Extraction and purification of magnetic nanoparticles from strain of Leptospirillum ferriphilum

1Introduction From1975,there is much interest in finding magne-totactic bacteria[1],because bacterial magnetosome particles,unlike those produced chemically,have a consistent shape,a unique crystallography,a narrow size distribution within the single magn…     

Fe2+对嗜铁钩端螺旋菌L. ferriphilum生长活性的影响

以分离于江西某铜矿的嗜铁钩端螺旋菌（L.ferriphilum YSK）菌株为研究对象,报道不同Fe^2＋浓度对L.ferriphilum生长活性的影响。结果表明,YSK菌株生长最适宜的Fe^2＋浓度约为0.1 mol/L。当初始Fe^2＋浓度为0.4 mol/L时,进入对数生长期前很明显需要一个较长的延迟期,表明该Fe^2＋浓度对细胞的生长产生较强的抑制作用;当初始Fe^2＋浓度为0.6 mol/L时,YSK菌株的生长完全受到抑制。尽管高浓度的Fe^2＋抑制细胞的生长,但受到抑制而不生长繁殖的YSK细胞仍然具有氧化Fe^2＋的能力。     

Enhancement of densification and sintering behavior of tungsten material via nano modification and magnetic mixing processed under spark plasma sintering

In the present study, the influence of nano additives (Ni, Fe) and different mixing (turbular and magnetic) on the densification, microstructure and micro-hardness of the tungsten material under spark plasma sintering is analyzed. After turbulent mixing the nanoparticles are distributed widely in the W interparticle gaps but after magnetic mixing the nanoparticles are distributed not only on the gaps of the W particles but also on the broken surfaces. Ni incorporated tungsten materials achieved the maximum density of 98.3% at 1400 °C (turbular mixing) and 97.9% at 1300 °C (magnetic mixing). Fe incorporated tungsten material showed density of 97.7% at 1600 °C and 97.2% at 1400 °C after turbular and magnetic mixing. The influence of nanoparticles in the densification process was explained by Laplace force, boundary slip and Agte-Vacek effect. The microstructural analysis showed that nano-modification reduced the degree of porosity, and provides a compact material at low temperatures. X-ray fluorescence analysis reveals that magnetic mixing shows more uniform distribution of nanoparticles than turbular mixing. The nanoparticles incorporation increased the micro hardness of tungsten material. Hence, it is clear that magnetic mixing and nano modification greatly improved the densification and sintering behavior of the tungsten material.     

Synthesis and characterization of aminated SiO2/CoFe2O4 nanoparticles

A kind of newly aminated CoFe2O4 nanoparticles were synthesized by grafting process for biomedical applications, which were coated primarily with silicon dioxide（SiO2）. The characterizations of aminated SiO2/CoFe2O4（ASCN） and SiO2-coated CoFe2O4（SCN） nanoparticles were investigated using elemental analysis, thermogravimetric analysis（TGA）, differential thermal analysis（DTA）, infi＇ared spectroscopy（IR）, atomic force microscopy（AFM）, zeta-potential measurement and vibrating sample magneto-metry（VSM） The AFM micrograph shows that the ASCN nanoparticles are approximately spherical with an average diameter of 30 nm. Based on IR and TGA results, it is suggested that the surface of the SiO2-coated CoFe2O4 nanoparticles are graiied with amino compounds. The elemental analysis also shows the presence of 0.98 mmol/g of organic moieties immobilized on the surface ofASCN nanoparticles. Zeta-potential data ofASCN nanoparticles also reveal that amino compounds are bonded onto the surface of SiO2-coated CoFe2O4 nanoparticles by ether linkage. The magnetic parameters show that ASCN nanoparticles still have good magnetic property.     

