Reverse Micelle Method Research Articles

Conducting polymeric nanoparticles synthesized in reverse micelles and their gas sensitivity based on quartz crystal microbalance

Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles were prepared by reverse micelle method, which could be well dispersed in water or alcoholic solvent with ultrasonic treatment. The formation and doped state of PEDOT nanoparticles were confirmed by UV–vis–near IR absorption spectrum, X-ray photoelectron spectroscopy (XPS) and FT-IR spectrum. The nanoparticles with the size of ca. 20–40nm were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compare to electrical conductivity of conventional PEDOT particles (ca. 0.5S/cm), the as-prepared palletized nanoparticles have higher conductivity (ca. 10.2S/cm) and the conductivity varies with the doped and de-doped states of PEDOT. As for sensing property, it has been found that QCM device coated with nanoparticles shows faster response and recovery to 20ppm ammonia gas (ca. 50s) than that of conventional PEDOT particles. The PEDOT nanoparticle covered device exhibits almost linear relation to lower NH3 gas concentration and shows a saturate tendency of gas sensitivity with the increase of gas concentration over 500ppm. The mechanisms of electrical conductivity and gas sensitivity of PEDOT nanoparticles were also discussed.

Size-controlled synthesis of ZrO 2–TiO 2 nanoparticles prepared via reverse micelle method : Investigation of particle size effect on the catalytic performance in vapor phase Beckmann rearrangement

Zirconium–titanium mixed oxide nanoparticles have been synthesized using microreactors made of bis-(2-ethylhexyl) sulfosuccinate (AOT)/water/ n-hexane microemulsions. The control of particle size was achieved by varying the process variables, such as water-to-surfactant molar ratio and reagent concentration. Their sizes, appearances, crystal structures, pore diameter and surface area were characterized by TEM, XRD, N 2 adsorption/desorption methods. The results revealed that samples prepared in reverse micelles had no crystalline phase. The Beckmann rearrangement of cyclohexanone oxime on ZrO 2–TiO 2 nanoparticles was carried out in a fixed-bed down flow reactor to investigate the effect of particle size on catalytic activity and selectivity. Samples synthesized in reverse micelles had better reaction performance than samples prepared via sol–gel method. A parallel relationship could be drawn between the catalytic activity and the particle size as well as the selectivity of the catalyst.

Reverse micelles directed synthesis of mesoporous ceria nanostructures

In this paper, mesoporous ceria nanofibers, nanobelts and rodlike nanoparticles were successfully synthesized by a reverse micelle method. Results from low-temperature N 2 adsorption–desorption experiment measurements showed that both the BET surface area and pore volume of the nanobelts (114.9 m 2/g and 0.1470 cm 3/g) are about two times as much as that of the nanofibers (54.41 m 2/g and 0.09051 cm 3/g). UV–vis absorption spectra of the ceria nanostructures had a broad absorption band in the UV region and the blue-shifting of the bands was observed due to the quantum size effect and the special structure. The influence of experimental conditions on the morphology and structure of the precursors was investigated, and the possible growth mechanism of cerium carbonate nanostructures was proposed according the interaction between inorganic crystal faces and the organic surfactant molecules.

Blue-emitting small silica particles incorporating ZnSe-based nanocrystals prepared by reverse micelle method.

ZnSe-based nanocrystals (ca. 4-5 nm in diameter) emitting in blue region (ca. 445 nm) were incorporated in spherical small silica particles (20–40 nm in diameter) by a reverse micelle method. During the preparation, alkaline solution was used to deposit the hydrolyzed alkoxide on the surface of nanocrystals. It was crucially important for this solution to include Zn2+ ions and surfactant molecules (thioglycolic acid) to preserve the spectral properties of the final silica particles. This is because these substances in the solution prevent the surface of nanocrystals from deterioration by dissolution during processing. The resultant silica particles have an emission efficiency of 16% with maintaining the photoluminescent spectral width and peak wavelength of the initial colloidal solution.

Production of l-aspartic acid by biotransformation and recovery using reverse micelle and gas hydrate methods

l-Aspartic acid (l-Asp) was produced using Escherichia coli (ATCC 11303), and its recovery from the reaction mixture was studied using reverse micelle and gas hydrate methods. The effect of initial substrate concentration on l-Asp production was also investigated, and inhibition was shown to occur above 0.75 mol L−1. The values of the kinetic constants were determined as rmax=2.33×10−4 mol L−1 min−1, KM=0.19 mol L−1, and Kss=3.98 mol L−1. The reverse micelle phase used for extraction contained Aliquat-336, 1-decanol and isooctane, and a micro-injection technique was used for extraction of l-Asp. The reverse micelle system is a useful technique for obtaining small particle sizes, which can be used for the synthesis of nanoparticle biomolecules. Recovery of l-Asp from reverse micelles using CO2 hydrates was carried out, giving a recovery of 55%. The formation of CO2 hydrate from the reverse micelle solution breaks the micelle by reducing the amount of water in the micelle structure, thus precipitating the l-Asp.

