Microemulsion Route Research Articles

On the Electronic Efffect of the Sn Atoms Towards Noble Metal Adsorption Sites: The Influence of the Structure on the Glycerol Electrooxidation Reaction

The searching for electrode materials with outstanding performance towards organic fuels electrooxidation reactions often is focused on polymetallic materials since they can exhibit a synergetic action resulting from electronic, geometric and/or bifunctional effects. However, as those effects are correlated, it is a difficult task to ascribe the improvement of the performance to a specific property and so to acquire a better understanding of the electrocatalytic process. It well known that Sn atoms exert a beneficial effect towards noble metal adsorption site that, on its turn, enhanced the kinetic of several organic fuels electrooxidation reactions. The enhancement is often suggested because of the electronic donor action of Sn atom; oxophilic action that provides the removal of intermediate species from the surface sites or a combination of these and other effects. The present work aims to elucidate the influence of the Sn atom present in the matrix of ordered intermetallic and alloy PtSn and PdSn (1:1 atomic ratio) nanoparticle materials towards the glycerol electrooxidation reaction in alkaline medium. Ordered intermetallic PtSn/C and PdSn/C nanoparticles were synthesized via modified polyol method and the same materials as alloys were synthesized via microemulsion route. All materials were obtained with similar particles diameters (~2nm) that assures the comparison of the electrode materials performances excluding the influence of the particle sizes. The materials were fully characterized by means of X-Ray Diffraction (XRD); Energy Dispersive Spectroscopy (EDS); High Resolution Transmission Electron Microscopy (HRTEM) and X-Ray Absorption Spectroscopy (XAS) techniques. Moreover, the electrochemical evaluation was performed by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques and the identification of stable intermediates and products of the reactions were obtained from Mass Spectrometry (MS) technique. The electrochemical experiments were carried out in 0.5 mol.L-1 KOH electrolyte solution and all the potentials cited herein are referred to the Reversible Hydrogen Electrode (RHE). The obtained results have pointed to the best performance of the ordered intermetallic material PtSn/C. This best performance was attributed to the electronic donor effect of the Sn atom towards Pt adsorption site that optimized the adsorption of the glycerol molecule causing the dissociative adsorption of the fuel with the cleavage of the C-C bond. The electronic action of the Sn atom was confirmed by the XAS data. This phenomenon was reinforced by the identification of the following intermediates/products of the electrode reaction: formic acid (higher amount from the reaction taking place at ordered intermetallic PtSn/C); glyceric acid and glyceraldehyde (higher amount from the reaction taking place at alloy PtSn/C); glyceraldehyde/dihydroxyacetone (higher amount for ordered intermetallic PdSn/C) and tartronic acid (higher amount for alloy PdSn/C). The electrode reactions mechanisms were proposed for all systems pointing out to the possibility of using different materials for energy or high aggregate value chemicals production. FAPESP Proc. # 2013/05634-8 Figure 1

Controllable synthesis of spherical hydroxyapatite nanoparticles using inverse microemulsion method

Spherical nanosized hydroxyapatite (HA) was successfully synthesized via a water-in-oil microemulsion route at room temperature in short time. The effect of water-to-oil and water-to-surfactant ratios on the stability of microemulsion system was investigated to establish a stable reaction system, with span-80, cyclohexane and Ca(NO3)2·4H2O((NH4)2HPO4) solution as surfactant, oil phase, and water phase, respectively. Size and morphology change of obtained HA under optimal microemulsion system were further studied under various reaction time and temperature, and a possible growth mechanism was proposed. A moderate reaction temperature of 25 °C and reaction time of 5 h facilitated the formation of spherical HA particles in the dimension of 70 nm with good uniformity and regularity, which served as a great candidate in biomedical applications.