Magnetization of superparamagnets in the state of mechanical anisotropy

The internal energy of magnetic anisotropy in some particles dominates over the thermal energy, even at room temperature. The existence of strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of superparamagnets. However, if the axes of magnetic anisotropy of nanoparticles are randomly oriented, then their presence does not affect the process of magnetization, which occurs according to the classical Langevin theory. However, if the axes of nanoparticles are polarized (mechanical anisotropy), then the magnetization curve of a superparamagnet under the conditions of mechanical anisotropy lies between the Langevin curve and the curve of hyperbolic tangent and with increasing anisotropy moves progressively farther from the Langevin curve and approaches the curve of hyperbolic tangent. It has also been shown that, in the case of powder superparamagnets, the presence of mechanical anisotropy leads to significant changes in the Curie constant.     

载银磁性Fe3O4纳米粒子的制备与催化及抗菌性能的研究

利用磁性纳米粒子Fe3O4表面的聚多巴胺 (PDA) 对银离子的吸附作用,采用种子诱导法制备了载银磁性纳米粒子 (PDA-Fe3O4@Ag)。采用UV-Vis (紫外-可见) 光谱对PDA-Fe3O4@Ag纳米粒子的制备过程进行了分析,采用FTIR (红外光谱)、XRD (X射线衍射仪)、TEM (透射电镜) 和VSM (振动样品磁强计) 等手段对所得的PDA-Fe3O4@Ag粒子进行表征;研究了PDA-Fe3O4@Ag对4-硝基苯酚还原反应的催化作用,还测试了其抗菌性能。结果表明,纳米金种子的存在是制备PDA-Fe3O4@Ag纳米粒子的关键;在外加磁场作用下该磁性催化剂可以容易地从反应体系中分离,经多次循环使用后仍具有良好的催化性能;此外PDA-Fe3O4@Ag纳米粒子具有杀菌性能,且经磁分离回收循环利用5次后仍呈现对金黄色葡萄球菌较好的杀菌效果。     

Comparative genome analysis on intraspecific evolution and nitrogen fixation of Leptospirillum ferriphilum isolates

To reveal the intraspecific evolution of Leptospirillum ferriphilum isolates which thrived in industrial bioleaching ecosystems and acid mine drainages, genome sequences of L. ferriphilum YSK, L. ferriphilum DX and L. ferriphilum ZJ were determined to compare with complete genome of L. ferriphilum ML-04. The genome comparisons reveal that extensive intraspecific variation occurs in their genomes, and that the loss and insertion of novel gene blocks of probable phage origin may mostly contribute to heterogeneity of gene content among L. ferriphilum genomes. Surprisingly, a nif gene cluster is identified in L. ferriphilum YSK and L. ferriphilum ZJ genomes. Intensive analysis and further experiments indicate that the nif gene cluster in L. ferriphilum YSK inherits from ancestor rather than lateral gene transfer. Overall, results suggest that the population of L. ferriphilum undergoes frequent genetic recombination, resulting in many closely related genome types in recent evolution. The combinatorial processes profoundly shape their physiologies and provide the basis for adaptation to different niches.     

Landau理论研究TiNi顺磁合金热/强磁场耦合下的马氏体相变

利用改进后的Landau理论模型研究了顺磁TiNi合金在热/强磁场耦合作用下的马氏体相变行为.利用第一原理计算了TiNi合金在不同相变剪切应变(序参量)下的Flermi面态密度,得到相变过程中磁化率和磁自由能的变化,把磁场效应引入到Landau模型中.结果表明,稳恒强磁场可使顺磁材料的相变温度(M6和T0)出现突变性的升高,这主要是因为相变驱动力随磁场增强而呈二次曲线上升规律.另外,因强磁场下马氏体变体之间的自由能差急剧增大,导致磁场对变体的促进和抑制作用变得明显,出现取向生长现象.在5 T稳恒强磁场下的TiNi合金相变实验中,利用TEM观察到了一些变体以相互垂直的二变体形式出现(即取向生长),证实了模型的结果.     

