多元醇还原法制备片状六边形Fe3O4纳米颗粒

在表面活性剂油酸和油胺,液相环境二苄醚体系中,利用多元醇还原法,采用1,2-十二烷二醇还原前驱体乙酰丙酮铁Fe(acac)3,通过表面活性剂、金属前驱体以及液相环境的共同作用,制备出了单分散片状六边形Fe3O4纳米颗粒。分析了表面活性剂以及还原剂多元醇对纳米颗粒尺寸及形貌的影响。TEM表征结果显示：与未使用表面活性剂的情况相比,油酸和油胺的加入抑制了颗粒的生长,使颗粒尺寸从24.2 nm降低到10.7 nm;颗粒形貌多样化,出现了片状六边形形貌的Fe3O4纳米颗粒。磁性能检测表明： Fe3O4纳米颗粒具有高饱和磁化强度（Ms=88 emu/g）和零剩磁的特点,有望作为磁标记材料应用在生物检测上     

Demulsification by increasing the gravitational force acting upon the dispersed phase owing to the adsorption/absorption of the magnetite particles

Demulsification using a magnetic demulsifier is commonly used to separate emulsions using an external magnetic field. However, this study presents a new demulsification method based on the increased weight of the dispersed phase due to the adsorption/absorption of the magnetite particles by the droplets. Micron-sized bare magnetite particles were used as the demulsifier in this method which does not necessarily need to apply a surface-active additive and the magnetic field for the demulsification. Magnetic responsivity of the demulsifier can only be used for the recovery of the demulsifier. The demulsification experiments were performed using the oil-in-water and water-in-oil emulsions. The effect of temperature, wettability, demulsifier dosage and activity, sedimentation rate and particles size were investigated. The results showed that the proposed method can remarkably improve the efficiency and speed of the demulsification, and has a great potential to be considered for the commercialization.     

Adsorption of fatty acids from solutions in organic solvents on the surface of finely dispersed magnetite: 1. Isotherms of adsorption of oleic,linoleic, and linolenic acid from carbon tetrachloride and hexane

Isotherms of adsorption of oleic, linoleic, and linolenic acids on magnetite from solutions in carbon tetrachloride and hexane are measured. When CCl₄ is used as a solvent, the adsorption values increase in the following order: oleic, linoleic, and linolenic acid. In the case of hexane, the order is opposite. Adsorption isotherms of the fatty acids on aggregated magnetite are described in terms of the theory of volume filling of micropores. It is disclosed that, in the case of CCl₄ , the limiting adsorption values and characteristic energies of the process increase in a series: oleic, linoleic, and linolenic acid, but in the case of hexane, they decrease in the same sequence. Upon the adsorption of fatty acids from solutions in CCl₄ and hexane on finely dispersed magnetite, molecules of the acids and solvents compete for the active sites on the adsorbent surface. The number of double bonds in the molecules of unsaturated fatty acids and the desolvation of both the adsorbent surface and adsorbate molecules substantially affect the adsorption of these acids. The effect of the solvents is most pronounced for the adsorption of oleic acid, decreasing with a rise in the number of double bonds in a fatty acid molecule.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 779–783.Original Russian Text Copyright © 2004 by Korolev, Ramazanova, Yashkova, Balmasova, Blinov.     

The sorption isotherms of oleic, linoleic, and linolenic acids from solutions in cyclohexane and heptane on magnetite

The adsorption-desorption isotherms of oleic, linoleic, and linolenic acids from solutions in cyclohexane and heptane on the surface of magnetite were obtained by the equilibrium adsorption method. The adsorption of fatty acids was described in terms of the theory of volume filling of micropores. This theory was used to calculate the limiting adsorption values, characteristic energy, and volume of the pore space. In solutions in cyclohexane, the adsorption-desorption isotherm of oleic acid was situated above the isotherms of linoleic and linolenic acids. The situation was opposite with adsorption from heptane. The conclusion was drawn that the limiting adsorption and characteristic energy values increased from linolenic to oleic acid in adsorption from cyclohexane and decreased from linolenic to oleic acid in adsorption from heptane. The adsorption-desorption isotherms exhibited hystereses. Original Russian Text ? V.V. Korolev, O.V. Balmasova, A.G. Ramazanova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1156–1160.     

