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:     

水煤气变换催化剂Fe~3O~4的亚稳结构

X射线Rietveld结构修正发现, α-Fe~2O~3与γ-Fe~2O~3在400℃用水煤气还原得到的尖晶石型水煤气变换催化剂Fe~3O~4有不同的氧密堆积结构参数。用键价理论估算四面体A位和八面体B位Fe原子电价, γ-Fe~2O~3还原的Fe~3O~4电价明显偏离α-Fe~2O~3还原的Fe~3O~4所具有的正常电价, 但经600℃热处理后, 回复到正常Fe~3O~4的电价。这二种Fe~3O~4的Mossbauer谱存在明显的差异, α-Fe~2O~3还原的Fe~3O~4的第一峰有明显分裂, A位和B位的同质异能位移的趋势反映出来的Fe原子电价变化趋势, 与用键价理论推算的Fe原子电价变化趋势一致。我们把这种由γ-Fe~2O~3还原、电价偏离正常Fe~3O~4、并与水煤气低温变换催化活性有关的Fe~3O~4称为亚稳态Fe~3O~4。     

电化学嵌锂尖晶石型Li~xFe~3-ωO~4的电子结构

Mossbauer谱学研究了Li│LiClO~4-PC│Fe~3-ωO~4电池放电过程中阳极反应电子在阴极Fe~3-ωO~4中的分布得出,一小部分电子进入氧化铁八面体FeO~6的t2~g非键轨道成为跳变电子,大部分电子则进入较高能量的反键轨道.     

氢还原下铁钼催化剂的表面性质

用XPS对H_2还原下的铁钼催化剂的表面性质进行了研究。实验表明:H_2还原使表面钼离子由Mo~(6+)还原为Mo~(5+)和Mo~(4+),并与Fe~(3+)作用氧化为Mo~(6+);Fe~(3+)则由于与Mo~(5+)和Mo~(4+)作用以及H_2还原而变为Fe~(2+),从而形成了一个没有O_2存在,仅有H_2作用下的Mars-Krevelen氧化还原循环过程。在催化剂表面上生成的FeMoO_4,其Mo~(6+)的3d3/2和3d5/2的结合能值比Fe_2(MoO_4)_3中的Mo~(6+)的3d能级结合能值低。Mo(或Mo和Fe)离子键合的O~(2-)与H_2作用生成的Mo(Fe)-OH,其Os结合能的测定值低于键合于Mo(Fe)离子中的O~(2-)的Os结合能值,并且该结合能峰由于-OH间的相互作用结合成的水的脱附而消失。此外.给出了还原过程中H_2与催化剂表面O~(2-)相互作用的反应图式。     

非晶Fe~90Zr~10合金氨合成催化剂的活化行为

在氨合成气氨中对非晶Fe~90Zr~10合金条带进行了活化。采用AES, XPS, SAM,SEM等分析方法, 并结合氩离子原位轰击剥层研究了非晶Fe~90Zr~10合金条带活化前后自由侧及贴辊侧的表层成分分布, 元素化学状态及表面形貌, 结果表明, 原始条带自由侧表层存在差显著的Zr偏聚, 而贴辊侧表层则存在着Fe的偏聚和Zr的贫集。贴辊侧和自由侧表面Fe氧化物分别为Fe~3O~4和Fe~2O~3。活化后, 自由侧表面Zr浓度下降,而贴辊侧表面Zr浓度增加, 贴辊侧Fe氧化物得到了全部还原, 活化后条带体结构发生了晶化, 表面形成了蜂窝状结构及许多环状裂纹, 对活化机理进行了讨论。     

按逆向而行的思路研究硫酸溶液中铁的电化学振荡

以发生电化学振荡为导向,设计可能引起振荡的化学与物理环境,由实验反向验证振荡机理,从而揭示金属电化学振荡的本质,这就是逆向而行的思路。本文通过改变Fe/H~2SO~4溶液界面附近溶液的pH,Fe^2^+浓度等因素,人为地促进或阻碍Fe(OH)~2膜或Fe~3O~4膜的生成与溶解,创造可能发生电化学振荡的外界环境,验证了有关Fe/H~2SO~4体系电化学振荡主要归因于铁电极表面Fe(OH)~2膜或Fe~3O~4膜的周期性生成与溶解的机理。这表明用逆向而行的思路研究金属的电化学振荡是可行的。     

碳钢钝化膜在碳酸盐溶液中的阴极还原机理

本文采用动电位和恒电流技术研究了pH8.31-11.37的酸盐缓冲溶液中, 低碳钢钝化膜的阴极还原机理。认为钝化膜的还原与溶液pH值密切相关, 当8.31≤pH≤9.80时, Fe~2O~3还原为Fe用FeOH^+;当9.80相似文献   