Effect of Pt Substitution by Cu on Structural and Morphological Changes in Fe-Pt Nanoparticles during Annealing as Studied by <I>In-situ</I> Transmission Electron Microscopy

Effects of substitution of Pt by Cu on the structural and morphological changes of Fe-Pt nanoparticles with chemical homogeneity and mono-dispersion, which were synthesized by the reverse micelle method, have been investigated by in-situ electron diffraction and HREM observation. In the Fe-Pt particles, initially with a chemically disordered face-centered cubic phase (Al), the phase transformation from Al to a chemically ordered face-centered tetragonal phase (L1 0 ) took place between 650 and 680°C. Polycrystalline Fe-Pt particles were reconstructed into Al single crystals between 550 and 650°C, followed by phase transformation from Al to L1 0 . The coalescence began almost concurrently with the phase transformation, i.e., between 650 and 680°C. Then, they turned to round-shaped single crystalline particles between 680 and 720°C. In the Fe(Pt,Cu) particles, the phase transformation from Al to L1 0 occurred between 550 and 600°C. Same processes, that is, the reconstruction to single crystals, the phase transformation from Al to L1 0 , the coalescence and the round-shaped particle formation were also observed in the Fe(Pt,Cu) nanoparticles. The temperatures, at which these processes took place, were substantially lower than those for the Fe-Pt nanoparticles.

Biomedical Applications of Colloidal Nanocrystals

Biomedical Applications of Colloidal Nanocrystals

<I>In-situ</I> Electron Holography Observation of FePt Nanoparticles at Elevated Temperatures

We have developed a method to observe the magnetic field around L10 FePt nanoparticles by in-situ electron holography at elevated temperatures. FePt Nanoparticles with sharp size distribution and chemical homogeneity were synthesized by the reverse micelle method. The as-prepared FePt nanoparticles, which had a disordered fcc structure (A1) with the diameter centered at 6 nm, were coated with a surfactant, dispersed onto a glass plate, and heated in order to undergo a transformation from A1 to an ordered fct structure (L10). The particles were kept separated by the surfactant with their original diameter during annealing. A submicron-size island comprising isolated particles was removed and dispersed on an electron transparent carbon film and then magnetized along one direction. We observed a magnetic field distribution of the submicron-size island of nanoparticles by means of electron holography during heating. Although magnetization decreased between 212C and 412C to 25% of the initial strength at 25C, it increased again during cooling and recovered 67% of its initial strength. However, when an island was heated to 512C, the magnetization diminished and did not recover again during cooling. The Curie temperature (Tc) of the FePt nanoparticles was determined to be 350C and was in good agreement with the Tc determined by bulk measurements using a VSM, which was approximately 100C lower than the reported Tc for bulk Fe55Pt45. [doi:10.2320/matertrans.MD200703]

Magnetization and structural studies of Mn doped ZnO nanoparticles: Prepared by reverse micelle method

Single phase Mn (2.5 at%) doped ZnO nanocrystalline samples were synthesized by reverse micelle method as characterized by Rietveld refinement analysis of X-ray diffraction data, high resolution transmission electron microscopy and selected area electron diffraction analyses. The X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR) studies indicated that manganese exist as Mn 2+ in ZnO lattice. DC magnetization measurements as a function of field and temperature, of 2.5 at% Mn doped ZnO nanoparticles annealed at 675 K, showed room temperature ferromagnetism (RTF). This observation is further confirmed by the EPR spectrum of the sample, which shows a distinct ferromagnetic resonance signal at room temperature. These results indicate that the observed RTF in Mn-doped ZnO may be attributed to the substitutional incorporation of Mn at Zn sites.

