Glycol Medium Research Articles

Microwave assisted synthesis of nickel nanostructures by hydrazine reduction route: Effect of solvent and capping agent on morphology and magnetic properties

The hydrazine reduction is one of the simplest and widely used method for the synthesis of nickel nanostructures. However, large-scale production of highly monodisperse nanoparticles with desired features is difficult to achieve using this method. In this study, we report, an evaluation of microwave assisted hydrazine reduction process and the effect of solvents namely water and ethylene glycol and capping agent thereupon. The study revealed that the reaction in the former failed to give the product when hydrazine (N2H4) and nickel Ni(II) are in the stoichiometric molar ratio, while the reaction in the later shows that the presence of the capping agent has pronounced effect on the morphology and magnetic properties of the product. Reaction in ethylene glycol in the presence of CTAB, gave 1D nanorods of about 100 nm in length and 4–6 nm in diameter, while in the absence of CTAB highly agglomerated spheres, are obtained. The magnetic property studies indicated the ferromagnetic nature of the product. The magnetic properties are, also affected by capping agent. In both, aqueous and ethylene glycol media, the product obtained exhibit lower saturation magnetization, whereas the product obtained in ethylene glycol with CTAB has highest saturation magnetization, 47.86 emu g−1.

Fe–Ni solid solutions in nano-size dimensions: Effect of hydrogen annealing

Nanoparticles of Ni0.50Fe0.50 and Ni0.75Fe0.25 alloys were prepared by chemical reduction in ethylene glycol medium. XRD and 57Fe Mössbauer studies have confirmed the formation of Fe–Ni solid solution in nano-size dimensions with FCC structure. These samples consist of both ferromagnetic and paramagnetic domains which have been attributed to the coexistence of large and small particles as confirmed by atomic force microscopic (AFM) and 57Fe Mössbauer spectroscopic studies. Improved extent of Fe–Fe exchange interaction existing in Ni0.50Fe0.50 alloy compared to Ni0.75Fe0.25 alloy explains the observed increase in the relative extent of ferromagnetic domains compared to paramagnetic domains in the former sample. Increase in the relative extent of ferromagnetic domains for hydrogenated alloys is due to increase in particle size brought about by the high temperature activation prior to hydrogenation.

An asymmetric supercapacitor with good electrochemical performances based on Ni(OH)2/AC/CNT and AC

Ni(OH)2/AC/CNT composite has been prepared via a green rapid microwave assisted method in an ethylene glycol medium. Scanning electron microscopy images show that Ni(OH)2 nanoparticles, activated carbon spheres and nanotubes constructed a three-dimensional (3-D) connected network, which lead to a high specific capacitance 1038Fg−1 at current density of 1Ag−1. Based on Ni(OH)2/AC/CNT composite as positive electrode material and activated carbon as negative electrode material, an asymmetric supercapacitor of AC//Ni(OH)2/AC/CNT was fabricated. The unit supercapacitor demonstrates excellent electrochemical performances using non-woven fabric as separator and 6M KOH as electrolyte within 1.6V operation window. The maximum specific capacitance of 82.1Fg−1 is achieved at 0.5Ag−1 and the energy density can reach up to 32.3Whkg−1 at power density of 504.8Wkg−1. Furthermore, 83.5% capacitance retention is obtained after 1000 charge-discharge cycles. These results indicate that the AC//Ni(OH)2/AC/CNT supercapacitor is promising to be applied in a practical device for energy storage devices.

The Role of Polyvinylpyrrolidone in Hydrothermally Synthesized Ag/ZnO Nanocomposites and Their Photocatalytic Activities.

Here we present a simple hydrothermal route for the preparation of photoactive ZnO and Ag/ZnO nanoparticles (NPs) synthesized in the presence and absence of polyvinylpyrrolidone (PVP). The low temperature synthesis is carried out in ethylene glycol (EG) medium at 180 degrees C, where EG is used as a reducing agent for the Ag+ ions. PVP is exploited as a size confining matrix for the Ag NPs. The present synthetic protocol allows the preparation of ZnO nanorods (NRs) with typical lengths of -200 nm and Ag/ZnO NPs with typical sizes of -100 nm. The photocatalytic activity of the as-prepared nanomaterials was tested for degradation of model pollutant methyl orange (MO) dye and terephthalic acid (TPA). We found that the Ag/ZnO NPs synthesized in PVP showed higher photoactivity than the commercial TiO2 (P25) powder or ZnO and Ag/ZnO NPs synthesized without PVP.