Structural, spectral, dielectric and magnetic properties of Tb–Dy doped Li-Ni nano-ferrites synthesized via micro-emulsion route

Terbium (Tb) and dysprosium (Dy) doped lithium-nickel nano-sized ferrites (Li0.2Ni0.8Tb0.5xDy0.5xFe2−xO4 where x=0.00−0.08) were prepared by micro-emulsion technique. The X-ray diffraction (XRD) patterns confirmed the single phase cubic spinel structure. The lattice constant was increased due to larger ionic radii of Tb3+ and Dy3+ cations. The crystallite size was found in the range 30–42nm. The FTIR (Fourier transform infrared spectroscopy) spectra revealed two significant absorption bands (~400–600cm−1) which indicate the formation of cubic spinel structure. The peaking behavior of dielectric parameters was observed beyond 1.5GHz. The dielectric constant and dielectric loss were found to decrease by the increase of Tb–Dy contents and frequency. The doping of Tb and Dy in Li–Ni ferrites led to increase the coercive field (120–156Oe). The smaller magnetic and dielectric parameters suggested the possible utility of these nano-materials in switching and microwave devices applications.

Surface Modification of Nickel Sulfide Nanoparticles: Towards Stable Ultra‐Dispersed Nanocatalysts for Residue Hydrocracking

AbstractUltra‐small nickel sulfide nanoparticles (NSNPs) of 5–8 nm are prepared by a reverse microemulsion route and then modified by oleic acid and 1‐dodecanethiol to replace the adsorbed surfactant. Experimental results reveal that the particle size and crystal structure of the NSNPs did not change significantly during the modification process. Different from the adsorption by the electrostatic attraction between the surfactant and NSNPs, oleic acid and 1‐dodecanethiol are adsorbed firmly on the NSNPs through chemisorption. Catalytic hydrocracking tests demonstrate that the surface modification enhances the hydrocracking activity of the NSNPs. The surfactant‐coated NSNPs disperse in toluene‐insoluble products in as agglomerates of 20–30 nm, whereas the modified NSNPs mainly disperse as their original size. The results prove that the chemisorption of oleic acid and 1‐dodecanethiol on NSNPs remains steady and maintains the stable dispersion of NSNPs under high temperature and pressure.

Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route

Terbium (Tb) doped X-type hexagonal nano-ferrites Sr2NiCoTbxFe28−xO46 (x=0.00, 0.05, 0.1, 0.15, 0.2) were synthesized via micro-emulsion route. Single phase X-type hexagonal structure was confirmed by X-ray diffraction (XRD) analysis. The crystallite size of the samples was found in the range of 15–25nm. The bulk density and X-ray density were enhanced while porosity was reduced with the increased Tb3+ contents. The development of hexagonal phase was investigated by thermogravimetric analysis. The fourier-transform infrared (FTIR) spectra revealed the formation of spectral bands (metal-oxygen stretching vibration) which confirmed the hexagonal ferrites. The dielectric constant has high value at low frequency and decreased with increased frequency. The dielectric loss is appreciably decreased by the Tb3+ incorporation and resonance phenomenon occurred beyond 1.7×109Hz. The saturation magnetization (76–54emu/g) and remanance (27–21emu/g) decreased while coercivity increased (610–747Oe) by Tb3+-incorporation in Sr2NiCoTbxFe28−xO46 ferrite. The values of squareness ratio (0.35–0.39) indicated that Tb-doped samples are single domain while un-doped material is multi domains. These synthesized nano-sized hexagonal ferrites have potential applications in high frequency and recording media devices.

Effect of Cobalt Concentration and Oxygen Vacancy on Magnetism of Co Doped ZnO Nanorods.

