金纳米线的制备及传感应用研究进展

金纳米材料除了具有普通纳米材料的特性(表面效应、介电限域效应、小尺寸效应及量子隧道效应等)外,还具备独特的稳定性、导电性,优良的生物相容性以及超分子和分子识别、荧光等特性,这使其在纳米电子学、光电子学、传感和催化、生物分子标记、生物传感等领域展现出广阔的应用前景。在多种形态各异的金纳米材料中,金纳米线一直受到研究者们的高度重视。探索制备金纳米线的新技术与新方法,进一步拓展其应用领域,是当前纳米材料领域的研究焦点之一。金纳米线因具有长径比大、柔性较高以及制备方法简便等优点,在传感器、微电子、光学器件、表面增强拉曼、生物检测等领域都展现出不可忽视的潜力。随着技术的发展,研究者们已开发了多种制备金纳米线的方法,如模板合成法、溶液法、阶边修饰法。然而近年来,纳米电子学与传感器等领域的应用需求对金纳米线的制备方法提出了更高的要求,如制备的金纳米线要有较为理想的形貌(金纳米线的直径与几何结构直接影响电子的传输性能),且要考虑方法的复杂性,是否对环境造成污染及金纳米线产量等因素。本文结合近十年来金纳米线的制备与应用研究成果,重新分类归纳了金纳米线的制备方法与调控方式,并对金纳米线在传感领域的应用进行了较为全面的总结,以期为后续研究提供参考。     

二氧化锡纳米线的生长机理研究

使用水平石英管式电炉，以二氧化锡和石墨的混合物为原材料、高纯氮气为载气，在850℃温度下用直接热蒸发法制备二氧化锡纳米线．衬底硅片的直径为10mm，其上覆盖一层5nm厚的金催化剂．原材料放在石英舟中，离原材料30mm的下风口处放置硅衬底，原材料和硅衬底都放置在石英管的中部电炉的恒温区内．用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察到二氧化锡的纳米线结构；X射线衍射（XRD）表明二氧化锡纳米线具有四方金红石结构；选区电子衍射（SAED）照片表明二氧化锡纳米线具有完善的晶体结构．不同生长时间下制备样品的扫描电子显微镜和透射电子显微镜照片再现了二氧化锡纳米线的生长过程，该纳米线的生长符合传统的VLS生长机制．     

十八胺作为还原剂和包裹剂制备具有SERS活性的金纳米线

采用化学还原方法,在有机相中利用十八胺作为还原剂和包裹剂,在油酸的辅助下,合成了具有一维结构的金纳米线,并将制得的金纳米线用作基底,在其表面获得了罗丹明B分子的SERS光谱,实验结果表明,金纳米线具有良好的SERS活性,有望应用于高灵敏度光学检测。     

贵金属纳米线的模板法制备及应用研究进展

贵金属纳米线因独特的光学性质吸引了人们的普遍关注,已经被广泛应用于生物传感器、太阳能电池、纳米尺度光电器件领域。其光学性能主要来源于贵金属表面的区域等离子体共振,而区域等离子体共振主要由金属纳米线的形状、尺寸、组成以及电磁常数决定。简要地回顾了模板法合成贵金属纳米线的方法,讨论了影响纳米线光学性质的因素,最后简述了应用前景。     

ZnO纳米线的催化合成及其光致发光性能

采用气相传输法,以金膜为催化剂,氧化锌和石墨混合粉末为锌源,制备氧化锌纳米材料。研究获得氧化锌纳米线的光致发光性能。初步探索了氧化锌纳米线的生长机理。实验结果表明,当衬底温度为600℃时,金颗粒的催化性能得到了较好的发挥,形成长度大于10μm,直径小于80 nm的均匀致密的氧化锌纳米线膜。这种氧化锌纳米线具有紫外发光特性。低于600℃时,锌氧蒸汽发生了自凝结,进而在金颗粒间隙形成氧化锌带(400℃时),或在金颗粒上吸附聚集形成花状氧化锌纳米棒(200℃时)。而在高于600℃时,金颗粒析出的锌迅速挥发或氧化、长大,出现了稀疏的针状氧化锌和颗粒。氧化锌纳米线可能的生长模式为“底端生长“模式。     

