Study the effect of HLB of surfactant on particle size distribution of hematite nanoparticles prepared via the reverse microemulsion

Hematite nanoparticles have been synthesized via reverse microemulsion route at room temperature. The microemulsion system, contained water, chloroform, 1-butanol, and surfactant, was combined with iron nitrate solution to result iron oxide nanoparticles precipitation. Three technical surfactants, with different structures and HLB (hydrophile–lipophile balance) values were employed and the effects of the HLB values on the hematite particle size were investigated. The prepared particles were evaluated by BET, XRD and TEM techniques. These results showed that the iron oxide particle size and particle size distribution increased with increasing surfactant HLB values.     

微乳液和均匀沉淀耦合法制备CeO2纳米粒子

用W/O微乳液和草酸二甲酯均匀沉淀耦合法制备出单分散性好并具有较窄粒度分布的CeO2纳米粒子,测试了其形貌、粒径及粒径分布和晶体结构等特征.实验结果表明,表面活性剂的种类和反应物的相对初始浓度对产物平均粒径具有规律性的影响;随着焙烧温度升高,产物的平均粒径明显增大.     

Span/Tween混合表面活性剂微乳液制备纳米铁及脱硝研究

研究了以Span 80和Tween 60为混合表面活性剂的微乳液的形成。以电导率及目测法为表征手段,利用正交试验,分析了多因素对W/O型微乳液最大增容水量的影响,探明了该乳液形成的适宜条件。     

Uniform metal nanoparticles produced at high yield in dense microemulsions

This article demonstrates that bicontinuous microemulsions are optimal templates for high yield production of metal nanoparticles. We have verified this for a variety of microemulsion systems having AOT (sodium bis (2-ethyhexyl) sulphosuccinate) or a fluorocarbon (perfluoro (4-methyl-3,6-dioxaoctane)sulphonate) as surfactant mixed with water and oils like n-heptane or n-dodecane. Several types of metal nanoparticles, including platinum, gold and iron, were produced in these microemulsions having a size range spanning 1.8-17 nm with a very narrow size distribution of ±1 nm. Remarkably high mass concentrations up to 3% were reached. Size and concentration of the nanoparticles could be varied with the stoichiometries of the reagents that constituted them. The optimization towards high yield while maintaining low size polydispersity is due to the decoupling of the time scales for the precipitation reaction and for coarsening. In actual fact, coalescence is essentially prevented by the immobilization of nanoparticles within the bicontinuous microemulsion structure.     

Preparation of Eu-Doped Y(2)O(3) Luminescent Nanoparticles in Nonionic Reverse Microemulsions

In this study, Y(2)O(3):Eu luminescent nanoparticles were prepared by precipitation of aqueous yttrium nitrate/europium nitrate solution using ammonium hydroxide in the reverse microemulsions based on polyoxyethylene (5) nonylphenyl ether/polyoxyethylene (9) nonylphenyl ether, cyclohexane, and water. With Eu-doped Y(2)O(3) nanoparticles obtained, particle size, shape, chemical composition, crystalline formation rate, crystallinity, and photoluminescence were measured and compared with those of particles formed by a bulk precipitation method. The nanoparticles synthesized in microemulsion showed a narrow size distribution, spherical shape, fast crystalline formation rate, high crystallinity, and strong photoluminescence. This stronger photoluminescence of particles formed in a microemulsion might be attributed to more densely packed particles with very few voids and higher crystallinity at a relatively low temperature than those synthesized through a bulk precipitation method. Copyright 2000 Academic Press.     

Fischer-Tropsch synthesis by nano-structured iron catalyst

Effects of nanoscale iron oxide particles on textural structure, reduction, carburization and catalytic behavior of precipitated iron catalyst in Fischer-Tropsch synthesis (FTS) are investigated. Nanostructured iron catalysts were prepared by microemulsion method in two series. Firstly, Fe2O3, CuO and La2O3 nanoparticles were prepared separately and were mixed to attain Fe/Cu/La nanostructured catalyst (sep-nano catalyst); Secondly nanostructured catalyst was prepared by co-precipitation in a water-in-oil microemulsion method (mix-nano catalyst). Also, conventional iron catalyst was prepared with common co-precipitation method. Structural characterizations of the catalysts were performed by TEM, XRD, H2 and CO-TPR tests. Particle size of iron oxides for sep-nano and mix-nano catalysts, which were determined by XRD pattern (Scherrer equation) and TEM images was about 20 and 21.6 nm, respectively. Catalyst evaluation was conducted in a fixed-bed stainless steel reactor and compared with conventional iron catalyst. The results revealed that FTS reaction increased while WGS reaction and olefin/paraffin ratio decreased in nanostructured iron catalysts.     

