直流碳弧法制备碳包覆铁纳米颗粒机理研究

采用直流碳弧等离子体法成功制备了碳包覆铁纳米颗粒,利用透射电子显微镜和高分辨透射电子显微镜、X射线衍射、X射线能谱仪对样品的形貌、物相结构、化学成分和粒度进行表征分析,并对碳包覆纳米金属颗粒的形成机理进行初步探讨。结果表明:直流碳弧等离子体技术制备的碳包覆纳米金属颗粒具有明显的铁核(bcc-Fe)/碳壳(石墨层片)包覆结构,颗粒大多呈球形和椭球形,粒径分布在20~60nm范围,平均粒径为44nm,铁粒子外碳层的厚度为5~8nm。碳包覆铁纳米铁颗粒是通过颗粒内部固态形式的碳自行扩散至颗粒表面和颗粒外部气态形式的碳沉积到颗粒表面形成的。     

氢电弧等离子体法制备碳包铁纳米粒子

采用氢电弧等离子体法制备了碳包铁纳米粒子,通过X射线衍射仪(XRD)、透射电镜(TEM)、扫描电镜(SEM)、X射线能谱仪(EDS)、热重-差热分析仪(TG-DSC)等分析手段对粒子的成分、形貌,相结构,热性能等进行了表征.结果表明,制备的粒子中含有α-Fe、Fe3 C、无定形碳和石墨,没有铁的氧化物相出现.铁粒子外碳层的厚度为5～15nm,碳包铁纳米粒子的熔点为1360℃,碳层的存在增强了纳米粒子的抗酸蚀能力.     

直流碳弧等离子体法制备碳包覆铁纳米颗粒研究

在惰性保护气氛下,采用直流碳弧等离子体法成功制备了碳包覆铁纳米颗粒,并利用x射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、X射线能谱仪(EDS)、透射电子显微镜(TEM)和相应选区电子衍射(ED)等测试手段,对样品的化学成分、形貌、物相结构、粒度等特征进行表征分析.实验结果表明:直流碳弧等离子体技术制备的碳包覆纳米金属颗粒具有明显的核-壳结构,内核金属结晶度较高,外壳碳为类石墨层结构,颗粒大多呈球形和椭球形,粒径分布在20nm～60nm范围,平均粒径为44nm.     

纳米钯/铁双金属颗粒对一氯乙酸的脱氯

为了提高零价铁对氯代有机物还原脱氯的性能,采用还原沉淀法制备了纳米钯/铁双金属颗粒.利用X射线衍射(XRD)、X射线荧光光谱(XRF)、扫描电子显微镜(SEM)、透射电镜(TEM)、以及BET-N2比表面积法对纳米钯/铁双金属颗粒进行了表征.结果表明,制备的纳米钯/铁双金属颗粒中Fe主要以α-Fe0形式存在.纳米钯/铁双金属颗粒的直径约为30～50nm,比表面积约51m2/g.纳米钯/铁双金属颗粒对一氯乙酸还原脱氯的脱氯率是还原铁粉和纳米铁粉对一氯乙酸还原脱氯的脱氯率的7.9倍和1.7倍.     

多元醇法合成高比表面积纳米碳颗粒

提出了一种多元醇法敞开体系下制备具有高比表面积的非晶态纳米碳颗粒的方法.以三甘醇作为高沸点溶剂溶解溴化铵,将溶解有二茂铁的无水乙醇在200℃有氧气氛下滴入三甘醇中,利用溴化铵与二茂铁在溶剂中反应制备尺寸均匀的纳米碳颗粒.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和氮气吸附-脱附等温线对纳米碳颗粒的微观结构进行了表征.结果表明碳颗粒近似为等轴状,尺寸分布在30～70nm之间,是完全的非晶态结构,比表面积为578.68m2/g,孔容为0.39cm3/g.反应物在三甘醇中的均匀溶解、反应是生成尺寸均一的纳米碳颗粒的主要因素.     