金属辅助化学刻蚀法制备硅纳米线的研究进展

硅纳米线(Si NWs)由于具有独特的一维结构、热电导率、光电性质、电化学性能等特点,被广泛应用于热电与传感器件、光电子元器件、太阳能电池、锂离子电池等领域。金属辅助化学刻蚀法(MACE)是制备Si NWs的常用方法之一,具有操作简便、设备简单、成本低廉和高效等优点,可大规模商业化应用,因而近年来被广泛研究。金属辅助化学刻蚀制备硅纳米线的过程可以分为两步:首先在洁净的硅衬底表面沉积一层金属(Ag、Au、Pt等)纳米颗粒,以催化、氧化它附近的硅原子;然后利用HF溶解氧化层,从而对硅晶片进行刻蚀,形成纳米线阵列。然而,这种简单高效的制备硅纳米线的方法存在一些难以控制的缺点:(1)金属纳米颗粒聚集、相连后造成Si NWs之间的缝隙比较大,从而导致Si NWs密度较低;(2)由于金属纳米颗粒沉积的随机性,在硅晶片表面分布不均匀,不仅导致刻蚀出的纳米线直径范围(50～200 nm)较宽,而且使制得的纳米线阵列排列无序且间距不易调控;(3)当刻蚀出的硅纳米线太长时,范德华力等作用会造成纳米线顶端出现严重的团簇现象。针对常规法存在的一些问题以及不同的器件对硅纳米线的形貌、类型和直径等的要求,近年来的研究主要集中在如何减少纳米线顶端团簇、调控纳米表面粗糙度和直径、低成本制备有序硅纳米线等方面。目前一些改进常规金属辅助化学刻蚀的方法取得了进展,比如:(1)用酸溶液或UV/Ozone对硅晶片预处理,在表面形成氧化层,可以使纳米线的均匀性得到改善并增大其密度(从18%提高到38%);(2)使用物理气相沉积法在硅晶片表面沉积一层金属纳米薄膜,然后再刻蚀,这种方法能够减少纳米线顶端团簇和有效调控纳米线直径;(3)利用模板法(聚苯乙烯小球模板、氧化铝模板、二氧化硅模板和光刻胶模板等)可以制备出有序的硅纳米线阵列。本课题组用离子束刻蚀的方法制备了直径范围可以控制在30～90 nm的聚苯乙烯小球模板,为小尺寸有序硅纳米线的制备打下了坚实的基础。本文简要介绍了常规MACE的原理和制备流程,总结了硅晶片的类型、刻蚀溶液的浓度、温度和刻蚀时间等因素对Si NWs形貌、尺度、表面粗糙度、刻蚀方向以及刻蚀速率的影响,用相关的机制解释了H2O2过量时刻蚀路径偏离垂直方向的机理以及刻蚀速率随溶液浓度变化的原因,重点综述了氧化层预处理、物理法沉积贵金属纳米薄膜、退火处理和模板法等改进方法在减少纳米线顶部团簇、改善均匀性、制备有序且直径和间距可控纳米线中的研究进展。     

爆炸辅助气相沉积法制备炭纳米线的研究

根据爆炸辅助气相沉积法生长碳纳米管的机理,设计了两种制备炭纳米线的方案:(1)使用低活性铁-镍二元金属催化剂;(2)对钴催化剂作用下碳纳米管的生长实施冷冻。透射电子显微镜显示这两种方法制备的炭纳米线均为纳米颗粒组装而成,具有非常粗糙的表面。其中,使用铁-镍二元催化剂所制炭纳米线直径分布不均匀,黏结情况严重;而在冷冻钴催化剂作用下炭纳米管生长过程所得的炭纳米线直径分布比较均匀,黏结情况也大为减少。这两种纳米线的差别与金属催化剂的活性有关。光催化降解亚甲基蓝实验表明:冷冻碳纳米管生长所得炭纳米线具有良好的催化辅助功能,可以提高ZnS纳米晶的光催化活性。     