Nanoparticle precipitation in reverse microemulsions: particle formation dynamics and tailoring of particle size distributions

In this work, a detailed experimental analysis of the nanoparticle formation dynamics and the formation mechanism in a reverse microemulsion system is given. The precipitation of barium sulfate nanoparticles inside microemulsion droplets is investigated at the molecular scale with respect to the evolution of the particle size distribution and the particle morphology by an extensive transmission electron microscope (TEM) analysis. Different mixing procedures (feeding strategies) of two reactants, barium chloride and potassium sulfate, are evaluated concerning their ability for a tailored particle design under consideration of the complete particle size distribution (modality and polydispersity). It is shown that improved knowledge about the particle formation mechanisms, the dynamics, and the influence of the colloidal microemulsion structure could be used for a tailored design of particles,for example, controlled synthesis of nanoparticles with a bimodal particle size distribution by the application of a sophisticated feeding strategy.     

FTIR–ATR studies of water structure in reverse micelles during the synthesis of oxalate precursor nanoparticles

The structure of water in water-in-oil microemulsions used to synthesize oxalate precusor nanoparticles for the production of YBa₂Cu₃O_7−x (YBCO) superconductor powder has been studied by FTIR–ATR spectroscopy of the OH stretching band. Two initial microemulsions are mixed together and nanoparticles are formed by a precipitation reaction in the cores of the reverse micelles of the resulting microemulsion. The shapes of the water OH stretching bands for the microemulsions before and after the reaction exhibit noticeable differences when normalized at their peaks. These differences have been quantified by decomposing the water OH stretching band into three components corresponding to water molecules with different types of hydrogen bonding. In the microemulsion after the precipitation and formation of oxalate precusor nanoparticles, the structure of water is characterized with an increased fraction of bound water. These bound water molecules are also connected with stronger H-bonds. We propose that upon synthesis of the precursor nanoparticles, the observed water structure changes are due to a thin water layer formed around the newly synthesized nanoparticles.     

Ultrasonically induced microemulsion polymerization of styrene

In this paper, ultrasonically induced microemulsion polymerization of styrene was successfully performed, possessing many merits such as high polymerization rate, the formation of small latex particles with a narrow size distribution, the absence of initiator and relatively low surfactant concentration. The monomer conversion reached 70% in 1 h, and the average diameter of polystyrene (PS) latex was about 30 nm which could be prepared with 3% surfactant (sodium dodecyl sulfate, SDS) concentration. The molecular weight of PS was around 10⁶ and the poly-distribution index was 1.06, indicating a very narrow distribution. Several influencing factors were investigated in detail, showing that ultrasonically induced microemulsion polymerization is a new route to prepare PS nanoparticles.     

Superparamagnetic Fe3O4SiO2 nanocomposites: enabling the tuning of both the iron oxide load and the size of the nanoparticles

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca. 100 nm and fully loaded with SPIOs, to smaller particles, ca. 30 nm containing only one or a few SPIOs. By varying the amount of silica precursor, the thickness of the silica shell was altered. Field dependent magnetization measurements showed the magnetic properties of the SPIOs were preserved after the synthesis.     

Effect of Preparation Methods of Bi2O3 Nanoparticles on their Photocatalytic Activity

Bi2O3 nanoparticles were prepared by means of ammonia precipitation, polyol mediated methods and microemulsion chemical method. The structure and properties of the as-prepared nanoparticles, having been submitted to a heat-treatment test at 750℃, were characterized by means of XRD. BET, XPS and UV-Vis absorption techniques. The photocatalytic oxidation reactions of benzene, toluene and xylene were used as the model reaction to measure the photocatalytic activity of Bi2O3 nanoparticles, respectively. The results show that the crystallite size of Bi2O3 prepared with different methods and calcined at 750℃ were 50. 6, 38.5 and 31.5 nm, respectively. The photocatalytic activity of Bi2O3 nanoparticles prepared with the microemulsion chemical method was higher than that of the particles prepared with the polyol mediated method; and that of the particles prepared with the micromulsion chemical method was the highest among the three. The degradation rates of the three pollutants xylene, toluene and benzene decreased in sequence.     