核壳型碳铁纳米粉体的制备及磁性能研究

采用直流碳弧法制备碳包铁纳米粒子,用透射电子显微镜(TEM)、X射线衍射仪(XRD)对产物的形貌和尺寸、物相结构组成进行分析,并在真空和氮气气氛下在200～800℃对制备的碳包铁纳米粒子进行热处理,用振动样品磁强计测量处理前后的碳包铁纳米粒子的剩磁强度、矫顽力和饱和磁化强度.结果表明,碳包铁纳米粒子的磁滞回线显示出较好的超顺磁特性;剩磁强度、矫顽力和饱和磁化强度随着粉体中铁含量的增加而增大.对碳包铁纳米粒子进行热处理,其磁性能随温度的升高首先改善,温度进一步升高又逐步劣化.在450℃退火,粉体磁性能最佳.     

碳包覆NiO纳米颗粒的制备与性能

采用直流电弧放电等离子体技术成功制备了碳包覆NiO(NiO@C)纳米颗粒,并对样品的形貌、晶体结构、粒度、比表面积和孔结构采用高分辨透射电子显微镜、X射线衍射、X射线能量色散分析谱仪、拉曼散射光谱和N_2吸-脱附等测试手段进行了分析。实验结果表明:直流电弧等离子体技术制备的NiO@C纳米颗粒具有典型的核壳结构,内核为面心立方结构的NiO纳米颗粒,外壳为碳层。颗粒形貌主要为立方体结构,粒度均匀,分散性良好,粒径分布在30~70nm范围,平均粒径为50nm,外壳碳层的厚度为5nm。NiO@C纳米颗粒BET比表面积为28m~2/g,等效直径为46nm,与TEM和XRD测得的结果基本一致。Raman光谱说明样品中碳包覆层的石墨化程度较低,发生了红移现象。     

纳米铜粉与碳包覆铜纳米粉的分散性能比较

采用直流碳弧法制备平均粒径为25 nm的碳包覆铜纳米粉,应用X射线衍射(XRD)、透射电镜(TEM)等分析手段对所制备的纳米颗粒物相、形貌等进行表征。采用超声波分散法对所制备的碳包覆铜纳米粉和市售的纳米铜粉进行分散,并通过分光光度法和沉降实验对两者的分散性能进行比较。结果表明:铜纳米颗粒具有很高的表面自由能,容易被氧化,在水性液相介质中分散时容易产生氢氧化铜絮状沉淀。碳包覆铜纳米颗粒表面有碳层的保护,且密度小、表面吸附性能好,分散性能明显优于铜纳米颗粒。     

氧化硅包覆铁“壳/核”型纳米复合粒子的制备及其吸波特性研究

采用非平衡物理气相蒸发法在氢气氩气混合气氛下制备了氧化硅包覆铁“壳/核”型纳米复合粒子. 通过X射线衍射(XRD)、透射电子显微镜(TEM)和能谱分析(EDS)等方法表征了纳米复合粒子的相组分、结构以及颗粒形貌. 结果表明,制备的氧化硅包覆铁纳米复合粒子的尺寸在50nm左右,在铁纳米粒子的表面还出现了非晶态的氧化硅纳米棒,长度为150~200nm. 利用电磁参数模拟微波吸收特性得出,涂层厚度为1.79mm时,在15.4GHz频率处达到最小反射损耗值为-14.5dB,反射损耗在8~18GHz的频段低于-10dB,且损耗机制为自然共振.     

碳微球负载钌纳米颗粒复合材料的化学镀制备

以碳微球(CMSs)为研究对象,首先通过不同的氧化方法对CMSs进行表面改性,再利用SnCl2敏化溶液对改性CMSs进行敏化.最后采用化学镀的方法制备Ru纳米颗粒/碳微球(Ru/CMSs)复合材料.考察了不同改性方法和敏化液用量对CMSs表面化学镀Ru的影响.采用场发射扫描电子显微镜、X射线衍射、X射线光电子能谱、热重分析和红外光谱等对产物的结构和形貌进行了表征和分析.结果表明,经400"C空气氧化改性后的CMSs制备出的Ru/CMSs样品纳米金属粒子均匀细小且加载率也较高;在其它条件不变的情况下,经0.5mol/L敏化液敏化处理制备的Ru/CMSs样品形貌最好.约15nm的钌纳米颗粒均匀地加载到碳微球表面.     