用催化剂控制硅纳米线直径的研究

本文研究了固－液－固（SLS）生长机制中催化剂与硅纳米线直径的关系。发现Si片上沉积的催化剂厚度和种类对硅纳米线的直径都有一定的影响，当使用Ni做催化剂时，硅纳米的直径与Ni膜厚度有关。其中硅纳米线的最大直径随催化剂厚度减小而减小，但最小直径基本不改变，当用Au做催化剂时，硅纳米线的平均直径和直径分布最小（10nm-20nm）。但硅纳米的直径不随Au膜厚度减小而减小。     

磁控溅射法可控制备有序碲纳米线阵列

采用磁控溅射法在较低基底温度下(200 ℃)制备了有序碲纳米线阵列, 并利用X射线衍射、扫描电镜和透射电镜对所制备薄膜进行了相、形貌和微观结构分析。结果表明, 所制备的纳米线阵列由单晶碲纳米线组成, 单根碲纳米线具有针状形貌, 并沿[101]晶向生长, 平均直径和长度分别为100 nm和1 μm。氩气压力和基底温度均对碲纳米线阵列的形成具有重要影响, 以平衡碲原子沿[101]晶向和(101)晶面方向的扩散和生长。提出了碲纳米线阵列的生长机制, 包括吸附、结合、成核和生长等过程。     

双扩散AAO模板法制备AgCl纳米线及其光催化性能

采用二次阳极氧化法,制得具有一定厚度有序性较高的阳极氧化铝(AAO)模板,并结合溶液的双扩散法制备AgCl纳米线,利用XRD、SEM和TEM等分析手段对模板和纳米线进行了表征,结果表明,用该方法制备的AgCl纳米线阵列分布均匀,取向性好,直径与AAO模板的孔径一致.通过纳米线阵列膜对罗丹明B的降解情况对其光催化活性进行了测试,结果表明,AgCl纳米线具有良好的光催化性能.     

Synthesis of platinum nanowire networks using a soft template

Platinum nanowire networks have been synthesized by chemical reduction of a platinum complex using sodium borohydride in the presence of a soft template formed by cetyltrimethylammonium bromide in a two-phase water-chloroform system. The interconnected polycrystalline nanowires possess the highest surface area (53 +/- 1 m2/g) and electroactive surface area (32.4 +/- 3.6 m2/g) reported for unsupported platinum nanomaterials; the high surface area results from the small average diameter of the nanowires (2.2 nm) and the 2-10 nm pores determined by nitrogen adsorption measurements. Synthetic control over the network was achieved simply by varying the stirring rate and reagent concentrations, in some cases leading to other types of nanostructures including wormlike platinum nanoparticles. Similarly, substitution of a palladium complex for platinum gives palladium nanowire networks. A mechanism of formation of the metal nanowire networks is proposed based on confined metal growth within a soft template consisting of a network of swollen inverse wormlike micelles.     

Development and characterization of fluorine tin oxide electrodes modified with high area porous thin films containing gold nanoparticles

Different electrode materials are prepared using fluoride doped tin oxide (FTO) electrodes modified with high area porous thin films of metal oxides containing gold nanoparticles. Three different metal oxides (TiO₂, MgO and SnO₂) have been assayed to this end. The effect of the metal oxide nature and gold loading on the structure and performance of the modified electrodes was examined by Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy and electrochemical techniques. XRD measurements reveal that MgO electrodes present the smallest gold nanoparticles after the sintering step however, the electrochemical response of these electrodes shows important problems of mass transport derived from the high porosity of these materials (Brunauer Emmett Teller area of 125 m²/g). The excellent sintering properties of titania nanoparticles result in robust films attached to the FTO electrodes which allow more reliable and reproducible results from an electroanalytical point of view.     