Radiation synthesis and magnetic properties of novel Co0.7Fe0.3/Chitosan compound nanoparticles for targeted drug carrier

Chitosan coated Co_0.7Fe_0.3 compound nanoparticles were successfully synthesized through a γ-radiation route in inverse microemulsion system. An observation of transmission electron microscope (TEM) showed that the diameter of these nanoparticles was about 50 nm with narrow size-distribution. Investigations of properties of nanoparticles were also conducted with fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and energy dispersion spectrum (EDS). Analysis of vibrating sample magnetometer (VSM) indicated that the nanoparticles were superparamagnetic with a saturation magnetization of 24 emu/g. These compound nanoparticles were undertaken to allow for the magnetically targeted cancer.     

Water-based wet chemical synthesis of (doped) ZnO nanostructures

Looking at its vast range of applications, nanostructured ZnO can be considered as a key technological material. Simple and ecological production techniques for this and other nanostructured materials can boost the detection of their unusual properties. In this context water-based wet chemical synthesis routes for nanostructured ZnO are explored in this study. The advantages and disadvantages of controlled double-jet precipitation, microemulsion preparation, hydrothermal synthesis and an aqueous solution-gel route are described for the formation of (doped) ZnO nanoparticles. The influence of the synthesis parameters on the particle size, size distribution and degree of agglomeration of the particles is reported. Thin films are prepared by chemical solution deposition from aqueous solution. The heat treatment profile and the precursor composition are seen to largely control the density, the grain size and the degree of preferential c-axis orientation.     

Characterization of iron hydroxide/oxide nanoparticles prepared in microemulsions stabilized with cationic/non-ionic surfactant mixtures

Iron oxide-hydroxide (α-Fe(2)O(3); Fe(OH)(3)) nanoparticles have been prepared by a microemulsion route using ammonia (NH(3)) solution or tetrabutylammonium hydroxide (TBAH) as precipitants. The iron oxide-hydroxide nanoparticles obtained were characterized by TGA, N(2) sorptiometry, XRD, IR, SEM, HR-TEM, and DLS techniques. Properties such as specific surface area (S(BET)), pore sizes and shapes, average particle size and distribution, crystallite structure, and thermal stability were determined. The properties of nanoparticles prepared using NH(3) and TBAH were compared after drying at 100°C and after being calcined in the temperature range 250-1100°C. It was found that the suspensions prepared using TBAH suffered immediate separation while those prepared using NH(3) resulted in very stable suspensions. Also, it was found that TBAH did not offer any advantage over NH(3) either in terms of specific surface area or in particle size of the prepared nanoparticles. Hence, the later part of the study was concentrated on the NH(3)-precipitated nanoparticles with particular emphasis on finding the most favorable, W (water-to-surfactant ratio) and/or surfactant concentration, S, to obtain the best conditions in terms of higher surface areas and narrower particle size distribution. It was found that the prepared suspension consisted of monodisperse nanoparticles (standard deviations <10%) and after separation and drying, high surface area powders were obtained. The highest surface area (315 m(2) g(-1)) was obtained when the smallest W (=20) and highest S (=0.20 mol L(-1)) were employed.     

琥珀酸二异辛酯磺酸钠微乳体系中纳米银的制备及其连续相的影响

在琥珀酸二异辛酯磺酸钠(AOT)为表面活性剂、环己烷为连续相形成的微乳体系中, 利用水合肼还原AgNO₃制备了分散性良好的纳米银. 利用紫外-可见(UV-Vis)光谱和透射电镜(TEM)对所得产物进行了表征, TEM显微图像表明形成粒子为球形结构, 平均粒径为5.10 nm, 标准偏差为2.84 nm. 分别利用正己烷、正庚烷、正辛烷、环己烷和十二烷等作连续介质, 研究了微乳液中连续相对纳米银形成的影响. 随着正烷烃碳链长度的增加, 微乳液中胶束之间的交换速率增大, 形成粒子的平均粒径逐渐减小. 十二烷形成的微乳体系制备的纳米银溶胶具有最宽的共振吸收峰, 所得的纳米银粒子平均粒径最小. 环己烷形成的微乳液中反胶束具有特殊的界面强度, 导致纳米银晶核的形成速率过低, 纳米银晶粒的生长不完全.     