Synthesis of ethylene glycol-treated Graphene Nanoplatelets with one-pot, microwave-assisted functionalization for use as a high performance engine coolant

An electrophilic addition reaction under microwave irradiation was developed as a promising, quick and cost-effective approach to functionalize Graphene Nanoplatelets (GNP) with ethylene glycol (EG). EG-treated GNP was synthesized to reach a promising dispersibility in the water–EG media without negative effects of acid-treatment. Surface functionality groups and the morphology of chemically-functionalized GNP were characterized by the vibration spectroscopies, temperature-programmed study, and microscopic method. Despite the fact that the main structures of GNP were remained reasonably intact, characterization results consistently verified the functionalization of GNP with EG functionalities. As new kinds of high-performance engine coolant, the EG-treated GNP based water–EG coolant (GNP-WEG) was prepared and its thermo-physical and rheological properties are evaluated. In particular, the thermal conductivity, viscosity, specific heat capacity, and density of all samples were experimentally measured to evaluate the thermal performance of the GNP-WEG coolant. The data showed insignificant increases in the pressure drop at different temperatures and concentrations, low friction factor, lack of corrosive condition, and the performance index larger than 1. In addition, no momentous change in the pumping power in the presence of GNP-WEG confirmed that it can be an appropriate alternative coolant for different thermal equipment in terms of economy and performance.

ZnO-dotted porous ZnS cluster microspheres for high efficient, Pt-free photocatalytic hydrogen evolution.

The Pt-free photocatalytic hydrogen evolution (PHE) has been the focus in the photocatalysis field. Here, the ZnO-dotted porous ZnS cluster microsphere (PCMS) is designed for high efficient, Pt-free PHE. The PCMS is designed through an easy “controlling competitive reaction” strategy by selecting the thiourea as S2− source and Zn(Ac)2·2H2O as Zn source in ethylene glycol medium. Under suitable conditions, one of the PCMS, named PCMS-1, with high SBET specific area of 194 m2g−1, microsphere size of 100 nm and grain size of 3 nm can be obtained. The formation of PCMS is verified by TEM, XAES, XPS, Raman and IR methods. Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE. As a result, the PCMS-1 shows the promising activity up to 367 μmol h−1 under Pt-free condition. The PHE activity has no obvious change after addition 1 wt.% Pt, implying the presence of active catalytic sites for hydrogen evolution in the PCMS-1. The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

Mixing strategies for zinc oxide nanoparticle synthesis via a polyol process

We report on the effect of mixing on the morphology of ultrafine zinc oxide nanoparticles synthesized via a polyol process using zinc acetate and water in a diethylene glycol medium. Three mixing strategies were considered: stirred batch, T‐mixer, and impinging free jets. The particle granulometry was accessed using the transmission electron microscopy and x‐ray diffraction methods. The nanoparticle size and polydispersity decreased with an increase in the local dissipated energy. In particular, the polyol process conducted in the same chemical environment at 353 K did not lead to the observation of nanoparticles in the stirred batch reactor but resulted in unconventionally small 6‐nm particles in the T‐mixer and impinging jet configurations. This result is apparently related to the micromixing eddy geometry described by the Kolmogorov length. The hydrodynamic flow patterns and energy dissipation were obtained from computational fluid dynamics simulations, which are essential in the design, optimization, and scale‐up of the polyol process. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1708–1721, 2015

Luminescence dynamics and concentration quenching in Gd2−xEuxO3 nanophosphor

Gd2−xEuxO3 nanophosphor with enhanced luminescence has been synthesized by solution combustion method in diethylene glycol medium. The effect of Eu3+ content on the structure, morphology and luminescence dynamics has been investigated. The observed red shift in charge transfer band of the nanophosphor with increase in Eu3+content is attributed to the increase in covalency and Eu–O bond length. Excess europium content leads to reduction in intensity of photoemission as a result of concentration quenching. Transient characteristics exhibit single exponential behaviour and the fitted life time values get shortened with increase of Eu3+ content, due to increase in non-radiative transition rate. The observed quenching of luminescence in the phosphor is found to be in agreement with the energy transfer theory proposed by Dexter and Schulman and found that dipole–dipole interaction between Eu3+ ions is the key mechanism responsible for quenching. Critical energy transfer distance between Eu3+ ions in Gd2−xEuxO3 is determined to be 1.148nm. Judd–Ofelt intensity parameters and the radiative parameters of the phosphors were evaluated from the emission spectrum to analyse the crystal field environment and the degree of covalency between the rare-earth ion and the surrounding ligands. The value of Ω2 intensity parameter confirmed the hypersensitive nature of the 5D0–7F2 transition with larger asymmetry around Eu3+ ions.