多元醇还原法制备NiPd磁性纳米合金

采用多元醇还原法,以乙二醇为反应溶剂和还原剂,PVP为稳定剂,制备尺寸约30nm、在极性溶剂中分散良好的NiPd纳米粒子。采用XRD、ICP和TEM等手段对所制备的不同组成的纳米粒子进行表征,证明所制纳米粒子为NiPd合金,采用PVP为稳定剂有效地阻止了纳米粒子的团聚与氧化。所制备的纳米粒子的磁学性质及磁热效应结果表明,NiPd纳米合金具有较大的矫顽力,表现为铁磁性,且随着组分中Ni含量的增加,纳米合金的饱和磁化强度和磁热效应均增加,纳米粒子在60kHz、7.5kA/m的交变磁场作用下,试样的悬浮液升温可达14℃左右,显示出较高的磁热性能。     

不同晶粒尺寸的(La0.47Gd0.2)Sr0.33MnO3纳米颗粒磁性能

采用非晶态多核配合的方法制备了(La0.47Gd0.2)Sr0.33MnO3纳米颗粒,用XRD、HRTEM和MPMS等手段对纳米颗粒的微观结构和磁性能进行研究。XRD和SAD分析表明,所有的样品都具有单相钙钛矿结构;TEM分析表明, 经过600,800和1000 ℃烧结10 h后的样品颗粒尺寸分别为40~50 nm,90~100 nm和140~150 nm。样品的磁学性能结果表明：(La0.47Gd0.2)Sr0.33MnO3纳米颗粒的居里温度TC (298 K)基本上不随颗粒尺寸的变化而变化,而相对磁制冷能力取决于颗粒尺寸;颗粒尺寸为90~100 nm的(La0.47Gd0.2)Sr0.33MnO3纳米颗粒的相对磁制冷能力最大,可以作为室温下使用的磁制冷工质侯选材料。     

The anti-microbial activity of titania-nickel ferrite composite nanoparticles

A novel approach to synthesize a new generation of composite nanoparticles consisting of a photocatalytic shell of anatase-titania and a magnetic core of nickel ferrite has been adopted combining reverse micelle and chemical hydrolysis techniques. Titania is an effective anti-microbial agent that can be directly sprayed on infected areas of the human body or environment. Unfortunately, titania is an electrical insulator and is difficult to extract from the sprayed surface after treatment. The titania photocatalytic shell provides good antimicrobial capability that renders the bacteria inactive and removes the organic pollutants, while the nickel ferrite magnetic core enables controlled delivery of composite nanoparticles through the application of a small magnetic field, encouraging their application as removable anti-microbial photocatalyst nanoparticles. For more information, contact R.D.K. Misra, University of Louisiana at Lafayette, Center for Structural and Functional Materials, P.O. Box 44130, Lafayette, LA 70504-4130; (337) 482-6430; e-mail dmisra@louisiana.edu.     

Sintering process and grain growth of Mn-Zn ferrite nanoparticles

The density, microstructure and magnetic properties of non-doped Mn-Zn ferrite nanoparticles sintered compacts were investigated. The compacts of non-doped Mn-Zn ferrite nanoparticles were sintered by segmented-sintering process at lower sintering temperature. The density of sintered samples was measured by Archimedes method, and the phase composition and microstructure were examined by XRD and SEM. The sintered Mn-Zn ferrite magnetic measurements were carried out with Vibrating Sample. The results show that the density of sintered compacts increases with the rising of sintering temperature, achieving 4.8245 g·cm-3 when sintered at 900 ℃, which is the optimal density of Mn-Zn functional ferrite needed and from the fractured surface of sintered samples, it can be seen that the grain grows well with small grain size and homogeneous distribution.     