铬在纳米晶氧化铁中的掺杂研究

Fe^3^+(Cr^3^+)/Fe^2^+混合离子(M^3^+/M^2^+原子比为2:1)共沉淀法制备的Cr~2O~3掺杂量O～14%(质量分数)系列纳米氧化铁,XRDRietveld分析表明全是晶态γ-Fe~2O~3和非晶Fe~2O~3的混合物。非晶丰度范围为21.72%～48.6%。Mossbauer谱分析发现,掺杂量少于2%(质量分数)的氧化铁,晶态和非晶态均是磁性六线谱,大于2%(质量分数)后,另出现强度随掺杂量增加线性递增的超顺磁二线谱。共沉淀过程中,Fe^3^+为主夹杂定量Cr^3^+的Fe^3^+水合配合物网络与Cr^3^+为主夹杂定量Fe^3^+的Cr^3^+水合配合物网络,是形成磁性氧化铁和非晶非磁氧化铁的基础,后者镶嵌在前者中间,阻碍其晶化和晶粒长大,自身形成非晶非磁含铬氧化铁。     

激光烧蚀La~2O~3产生的等离子体的发光光谱研究

用发光光谱法研究了355nm脉冲激光在真空和O~2气氛中烧蚀La~2O~3产生的等离子体的组成和形成过程。对等离子体中La^+离子和LaO的空间和时间分辨发光光谱分析表明,在O~2气氛中LaO有两个生成通道:一是在靶附近的等离子体内直接生成的,另一是由La,La^+与O^2发生氧化反应而生成的。测定了激光能量密度,离靶表面的距离和O~2压力对产物发光的延迟时间和发光强度的影响。此外,还讨论了激光烧蚀La~2O~3诱导产生等离子体的形成和演化机理。     

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.     

不同形貌的Fe3O4微-纳米粒子的溶剂热合成

以FeCl3?6H2O为铁源,用乙二醇或1,2丙二醇为溶剂,PEG为表面活性剂,以及NaOH或KOH为碱源,采用溶剂热法,制备出具有亲水性、分散性较好、超顺磁性和形貌各异的Fe3O4微、纳米颗粒,并对其形貌、结构和磁性进行了表征. 结果表明,产物是均为立方晶系Fe3O4,其颗粒尺寸从20nm-600nm可调. 我们观察到碱源的种类和用量、反应时间、溶剂等对产物形貌的影响,其中碱的用量影响最大. 本文对不同形貌Fe3O4的形成过程进行了探讨,并提出了合理的解释. 所得到的室温下呈现超顺磁性的Fe3O4粒子可以初步满足了生物医学中的应用.     

Porous Fe3O4 nanoparticles: synthesis and application in catalyzing epoxidation of styrene

A facile route was employed to synthesize porous magnetite via reaction of FeCl(3)·6H(2)O with N(2)H(4)·H(2)O in ethylene glycol without any structure-directing agent. The resultant Fe(3)O(4) particles were characterized by transmission electron microscopy, N(2) adsorption, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. It was demonstrated that the particle size varied in the range of 40-220 nm, and the pore size of particles was centered around 2 nm. The gases produced in the formation process of the particles played key role in the formation of the porous structure. The obtained porous magnetite was used as support to immobilize Au nanoparticles with size less than 2 nm with the assistance of L-cysteine. The as-prepared Fe(3)O(4) particles can effectively catalyze epoxidation of styrene, and the immobilization of Au nanoparticles on the Fe(3)O(4) support significantly improved the activity of the catalyst.     

Preparation and characterization of Fe_3O_4/Au composite particles

Colloid gold with different sizes has been widely used in immunoassay and nucleic acid detection mainly because of their properties for immobilization of biomolecules, such as antibodies and oligonucleo-tides, through chemical reactions via active group SH on the biomolecules. Magnetic particles modified with various chemical groups on their surface can not only exhibit good magnetic responsiveness to an external magnetic field but also immobilize biomolecules through these chemical groups. As…     

钾助催化剂与Fe3O4相互作用行为的XRD表征

XRD研究表明 ,作为乙苯脱氢催化剂中的氧化铁活性组分 ,具有反式尖晶石结构的Fe3O4 比刚玉型的α Fe2O3 更易与钾助催化剂发生相互作用 :α Fe2O3-K2O需经850℃煅烧才能生成多铁酸钾 ,但在Fe3O4 -K2O体系中只需700℃即可.而且 ,钾还可抑制Fe3O4 被氧化为α Fe2O3 的进程 ,在空气中 ,Fe3O4 只需300℃煅烧即可明显转化为α Fe2O3 ,但同样的转化在Fe3O4 K2O体系中要经700℃煅烧才会明显地发生.实验结果表明 ,某种形态的多铁酸钾可能是催化剂中的储钾相.     

