalyst supports

Alumina cryogels were synthesized from a colloidal boehmite sol through a sol–gel processing and subsequent freeze drying, and thermal stability was examined by comparison to that of the corresponding xerogel, precipitate and commercial alumina. N₂ adsorption, X-ray powder diffraction and transmittance electron micrography observations revealed that the stability was higher for the cryogel than for others in particular at temperatures above 1,000 °C. The higher stability was ascribed to the fine and uniform primary particles with fibrous shapes formed by the sol–gel technique and furthermore to the suppression of aggregation of the primary particles owing to the subsequent freeze drying. It was also found that aluminum sec-butoxide employed as a precursor for the preparation of boehmite sol was preferable compared to aluminum iso-propoxide.     

Sol–gel matrices for controlled release: from macro to nano using emulsion polymerisation

By combining sol–gel technology with emulsion chemistry, it is possible to produce spherical particles with a designed microstructure based on a judicious choice of solvent/surfactant and sol–gel reaction parameters. When an active molecule is located in the aqueous droplet of a water-in-oil (W/O) emulsion, encapsulation occurs as the silicon precursors polymerise to build an oxide cage around the active species. By changing the solvent–surfactant combination, the particle size can be varied from 10 nm to 100 μm. The size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol–gel reaction. The release profiles can be tailored, independently of the particle size, by controlling the internal structure of the particles: pore volume, pore size, tortuosity, and surface chemistry (e.g. by introduction of trialkoxysilane). This can be easily achieved by controlling sol–gel processing parameters such as the water-to-alkoxide ratio, pH, alkoxide concentration, ageing, drying time and temperature. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

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.     

Sol–gel immobilization of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> on hydrophobic clay and its removal of methyl orange from water

In this study, SiO₂/TiO₂–organoclay hybrids with high adsorption capability and high photocatalytic activity were synthesized by immobilizing mixed silica and titanium dioxide nanoparticles on organically modified clay via a hydrothermal sol–gel method. Addition of negatively charged silica particles enhanced the uniform dispersion of titanium dioxide nanoparticles on organoclay layers by decreasing the system tension, which resulted in high photocatalytic activity of SiO₂/TiO₂–organoclay hybrids. The high adsorption capability endowed by organically modified clay enriched the organic compounds around the photoactive sites, and thus greatly improved the photodegradation efficiency. Combining the high adsorption capability of organoclay with the high photocatalytic activity of TiO₂ nanoparticles, SiO₂/TiO₂–organoclay hybrids were promising and cost-effective photocatalysts in removal of pollutants from wastewater.     

Sol–gel encapsulation of acid phosphatase in the presence of the ionic liquid [BMIM][BF4]

Abstract  

The effect of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) on acid phosphatase (APase) from wheat germ in solution and in the sol–gel-encapsulated form was investigated to explore new methods of enzyme preparation with improved catalytic performance. APase was encapsulated in hydrogel beads made from tetramethyl orthosilicate. Compared with free APase, 20–28% enzymatic activity was retained in over nine catalytic cycles. Sol–gel encapsulation improved the thermal stability of APase. Heat shock exposure at 60 °C for 1 h resulted in activity decreasing by a factor of three, only, for sol–gel-encapsulated APase, in contrast with a factor of nine decrease for free APase. Addition of 10% v/v [BMIM][BF₄] did result in a slight decrease of enzymatic activity for free and sol–gel-encapsulated APase, but resulted in a remarkable increase in alkaline pH tolerance of sol–gel-encapsulated APase.     

Preparation and characterization of SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Na<Subscript>2</Subscript>O glass coated cBN abrasive particles via sol–gel route

SiO₂–Al₂O₃–Na₂O glass coated cubic boron nitride (cBN) abrasive particles were prepared by sol–gel technique. The results indicated that SiO₂–Al₂O₃–Na₂O glass was excellent material for oxidation protection of cBN abrasive grains because coefficient of thermal expansion of this glass closely matched that of cBN materials. The single particle compressive strength and impact toughness of this glass coated cBN abrasive particles were significantly increased. For the application of glass coated cBN abrasives to vitrified grinding wheels, it was evident that the glass coating provided high bonding strength between cBN abrasive grains and vitrified bond system.     

Structural and morphological characteristics of polycrystalline BaTiO<Subscript>3</Subscript>:Er<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> ceramics synthesized by the sol–gel route: influence of chelating agents

The preparation of a co-doped BaTiO₃:Er, Yb compound was investigated using alkoxide precursors. The complex alkoxide was hydrolyzed under specific conditions using chelating agents [(AcAc)H and H–(OAc)], and nano-size powders and films of perovskite compounds were obtained. The nanostructure materials were formed through nucleation-aggregation growth. Through a comparison of co-doped BaTiO₃:Er, Yb compounds (with and without chelating agents), important differences in shape and size of the particles were found. In addition, the use of chelating agents during the sol–gel process allowed us to obtain optical BaTiO₃:Er, Yb thin films. The results suggest that the particle size and shape can be tailored in the current system by manipulating the simultaneous use of chelating agents and the crystallization temperature. Consequently, a wide range of particle size has an effect on the crystal structures.