Metal magnetic memory signal response to plastic deformation of low carbon steel

Metal magnetic memory (MMM) technique can be potentially used to evaluate early damage of ferromagnetic materials nondestructively due to its high sensitivity to stress and stress–strain state. An experimental investigation of the effect of plastic deformation on magnetic behavior has been undertaken in low carbon steel specimens. The measurements were made under applied tension after unloading in the elastic–plastic region for different strain levels. Magnetic memory signals show apparently different variation characteristics in the elastic and plastic ranges, and the magnetic signals are sharply changed by a rather small plastic deformation, which is in agreement with the predictions of the modified magnetomechanical effect model correlating magnetic memory signal with plastic strain. The results of the present work indicate that the MMM method can detect macroyielding and early stage of plastic deformation effectively.     

PVP对FePt纳米颗粒磁性能的影响

以乙酰丙酮铁(Fe(acac)3)和氯铂酸(H2PtCl6·6H2O)作为Fe源和Pt源,硼氢化钠(NaBH4)作为还原剂,PVP作为表面活性剂,通过化学还原法制备出单分散的FePt纳米颗粒,研究PVP对FePt纳米颗粒磁性能的影响。通过X射线衍射(XRD)仪,透射电子显微镜(TEM)和振动样品磁强计(VSM)对纳米颗粒进行表征。结果表明:PVP修饰的FePt纳米颗粒为面心立方(fcc)结构,形状近似球形且分散性良好,矫顽力为零,呈超顺磁性。当PVP与Fe(acac)3的比例为7:1时,经600℃热处理保温30min,FePt纳米颗粒从无序的fcc结构转变为有序的fct结构,矫顽力最大,可达5460A·m-1。     

Characterization of copper nanoparticles synthesized by a novel microbiological method

The exploitation of various biomaterials for the biosynthesis of nanoparticles is considered as green technology as it does not involve any harmful chemicals. The present study reports the synthesis of copper nanoparticles which involves non-pathogenic bacterial strain Pseudomonas stutzeri, isolated from soil. These copper nanoparticles are further characterized for size and shape distributions by ultraviolet-visible spectroscopy, x-ray diffraction, and high resolution transmission electron microscopy techniques. The results showed that the particles are spherical and quite stable in nature and shows surface plasmon resonance clearly featured in the optical spectra in visible region.     

DTAB溶液中纳米银的制备

常温磁力搅拌下,在十二烷基三甲基溴化铵(DTAB)体系中用水合肼还原硝酸银制备了颗粒细小均匀的纳米银粉。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见光谱(UV-vis)对产品进行了分析表征。结果表明,纳米银并非是由水合肼直接还原Ag+生成,而是生成的溴化银逐渐被还原后的产物。随着反应时间的变化,体系中首先形成粒度均匀的类球形溴化银,随后转变为多面体的溴化银,最后转变为颗粒细小的纳米银。     

热处理对FePt纳米颗粒磁性能的影响

通过多重还原法制备FePt纳米颗粒,并研究不同热处理温度对其磁性能影响.XRD及TEM分析表明:所制备的FePt纳米颗粒为fcc结构,颗粒为类球形且分散性较好,尺寸在5.0 nm左右.DSC及VSM显示,高温退火处理可以使FePt纳米颗粒从无序的fcc相变成有序的fct相,随着温度的升高矫顽力变大,600 ℃时可达240 kA/m,但是在高温区(550 ℃及以上)矫顽力的变化并不明显,这主要是由高温退火过程中纳米颗粒的团聚导致的.     

Ni46Mn35Ga19单晶大的磁熵变和磁控形状记忆效应

采用多种测量手段,对制备出的转变温度在室温以上的Ni46Mn35Ga19单晶的物性进行表征。电阻和交流磁化率结果表明,该材料的磁转变和马氏体相变是同时发生的。定温磁化强度测量得出材料磁熵变的增长速率高达9.0J/kg·K·T,在1274kA/m(1.6T)的磁场下,磁熵变达13.8J/kg·K。此外,应变测量表明,伴随该磁熵变,材料展现出应变量分别高达–0.89%和–1.90%的自发和磁控双向形状记忆效应。