Inorganic nanocrystal self-assembly via the inclusion interaction of beta-cyclodextrins: toward 3D spherical magnetite

Synthesis and three-dimensional (3D) assembly of magnetite nanocrystals were realized by a one-pot procedure, in which Fe(acac)3 (acac = acetylacetonate) was partly reduced by hydrazine accompanied with ethylene glycol and spontaneously assembled into spherical nanostructures in the presence of surfactants including beta-cyclodextrin, oleic acid, and oleylamine. The size of the assembled spheres can coarsely be controlled in a limited range (100 nm to 2 microm) by changing the reaction temperature and the concentration of beta-cyclodextrin. X-ray diffraction and far Fourier transform infrared spectroscopy were employed to clarify the structures of magnetite in the assembled spheres. Electron diffraction pattern in a selected-area exhibits a high-crystallinity characteristic of cubic structure magnetite. We found that the formation of spherical magnetite aggregates highly depends on the presence of beta-cyclodextrin, while oleic acid and oleylamine improve the morphology of individual magnetite nanoparticles in the assembled spheres. In addition, the thermal gravimetric analysis and differential thermal analysis were applied to determine the content of magnetite in the products. Magnetic properties were also studied by using a superconducting quantum interference device magnetometer.     

New insight into mesoporous silica for nano metal-organic framework

In this paper the particle volume fraction and temperature dependence of the dynamic viscosity of highly concentrated transformer oil based magnetic nanofluids was investigated in the absence of an external magnetic field. The solid particle volume fraction dependence of the relative viscosity was found to be very well fitted by the Krieger-Dougherty formula, whence the mean ellipticity of the colloidal particles and the effective surfactant layer thickness were obtained. Using the information on the particles' size and shape statistics obtained from TEM, DLS and magnetogranulometry investigations, it was concluded that the magnetite nanoparticles agglomerate in small clusters of about 1.3 particles/cluster, due to the van der Waals interactions. The effective thickness of the oleic acid surfactant layer was estimated as about 1.4 nm, in very good agreement with the value resulted from previous SANS investigations.     

Synthesis of magnetic chelator for high-capacity immobilized metal affinity adsorption of protein by cerium initiated graft polymerization

A novel magnetic chelator with high adsorption capacity of protein by immobilized metal affinity adsorption was prepared by cerium (IV) initiated graft polymerization of tentacle-type polymer chains with iminodiacetic acid (IDA) chelating group on magnetic particles with hydroxyl groups. The micron-sized magnetic poly(vinyl acetate-divinylbenzene) (PVAc-DVB) particles were prepared by a modified suspension polymerization in the presence of oleic acid-coated magnetite nanoparticles and subsequently modified by ester exchange reaction to introduce functional hydroxyl groups. Bovine hemoglobin (BHb) was selected as a model protein to investigate the adsorption capacity of these magnetic particles. The magnetic particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), superconducting quantum interference device (SQUID) magnetometry, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray diffraction (XRD). The results showed that the magnetic particles had an average size of 5 microm and superparamagnetism with saturation magnetization of 20.0 emu/g at room temperature. The protein adsorption indicated that the graft polymerization of tentacle type polymer chains on the magnetic particles could produce magnetic adsorbents with high adsorption capacity (1428.21 mg/g) and low nonspecific adsorption of protein. The magnetic particles with grafted tentacle polymer chains have potential application in large-scale affinity separation of proteins.     

Nanocomposite particles with core-shell morphology II. An investigation into the affecting parameters on preparation of Fe3O4-poly (butyl acrylate-styrene) particles via miniemulsion polymerization

The encapsulation of inorganic particles with polymers is desirable for many applications in order to improve the stability of the encapsulated products and disperse ability in different media. Colloidal particles with magnetic properties have become increasingly important both technologically and for fundamental studies. This is due to their tunable anisotropic. In the absence of an applied magnetic field, the particles have isotropic sphere dispersion, whereas in an external magnetic field the particles form anisotropic structures. Here, latexes containing nanocomposite particles of styrene-butyl acrylate/Fe₃O₄ with core-shell structure were prepared through miniemulsion polymerization technique. Magnetic composite nanospheres with high magnetic content were synthesized through miniemulsion polymerization using a new process based on a three-steps preparation route including two miniemulsion processes: (1) preparing a dispersion of oleic acid coated magnetite particles in water; (2) mixing of modified magnetite particles with styrene/butyl acrylate in the presence of sodium dodecyl sulfate (SDS), sorbitane mono oleate (Span 80), hexadecane (HD) and (3) miniemulsification of the modified Fe₃O₄ into the monomer droplets to reach to complete encapsulation. Subsequent polymerization generated magnetic nanocomposite spheres. Hence, the copolymerization reaction was performed on the surface of such particles in order to obtain core-shell morphology for these nanoparticles, which were characterized by several techniques such as TEM, SEM, DLS, TGA, VSM and FT-IR. The magnetic copolymer particles with diameter of 120-170 nm were obtained. The effect of several parameters such as magnetite, surfactants and hydrophobe amounts on the stability, particle size and magnetization were investigated and also optimized.     

