Glycol Medium Research Articles

Lifetime and quantum yield studies of Dy3+ doped GdVO4 nanoparticles: Concentration and annealing effect

GdVO 4 nanoparticles doped with Dy3+ have been prepared using urea hydrolysis method in ethylene glycol medium. Linear decrease in the unit cell volume indicates the quantitative substitution of Gd3+ lattice sites by Dy3+ in GdVO4. The luminescence intensity of electric dipole transition at 573 nm is more than that of magnetic dipole transition at 483 nm. This has been attributed to the asymmetric environment of Dy3+ ion in GdVO4. Luminescence intensity decreases with increasing Dy3+ concentrations due to concentration quenching. This is supported by lifetime decay studies. There is no particle size effect on the peak positions of Dy3+ emission. There is an increase in the decay lifetime for F49/2 level with increase in heat treatment from 500 to 900 °C. This is attributed to the reduction in nonradiative process arose from surface inhomogeneities. The decay lifetime data follow the biexponential to monoexponential nature with increase of Dy3+ concentrations. There is an increase in the quantum yield with the increase in heat treatment temperature.

Nanoscale assembly of amine-functionalized colloidal iron oxide

We demonstrate a single-step facile approach for highly water-stable assembly of amine-functionalized Fe 3O 4 nanoparticles using thermal decomposition of Fe-chloride precursors in ethylene glycol medium in the presence of ethylenediamine. The average size of nanoassemblies is 40±1 nm, wherein the individual nanoparticles are about 6 nm. Amine-functionalized properties are evident from Fourier transform infrared spectrometer (FTIR), thermal and elemental analyses. The saturation magnetization and spin-echo r 2 of the nanoassemblies were measured to be 64.3 emu/g and 314.6 mM −1 s −1, respectively. The higher value of relaxivity ratio ( r 2/ r 1=143) indicates that nanoassemblies are a promising high-efficiency T2 contrast agent platform.

Al nanoparticles: Impact of media and current on the arc fabrication

To optimize the arc fabrication of aluminum nanoparticles (Al Nps), six diverse media were probed including ethylene glycol (EG), distilled water, liquid nitrogen, gaseous nitrogen, sunflower oil, and tap water (all free of any surfactant or stabilizer). These were investigated at three different currents: 50, 100 and 150 A/cm 2. EG at 50 A/cm 2 provides the best recipe for the arc fabrication, giving the relatively purest, most dispersed and the smallest size Al Nps (26.6 nm), with the highest yield (91.5 %). Regardless of the medium used, the SEM analyses show that the size increases of Al Nps are directly proportional to the current density employed. The observed sizes for Al Nps in EG (at three different currents/A cm - 2) are 26.6 nm (50), 64.9 nm (100), and 72.5 nm (150). Also, regardless of the current employed, the SEM analyses show different Al Nps size distributions, depending on the medium nature. The XRD extracted average sizes of the arc fabricated Al Nps show reasonable linear correlations with their corresponding elemental weight% or atomic%, acquired through energy-dispersive X-ray spectroscopy (EDX). High quantities of separable industrially significant nanoAl oxides (γ-Al 2O 3, Al(OH) 3) are fabricated along with Al Nps in tap water. In EG medium, TGA revealed only ∼7% weight loss, indicating thermal stability of the fabricated Al Nps.

Effect of the degree of cross-linking on the properties of different CLEAs of penicillin acylase

Cross-linked enzyme aggregates (CLEAs) are novel type biocatalysts well suited to catalyze reactions of organic synthesis. Penicillin acylase is a versatile enzyme that can both hydrolyze and synthesize β-lactam antibiotics. CLEAs and CLEAs covered with polyionic polymers (polyethyleneimine and dextran sulfate at two different enzyme to polymer ratios) were prepared at varying cross-linking agent to enzyme ratio: 0.15 and 0.25. Results are presented on the effect of such variables on immobilization yield, specific activity, stability and performance of penicillin acylase CLEAs in the kinetically controlled synthesis of cephalexin. The cross-linking agent to enzyme ratio had no significant effect on the specific activity of the CLEAs, but affected immobilization yield, stability in ethylene glycol medium and conversion yield and productivity in the synthesis of cephalexin, being always higher at the lower cross-linking agent to enzyme ratio. Best results were obtained with CLEAs at 0.15 glutaraldehyde to enzyme protein ratio: specific activity of hydrolysis and synthesis was 708 and 325 UI/g CLEA respectively, conversion yield was 87%, specific productivity was 5.4 mmol cephalexin/(g CLEA·h) and 90% of the enzyme remained active after 170 h at operating conditions.