Uniform spheroidal nanoassemblies of magnetite using Tween surfactants: influence of surfactant structure on the morphology and electrochemical performance

Uniform spherical nanoassemblies of Fe3O4 prepared using tween surfactants.

Black lead molybdate nanoparticles: Facile synthesis and photocatalytic properties responding to visible light

Black lead molybdate (PbMoO4) nanoparticles were first synthesized by the glycol–solvothermal method. Phase, morphology, crystal lattice, and specific surface of products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller nitrogen adsorption–desorption, respectively. Results revealed that the as-synthesized PbMoO4 nanoparticles are the scheelite-type tetragonal structure with 30–50nm in size. Also, glycol played a dual function in present synthetic system: solvent and surface modification agent. Optical properties reveal glycol-modification on the surface of PbMoO4 nanoparticles can generate new energy level between the original conduction band and valence band, leading to better absorption of visible light and the black appearance. Photocatalytic experimental results demonstrate that black PbMoO4 nanoparticles synthesized in glycol medium have pretty visible-light-responsive photocatalytic degradation performance on methylene blue and phenol solution. Reaction mechanism investigations show that the excellent photocatalytic activities of black PbMoO4 nanoparticles derive from the novel energy band structure, smaller size, and larger specific surface area. Hence one can see that black PbMoO4 nanoparticles are a type of visible-light-responsive photocatalysts with excellent photocatalytic activities and potentially applied prospects in dye wastewater treatment and environmental protection. Meanwhile, the present work provides an innovative strategy for adjusting the energy band structure of wide band-gap semiconductors.

Synthesis And Luminescent Performance Of LaPO4: Dy Nanophosphor

Nowadays the research on synthesis of inorganic luminescent material with proper dimensions and morphologies has attracted great attention. Inorganic luminescent materials like LaPO4 have found many practical applications in the field of electroluminescent devices, integrated optics, biological labels, modern lighting and display fields. We have prepared Dysprosium (Dy) doped LaPO4 nanoparticles at relatively low temperature in polyethylene glycol (PEG) medium by wet chemical method. Dy 3+ is doped in LaPO4 at various atomic concentrations (1, 2, 5 and 10 at %). All the samples have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and thermoluminescence (TL) techniques. XRD study reveals the monoclinic structure of prepared nanoparticles. Unit cell volume is found to be decrease linearly with increasing Dy 3+ concentration indicating homogeneous substitution of La 3+ ions in LaPO4 by Dy 3+ . From the FTIR study it is found that the band at 1044 cm -1 assigned to the phosphate group PO4 3- in the region of υ3 anti-symmetric stretching of P-O band. The PL spectrum shows emission band at about 435 nm is observed due to the transision of Dy 3+ ions corresponding to wavelength in the blue color region. The glow curve of LaPO4: Dy phosphor obeys second order kinetics. Copyright © 2014 VBRI press.

In-situ growth of Cu nanoparticles on reduced graphene oxide nanosheets and their excellent catalytic performance

Reduced graphene oxide (RGO)-Cu nanocomposites were prepared for the first time through one-pot co-reduction of graphene oxide and Cu2+ ions in ethylene glycol medium. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy. The in-situ grown Cu nanoparticles with adjustable loading amount are uniformly anchored on the surface of RGO nanosheets. The RGO-Cu nanocomposites exhibit extraordinarily superior catalytic performance, with which the catalytic reduction of 4-nitrophenol into 4-Aminophenol can finish within 40s and the apparent rate constant is as high as 6.0min−1 under 25°C. It was found that a suitable copper content is important to optimizing the catalytic activity of the nanocomposites. The kinetics of the reduction reaction at different temperatures was systematically investigated to determine the activation parameters, from which the mechanism of the enhanced catalytic activity is revealed. The RGO-Cu catalysts with excellent catalytic performance and relatively low cost show great promise for the catalytic applications.

Study of antibacterial activity of Ag and Ag2CO3 nanoparticles stabilized over montmorillonite

Silver carbonate and silver nanoparticles (NPs) over of stabilizer montmorillonite (MMT) have been synthesized in aqueous and polyol solvent, respectively. Dispersions of silver nanoparticles have been prepared by the reduction of silver nitrate over of MMT in presence and absence of Na2CO3 compound in ethylene glycol. It was observed that montmorillonite was capable of stabilizing formed Ag nanoparticles through the reduction of Ag+ ions in ethylene glycol. Na2CO3 was used as carbonate source in synthesis of Ag2CO3 NPs in water solvent and also for controlling of Ag nanoparticles size in ethylene glycol medium. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and ultraviolet–visible diffuse reflectance spectroscopy (DRS). The TEM images showed that Ag NPs size in presence Na2CO3 salts was smaller than without that. The results indicated intercalation of Ag and Ag2CO3 nanoparticles into the montmorillonite clay layers. The diffuse reflectance spectra exhibited a strong surface plasmon resonance (SPR) adsorption peak in the visible region, resulting from Ag nanoparticles. The antibacterial testing results showed that the Ag2CO3-MMT nanocomposite exhibited an antibacterial activity higher than Ag-MMT sample against Escherichia coli.