Zn(1-x)Co(x)O (x = 0-0.07) single-crystalline nanorods were prepared by a modified microemulsion route. The crystalline structure, morphology, optical, and hysteresis loop at low and room temperature of as-prepared materials were characterized by XRD, TEM, PL spectra, and magnetic measurement respectively. The nanorods are 80-250 nm in diameter and about 3 μm in length. X-ray diffraction data, TEM images confirm that the materials synthesized in optimal conditions are ZnO:Co single crystalline solid solution without any impurities related to Co. The PL spectra show that the ferromagnetic samples exhibit strong Zn interstitials and oxygen vacancy emission indicating defects may stabilize ferromagnetic order in the obtained diluted magnetic semiconductors. Magnetic measurements show that the Zn(1-x)Co(x)O nanorods exist obvious ferromagnetic characteristics with T(c) above 300 K. M(s) and coercivities first increase and then decrease with dopant concentration increasing, reaching the highest for 3% doping level. The structural and magnetic properties of these samples support the hypothesis that the FM of DMS nanorods is due to a defect mediated mechanism instead of cobalt nanoclusters and carrier mediated.

Structural elucidation and magnetic behavior evaluation of rare earth (La, Nd, Gd, Tb, Dy) doped BaCoNi-X hexagonal nano-sized ferrites

Rare-earth (RE=La3+, Nd3+, Gd3+, Tb3+, Dy3+) doped Ba2NiCoRExFe28−xO46 (x=0.25) hexagonal ferrites were synthesized for the first time via micro-emulsion route, which is a fast chemistry route for obtaining nano-sized ferrite powders. These nanomaterials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as vibrating sample magnetometer (VSM). The XRD analysis exhibited that all the samples crystallized into single X-type hexagonal phase. The crystalline size calculated by Scherrer's formula was found in the range 7–19nm. The variations in lattice parameters elucidated the incorporation of rare-earth cations in these nanomaterials. FTIR absorption spectra of these X-type ferrites were investigated in the wave number range 500–2400cm−1. Each spectrum exhibited absorption bands in the low wave number range, thereby confirming the X-type hexagonal structure. The enhancement in the coercivity was observed with the doping of rare-earth cations. The saturation magnetization was lowered owing to the redistribution of rare-earth cations on the octahedral site (3bVI). The higher values of coercivity (664–926Oe) of these nanomaterials suggest their use in longitudinal recording media.

Stable Dispersed MoS2 Nanosheets in Liquid Lubricant with Enhanced Rate of Penetration for Directional Well

MoS2 nanosheets of approx. 100 nm were synthesized by a reverse microemulsion route firstly, then were annealed under nitrogen atmosphere, and were finally modified with 1-dodecanethiol. The prepared MoS2 nanosheets were characterized by XRD, TEM, FTIR, and so forth. Experimental results show that MoS2 nanosheets with the typical layer structure can be easily dispersed in oil lubricant for rate of penetration (ROP) increasing in directional well. The ROP of directional well with the prepared liquid lubricant was 52.9% higher than that of the similar directional wells at least, and the drilling velocity was increased 20% while the total proportion of lubricant in drilling fluid was 1.5%.

Synthesis of Nanostructured Catalytic Materials from Microemulsions

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Magnetically separable and recyclable graphene-MgFe2O4 nanocomposites for enhanced photocatalytic applications

MgFe2O4 nanoparticles were prepared by adopting the micro-emulsion route. Graphene-MgFe2O4 nanocomposites were prepared via ultra-sonication route. The characterization of MgFe2O4 nanoparticles and their nanocomposites was carried out by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM). XRD and FTIR confirmed the cubic spinel structure of MgFe2O4. VSM exhibited the magnetic behavior of MgFe2O4 while SEM estimated the particle size in the range of 50 nm. The photocatalytic activity of MgFe2O4 and nanocomposites were carried out using methylene blue as model compound in the visible light. The photocatalytic activity showed that the synthesized magnetic particles and their nanocomposites with graphene can be utilized as photocatalyst materials. These new photocatalyst could also be recycled and separated by applying an external magnetic field.