Adsorption of surfactants onto acrylic ester resins with different pore size distribution

In this study, a series of acrylic ester resins with different pore size distribution were prepared successfully by varying the type and the amount of pore-forming agents. In order to inves-tigate the adsorption behavior and mechanism of surfactants on acrylic ester resins, three kinds of surfactants were utilized as adsorbates that were sodium 6-dodecyl benzenesulfonate (6-NaDBS), sodium 1-dodecyl benzene sulfonate (1-NaDBS) and sodium 1-dodecyl sulfonate, respectively. It was observed that the surface area was available in a particular pore size and an appropriate pore size of resins appeared to be more important for the adsorption of surfactants. As compared to commercial acrylic ester resins XAD-7 and HP2MG, 50# and 38# resins exhibited more excellent adsorption properties toward 1-NaDBS and 6-NaDBS. The experimental equilibrium data were fitted to the Langmuir, and double-Langmuir models. Two models provided very good fittings for all resins over the temperature range studied. The investigation indicated that electrostatic attraction and hydrogen bond between resins and surfactants were the main forces and had an obvious effect on adsorption proc-ess.     

Fe3O4-LiMo3Se3 nanoparticle clusters as superparamagnetic nanocompasses

A scaleable chemical approach to functional nanoscale analogues of the magnetic compasses in magnetotactic bacteria is described. LiMo(3)Se(3)-Fe(3)O(4) nanowire-nanoparticle composites were synthesized by a reaction of 3-iodopropionic acid treated LiMo(3)Se(3) nanowire bundles with oleic acid-stabilized Fe(3)O(4) nanoparticles of 2.8, 5.3, and 12.5 nm size in tetrahydrofuran. Transmission electron micrographs show that the composite consists of Fe(3)O(4) nanoparticles attached to the surfaces of the 4-6 nm thick nanowire bundles. UV/vis spectra reveal absorptions from the nanowire (506 nm) and magnetite components (280-450 nm), and IR spectra show characteristic bands for the propionic acid linkers and for the residual oleic acid ligands on the magnetite particles. In the presence of excess oleic acid, the nanocomposites undergo rapid disassembly, suggesting that Fe(3)O(4) nanoparticles are bonded to nanowires via carboxylate groups from the linkers. Ultrasonication of a dispersion of the composite in THF produces individual LiMo(3)Se(3)-Fe(3)O(4) clusters, which are 340 +/- 107 nm long and 20 +/- 5 nm thick, depending on the sonication time and Fe(3)O(4) nanoparticle size. Field cooled and zero-field cooled magnetization measurements reveal that the blocking temperature (T(B) = 100 K) of the clusters with 5.3 nm Fe(3)O(4) is increased as compared to the free nanoparticles (T(B) = 30 K). Directional dipolar interactions in the clusters lead to magnetic anisotropy, which makes it possible to align the clusters in a magnetic field (900 Oe).     

Interrelation between parameters of isotherms of adsorption of fatty acids on the surface of magnetite and volume effects of their dissolution in n-hexane and carbon tetrachloride at 298.15 K

The adsorption of unsaturated C_18:n fatty acids on magnetite and volume effects of their dissolution in n-hexane and carbon tetrachloride are studied. It is established that an increase in the values of limiting adsorption of a series of oleic, linolic, and linolenic acids corresponds to positive volume effects of their dissolution in CCl₄. Opposite picture of the adsorption behavior of studied acids in n-hexane corresponds to negative volume effects of the dissolution of the acids in this solvent.     

Assessment of surfactant adsorption in oil-based magnetic colloids

We describe in this paper different and complementary experimental methods for assessing the adsorption of surfactants on metal particles in oil-based suspensions. Two different kinds of particles are dispersed in mineral oil: iron microparticles and CoNi nanoparticles. The adsorption of oleic acid in the Fe/oil interface in diluted suspensions can be determined by obtaining the adsorption isotherm. In addition, we present a method based on the time evolution of the optical absorbance of suspensions, from which the existence of adsorption can be inferred. For concentrated suspensions, the used of optical methods is not recommended, since they are affected by a significant inaccuracy. We present here a useful alternative based on electromagnetic induction phenomena. The results obtained allow a more comprehensive knowledge of the aggregation process in concentrated suspensions. With the same purpose, a third group of experiments, based on rheological techniques, is carried out in Fe/oil and CoNi/oil concentrated suspensions. In these series of experiments, the effect of three surfactants (oleic acid, aluminum stearate and lecithin) is tested by measuring either the viscosity, or the magnetic field-induced yield stress of the suspensions. The combination of these series of experiments gives us valuable information about the most appropriate surfactant/carrier combination capable of imparting a high stability and a strong magnetorheological response in magnetic colloids.     