Polyethylene glycol (PEG-400): an efficient green reaction medium for the synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones under catalyst-free conditions

A simple and an efficient eco-friendly methodology has been developed for the synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones in excellent yields under catalyst-free-conditions using inexpensive and non-toxic polyethylene glycol (PEG-400) medium. This new protocol offers an environmental acceptability, shorter reaction time, room temperature, low cost, high yields, and recyclability of the PEG-400 medium are the important features. This method provides a green and much improved protocol over the existing methods.

Soft chemical synthesis of Ag3SbS3 with efficient and recyclable visible light photocatalytic properties

Application of Ag3SbS3, obtained by soft chemical approach involving rapid reaction of air stable metal–thiourea complexes in ethylene glycol medium, as visible light photocatalyst for the degradation of dye solutions was investigated. Ag3SbS3 was confirmed by high resolution powder X-ray diffraction pattern and its no defined morphology was present in SEM images. From UV–vis spectroscopy measurements, optical band gap of 1.77eV was deduced for Ag3SbS3. Rapid degradation kinetics and recyclability was exhibited by Ag3SbS3 towards Methylene Blue, Methyl Orange, Malachite Green, and Rhodamine 6G dye solutions under visible radiation. All these processes followed pseudo first order kinetics. High surface area (6.39m2/g), with mesopores (3.81nm), arising from solvent mediated synthesis of Ag3SbS3 has been correlated to its catalytic activity.

Hydrogen production from methane dry reforming over nickel-based nanocatalysts using surfactant-assisted or polyol method

In this study, two series of Ni-based nanocatalysts were synthesized successfully by the polyol and surfactant-assisted methods and subsequently tested for hydrogen production from CO2–CH4 reforming. Surfactant-assisted catalysts were prepared by using cetyl trimethyl ammonium bromide (CTAB) as a surfactant, whereas polyol catalysts were prepared in ethylene glycol (EG) medium with polyvinylpyrrolidone (PVP) as a nucleation-protective agent. The catalytic performance of each catalyst, in terms of H2 yield and selectivity, was evaluated at different temperatures (500–800 °C). In order to clarify and explain the differences in catalytic activities of catalysts, the prepared samples were characterized by various techniques, such as BET, H2-TPR, CO2-TPD, XRD, TGA, SEM, HRTEM and CO pulse chemisorption. The results demonstrated that the method of preparation had a significant effect on the catalytic performance of tested catalysts. Overall, polyol catalysts showed high activity and selectivity for hydrogen production, while surfactant-assisted catalysts exhibited a fairly high resistance towards carbon deposition under similar reaction conditions of dry reforming of methane. Moreover, due to the reverse water gas shift reaction (RWGS), surfactant-assisted catalysts always produced smaller values of H2/CO product ratio than their corresponding polyol catalysts.

Binding of phenol red to cetylpyridinium chloride at air–solution and micelle–solution interfaces in aqueous ethylene glycol media

Knowledge about the fundamental aspects of dye–surfactant interactions is important for developing better formulations required in textile and other coloring industries, and also for improving the efficacy of dye separation processes. In this paper, the interaction between cetylpyridinium chloride (CPC) surfactant and phenol red (PR) dye has been investigated in water and water+ethylene glycol (EG) media using surface tension and spectrophotometric methods. The synergetic effect of PR on the surface tension reducing ability of CPC decreases on adding EG. The modified Corrin–Harkins equation has been derived using the Gibbs–Duhem approach, and by applying this equation CP (cetylpyridinium) micelles are found to be bound predominantly by PR− which is shown to be in accordance with the Collins’ ion-specificity rule. From the absorbance data, using an equation that accounts for the stoichiometry of dye–micelle interaction, the values of binding constant were determined and in water+EG media the electrostatic interactions are found to control the binding of PR− to CP micelles. A spectrophotometric method to determine the counterion binding constant is illustrated. A simple expression that can predict the value of the binding constant of dye–micelle interaction at the cmc is proposed. Dynamic light scattering measurements showed that the amount of dye required to increase the micellar size is dependent on the solvophobicity of the medium. Surface excess values indicate that at the air–solution interface the monolayer consists of both CP+ and PR− when the medium is water, whereas in water+EG the monolayer has CP+ alone and PR− resides in the subsurface.

