均匀Fe3O4胶体粒子形成过程的Mossbauer研究

应用经过改进的实验方法制得均匀球状Fe3O4胶体粒子, 通过对多种Fe3O4粒子的Mossbauer测量并结合发析, 我们发现, 在制备过程中, 反应浓度、加液次序以及陈化时间的不同对所生成的Fe3O4晶体的基本骨架与结构影响极小, 而随着陈化时间的不断增加, Fe3O4粒子的组成将逐渐接近化学计量, 以这些实验结果及文献报道为基础, 本文讨论了均匀Fe3O4胶体粒子的形成机理。     

均匀球形α-Fe_2O_3胶体粒子的形成机理

在有关均匀胶体粒子的研究中,人们大多关注的是均匀胶体粒子的制备方法和实验条件的控制,其中包括溶液的组成,陈化温度和时间以及起决定作用的特殊阴离子.然而涉及其形成机理的分析很少,因为均匀胶体粒子的形成是个微观过程:成核、成长、相转变和微粒子的聚集等过程瞬息完成,难于捕捉到各个过程发生的具体时机.Sugimoto和Matijevic将含一定比例的FeSO_4,KOH和KNO_3溶液经85℃陈化制备均匀球状Fe_3O_4的实验中发现,陈化液中最初生成的Fe(OH)_2在硝酸根离子作用下经相转化生成Fe_3O_4微粒子,     

均匀Fe_3O_4胶体粒子形成过程的Mssbauer研究

应用经过改进的实验方法制得均匀球状Fe_3O_4胶体粒子,通过对多种Fe_3O_4粒子的Mossbauer测量并结合化学分析,我们发现,在制备过程中,反应浓度、加液次序以及陈化时间的不同,对所生成的Fe_3O_4晶体的基本骨架与结构影响极小,而随着陈化时间的不断增加,Fe_3O_4粒子的组成将逐渐接近化学计量.以这些实验结果及文献报道为基础,本文讨论了均匀Fe_3O_4胶体粒子的形成机理.     

Fe_3O_4/P(NaUA-St-BA)核-壳纳米磁性复合粒子的合成与表征

以表面包敷有反应型的表面活性剂NaUA(十一烯酸钠)的Fe3O4磁性胶体粒子为种子,运用无皂乳液聚合方法原位制备出Fe3O4P(NaUAStBA)核壳纳米磁性复合粒子.Fe3O4磁性胶体粒子的粒径为10nm左右.IR和TG结果分析表明,苯乙烯、丙烯酸酯和NaUA在Fe3O4粒子的表面发生了聚合反应,形成P(NaUAStBA);TEM和激光粒度分析仪测试结果显示,Fe3O4P(NaUAStBA)复合粒子具有核壳结构而且粒子分布均匀、平均粒径60nm;TG测试的结果表明,NaUA在Fe3O4粒子的包覆率为13.83%,P(NaUAStBA)共聚物的包覆率71.85%;振动样品磁强仪(VSM)测试的磁滞回线则表明由无皂乳液聚合得到的Fe3O4P(NaUAStBA)复合粒子具有超顺磁性,可避免磁性微球在磁场中的团聚.另外,合成的磁性胶乳可稳定存放数月.     

Fe3O4/P(NaUA-St-BA)核-壳纳米磁性复合粒子的合成与表征

以表面包敷有反应型的表面活性剂NaUA（十一烯酸钠）的Fe3O4磁性胶体粒子为种子,运用无皂乳液聚合方法原位制备出Fe3O4／P（NaUA-St-BA）核-壳纳米磁性复合粒子,Fe3O4磁性胶体粒子的粒径为10nm左右,IR和TG结果分析表明,苯乙烯、丙烯酸酯和NaUA在Fe3O4粒子的表面发生了聚合反应,形成P（NaUA-St-BA）;TEM和激光粒度分析仪测试结果显示,Fe3O4／P（NaUA-St-BA）复合粒子具有核-壳结构而且粒子分布均匀、平均粒径60nm;TG测试的结果表明,NaUA在Fe3O4粒子的包覆率为13．83％,P（NaUA-St-BA）共聚物的包覆率71．85％;振动样品磁强仪（VSM）测试的磁滞回线则表明由无皂乳液聚合得到的Fe3O4／P（NaUA-St-BA）复合粒子具有超顺磁性,可避免磁性微球在磁场中的团聚。另外,合成的磁性胶乳可稳定存放数月。     