Surfactant-free miniemulsion polymerization as a simple synthetic route to a successful encapsulation of magnetite nanoparticles

Due to the existing interest in new hybrid particles in the colloidal range based on both magnetic and polymeric materials for applications in biotechnological fields, this work is focused on the preparation of magnetic polymer nanoparticles (MPNPs) by a single-step miniemulsion process developed to achieve better control of the morphology of the magnetic nanocomposite particles. MPNPs are prepared by surfactant-free miniemulsion polymerization using styrene (St) as a monomer, hexadecane (HD) as a hydrophobe, and potassium persulfate (KPS) as an initiator in the presence of oleic acid (OA)-modified magnetite nanoparticles. The effect of the type of cross-linker used [divinylbenzene (DVB) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP)] together with the effect of the amount of an aid stabilizer (dextran) on size, particle size distribution (PSD), and morphology of the hybrid nanoparticles synthesized is analyzed in detail. The mixture of different surface modifiers produces hybrid nanocolloids with various morphologies: from a typical core-shell composed by a magnetite core surrounded by a polymer shell to a homogeneously distributed morphology where the magnetite is uniformly distributed throughout the entire nanocomposite.     

Large low-field magnetoresistance in nanocrystalline magnetite prepared by sol-gel method

Nanocrystalline magnetite Fe3O4 samples with a grain size of about 40 nm have been synthesized by an optimized sol-gel method. The single phase of spinel magnetite was confirmed by both X-ray diffraction and transmission electron microscopy. It has been found that the magnetoresistance of the samples at low field (LFMR) is relatively large, and with the decrease of temperature its value at a field of 0.5 T changes dramatically from -2.5% at 300 K to -17.0% at 55 K. With the further decrease of temperature a sharp drop occurs for the magnitude of the magnetoresistance (MR), regarded as a spin (cluster) glass transition in the surface region of the grains that can be confirmed by the zero-field-cooled and field-cooled magnetization and ac susceptibility measurement. The mechanism of the magnetic and transport properties was discussed.     

磁性Fe3O4@SiO2@ZrO2对水中磷酸盐的吸附研究

合成了以Fe₃O₄为核,以SiO₂为壳的磁性纳米微粒（Fe₃O₄@SiO₂）,并采用沉淀沉积法将ZrO₂包覆到材料表面。通过XRD、TEM、XPS和N₂吸附/脱附等手段对材料进行表征,结果表明材料Fe₃O₄@SiO₂@ZrO₂上沉积了氧化锆纳米颗粒,具有超顺磁性,可在外加磁场作用下实现从水中快速分离。同时系统研究了材料对水中磷酸盐的吸附行为,结果表明沉积ZrO₂使得材料对磷酸盐表现出良好的吸附性能,并且随着沉积量的增大吸附量增加。吸附等温线可用Freundlich方程拟合。吸附动力学可用拟二级动力学模型拟合,吸附速率随初始浓度增加而减缓。磷酸盐吸附量随溶液pH值的增大而减小,但几乎不受离子强度影响。     

Preparation of Surface-Imprinted Polymer Magnetic Nanoparticles with Miniemulsion Polymerization for Recognition of Salicylic Acid

Molecular surface-imprinted polymers nanoparticles encapsulating magnetite modified with oleic acid, for recognition of salicylic acid was prepared by three-step miniemulsion polymerization. The important factors including polymerization process, solvents, miniemulsifying approaches, and co-stabilizer have been investigated to obtain magnetic molecular imprinting polymers (MMIPs) nanoparticles (NPs) with high saturation magnetization (Ms), regular morphology, and good monodispersion. The results showed that the amount of magnetite encapsulated in MMIPs NPs was 43.4 wt% and Ms was 33.584 emu/g. Thus, MMIPs NPs could be separated easily within 2 minutes by an external magnetic field. The transmission electron microscope (TEM) showed MMIPs NPs were of regular sphere with core-shell structure, where magnetite NPs were uniformly encapsulated in homogeneous polymer shells. The average diameter of MMIPs NPs was 98 nm with RSD of 6.6%. Good recognition and high loading of target molecule were achieved by MMIPs NPs in batch rebinding tests.     