The chemical interaction of metals with polytetrafluoroethylene

Chemical reactions of cadmium, indium and tin with PTFE have been found to occur when mixtures of the metal and polymer were heated in a differential scanning calorimeter to 773 K. Analysis of the residues by X-ray photoelectron spectroscopy (XPS) showed the presence of fluoride ions. The evaporation of a metal film on to the clean polymer surface has also been found by XPS to produce metal fluoride for nickel, cadmium, tin, indium and lead but not silver or gold. The rubbing of aluminium on to PTFE also produces reaction to give fluoride. The PTFE polymer molecules have been found to diffuse to the surface of metal/polymer composites at a significant rate. This latter process may be important in the use of this polymer in bearing materials.     

Organo-functionalized mesoporous supports for Jacobsen-type catalyst: Laponite versus MCM-41

In order to exploit the different textural properties of Laponite and MCM-41, specifically in terms of their external versus internal surface areas, in the covalent anchoring of a chiral Mn(III) salen complex, these materials were functionalized with 3-aminopropyltriethoxysilane (APTES), subsequently activated with sodium ethoxide, and finally used to anchor the Jacobsen catalyst derivative C1. All the materials were characterized by nitrogen elemental analysis, XPS, PXRD, nitrogen adsorption at −196 °C, FTIR and for those with the immobilized complex, they were additionally characterized by Mn AAS. The APTES anchored at the edges of the Laponite single crystals and inside the MCM-41 pores. Moreover, under the same preparative conditions, higher amount of APTES was anchored onto MCM-41 than onto Laponite, which is due to the higher surface area of MCM-41 compared to Laponite, as well as to its more exposed SiO₄ tetrahedra. Activation of the two organo-functionalized materials with sodium ethoxide originated anionic nitrogen groups as deduced by the increase of surface sodium content of these materials and N1s binding energy changes, but led to a small decrease in N bulk content as a result of some APTES leaching. Moreover, for MCM-41 some disruption of the silica framework occurred as a consequence of the basic treatment, as suggested by XPS, PXRD, and nitrogen adsorption study. The APTES functionalized Laponite and MCM-41 materials, as well as the activated analogs, were able to anchor C1 through axial coordination of the metal centre to the grafted surface nitrogen atoms. APTES functionalized MCM-41 presented similar complex content to Laponite analog, what points out for the fact that, at least for the bulky complex used in this work, there was no clear benefit in using a material of high internal area; for the ethoxide activated analogs, Laponite showed the highest complex content of all materials, but MCM-41 was able to anchor the lowest complex quantity, probably as a consequence of damaging effect caused by the basic treatment within its porous structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Bio-synthesis of gold and silver nanoparticles from Candida guilliermondii and their antimicrobial effect against pathogenic bacteria

In the present study we investigated the extra cellular synthesis of gold and silver nanoparticles by using the yeast Candida guilliermondii. The formation of noble metal nanoparticles was monitored by the UV-Visible spectroscopy. As prepared gold and silver nanoparticles showed distinct surface plasmon peaks at 530 nm and 425 nm respectively. Phase and morphology of the as synthesized materials were investigated by X-ray diffraction and electron microscopy techniques respectively. XRD patterns confirmed the formation of gold and silver nanoparticles with face centered cubic structures. Bio-TEM images showed the formation of near spherical, well dispersed gold and silver nanoparticles in the size range of 50-70 nm and 10-20 nm respectively. The biosynthesized nanoparticles were tested for their antimicrobial activity against five pathogenic bacterial strains. The highest efficiency for both gold and silver nanoparticles was observed against Staphylococcus aureus. A comparative study was also done to find the effect of chemically synthesized noble metal nanoparticles against the above test strains. Chemically synthesized particles had no antimicrobial activity against any of the pathogenic strains. The results obtained suggest that biosynthesized gold and silver nanoparticles can be used as effective antimicrobial agents against some of the potential harmful pathogenic microorganisms.     