Investigation of the structural, optical and magnetic properties of CuO/CuFe2O4 nanocomposites synthesized via simple microemulsion method

Copper oxide CuO/tetragonal CuFe2O4 nanocomposites have been synthesized via the simple microemulsion route by addition of different Fe3+ ion ratios (where Fe3+ content=0, 0.05, 0.10, 0.15 and 0.20). It is clear that the pure CuO phase was observed from the precipitated copper hydroxide precursor at pH 12 as prepared and annealed at 600 to 800°C for 2h. Meanwhile, Fe3+ addition at low substitution concentration (0.05) was indexed pure CuO phase. Further enhancing the Fe3+ up to different concentration from 0.10 to 0.20 was confirmed CuO/t-CuFe2O4 nanocomposites. The ratio of t-CuFe2O4 phase in the composite was increment with increasing the Fe3+ addition. It was increased up to 28% by addition of Fe3+ content of 0.20 and annealed at 800°C for 2h. Indeed, the crystallite size and the theoretical density calculated from XRD pattern were decreased whereas the unit cell volume was increased as the result of Fe3+-addition. The microstructures of the produced pure CuO powders were exhibited pseudo-cubic like structure whereas they were appeared as spherical like structure by addition of Fe3+ ion. Ultraviolet-visible spectrum revealed that three strong band transitions were assigned in the range of 450–950nm, characteristics to the iron substitution. Of note, the band gap energies of pure and CuO/t-CuFe2O4 powders were in the range from 1.38 to 1.47eV. Otherwise, magnetic properties evinced that pure CuO particles have weak ferromagnetic characteristics. Furthermore, the magnetic properties were enhanced with increasing the Fe3+ addition corresponding to increase t-CuFe2O4 phase content.

Impacts of neodymium on structural, spectral and dielectric properties of LiNi0.5Fe2O4 nanocrystalline ferrites fabricated via micro-emulsion technique

Soft ferrites are technologically advanced smart materials and their properties can be tailored by controlling the chemical composition and judicial choice of the metal elements. In this article we discussed the effect of rare earth neodymium (Nd3+) on various properties of LiNi0.5NdxFe2−xO4 spinel ferrites. These ferrites have been synthesized by facile micro-emulsion route and characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), a.c. electrical conductivity and thermal analysis. The influence of Nd3+ doping on structural and electrical parameters has been investigated. XRD analysis revealed the formation of single cubic spinel structure for x≤0.07. Few traces of secondary phase (NdFeO3) were found for x≥0.105. The secondary phase induced owing to the solubility limit of Nd3+ cations in these ferrites. The lattice parameter (a) and crystallite size (D) both exhibit non-linear relation. The values of “a” and “D” were found in the range 8.322–8.329Å and 25–32nm respectively. These variations were attributed to the larger ionic radius of Nd3+ cations as compared to the host cations and lattice strain produced in these ferrites. The dielectric parameters were studied in the range 1MHz to 3GHz and these parameters were damped by Nd3+ incorporation and also by increasing the frequency. The reduced dielectric parameters observed in wide frequency range proposed that these nanocrystalline ferrites are potential candidates for fabricating the devices which are required to operate at GHz frequencies.

Synthesis and characterization of hexagonal ferrite Sr1.8Sm0.2Co2Ni1.50Fe10.50O22/PST thin films for high frequency application

Y-type hexagonal ferrite (Sr1.8Sm0.2Co2Ni1.50 Fe10.50O22) was prepared by a normal microemulsion route. The ferrite/polymer composites thin films are formed at different ferrite ratios in pure polystyrene matrix. The X-ray diffraction analysis shows broad peak at low angles which is due to the PST and the peaks for Y-type ferrite are also observed in composite samples. The peaks become more intense and show less broadening with increasing concentration of ferrite which suggests that crystallinity is improved with the addition of ferrite. DC resistivity of the composites samples is lower than that of the pure PST and decreases by increasing ferrite filler into the polymer. This decrease of resistivity is mainly due to the addition of comparatively less resistive ferrite into the highly insulating polymer matrix of PST. The observed increase in the dielectric constant (permittivity) with increasing concentration ratio of ferrites is mainly due to the electron exchange between Fe2+↔Fe3++e− which consequently results in enhancement of electric polarization as well as dielectric constant. The existence of resonances peaks in the dielectric loss tangent spectra is due to the fact when the external applied frequency becomes equal to the jumping frequency of electrons between Fe2+ and Fe3+. The increasing behavior of the dielectric constant, dielectric loss and AC conductivity with increasing ferrite ratio in PST matrix proposes their versatile use in different technological applications especially for electromagnetic shielding.