Manipulation of the magnetic properties of magnetite-silica nanocomposite materials by controlled Stober synthesis

The paper describes the synthesis and characterization of the magnetic properties of magnetite/silica nanocomposites using a modified Stober method. Magnetite nanoparticles averaging 8-10 nm in diameter and stabilized with oleic acid in toluene were used as the magnetic component of the nanocomposites. SQUID magnetic measurements and ferromagnetic resonance spectroscopy measurements were performed at each stage of the synthesis to understand the properties of the formed composites. Changes of blocking temperature in ZFC/FC SQUID curves correlated with corresponding changes of the resonance field in the ferromagnetic spectra of the sample at each stage of formation. The paper concludes that it is possible to manipulate the magnetic properties of silica/magnetite composite materials by controlling their surface properties and silica coating thickness.     

ADSORPTION OF 1,2,4-ACID BY WEAKLY BASIC RESIN： ISOTHERMS, THERMODYNAMICS AND KINETICS

The adsorption properties, including the adsorption isotherms, thermodynamics and kinetics, of l-amino-2-naphthol-4-sulfonic acid (1,2,4-acid) onto weakly basic resin ND900 are investigated. Both the Langmuir and Freundlich equations can give a good fit to the adsorption isotherms, which indicates an endothermic and a favorable adsorption in our study range. A high yield in elimination of about 45.21%-97.28% is obtained for the tested adsorption systems. The capacity and affinity of the adsorption increase with temperature, due to the phenomena of “solvent-motivated” effects. The value of ΔH is 51.59 kJ/mol, which indicates a chemical adsorption and then expects the poor desorption property of ND900. The negative value of ΔG indicates the spontaneous nature of the adsorption process, and the positive value of ΔS shows the increased randomness at the solid/solution interface during the adsorption process. The value of the adsorption rate constant lower than 0.013 min^-1 is indicative of a slow adsorption rate. The intra-particle diffusion must be one of the rate limiting steps.     

磁性壳聚糖微球的制备及对Cr(Ⅵ)的吸附性能研究

用壳聚糖包埋磁流体,用戊二醛交联制成磁性壳聚糖微球,并用红外光谱表征其结构。用制备的磁性壳聚糖微球吸附Cr(Ⅵ)离子,考察了其对Cr(Ⅵ)离子的吸附性能;探讨了吸附时间、溶液pH值、吸附剂用量、温度、Cr(Ⅵ)起始浓度以及其他离子存在对Cr(Ⅵ)离子去除率的影响。实验结果表明,磁性壳聚糖微球吸附Cr(Ⅵ)离子的最佳条件为:吸附平衡时间40 min,最佳吸附pH值6左右,磁性壳聚糖微球用量10 mg,温度升高有利于提高磁性壳聚糖微球的吸附效率,Cr(Ⅵ)离子起始质量浓度为12μg/mL,无机盐的存在引起磁性壳聚糖微球的吸附性能降低。并且考察了吸附剂的再生性能,实验结果表明磁性壳聚糖微球具有良好的重复使用性。     

Effect of Polymer on Dynamic Interfacial Tensions of Anionic–nonionic Surfactant Solutions

The dynamic interfacial tensions (IFTs) of enhanced oil recovery (EOR) surfactant/polymer systems against n-decane have been investigated using a spinning drop interfacial tensiometer in this paper. Two anionic–nonionic surfactants with different hydrophilic groups, C₈PO₆EO₃S (6-3) and C₈PO₆EO₆S (6-6), were selected as model surfactants. Partially hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM) were employed. The influences of surfactant concentration, temperature, polymer concentration, and oleic acid in the oil on IFTs have been studied. The experimental results show that anionic–nonionic surfactants can form compact adsorption films and reach ultralow IFT (10^?3 mN/m) under optimum conditions. The addition of polymer has great influence on dynamic IFTs between surfactant solutions and n-decane mainly by the formation of looser mixed films resulting from the penetration of polymer chains into the interface. The compact surfactant film will also be weakened by the competitive adsorption of oleic acid, which results in the increase of IFT. Moreover, the penetration of polymer chains will be further destroyed surfactant/polymer mixed layer and lead to the obvious increase of IFT. On the other hand, polymers show little effect on the IFTs of 6-6 systems than those of 6-3 because of the hindrance of longer EO chain of 6-6 at the interface.