紫外光辐照法制备金纳米盘及其反应机理

用紫外光辐照氯金酸、聚乙烯吡咯烷酮(PVP)和纳米金种子的混合溶液, 在室温下用30 min制备出尺度小于100 nm的截角三角形或六边形金纳米盘. X射线能谱和衍射分析表明粒子是以{111}面为盘状面的高纯面心立方金单晶, 红外透射光谱表明金粒子与PVP之间存在作用. 产物的可见吸收光谱表现出纳米盘的各向异性表面等离子体共振吸收峰. 不同实验条件下产物的吸收光谱分析表明: PVP起还原剂和包覆剂的作用; 高强度紫外光加速了反应进行; 种子对反应具有催化作用; 种子的加入量有最佳值, 在该值下纳米盘平均尺度最大(达80 nm), 吸收谱上的面内偶极共振峰位于950 nm处; 种子的加入量超过该值时, 纳米盘尺度变小, 面内偶极共振峰发生蓝移.     

Surface enhanced Raman scattering effects of silver colloids with different shapes

By solution-based method, three kinds of silver colloids, self-assembled nanowires, triangular nanoplates and quasispherical nanoparticles, have been synthesized. TEM studies revealed that they exposed different crystal planes, such as {111} crystal planes to triangular nanoplates, mainly {100} and {111} planes to self-assembly nanowires. Hereby, do the distinct shapes and crystal planes have an impact on the surface enhanced Raman scattering (SERS)? The great differences of the SERS spectra of rhodamine B at these Ag colloids confirmed that the shapes and crystal planes of silver have great effect on Raman enhancement, especially the crystal planes.     

Thermal aqueous solution approach for the synthesis of triangular and hexagonal gold nanoplates with three different size ranges

The synthesis of gold nanoplates was carried out in an aqueous solution by thermal reduction of HAuCl(4) with trisodium citrate in the presence of cetyltrimethylammonium bromide (CTAB) surfactant in just 5-40 min. The sizes of the gold nanoplates can be varied from as small as tens of nanometers in width, to several hundreds of nanometers, and even a few microns in width by changing the reagent concentrations, solution temperature, and the reaction time. A [CTAB]/[HAuCl(4)] ratio of 6 in the reaction solution was found to be favorable for the formation of gold nanoplates. The nanoplates possess well-defined shapes with sharp edges. The small nanoplates exhibit mainly a triangular shape, while larger nanoplates show a mixture of triangular, hexagonal, truncated triangular, and other symmetrical structures. The nanoplates are composed of essentially (111) lattice planes, as revealed by both XRD and TEM results. Nanoplates with widths from several hundreds of nanometers to a few microns absorb light strongly in the near-infrared region. The growth mechanism of these nanoplates was investigated. The ability to synthesize gold nanoplates with these different size ranges in large scale in aqueous solution using simple CTAB capping surfactant should allow more diverse applications of gold nanoplates.     

Shape‐Dependent Catalytic Activity of Silver Nanoparticles for the Oxidation of Styrene

Metal nanoparticles with different shapes have different crystallographic faces. It is therefore of interest to study the effect of the shape of metal nanoparticles on their catalytic activity in various organic and inorganic reactions. Truncated triangular silver nanoplates with well‐defined planes were synthesized by a simple solvothermal approach. The activity of these truncated triangular silver nanoparticles was compared with that of cubic and near‐spherical silver nanoparticles in the oxidation of styrene in colloidal solution. It was found that the crystal faces of silver nanoparticles play an essential role in determining the catalytic oxidation properties. The silver nanocubes had the {100} crystal faces as the basal plane, whereas truncated triangular nanoplates and near‐spherical nanoparticles predominantly exposed the most‐stable {111} crystal faces. As a result, the rate of the reaction over the nanocubes was more than 14 times higher than that on nanoplates and four times higher than that on near‐spherical nanoparticles.     

新形金纳米片的简单制备与生长机制

在室温(~30 ℃)条件下,氯金酸(HAuCl₄)均匀混合在粘稠的表面活性剂聚乙烯吡咯烷酮(PVP)胶体(水为溶剂)中,HAuCl₄可以被PVP还原,从而形成纳米片. 本工作中,通过调整晶体生长条件,成功合成了大量新形貌的单晶金纳米片(厚度数十纳米,尺寸为数个微米). 例如,在晶体生长初期阶段,通过引入温度变化(如降温10-20 ℃),形成的金纳米片主要是六角星形,并伴有盾状、内凹外凸的三角状、截角的、三叉的及多台阶等新形纳米片. 结合理论计算,阐明了金纳米片的生长机制：在一定条件下,金(111)晶面不仅可以沿着<110>方向生长成为常规的三角或六角纳米片,还可以沿<211>、<321>等不同方向生长成含有更高指数侧面的新形金纳米片.     

壳聚糖介质金纳米盘的可控合成及生长机理

水浴加热氯金酸、壳聚糖和纳米金种子的混合液,以壳聚糖为稳定剂和还原剂成功合成了表面等离子体共振(SPR)吸收峰位可调的金纳米盘.SEM电镜图像表明纳米金盘主要为三角形和截角三角形,其边长在170 nm左右.X射线衍射分析表明金纳米盘是以{111}面为盘状面的高纯金单晶.讨论了金纳米盘的生长机理.在最佳条件下金纳米盘的面内偶极等离子共振吸收峰位于920 nm.实验结果表明通过控制壳聚糖的量、金种子的加入量、水浴温度及水浴时间可以有效地控制近红外等离子吸收峰位及吸收强度.     