Luminescence Studies on Low Temperature Synthesized ZnGa2O4:Ln3+ (Ln = Tb and Eu) Nanoparticles

ZnGa2O4 nanoparticles doped with lanthanide ions (Tb3+ and Eu3+) were prepared at a low temperature of 120 degrees C based on urea hydrolysis in ethylene glycol medium. X-ray diffraction studies have confirmed that strain associated with nanoparticles changes as Tb3+ gets incorporated in the ZnGa2O4 lattice. Based on steady state emission and excitation studies of ZnGa2O4:Tb nanoparticles, it has been inferred that ZnGa2O4 host is characterized by a broad emission around 427 nm and there exists energy transfer between the host and Tb3+ ions. Unlike this, for ZnGa2O4:Eu nanoparticles, very poor energy transfer between the host and Eu3+ ions is observed. These nanoparticles when coated with ligands like oleic acid results in their improved dispersion in organic solvents like chloroform and dichloromethane.

Viscoelastic and Shear Viscosity Studies of Colloidal Silica Particles Dispersed in Monoethylene Glycol (MEG), Diethylene Glycol (DEG), and Dodecane Stabilized by Dodecyl Hexaethylene Glycol Monoether (C12E6)

Silica dispersions stabilized by a nonionic surfactant, dodecyl hexaethylene glycol monoether (C 12E 6), were studied using rheological measurements. The viscosity-shear rate flow behavior of silica in monoethylene glycol (MEG) is shear thinning at low shear rates, leading to a Newtonian plateau at high shear rates for all dispersions studied. All rheological properties showed an increase above a critical surfactant concentration. The dispersions were stable at low levels of C 12E 6 concentrations because of electrostatic repulsions as deduced from the zeta potentials of silica that were on the order of about -30 to -65 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high-molecular-weight polymers, was observed in MEG. Viscoelatic measurements of silica in monoethylene glycol at various surfactant concentrations showed a predominantly viscous response at low frequency and a predominantly elastic response at high frequencies, indicative of weak flocculation. Instability is explained in terms of hydrophobic and bridging interactions. Restabilization observed at high surfactant concentration was due to the steric repulsion of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion that moderated rheological measurements in glycol media and introduced the charge reversal of silica particles in dodecane.

Dispersion properties of silica particles in nonaqueous media with a non-ionic surfactant, dodecyl hexaethylene glycol monoether, C 12E 6

An experimental programme is described that evaluated the role of charge and steric stabilisation in glycol and dodecane dispersions of colloidal silica particles on addition of trace water and acid. The surfactant used for steric stabilisation was a non-ionic surfactant, Dodecyl hexaethylene glycol monoether, C 12E 6 with a geometric head-to-tail length of 3.85 nm. The study showed using the self-consistent field theory of adsorption (SCFA), electrophoresis and electroacoustic sonic amplitude (ESA), that the C 12E 6 molecules adsorbed with the ethoxy group attached to the silica surface and the alkyl group in the bulk glycol solution. The thickness of the adsorbed layer as estimated from electrophoretic and viscosity measurements was found to be 8 and 10 nm, respectively, indicative of globular aggregation. The dispersions were stable at low levels of C 12E 6 concentrations due to electrostatic repulsions as deduced from the zeta potentials of silica which were of the order of about −30 to −50 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high molecular weight polymers, was observed in MEG. Critical flocculation concentrations of C 12E 6, ϕ floc, increased with decrease in volume fraction of the silica particles in MEG. Instability is suggested to be from bridging interactions. Restabilisation observed at high surfactant concentration was due to steric repulsions of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion which moderated rheological measurements in glycol media and introduced reversal of charge of silica particles in dodecane.