Microemulsion-derived ZrO2:Ce3 + nanoparticles: Phase transformation and photoluminescence characterization

Bluish green-emitting ZrO2:Ce3+ nanoparticles were synthesized via a microemulsion route. The effects of the annealing temperature on the phase evolution and luminescence properties were investigated in detail. As the aqueous micelles confined the constituent cations during crystallization, nanosized particles were formed. The formed ZrO2 nanoparticles were observed to undergo a phase transition from tetragonal to monoclinic structure with the increase in annealing temperatures. The reduction of structural defects with annealing temperatures promoted the phase transformation. When the annealing temperature exceeded 900°C, only the monoclinic phase was present. The photoluminescence emission appeared in the bluish green region around 487nm under ultraviolet excitation. The emission intensity increased with the annealing temperatures. The optimal Ce3+-dopant concentration in ZrO2 nanoparticles was determined, and the concentration quenching mechanism was discussed. The present work suggests that microemulsion-derived ZrO2:Ce3+ nanoparticles are suitable for optoelectronic applications.

Investigation of the magnetic properties of nanometric SrSmCoNi ferrite/PST matrix

Y-type hexa-ferrite Sr1.8Sm0.2Co2Ni1.50Fe10.50O22 was synthesized via micro-emulsion route. Ferrite/PST composites were obtained by mixing the different ferrite ratio in the pure PST matrix. The microstructure was examined by scanning electron microscopy (SEM) and exhibited heterogonous distribution of grains. A keen observation of these SEM images revealed that the grain morphology changes noticeably with increasing ferrite filler contents. The electrical modulus, Cole–Cole plots and quality factor of ferrite polymer composites have been investigated in the frequency range (1MHz to 3GHz). The field dependent magnetic properties of the prepared samples were investigated at room temperature by using vibrating sample magnetometer (VSM). The shape of hysteresis loops and linearity of Ms, Mr, Hc values vs. ferrite contents unfold that the ferrite nanoparticles are evenly dispersed within the composite. The occurrence of resonance at high frequency suggests that the present investigated composite samples are best candidate for multilayer chip inductors.

Structural, electrical, dielectric and magnetic behavior of Gd1−xBixFe1−yZryO3 nanoparticles for advanced technological applications

Gd1−xBixFe1−yZryO3 nanoparticles were synthesized via micro-emulsion route with different molar concentrations of Bi+3 (x) and Zr+4 (y). The values of x and y were kept in the range 0.00, 0.15, 0.30, 0.45 and 0.60. The characterizations were done by the thermo-gravimetric analysis (TGA), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The average particle size was ~50nm. The effect of Bi3+ and Zr4+ contents on electrical, dielectric and magnetic parameters were studied. The DC resistivity measurements showed at certain Bi3+ and Zr4+ contents, more than two fold increase in electrical resistivity from 68×108Ωcm to 150×108Ωcm. The magnetic measurements showed the paramagnetic nature of Gd1−xBixFe1−yZryO3 nanoparticles. The electrical and magnetic properties of these nanoparticles suggested that these materials are potential candidates for the fabrication of telecommunication and switching devices.