均匀Fe~3O~4胶体粒子形成机理II. 低温Mossbauer谱研究

在液氮温度下, 测定了均匀Fe~3O~4胶体粒子制备过程中陈化时间为1小时内的不同时间所得样品的Mossbauer谱。结果表明, γ-FeOOH为Fe~3O~4均匀胶粒形成过程的中间产物, 并提出均匀Fe~3O~4胶粒的形成机理。     

均匀Fe~3O~4胶体粒子形成机理II. 低温Mossbauer谱研究

在液氮温度下, 测定了均匀Fe~3O~4胶体粒子制备过程中陈化时间为1小时内的不同时间所得样品的Mossbauer谱。结果表明, γ-FeOOH为Fe~3O~4均匀胶粒形成过程的中间产物, 并提出均匀Fe~3O~4胶粒的形成机理。     

均匀Fe_3O_4胶体粒子形成机理 Ⅱ.低温Mssbauer谱研究

在液氮温度下,测定了均匀Fe_3O_4胶体粒子制备过程中陈化时间为1小时内的不同时间所得样品的Μssbauer谱,结果表明,γ-FeOOH为Fe_3O_4均匀胶粒形成过程的中间产物,并提出均匀Fe_3O_4胶粒的形成机理为:     

正电性磁性氧化铁胶粒负载钯催化的Suzuki偶联反应

发展了一种超顺磁性Fe3O4纳米粒子负载Pd0的简易方法. 利用Fe3O4溶胶带正电荷的特性, 将负离子 通过静电作用吸附在Fe3O4胶体粒子表面( /Fe3O4), 以抗坏血酸(Vc)进一步还原即得到载有金属Pd团簇的Fe3O4胶体粒子(Pd0/Fe3O4). 该磁性载体负载的Pd催化剂对Suzuki反应表现出良好的催化活性, 且在反应后, 可方便地通过永久磁铁将催化剂从反应体系中分离出来, 进行循环使用. 试验表明, 该催化剂在循环使用五次后反应活性无明显下降. 进一步试验发现, 这种磁性纳米粒子负载的金属钯对一系列卤代芳烃的Suzuki偶联反应均表现出较优的催化活性.     

均匀铁氧化物（含水）胶体粒子的制备

均匀胶体具有广阔的应用前景,开展这种胶体的研究具有重要的理论和实际意义。铁氧化物(含水)均匀胶体粒子首先在Matijevi’c的实验室制得。不久前,我们在无防尘设备的一般实验室条件下成功地制得了二种直径为0.090μm的球状α-Fe_2O_3胶体粒子,并开展了均匀胶体的性质研究。为了进一步开展均匀胶体特性及其表面性质的研究,就要制取不同大小和不同形状的胶体粒子,并掌握其制备规律。本文旨在探讨制备铁氧化物胶体粒子对反应液铁离子的浓度、盐酸量以及陈化时间等因素对粒子物相、形状等的影响。     

Systematic control of size,shape, structure,and magnetic properties of uniform magnetite and maghemite particles

As an application of the gel-sol method especially developed for the synthesis of general monodisperse particles in large quantities, uniform hematite (alpha-Fe2O3), magnetite (Fe3O4), and maghemite (gamma-Fe2O3) particles, precisely controlled in size, aspect ratio, and internal structure, have been prepared. For the synthesis of uniform ellipsoidal single-crystal particles of alpha-Fe2O3, a highly condensed suspension of fine beta-FeOOH particles doped with a prescribed amount of PO4(3-) ion in their interiors was aged at 140 degrees C for 24 h with seed particles of alpha-Fe2O3 in an acidic medium containing optimum concentrations of HCl and NaNO3. Systematic control of the aspect ratio and mean size was achieved by regulating the concentration of PO4(3-) ion incorporated into the beta-FeOOH particles and the number of seeds added. The resulting hematite particles were converted into magnetite by reduction in a H2 stream at 330 degrees C for 6 h; the magnetite was then oxidized to maghemite in an air stream at 240 degrees C for 2 h. Magnetite and maghemite thus prepared retained the original shape of the hematite. On the other hand, polycrystalline hematite particles of different sizes and aspect ratios were also prepared by aging a condensed Fe(OH)3 gel in the presence of different concentrations of SO4(2-) ion and seeds. The polycrystalline hematite particles were similarly converted into magnetite and then maghemite. The magnetic properties of these magnetite and maghemite particles were analyzed as a function of their mean particle volume, aspect ratio, and internal structure.     