Effects of magnetite nanoparticles on the thermorheological properties of carrageenan hydrogels

The influence of magnetite (Fe(3)O(4)) nanoparticles on the rheological properties of kappa-, iota- and lambda-carrageenan gels has been investigated. Small amplitude oscillatory shear measurements were performed to study the effect of the presence of Fe(3)O(4) nanoparticles with particle sizes of ca. 10 nm on the gel properties, as a function of carrageenan type, carrageenan concentration and magnetite load. The formation of Fe(3)O(4) nanoparticles on the presence of biopolymer was observed to promote the gelation process and lead to stronger gels as indicated by an increase in the gel viscoelastic moduli and of the gelation temperature. This effect was more marked for kappa-carrageenan than for iota- and lambda-carrageenan and has been proposed to depend not only on Fe(3)O(4) concentration but also on the concentration of potassium ions. A mechanism based on the combined effect of Fe(3)O(4) nanoparticles and potassium ions was suggested, involving the adsorption of potassium ions on the negatively charged surface of the Fe(3)O(4) nanoparticles, thus leading to an increase of the potassium ion concentration within the "carrageenan cages" containing the magnetite. This would, therefore, promote more extensive biopolymer helical aggregation, thus resulting in the formation of a stronger kappa-carrageenan gel in the presence of Fe(3)O(4), as observed. Since iota- and lambda-carrageenan gels are known to be less sensitive to potassium ions concentration, the effect of precipitating Fe(3)O(4) within these biopolymers is reduced.     

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。     

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     

Control on size and adsorptive properties of spherical ferric phosphate particles

Ferric phosphate particles were prepared by aging a solution dissolving Fe(ClO4)(3) and H3PO(4) at 40-80 degrees C for 16 h in a Teflon-lined screw-capped Pyrex test tube. The spherical or agglomerated fine particles were only precipitated with an extremely fast rate of reaction. The spherical particles were only produced at a very narrow region in fairly low pH solutions. TEM observation revealed that these particles grew in spherical structure by aggregation of primary small particles. The size of spherical particles was decreased by increase in the solute concentration or raising the aging temperature. Therefore, the formation of spherical particles was explained by a polynuclear layer mechanism proposed by Nielsen. The uniform spherical particles produced are amorphous, but they were crystallized to FePO(4) after calcining above 600 degrees C. It was suggested that the voids between the primary particles within the secondary agglomerated particles constitute mesopores. The Fe/P molar ratio determined and weight loss in TG curves gave the chemical formulas of the particles as Fe(PO4)x(H2PO4)y.nH2O (x: 0.93-1.00, y: 0-0.22, n: 2.4-2.7). The amorphous spherical ferric phosphate particles showed a high selective adsorption of H2O by penetration of H2O molecules into ultramicropores, produced after outgassing pretreatment, of that size is smaller than N2 molecule. The more particles grew, the more adsorption selectivity of H(2)O became remarkable.     

Preparation of silica-magnetite nanoparticle mixed hemimicelle sorbents for extraction of several typical phenolic compounds from environmental water samples

A novel type of superparamagnetic silica-coated (Fe3O4/SiO2 core/shell) magnetite nanoparticle modified by surfactants has been successfully synthesized and was applied as an effective sorbent material for the pre-concentration of several typical phenolic compounds (bisphenol A (BPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP)) from environmental water samples. Compared with pure magnetic particles, a thin and dense silica layer would protect the iron oxide core from leaching out in acidic conditions. In order to enhance their adsorptive tendency towards organic compounds, cetylpyridinium chloride (CPC) or cetyltrimethylammonium bromide (CTAB) were added, which adsorbed on the surface of the Fe3O4/SiO2 nanoparticles (Fe3O4/SiO2 NPs) and formed mixed hemimicelles. Main factors affecting the adsolubilization of analytes were optimized and comparative study on the use of CPC and CTAB-coated Fe3O4/SiO2 NPs mixed hemimicelles-based SPE was also carried out. CPC-coated Fe3O4/SiO2 NPs system was selected due to lower elution volume required and more effective adsorption of the target compounds. Under selected conditions, concentration factor of 1600 was achieved by using this method to extract 800 mL of different environmental water samples. The detection limits obtained for BPA, 4-OP and 4-NP with HPLC-FLD were 7, 14, and 20 ng/L, respectively.