Synthesis of carbon-coated iron nanoparticles by detonation technique

Carbon-coated iron nanoparticles were synthesized by detonating a mixture of ferrocene, naphthalene and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in an explosion vessel under low vacuum conditions (8.1 kPa). The RDX functioned as an energy source for the decomposition of ferrocene and naphthalene. The carbon-coated iron nanoparticles were formed as soot-like deposits on the inner surface of the reactor, which were characterized by XRD, TEM, HRTEM, Raman spectroscopy and vibrating sample magnetometer. And a portion of the detonation soot was treated with hydrochloric acid. The product was carbon-coated nanoparticles in perfect core-shell structures with graphitic shells and bcc-Fe cores. The detonation technique offers an energy-saving route to the synthesis of carbon-coated nanomaterials.     

Effect of oxidation and heat treatment on the morphology and electronic structure of carbon-encapsulated iron carbide nanoparticles

Carbon-encapsulated iron carbide nanoparticles have been produced by co-carbonization of a mixture of an aromatic heavy oil and ferrocene at 450 °C under autogenous pressure. Transformations of the morphology and electronic structure of nanoparticles induced by air oxidation and subsequent heat treatment in a nitrogen atmosphere were examined using transmission electron microscopy, X-ray diffraction, near edge X-ray absorption fine structure spectroscopy, and X-ray emission spectroscopy. It was found that hollow nanoparticles, composed of iron oxides and oxidized carbon, were developed with thermal air oxidation of the initial product at 280 °C for 5 h. The mild oxidation of the product (250 °C for 3 h) followed by the carbonization at 500–550 °C yielded the hollow nanoparticles containing iron carbide/oxides and defective graphite-like carbon. The further annealing of nanoparticles at 1000 °C produced carbon nanocapsules with highly graphitized carbon walls and partially filled by spherical iron carbide nanoparticles.     

Synthesis of Hybrid Materials Based on Iron Nanoparticle-Decorated Multiwalled Carbon Nanotubes

Fe-containing nanoparticles have been grown for the first time on the surface of multiwalled carbon nanotubes by metalorganic chemical vapor deposition using iron acetylacetonate, Fe(acac)₃, as a precursor. The resultant hybrid nanomaterial has been characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the synthesized material consists of multiwalled carbon nanotubes whose surface is decorated with iron nanoparticles.     

Synthesis of carbon-encapsulated iron nanoparticles by pyrolysis of iron citrate and poly(vinyl alcohol): a critical evaluation of yield and selectivity

Carbon-encapsulated iron nanoparticles were synthesized by pyrolysis at 1000?°C of two solid precursors: poly(vinyl alcohol) and iron citrate. The weight ratio between the precursors controlled the reaction yield, crystallinity, morphological features and magnetic properties of the products. The encapsulation yield of iron nanoparticles in carbon shells was strongly influenced by the iron-to-carbon ratio and depended on the iron citrate content in the initial reactant mixtures. Despite the inherent simplicity of the process and the use of low cost starting materials the demonstrated route possesses limited selectivity, especially at high iron-to-carbon ratios. At these experimental conditions the as-obtained products contained non-encapsulated Fe particles and graphite in addition to magnetic carbon encapsulates. These by-products were effectively removed by a one-pot purification procedure that included acid treatment.     

Synthesis and surface plasmon resonance properties of carbon-coated Cu and Co nanoparticles

Carbon-coated Cu and Co nanoparticles were synthesized by the carbonization of PVA-metal hydroxide complexes. The possible reaction process and surface plasmon resonance (SPR) properties of the Cu and Co nanoparticles enwrapped in carbon layer were explored. The XRD results showed that no byproducts, such as oxides and carbides, were formed in the products, and the Cu and Co nanoparticles were effectively protected against oxidation by the carbon layer. The size ranges of the metal nanoparticles were 20-50 nm for Cu and 15-65 nm for Co, respectively. UV-vis absorption spectra showed that the SPR bands of the Cu and Co nanoparticles coated with carbon were red-shifted mainly due to the increase of the effective dielectric constant of the surrounding medium induced by the carbon layer.     