Re-Dispersible Li+ and Eu3+ Co-Doped Nanocrystalline ZnO: Luminescence and EPR Studies

Nano-crystals of ZnO, Eu3+ doped ZnO, and Li+, Eu3+ co-doped ZnO have been prepared by urea hydrolysis in ethylene glycol medium at 150 degrees C. Ethylene glycol acts as capping agent for nanoparticles. Three colors 437 (blue), 540 (green) and 615 nm (red) from 2 at.% Li+ and 5 at.% Eu3+ co-doped ZnO have been observed from luminescence studies compared to that from 5 at.%. Eu3+ doped ZnO, which shows emission at 437 and 615 nm. It is established that green light is originated from the oxygen vacancy brought by Li+ incorporation into ZnO. Particles are redispersible in organic solvent such as ethanol, and are able to incorporate into polymer-based material such as SiO2 matrix.

Synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes

Fe-, Y-Fe-Al- and Y-Ce-Fe- citrates were synthesized in ethylene glycol (EG) medium under conditions similar to those used in the polymerized complex method. Their elemental composition, IR, 13C and 1H NMR, X-ray photoelectron and Mössbauer spectra were studied, and formulae describing their composition were proposed. The complexes contained EG bonded as adduct and ester with citric acid ligand and did not contain ligands with deprotonated alcoholic groups. The complexes consisted of agglomerated spheres, 0.7–3μm in diameter. The local composition of the products was established by energy dispersive X-ray microanalysis. The comparison of the number of the ligands, their average electrical charge and the esterification degree of mono-, di- and trimetallic complexes proved the mixed-metal nature of the species studied. The thermal decomposition of the complexes was studied and a general scheme of the processes taking place was proposed. Highly crystalline, phase homogeneous Y 3Fe 4AlO 12 was produced after heating the respective complex at 1000 °C. Ce-doped yttrium-iron garnet, similarly prepared, contained traces of CeO 2.

Synthesis of malachite nanoparticles and their evolution during transmission electron microscopy

Malachite nanoparticles have been synthesized utilising the polyol-mediated synthesis. Reaction of copper sulphate with sodium carbonate in ethylene glycol medium results in the formation of malachite nanoparticles of sub-10 nm dimensions. The structure of malachite in the synthesized product was confirmed by X-ray diffraction and FTIR spectroscopy. Examination by high-resolution transmission electron microscopy revealed that nanoparticles are thermally decomposed to Cu 2O and copper during exposure to the electron beam.

Luminescence Properties of SnO2 Nanoparticles Dispersed in Eu3+ Doped SiO2 Matrix

Multiwall carbon nanotubes (MWNT) were melt-mixed with poly(ethylene-co-methacrylic acid) ionomers (Surlyn) using twin screw microcompounder. The specific interactions existing between the Na+ moieties in Surlyn and the pi electron clouds of MWNT were supported by FTIR and Raman spectroscopic analysis. SAXS scattering patterns were found to be progressively broadened in presence of MWNT in Surlyn/MWNT composites. Morphological investigations revealed selective clustering of MWNT in the vicinity of the ionic domains in Surlyn. Further, the domain size of the ionic clusters was found to increase with increasing MWNT content disrupting the ionic pairs apart in the ionic domain. The melt rheological response of Surlyn was significantly affected in presence of MWNT and was profoundly dependent on the ionic clusters. The state of dispersion of MWNT was assessed by AC electrical conductivity measurements. The associated percolation threshold was observed between 1.5-2 wt% of MWNT.

Luminescence Properties of SnO2 Nanoparticles Dispersed in Eu3+ Doped SiO2 Matrix

SnO2 nanoparticles dispersed in Eu3+ doped silica (SnO2-SiO2:Eu3+) were prepared at a low temperature (185 degrees C) in ethylene glycol medium. Transmission electron microscopy studies on as-prepared samples have established that SnO2 nanoparticles having size of 4.6 nm are uniformly covered by the SiO2 matrix. Significant extent of exciton mediated energy transfer between SnO2 and Eu3+ ions in heat treated SnO2-SiO2:Eu3+ samples has been attributed to the diffusion of Eu3+ ions from the SiO2 matrix to the near vicinity of SnO2 nanoparticles and its incorporation in the SnO2 matrix. On the other hand, very weak energy transfer exists for SnO2:Eu3+ nanoparticles heated at different temperatures due to the phase segregation of Eu3+ ions from the matrix.