Synthesis and magnetic relaxation properties of a porous glass magnetic microcarrier

The reaction of formation of magnetic iron oxide nanoparticles from aqueous solutions of Fe(+2,+3) salts was studied under homo- and heterophase conditions of capillary-porous bodies by the nuclear magnetic resonance relaxometry method. Magnetic composites based on Bio-Glas porous glasses were obtained by precipitation of iron oxide nanoparticles in pores ranging in size from 50 to 250 nm. The magnetic relaxation rate of water protons during the heterophase precipitation reaction was examined.     

An efficient method for recovery of target ssDNA based on amino-modified silica-coated magnetic nanoparticles

In this paper, an improved recovery method for target ssDNA using amino-modified silica-coated magnetic nanoparticles (ASMNPs) is reported. This method takes advantages of the amino-modified silica-coated magnetic nanoparticles prepared using water-in-oil microemulsion technique, which employs amino-modified silica as the shell and iron oxide as the core of the magnetic nanoparticles. The nanoparticles have a silica surface with amino groups and can be conjugated with any desired bio-molecules through many existing amino group chemistry. In this research, a linear DNA probe was immobilized onto nanoparticles through streptavidin conjugation using covalent bonds. A target ssDNA(I) (5′-TMR-CGCATAGGGCCTCGTGATAC-3′) has been successfully recovered from a crude sample under a magnet field through their special recognition and hybridization. A designed ssDNA fragment of severe acute respiratory syndrome (SARS) virus at a much lower concentration than the target ssDNA(I) was also recovered with high efficiency and good selectivity.     

Functional silica nanoparticles synthesized by water-in-oil microemulsion processes

Water-in-oil (W/O) microemulsion is a well-suitable confined reacting medium for the synthesis of structured functional nanoparticles of controlled size and shape. During the last decade, it allowed the synthesis of multi-functional silica nanoparticles with morphologies as various as core–shell, homogenous dispersion or both together. The morphology and properties of the different intermediates and final materials obtained through this route are discussed in the light of UV–Vis–NIR spectroscopy, dynamic light scattering (DLS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and magnetometer SQUID analysis.     

超顺磁性DNA纳米富集器应用于痕量寡聚核苷酸的富集

随着纳米技术的迅速发展 ,纳米材料逐渐被应用到细胞生物学和分子生物学研究领域 ,为生物医学的研究和发展提供了新的技术和手段 [1～ 4 ] .如超顺磁性纳米颗粒由于具有尺寸小、比表面积大、悬浮稳定性好及在外磁场作用下的磁导向性运输和富集等优良特性 ,使其在细胞和生物活性     

Formation of organically and inorganically passivated CdS nanoparticles in reverse microemulsions

This paper is focused on the formation of organically and inorganically passivated cadmium sulfide (CdS) nanoparticles in two different types of microemulsions. On the one hand, we used a ternary inverse microemulsion consisting of water, heptanol, and 3-(N,N-dimethyldodecylammonio)propanesulfonate and on the other hand, a poly(ethyleneimine)-based quaternary microemulsion containing water, toluene, pentanol, and sodium dodecylsulfate. UV-vis measurements confirm the formation of CdS-ZnS core-shell nanoparticles in the ternary microemulsion. Using the quaternary microemulsion template phase, polymer capped luminescent CdS nanoparticles can be formed. After a complete solvent evaporation, the nanoparticles are redispersed in water and characterized by means of dynamic light scattering and transmission electron microscopy. From the ternary microemulsion, well-stabilized CdS-ZnS core-shell nanoparticles with diameters of about 5 nm can be redispersed, but from the quaternary microemulsion, only nanoparticle aggregates of about 100 nm.