碳包覆纳米铜的原位热解法制备及其稳定性

以天然棉纤维为模板用一步热解法在氮气气氛中原位制备纳米铜碳复合材料(NCCC),再以浸泡了硫酸铜的棉纤维为热解碳源、以商业纳米铜和微米铜为铜源原位制备了碳包覆纳米/微米铜。使用TEM、XRD和Raman等手段对其表征,研究了这种材料的稳定性。结果表明,NCCC是一种典型的具有碳包覆纳米铜核壳结构的材料;用原位热解法制备碳包覆金属纳米/微米材料,进一步证实棉纤维热解气氛为碳源及原位还原剂。验证了碳包覆材料的抗氧化性：碳壳的形成使NCCC暴露在空气中180 d或水中35 d后仍保持铜和氧化亚铜的物相组成;受碳壳保护的商业纳米铜,暴露空气中120 d仍未氧化。     

Preparation and magnetic behavior of carbon-encapsulated iron nanoparticles by detonation method

Carbon-encapsulated iron (Fe@C) nanoparticles with core/shell structure have been successfully synthesized by detonation method, using a homemade composite explosive precursor. The detonation reaction was ignited by a non-electric detonator in nitrogen gas in an explosion vessel. The as-prepared detonation products were characterized by X-ray Diffraction, Transmission electron Microscopy, Raman spectroscopy and X-ray fluorescence. The magnetic behavior of the Fe@C materials was measured by vibrating sample magnetometer. The results showed that the detonation products were made up of the body centered cubic iron core and the graphitic carbon shell, of which the core diameter was in the range of 15–50 nm. Raman spectroscopy indicated that both graphitic and amorphous carbon occured in the outside shell structures. The hysteresis loops showed the as-made Fe@C nanoparticles were of superparamagnetic at 300 K temperature. A detonation reaction mechanism was proposed to explain the growth process of Fe@C nanoparticles based on these results.     

Fe@Ag core-shell nanoparticles with both sensitive plasmonic properties and tunable magnetism

Monodisperse Fe@Ag core-shell nanoparticles with relatively uniform Fe cores and Ag shells have been successfully fabricated by a seed mediated method in a two-step reducing process, and then characterized by electron microscopy techniques (HRTEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy,and magnetometry. The results demonstrate unique optical and magnetic properties for Fe@Ag core-shell nanoparticles. The surface plasmon resonance of Fe@Ag core-shell nanoparticles is red shifted as compared with that of pure colloidal nano-silver, while the plasmon band of Fe@Ag core-shell nanoparticles with thinner Ag shells is shifted to a longer wavelength. Fe@Ag core-shell nanoparticles have a narrow plasmon band and therefore sensitive plasmonic properties. The magnetism of Fe@Ag nanoparticles can be tuned from superparamagnetic to ferromagnetic by modifying the proportion between Fe and Ag contents. The multifunctional Fe@Ag core-shell nanoparticles have potential in optoelectronic, spintronic, and biomedicine applications.     

Interface evolution in the platelet-like SiC@C and SiC@SiO<Subscript>2</Subscript> monocrystal nanocapsules

Carbon-coated SiC@C nanocapsules (NCs) with a hexagonal platelet-like morphology were fabricated by a simple direct current (DC) arc-discharge plasma method.The SiC@C NCs were monocrystalline,120-150 nm in size,and approximately 50 nm thick.The formation of the as-prepared SiC@C NCs included nucleation of truncated octahedral SiC seeds and subsequent anisotropic growth of the seeds into hexagonal nanoplatelets in a carbon-rich atmosphere.The disordered carbon layers on the SiC@C NCs were converted into SiO2 shells of SiC@SiO2 NCs by heat treatment at 650 ℃ in air,during which the shape and inherent characteristics of the crystalline SiC core were obtained.The interface evolution from carbon to SiO2 shells endowed the SiC@SiO2 NCs with enhanced photocatalytic activity due to the hydrophilic and transparent nature of the SiO2 shell,as well as to the photosensitive SiC nanocrystals.The band gap of the nanostructured SiC core was determined to be 2.70 eV.The SiC@SiO2 NCs degraded approximately 95％ of methylene blue in 160 min under visible light irradiation.