Micelle-assisted synthesis of polyaniline/magnetite nanorods by in situ self-assembly process

Polyaniline/magnetite nanocomposites consisting of polyaniline (PANI) nanorods surrounded by magnetite nanoparticles were prepared via an in situ self-assembly process in the presence of PANI nanorods. The synthesis is based on the well-known chemical oxidative polymerization of aniline in an acidic environment, with ammonium persulfate (APS) as the oxidant. An organic acid (dodecylbenzenesulfonic acid, DBSA) was used to replace the conventional strong acidic (1 M HCl) environment. Here, dodecylbenzenesulfonic acid is used not only as dopant, but also as surfactant in our reaction system. So, DBSA can excellently control the morphology and size of PANI nanorods and magnetite particles. Magnetite particles were formed simultaneously during sedimentation, and the formed nanorods were also decorated by the particles. The resulting PANI/magnetite composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). It is found that PANI/magnetite nanorod composites have uniform size, superparamagnetism and a small mass fraction of magnetite, thermal stabilization even at a higher temperature.     

Development of novel magnetic nano-carriers for high-performance affinity purification

We developed novel magnetic nano-carriers around 180 nm in diameter for affinity purification. Prepared magnetic nano-carriers possessed uniform core/shell/shell nano-structure composed of 40 nm magnetite particles/poly(styrene-co-glycidyl methacrylate (GMA))/polyGMA, which was constructed by admicellar polymerization. By utilizing relatively large 40 nm magnetite particles with large magnetization, the magnetic nano-carriers could show good response to permanent magnet. Thanks to uniform polymer shell with high physical/chemical stability, the magnetic nano-carriers could disperse in a wide range of organic solvent without disruption of core/shell structure and could immobilize various kinds of drugs. We examined affinity purification using our prepared magnetic nano-carriers with anti-cancer agent methotrexate (MTX) as ligand. Our magnetic nano-carriers showed higher performance compared to commercially available magnetic beads in terms of purification efficiency of target including extent of non-specific binding protein.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

Molecular composition of iron oxide nanoparticles, precursors for magnetic drug targeting, as characterized by confocal Raman microspectroscopy

The chemical and structural properties of ferrite-based nanoparticles, precursors for magnetic drug targeting, have been studied by Raman confocal multispectral imaging. The nanoparticles were synthesised as aqueous magnetic fluids by co-precipitation of ferrous and ferric salts. Dehydrated particles corresponding to co-precipitation (CP) and oxidation (OX) steps of the magnetic fluid preparation have been compared in order to establish oxidation-related Raman features. These are discussed in correlation with the spectra of bulk iron oxides (magnetite, maghemite and hematite) recorded under the same experimental conditions. Considering a risk of laser-induced conversion of magnetite into hematite, this reaction was studied as a function of laser power and exposure to oxygen. Under hematite-free conditions, the Raman data indicated that nanoparticles consisted of magnetite and maghemite, and no oxyhydroxide species were detected. The relative maghemite/magnetite spectral contributions were quantified via fitting of their characteristic bands with Lorentzian profiles. Another quality parameter, contamination of the samples with carbon-related species, was assessed via a broad Raman band at 1580 cm(-1). The optimised Raman parameters permitted assessment of the homogeneity and stability of the solid phase of prepared magnetic fluids using chemical imaging by Raman multispectral mapping. These data were statistically averaged over each image and over six independently prepared lots of each of the CP and OX nanoparticles. The reproducibility of oxidation rates of the particles was satisfactory: the maghemite spectral fraction varied from 27.8 +/- 3.6% for the CP to 43.5 +/- 5.6% for the OX samples. These values were used to speculate about the layered structure of isolated particles. Our data were in agreement with a model with maghemite core and magnetite nucleus. The overall oxidation state of the particles remained nearly unchanged for at least one month.     