Metal–Organic Framework‐Derived Materials for Sodium Energy Storage

Recently, sodium‐ion batteries (SIBs) are extensively explored and are regarded as one of the most promising alternatives to lithium‐ion batteries for electrochemical energy conversion and storage, owing to the abundant raw material resources, low cost, and similar electrochemical behavior of elemental sodium compared to lithium. Metal–organic frameworks (MOFs) have attracted enormous attention due to their high surface areas, tunable structures, and diverse applications in drug delivery, gas storage, and catalysis. Recently, there has been an escalating interest in exploiting MOF‐derived materials as anodes for sodium energy storage due to their fast mass transport resulting from their highly porous structures and relatively simple preparation methods originating from in situ thermal treatment processes. In this Review, the recent progress of the sodium‐ion storage performances of MOF‐derived materials, including MOF‐derived porous carbons, metal oxides, metal oxide/carbon nanocomposites, and other materials (e.g., metal phosphides, metal sulfides, and metal selenides), as SIB anodes is systematically and completely presented and discussed. Moreover, the current challenges and perspectives of MOF‐derived materials in electrochemical energy storage are discussed.     

REVIEW Bioactive metals: preparation and properties

Some ceramics, such as Bioglass, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously form a bone-like apatite layer on their surface in the living body, and bond to bone through the apatite layer. These materials are called bioactive ceramics, and are clinically important for use as bone-repairing materials. However, they cannot be used at high-load sites, such as is found in femoral and tibial bones, because their fracture toughness values are not as high as that of human cortical bone. Titanium metal and its alloys have high fracture toughness, and form a sodium titanate layer on its surface when soaked in a 5 M-NaOH solution at 60 degrees C for 24 h, followed by a heat treatment at 600 degrees C for 1 h. On moving toward the metal interior, the sodium titanate layer gradually changes into the pure metal within a distance of 1 microm from the surface. The mechanical strength of the titanium metal or a titanium alloy is not adversely affected by these chemical and thermal treatments. The titanium metal and its alloys resulting from the above treatment can release Na+ ions from its surface into a surrounding body fluid via an ion exchange reaction with H3O+ ions, resulting in many Ti-OH groups forming on its surface. These Ti-OH groups initially combine with Ca2+ ions to form amorphous calcium titanate in the body environment, and later the calcium titanate combines with phosphate ions to form amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms into bone-like apatite, and by this process the titanium metals are soon tightly bonded to the surrounding living bone through the bone-like apatite layer. The treated metals have already been subjected to clinical trials for applications in artificial total hip joints. Metallic tantalum has also been found to bond to living bone after it has been subjected to the NaOH and heat treatment to form a sodium tantalate layer on its surface.     

The influence of ordered surface point defect arrays on the epitaxial deposition of gold upon (100) surfaces of sodium chloride

The effect of an ordered array of sodium ion vacancies (incorporated into a (100) surface of sodium chloride) upon the epitaxial temperature associated with gold being deposited onto that (100) surface has been investigated. A dramatic reduction in the epitaxial temperature has been observed, and single-crystal correctly oriented gold films have been achieved at - 30 °C upon those areas of the sodium chloride surface containing the point defects.     

退火温度对宽带脉冲压缩光栅载体金属/介质多层高反膜的影响

分别以金(Au)作为金属层材料, 氧化铪(HfO₂)与氧化硅(SiO₂)作为高低折射率层材料, 利用物理气相沉积方法制备了用于宽带脉冲压缩光栅制作的金属/介质多层高反膜, 研究了退火温度对其表面均方根粗糙度、反射率及抗化学清洗破坏能力的影响。实验结果表明: 退火前后样品表面均方根粗糙度变化很小; 提高退火温度能提高金属/介质多层膜的抗化学清洗破坏能力, 但反射率会随之下降。250℃退火10 h后金属/介质多层膜不仅可以承受住化学清洗过程, 而且反射率下降也比较小, 可以作为金属/介质多层膜的最佳退火工艺。     

Cover Picture: Direct Growth of Flexible Carbon Nanotube Electrodes (Adv. Mater. 3/2008)

Entangled networks of multiwalled carbon nanotubes (CNTs) integrated into a highly conducting carbon layer can be grown on a range of substrates including glassy carbon and metal foils. On p. 566, Gordon Wallace and co‐workers report the fabrication of a continuous flexible CNT electrode with high surface area and conductivity. The electrode demonstrates a stable battery capacity of 572 mAh g^–1. This discovery provides a direct route for the generation of large‐scale flexible CNT electrode materials.