New La1−xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic and dielectric behavior evaluation

La1−xCr0.7xEu0.3xFeO3 nanoparticles were fabricated by micro-emulsion route. The value of x was kept in the range of 0.00 to 0.04. The synthesized nanoparticles were then characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD confirmed the orthorhombic phase and estimated the crystallite size in the range of 30–90nm. The nanoparticles estimated by SEM were in the range 60–100nm. The XRD data was further supported by FTIR spectrum. The main FTIR bands observed were: Fe–O (418cm−1), Cr–O (545cm−1), La–O (570cm−1) and Eu–O (416cm−1). After structural elucidation, the La1−xCr0.7xEu0.3xFeO3 nanoparticles were subjected to magnetic parameters and dielectric behavior evaluation. The replacement of La3+ ions, with Cr3+ and rare earth Eu3+ exhibited interesting magnetic and dielectric behavior. The LaFeO3 nanoparticles without any dopants showed the paramagnetic behavior. However as the La3+ was substituted by Cr3+ and Eu3+, the ferromagnetic behavior was observed. Similarly the dielectric parameters were reduced by the replacement of La3+ ions with Cr3+ and Eu3+ metal ions. The maximum magnetic parameters were observed for La0.6Cr0.28Eu0.12FeO3 (Coercivity~0.04T, Saturation magnetization ~0.728emug−1 and Retentivity ~0.0.6783emug−1). The maximum dielectric constant (23.52 at 1.5×10−2GHz) was observed for LaFeO3 nanoparticles, while the minimum value of dielectric constant (10.32 at 1.5×10−2GHz) was exhibited by La0.8Cr0.14Eu0.06FeO3 nanoparticles.

Nanocrystalline Co0.5Zn0.5Fe2O4 ferrite: Synthesis, characterization and study of their magnetic behavior at different temperatures

Co0.5Zn0.5Fe2O4 ferrite nanocrystals with average diameter in the range of 5–6nm have been synthesized by reverse microemulsion technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) are used to characterize the structural, morphological, and magnetic properties. X-ray analysis showed that the nanocrystals possess cubic spinel structure. The absence of hysteresis, negligible remanence, and coercivity at 300K indicate the superparamagnetic character and single domain in the nanocrystalline Co0.5Zn0.5Fe2O4 ferrite materials. The nanocrystalline Co0.5Zn0.5Fe2O4 ferrite was annealed at 600°C. As a result of heat treatment, the average particle size increases from 5nm to 7nm and the corresponding magnetization value increases to 15.94emu/g at 300K. However, at a low temperature of 100K, the annealed samples show hysteresis loop which is the characteristic of a superparamagnetic to ferromagnetic transition. A comparative study of the magnetic properties of Co0.5Zn0.5Fe2O4 ferrite nanocrystals obtained from (1) reverse microemulsion and (2) chemical co-precipitation route has also been carried out.

Synthesis, Characterization, and Formation Mechanism of Nanoparticles and Rods of 1,5-Bis(2-Halophenyl)Penta-1,4-Dien-3-One

Synthesis, Characterization, and Formation Mechanism of Nanoparticles and Rods of 1,5-Bis(2-Halophenyl)Penta-1,4-Dien-3-One For the first time nano sized particles of 1,5-bis(2-bromophenyl) penta-1,4-dien-3-one (I) and 1,5-bis(2-flourophenyl)penta-1,4- dien-3-one(II) were synthesised by facile reverse microemulsion route. Amazingly, I & II possessed spherical morphology and fibrous morphology respectively, as revealed by FTIR, FE-SEM with EDAX, HR-TEM with SAED. The detailed mechanism has been discussed.

Kinetic Study on the Formation of Bimetallic Core-Shell Nanoparticles via Microemulsions

Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction rate ratios between both metal and metal salt concentration inside the micelles. Model predictions show that, even in the case of a very small difference in reduction potential of both metals, the formation of an external shell in a bimetallic nanoparticle is possible if a large reactant concentration is used. The modification of metal arrangement with concentration was analyzed from a mechanistic point of view, and proved to be due to the different impact of confinement on each metal: the reaction rate of the faster metal is only controlled by the intermicellar exchange rate but the slower metal is also affected by a cage-like effect.