Microwave-assisted solvothermal synthesis of spinel AV2O4 (M = Mg, Mn, Fe, and Co).

Lower-valent vanadium oxide spinels AV2O4 (A = Mg, Mn, Fe, and Co) consisting of A(2+) and V(3+) ions have been synthesized by a low-temperature microwave-assisted solvothermal (MW-ST) synthesis process in a tetraethylene glycol (TEG) medium. The oxides are formed within a short reaction time of 30 min at 300 °C. Subsequent postheat treatment of the oxides at elevated temperatures in inert or reducing atmospheres results in an instability of the spinel phase, especially CoV2O4 due to the ease of formation of metallic Co, demonstrating the advantage of the low-temperature MW-ST process in accessing these oxides. This MW-ST synthesis approach is attractive for synthesizing other lower-valent transition-metal oxides that are otherwise difficult to obtain by conventional synthesis methods and for subsequent study of their unique physical and chemical properties.

Is higher ratio of monoclinic to tetragonal in LaVO4 a better luminescence host? Redispersion and polymer film formation.

Crystalline LaVO4:Eu(3+) nanophosphors (NPs) codoped with metal ions (M(n+) = Li(+), Sr(2+), and Bi(3+)) are prepared in ethylene glycol (EG) medium at temperature ∼140 °C in 3 h. A mixture of monoclinic and tetragonal phases is observed. The ratio of tetragonal to monoclinic phases increases with increase of Li(+) and Sr(2+) concentration, but this is opposite in case of Bi(3+) concentration. Lattice expansion occurs in the case of Li(+) and Sr(2+) codoping. Li(+) ions occupy the interstitial sites instead of La(3+) sites. Lattice contraction occurs in case of Bi(3+) codoping indicating substitution of La(3+) sites. Luminescence intensity is improved by codoping of M(n+) irrespective of crystal structure. Charges of Li(+) and Sr(2+) are different from that of La(3+) (host lattice), whereas the charge of Bi(3+) is same as that of La(3+). One interesting observation is in magnetic dipole transition that the intensity of the peak at 594 nm is more than that at 587 nm in the case of charge imbalance, whereas the reverse occurs in the case of charge balance. LaVO4:Eu(3+) nanophosphors prepared in water medium have more luminescence intensity when compared to those prepared in ethylene glycol, and this is related to variation of ratio of tetragonal to monoclinic phases. The luminescence intensity is also enhanced as annealing temperature increases from 600 to 800 °C due to the improved crystallinity. Lifetime data are analyzed on the basis of exponential and nonexponential decay equations. Samples are dispersible in polar medium due to capping of particles by EG. Polymer films are prepared by dispersion of NPs in poly(vinyl alcohol), and extra borax is added in order to make cross-link between polymer molecules. Samples of NPs in the forms of powder, dispersion in liquid medium, and film show the red emission.

Stability of luminescence in LaPO4, LaPO4 :RE(3+) (RE = Dy, Eu) nanophosphors.

The property of high refractive index, low solubility in water as well as stability to high temperature variation of lanthanum phosphate (LaPO4 ) proved it was the most effective candidate for the production of display lamps, and plasma display panel devices and sensors. The morphological and nanostructural characteristics play a key role in the working efficiency of the luminescent material. These properties can be controlled by the synthesis method, which we have adopted in this paper. We have prepared LaPO4 nanoparticles at a relatively low temperature (110 ºC) in polyethylene glycol medium by using a wet chemical one-step synthesis. The phase composition and structural properties of the sample have been characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy and the luminescent property by photoluminescence and thermoluminescence. The samples were well crystallized and the average crystallite size of 15 nm has been calculated for pure LaPO4 using the Debye-Scherrer equation. The result from heat-treated samples shows the phase combination and morphological structure of the powder depend on the annealing temperature. The heat treatment changes the structure of LaPO4 from cuboid rods to fine grains at about 600 °C. The emission spectrum of LaPO4 shows the broad emission band at 368 nm and shoulder at 465 nm with emission of blue color when monitored at an excitation wavelength at 256 nm. The stability of phosphor has been studied with respect to humidity, temperature, doping, doping concentration, γ-ray exposures, etc. The prepared nanosized phosphors were thermally stable and may be a promising blue phosphor for lighting technology as well as radiation dosimetry.