Re-dispersible Li+ and Eu3+ co-doped CdS nanoparticles: Luminescence studies

Re-dispersible CdS, 5 at.% Eu3+-doped CdS, 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS nanoparticles in organic solvent are prepared by urea hydrolysis in ethylene glycol medium at a low temperature of 170°C. CdS nanoparticles have spherical shape with a diameter of ∼80 nm. The asymmetric ratio (A21) of the integrated intensities of the electrical dipole transition to the magnetic dipole transition for 5 at.% Eu3+-doped CdS is found to be 3.8 and this ratio is significantly decreased for 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS (A21 = 2.6). It establishes that the symmetry environment of Eu3+ ion is more favored by Li-doping. Extra peak at 550 nm (green emission) could be seen for 2 and 5 at.% Eu3+ co-doped CdS. Also, the significant energy transfer from host CdS to Eu3+ is found for 5 at.% Eu3+-doped CdS compared to that for 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS.

Vapor-phase Hydrosilylation Using a Transition Metal Complex Catalyst in a Liquid Polymer Medium Supported on Silica Gel

Transition metal catalysts in various liquid polymer media supported on silica gel were prepared and used for vapor-phase hydrosilylation. Tetraammineplatinum(II) chloride and potassium hexachloroplatinate(IV) in a polyethylene glycol (PEG) medium showed high and stable activity. Deactivation of the catalyst was not observed unless a high platinum concentration in PEG was used. When the amount of PEG was 40 vol% of the pore volume of silica gel, PEG was coated on the pore walls of the silica gel, and did not block the pore openings. Active species in the PEG were formed only during the reaction.

Luminescence study on Eu3+ doped Y2O3 nanoparticles: particle size, concentration and core–shell formation effects

Nanoparticles of Eu3+ doped Y2O3 (core)and Eu3+ dopedY2O3 coveredwith Y2O3 shell(core–shell) are prepared by urea hydrolysis for 3 h in ethylene glycol medium at a relatively low temperature of140 °C, followed byheating at 500 and 900 °C. Particle sizes determined from x-ray diffraction and transmissionelectron microscopic studies are 11 and 18 nm for 500 and900 °C heated samples respectively. Based on the luminescence studies of 500 and900 °C heated samples, it is confirmed that there is no particle size effect on the peak positions ofEu3+ emission, and optimum luminescence intensity is observed from the nanoparticles with aEu3+ concentration of 4–5 at.%. A luminescence study establishes that theEu3+ environment in amorphousY (OH)3 is different from that incrystalline Y2O3. For a fixedconcentration of Eu3+ doping,there is a reduction in Eu3+ emission intensity for core–shell nanoparticles compared to that of core nanoparticles, and thishas been attributed to the concentration dilution effect. Energy transfer from the host toEu3+ increases with increase of crystallinity.

Microwave-assisted rapid synthesis of anisotropic Ag nanoparticles by solid statetransformation

Anisotropic silver nanoparticles (NPs) have been synthesized rapidly using microwaveirradiation by the decomposition of silver oxalate in a glycol medium using polyvinylpyrolidone (PVP) as the capping agent. The obtained Ag nanoparticles havebeen characterized by UV–visible spectroscopy, powder x-ray diffraction (XRD),transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies.Anisotropic Ag nanoparticles of average size around 30 nm have been observed in thecase of microwave irradiation for 75 s whereas spherical particles of a size around5–6 nm are formed for 60 s of irradiation. The texture coefficient and particle sizecalculated from XRD patterns of anisotropic nanoparticles reveal the preferentialorientation of (111) facets in the Ag sample. Ethylene glycol is found to be amore suitable medium than diethylene glycol. A plausible mechanism has beenproposed for the formation of anisotropic Ag nanoparticles from silver oxalate.