Magnetite 3D colloidal crystals formed in the early solar system 4.6 billion years ago

Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because of the strong attractive magnetic interaction. However, we discovered colloidal crystals composed of polyhedral magnetite nanocrystallites of uniform size in the range of a few hundred nanometers in the Tagish Lake meteorite. Those colloidal crystals were formed 4.6 billion years ago and thus are much older than natural colloidal crystals on earth, such as opals, which formed about 100 million years ago. We found that the size of each individual magnetite particle determines its morphology, which in turn plays an important role in deciding the packing structure of the colloidal crystals. We also hypothesize that each particle has a flux-closed magnetic domain structure, which reduces the interparticle magnetic force significantly.     

Preparation and characterization of magnetic polymeric composite particles by miniemulsion polymerization

A water‐based magnetite ferrofluid, with an average size of about 10 nm, was prepared in a first step by the chemical coprecipitation of ferrous and ferric salts. Oil‐based styrene (St) magnetite ferrofluid was obtained by the acidification of the water‐based magnetite ferrofluid and the dispersion of the acidified magnetite in St. Magnetic polymeric composite particles (MPCPs) were prepared by miniemulsion polymerization in the presence of the oil‐based St magnetite ferrofluid with hexadecane as a hydrophobe, 2,2′‐azobisisobutyronitrile as an initiator, and sodium dodecyl sulfate as an emulsifier. Methacrylic acid was used as a comonomer, and hydroxyethyl cellulose and polyvinylpyrrolidone were used as aid stabilizers subsequently. With the aim of improving the encapsulation degree of magnetite, avoiding pure polymer particles and exposed magnetite particles, and obtaining the narrowest particle size distributions, the encapsulation conditions of magnetite were investigated in detail. The results show that miniemulsion polymerization is an effective method for encapsulating magnetite into a hydrophobic polymer successfully. Exposed magnetite particles and pure polymer particles can be avoided completely by the selection of the appropriate preparation conditions. All the resulting MPCPs exhibited superparamagnetism and possessed some magnetic response. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4187–4203, 2006     

Magnetically immobilized frits for the preparation of packed columns used in capillary electrochromatography

Fabrication of porous frits to retain stationary phases is a critical issue in column preparation for capillary electrochromatography (CEC). In this work, porous frits were prepared by applying an external magnetic field to magnetically responsive particles placed inside a fused-silica capillary. Three batches of uniform magnetite spheres with particle diameters of 0.3, 0.4, and 0.6 μm and saturation magnetization values of 73.03, 74.41, and 77.83 emu/g, respectively, were used as frit particles and octadecyl- and phenyl-bonded silica gels were packed successfully into frit-containing capillaries. The performance of the resulting magnetically immobilized frits and packed columns was evaluated. The electroosmotic mobilities in capillaries containing outlet frit only were found to be reduced by 2–4% whereas the plate heights of an unretained marker increased by 30–50% as compared to those in open capillaries. These variations are believed to be associated with the inhomogeneities of the packed structure of the frits. The magnetically immobilized frits showed adequate mechanical strength to withstand the flow drag force, allowing separation in capillaries packed with 5-μm stationary phases up to 10–15 cm, thus rendering column efficiency and reproducibility comparable with those obtained with sintered frits. Taken together, retaining frits made of uniform magnetite particles serves as a viable alternative to sintered frits for column preparation, which offers several distinct advantages such as ease of preparation, improved durability as compared to sintered frits where the removal of the polyimide coating makes the packed column susceptible to breakage, and use of large-bore capillaries for semipreparative separations.     

细乳液聚合法制备磁性复合微球及其表征

在制备超细Fe3O4 磁性粒子的基础上 ,以 3种低分子量聚合物Disperbyk 1 0 6、Disperbyk 1 0 8和Disperbyk 1 1 1为Fe3O4 微粒在单体相中的分散稳定剂 ,采用细乳液聚合法制备了平均粒径为 3 40nm的PS Fe3O4 磁性复合微球 .详细研究了分散剂种类对细乳液聚合制备磁性复合微球的影响 ,并采用XRD、TGA和TEM等手段对磁性复合微球的形态、结构及磁响应性等进行了表征 .实验结果证明分散剂的选择对磁性复合微球的成功制备起着至关重要的作用 ,兼具酸性和碱性功能基的分散剂Disperbyk 1 0 6具有更好的分散和稳定效果 .TEM结果表明 ,所制备的复合微球具有一些缺陷 ,而缺陷处往往是Fe3O4 磁性粒子聚集的地方