Electrochemical and morphological stabilization of V 2O 5 nanofibers by the addition of polyaniline

In this work, the relationship between the nanoscale morphology and electrochemical performance of vanadium oxide and vanadium oxide/polyaniline nanofibers is analyzed. The nanofibers were prepared by reverse micelle method and their electrochemical performances were evaluated as potential cathode materials for secondary Li-ion batteries. Both types of samples were examined by electroacoustic impedance, ex situ X-ray diffraction, Raman and infrared spectroscopies, transmission and scanning electron microscopies to characterize their structure and morphology. It was found that vanadium oxide/polyaniline nanofibers show improved cycling behavior compared to the vanadium oxide ones. Nanofibers of vanadium oxide exhibit the largest capacity fading during cycling; on the other hand, the nanohybrid containing 30 mol% polyaniline exhibits a stable capacity of ∼300 mAh g −1. Scanning electron microscopy analyses indicated that the vanadium oxide nanofibers change the morphology after 10 charge/discharge cycles while hybrid nanofibers retain the defined morphology after electrochemical cycling. The role of the polymeric component of the hybrid material seems to be the stabilization of the capacity due to a probable homogeneous distribution of the induced stress during cycling.

Photoluminescence properties and energy transfer processes from excitons to Mn2+ ions in Mn2+-doped CdS quantum dots prepared by a reverse-micelle method

We investigated the photoluminescence (PL) properties of Mn2+-doped CdS (CdS:Mn2+) quantum dots (QDs) prepared by a reverse-micelle method. A PL band which originates from the intracation transition, the so-called d-d transition, of tetrahedrally coordinated Mn2+ ions, is clearly observed at ∼2.1eV, indicating that Mn2+ ions are thoroughly doped inside CdS QDs. By surface modification with a Cd(OH)2 layer, the intensity of the Mn2+-related PL band is increased approximately ten times compared with that without modification, and strong enhancement of the band-edge PL band is observed. The decay profile of the band-edge PL in surface-modified CdS:Mn2+ QDs is much faster than that in undoped CdS QDs; this shortened decay time originates from the effective energy transfer process from the excitons of host QDs to Mn2+ ions. The PL decay profiles are quantitatively explained on the basis of a three-level model including both the dark-exciton state and the energy transfer process.

Fabrication of high‐performance, gradient‐refractive‐index plastic rods with surfmer‐cluster‐stabilized nanoparticles

AbstractA novel method was developed with surfmer‐cluster‐stabilized silver nanoparticles to prepare high‐performance, gradient‐refractive‐index (GRIN) plastic rods based on methyl methacrylate. To fabricate the GRIN plastic rods, a novel polymerizable surfactant (surfmer) of 4‐(11‐acryloxyundecyloxy)benzoic acid (AUBA) was synthesized. Silver nanoparticles were prepared with a reverse micelle method in the presence of the novel surfmer. During the fabrication of the silver nanoparticles, the sodium salt of AUBA was formed. GRIN plastic rods were fabricated through centrifugal polymerization and then were heat‐treated at 100 °C under 0.1 Torr for 24 h to remove residual monomers and water. The distribution of the surfmer‐cluster‐stabilized nanoparticles inside the plastic rods was studied with transmission electron microscopy (TEM). The real‐image transmission through the fabricated rods was also confirmed. The results obtained in this investigation suggested that the control of the distribution of surfmer‐cluster‐stabilized nanoparticles could be used to fabricate GRIN rods. Furthermore, the existence of the crosslink‐like surfmers increased the thermal stability of the plastic rods. The GRIN distribution of the rods was established by the dispersion of nanoparticles inside the plastic rods through TEM analysis, refractive‐index analysis, and real‐image transmission. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5933–5942, 2006

Low‐temperature wet chemical syntheses of nanocrystal phosphors with surface modification and their characterization

AbstractWe report photoluminescence (PL) and chemical properties of nanocrystal phosphors synthesized by low‐temperature wet chemical processing. YAG:Ce3+ nanocrystals were synthesized from aluminium isopropoxide, yttrium(III) acetate tetrahydrate and cerium(III) acetate monohydrate in the mixed solvent of 1,4‐butylene glycol and polyethylene glycol (PEG) in an autoclave at 300 °C to discuss roles of PEG surface modification on PL enhancement. We also discuss roles of a lauryl phosphate surface modifier on PL enhancement in two systems of LaPO4:Ce3+,Tb3+ nanocrystals synthesized at 140 °C in the autoclave and ZnS:Mn2+ nanocrystals synthesized by a reverse micelle method. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence shifts in silver-doped nanocrystalline Cd 1− xZn xS

The change of properties in silver-doped nanogranular cubic Cd 1− x Zn x S with different percentages of Cd (up to 40%) prepared by Reverse Micelle method has been discussed. There was a strong modification of photoluminescence (PL) spectra and systematic PL peak shift with change of Cd concentration. The PL was attributed to transitions to silver from defect and other donor levels. Cd alloying variation in Cd 1− x Zn x S and a related band structure change led to a shift in relative positions of the donor and acceptor levels and a consequent systematic change in the observed PL emission wavelength.