The chemistry of the processes involved in the production of lanthanide titanates by the polymerized-complex method

The composition, some spectral characteristics, and thermal decomposition of solid lanthanide–titanium (lanthanide (Ln) = Y, La, Ce) and lanthanide–titanium citrates (CA) and tartrates (TA) have been studied. The complexes have been prepared in ethylene glycol medium at conditions modeling those of the polymerized-complex method applied for Ln2Ti2O7 preparation. Special attention has been paid to the chemical nature of the bimetallic products as well as to the factors influencing the deprotonation of the alcoholic OH groups of the acidic ligands. The results contribute to further elucidation of the complexation and thermal decomposition processes involved in the polymerized-complex method.Key words: inorganic compounds, sol–gel chemistry, infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis (TGA).

SnO 2:Eu nanoparticles dispersed in silica: A low-temperature synthesis and photoluminescence study

SnO 2:Eu and SnO 2:Eu nanoparticles dispersed in silica matrix were prepared at a relatively low temperature of 185 °C in ethylene glycol medium. For as-prepared SnO 2:Eu nanoparticles there exists a weak energy transfer from the SnO 2 host to the Eu 3+ ions. However, the energy transfer can be significantly improved by dispersing the Eu 3+-doped SnO 2 nanoparticles in silica matrix. Effective shielding of surface Eu 3+ ions in SnO 2:Eu nanoparticles from the stabilizing ligand by silica matrix is the reason for the improved extent of energy transfer. Increase in asymmetric ratio of luminescence (ratio of the intensity of the electric dipole allowed transition, 5D 0→ 7F 2, to magnetic dipole allowed transition, 5D 0→ 7F 1) for SnO 2:Eu nanoparticles dispersed in silica compared to that of SnO 2:Eu nanoparticles, has been attributed to the distorted environment around surface Eu 3+ ions brought about by the presence of both tin and silicon structural units. 119Sn and 29Si MAS NMR studies on this sample confirmed that there is no interaction between the tin and silicon structural units even after heating the samples at 900 °C.

Synthesis of cephalexin with immobilized penicillin acylase at very high substrate concentrations in fully aqueous medium

The presence of organic cosolvents was previously considered necessary to obtain high conversion yields in the synthesis of β-lactam antibiotics with immobilized penicillin acylase, and it is so when working at moderate substrate concentrations. Conversion yields close to stoichiometric and high productivities were recently reported for the synthesis of cephalexin at high substrate concentrations in ethylene glycol medium. Under such conditions, the effect of cosolvent concentration on yield is not significant so we raised the hypothesis that stoichiometric yields and high productivities are attainable at very high substrate concentrations in fully aqueous medium leading to substantial process improvement in terms of costs and environment. To test the hypothesis, the kinetically controlled synthesis of cephalexin with immobilized penicillin acylase was conducted in aqueous medium at substrates concentrations up to and beyond their solubilities at varying temperature, pH, enzyme to substrate and acyl donor to nucleophile ratios. At the best conditions, 99% conversion yield was attained with volumetric productivity of 300 mM/h and specific productivity of 7.8 mmol/h g cat. These values are slightly higher than those previously obtained under optimized conditions in organic medium so that the hypothesis has been confirmed, which opens up the possibility of efficiently produce the antibiotic through an environmentally friendly process.

Cerium(III/IV) and Cerium(IV)–Titanium(IV) Citric Complexes Prepared in Ethylene Glycol Medium

Cerium(III/IV) and Ce(IV)–Ti(IV) citric complexes were synthesized in ethylene glycol medium under conditions similar to those of the polymerized complex method (PCM). Solution phase 1H, 13C NMR, solid state 13C CP MAS NMR and IR spectroscopy, and X-ray powder diffractometry were used to characterize the composition and structure of the synthesized products. Thermal decomposition of the isolated complexes was studied and a scheme of the processes taking place is proposed. Complexes of Ce(III) can be prepared at low temperature (40°C), only. In the presence of Ti(IV) ions, the oxidation takes place even at this temperature. A mixed-metal nature of the Ce(IV)–Ti(IV) complexes is established. The comparison between their composition and the one of analogous lanthanide(III)–Ti(IV) citrates contributes to the elucidation of the complexation process mechanism in the case of the PCM application. The increased charge of the complexation agent in the Ce4+–Ti4+ complex (in comparison with Ln3+–Ti4+ citrates) is “compensated” by the increase of the relative number of the ligands with deprotonated OH group.