Synthesis and optical characterizations of undoped and rare-earth-doped CaF 2 nanoparticles

The synthesis of undoped as well as Yb or Er-doped CaF 2 nanocrystals using a reverse micelle method is reported. X-ray powder diffraction and transmission electron microscopy analysis showed that the products were single phased and rather monodispersed with an average particles size around 20 nm. The emission spectra and fluorescence decay times of both Yb 3+ and Er 3+ rare earths (RE) ions in CaF 2 nanoparticles are presented. The particles size is increased by heating the as-obtained nanoparticles at different temperatures. The effect of annealing on the optical properties of the two RE ions in CaF 2 is also investigated.

CdSe nanoparticles grown with different chelates

Modified reverse micelles method allowing fabrication of CdSe nanoparticles in toluene solution in series of sizes with average diameter from 1.2 to 3.2 nm and size distribution ∼ 12-30 % is presented. Simple empirical relation between the CdSe nanoparticle diameter and exciton absorption wavelength is proposed, which allows to do prompt and effective monitoring the particles size and size distribution during the synthesis. Optical absorption and photoluminescence measurements as well as EDX demonstrated good quality of obtained nanocrystallites. Besides, study of nanoparticles produced using two complexing agents (SNTA and Trilon B) revealed similar stoichiometric and optical properties. Trilon B is suitable for CdSe nanoparticles growth instead of SNTA. Because of higher stability of the chelate complex of Trilon B and Cd 2+ ions, it is possible to use higher temperature for growth which allows preparation of large size nanocrystals.

Gold-coated iron nanoparticles: a novel magnetic resonance agent forT1 and T2 weighted imaging

Core/shell structured iron(Fe)/gold(Au) nanoparticles have been prepared by a reversemicelle method, and their potential application as magnetic resonance (MR) contrast agentinvestigated. The average nanoparticle size is 19 nm, as determined by x-ray powderdiffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties andrelaxivities of nanoparticles are presented and compared. The saturation magnetization is81 emu g−1 Fe for freshly prepared nanoparticles and the particles have highr1(6.87 mM−1 s−1) when the Fe core is kept from oxidation. These nanoparticles may be used asT1 agents in the unoxidized form.

Electroluminescent properties of device based on ZnS:Tb/CdS core-shell nanocrystals

ZnS:Tb/CdS core/shell nanocrystals (NCs) were synthesized by reverse micelle method, and with a core crystal diameter of 3.0 and a 0.5 nm thick CdS shell and used as an electroluminescent material. Electroluminescent (EL) devices having a hybrid organic/inorganic multilayer structure were fabricated. Electron–hole recombination was confined at the ZnS:Tb/CdS NCs layer. Three emissions peaked at 440 nm form ZnS host, 546 nm ( 5D 4– 7F 5) and 577 nm ( 5D 4– 7F 4) of Tb 3+ center were observed when the hybrid EL device at a bias of 13 V. The maximum luminance of the ZnS:Tb/CdS NCs-based reached 19 cd/m 2 at 25 V.

Luminescent properties of CdS nanoclusters dispersed in solution—Effects of size and surface termination

Steady-state and ultrafast transient luminescent properties of CdS nanoclusters prepared by the Aerosol-OT (AOT)/ n-heptane reverse micelle method and those modified with 2-mercaptoethanesulfonate were investigated in heptane and water, respectively. A very short luminescence component (∼200 fs) was observed for the first time for CdS nanoclusters dispersed in solution. The luminescence mechanism of CdS nanoclusters is proposed.

Strong enhancement of band-edge photoluminescence in CdS quantum dots prepared by a reverse-micelle method

We have investigated the effects of surface modification on photoluminescence (PL) properties of CdS quantum dots (QDs) prepared by a reverse-micelle method. It is demonstrated that the modification of QD surface with a Cd(OH)2 layer leads to a strong enhancement of the band-edge PL intensity of CdS QDs in reverse micelles. The PL-decay profile before the surface modification exhibits a fast decay component less than 50ps. After the modification, the fast-decay component disappears. The drastic change of the PL-decay profiles before and after the surface modification corresponds to the marked increase of the PL intensity. This suggests that the strong enhancement of the band-edge PL intensity originates from the remarkable reduction of nonradiative recombination processes, which usually result in a very short decay time, due to surface defects of QDs.