Polymer-controlled crystallization of zinc oxide hexagonal nanorings and disks

In this study, we have developed a novel route to the synthesis of ZnO nanorings, disks, and diskoidlike crystals on a large scale by a facile solution-based method by using polymers as crystal growth modifiers. The crystals precipitated with polyacrylamide (PAM) as the additive show ringlike morphology. A possible growth mechanism of the ZnO nanostructures based on typical polymer-crystals interactions in a mild aqueous solution is given. The polymer contains in the side chain a large number of amide ligands that are able to coordinate with Zn(2+) ions, that is, the otherwise just weakly exposed (001) face, leading to a lowering of surface energy and inhibition of growth along this direction and the formation of ringlike morphologies. While in the presence of carboxyl-functionalized polyacrylamide (PAM-COOH), nearly monodispersed disklike crystals were observed and finally evolved into diskoidlike microstructures with the reaction time prolonged. Polymer-directed crystal growth and mediated self-assembly of nanocrystals may provide promising routes to rational synthesis of various ordered inorganic and inorganic-organic hybrid materials with complex form and structural specialization.     

Comparison of Surface-enhanced Raman Scattering Spectra of Two Kinds of Silver Nanoplate Films

Surface-enhanced Raman scattering(SERS) spectra of different silver nanoplate self-assembled films at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out. The SERS spectra of 4-mercaptopyridine(4-MPY) on these anisotropic silver nanoparticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance(SPR) band of silver substrate overlapped. In this model, the influence of the crystal planes of silver nanoplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.     

边长为微米级的银纳米片的简易合成与形成机理

用低温(60 ℃)溶剂热法, 以N,N-二甲基甲酰胺(DMF)为主还原剂和溶剂, 以聚乙烯吡咯烷酮(PVP)为辅助还原剂和晶面生长控制剂, 以硝酸银为前驱物, 大量制备了高纯度的、边长为微米级、宽厚比≥10的单晶银纳米片. 采用粉末X射线衍射(PXRD)、场发射扫描电镜(FE-SEM)、透射电子显微镜(TEM)等表征和分析了合成产物的成分、形貌和结构. 结果表明, 合成的银纳米片为面心立方单晶, 边长为1-4 μm, 厚度为50-100 nm. 考察了不同溶剂对银纳米结构的影响, 并提出了大尺寸的银纳米片的形成机理. 本文为调控单晶银纳米片的边长和宽厚比提供了一种新的可靠的动力学方法, 制备的长边长、大宽厚比的单晶银纳米片在聚合物基导电复合材料和电磁屏蔽材料方面有潜在的重要应用.     

Effect of magnesium ions on oriented growth of calcite on carboxylic acid functionalized self-assembled monolayer

The combined effect of templating and solution additives on calcite crystallization was studied. Self-assembled monolayers of mercaptoundecanoic acid supported on silver, as templates, induced the uniform, oriented nucleation of calcite from the (012) plane. The presence of Mg2+ in the crystallizing solution affected the crystal growth dramatically, due to the selective Mg binding to the calcite planes roughly parallel to the c-axis. Highly homogeneous arrays of oriented crystals with characteristic sizes, shapes, and morphology, depending on the relative concentration of Mg and Ca ions, were synthesized.     

Preparation of novel silver-gold bimetallic nanostructures by seeding with silver nanoplates and application in surface-enhanced Raman scattering

Novel silver-gold bimetallic nanostructures were prepared by seeding with silver nanoplates in the absence of any surfactants. During the synthesis process, it was found that the frameworks of silver nanoplates were normally kept though the basal plane of silver nanoplates became rugged. The real morphology of these nanostructures depended on the molar ratio of gold ions to the seed particles. When the molar ratio of gold ions to silver atoms increased from 0.5 to 4, porous or branched silver-gold bimetallic nanostructures could be made. The growth mechanism was qualitatively discussed based on template-engaged replacement reactions and seed-mediated deposition reactions. Due to the unusual structures, they exhibited interesting optical properties. Moreover, they were shown to be an active substrate for surface-enhanced Raman scattering measurements.     

Green, effective chemical route for the synthesis of silver nanoplates in tannic acid aqueous solution

Silver nanoplates, with average size tunable from 50 to 500 nm, have been synthesized via a simple room-temperature tannic acid (TA) solution-phase chemical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent to direct the anisotropic growth of the silver nanoparticles. The morphology of silver nanoplates has been confirmed by transmission electron microscopy, the growth process of nanoplates has been studied by UV/vis spectroscopy. Control experiments have been explored for a more thorough understanding of the growth mechanism. It was found that both the concentrations of TA and the pH of solution were the key elements to control the morphology silver nanoplates. The optical in-plane dipole plasmon resonance bands of these silver plates could be tuned from 520 to 1100 nm.     

Effects of alkylated polyethylenimines on the formation of gold nanoplates

Mono- and dialkylated polyethylenimines (PEI-1R and PEI-2R) were used for the facile synthesis of gold nanoplates with a preferential growth direction along the Au (111) plane. It was found that polymer hydrophobicity greatly influenced the nanoparticle morphology. PEI-1R in the acidic aqueous solution with a smaller degree of alkylation effectively adsorbed on the surface of gold nanoplates with the protonated ethylenimine groups rather than being aggregated in the bulk aqueous phase to form polymer aggregates as compared to the situation for PEI-2R. Loose alkylated PEI aggregates in acidic solution promote the formation of gold nanoplates by means of the anion-induced cation adsorption on certain crystallographic facets during the growth of gold particles. Without incorporating alkyl groups, however, the TEM image of the gold colloid solution with PEI showed only the formation of spherical gold nanoparticles by the same process. The morphology of gold nanoparticles was tuned not only by varying the degree of alkylation of PEI samples but also by the solvent type and pH value of the solution. By utilizing differently alkylated PEIs as reducing agents, this facile synthetic procedure can selectively result in the formation of gold nanoplates at room temperature without an extra inducing process.     

Organic dye molecules as reducing agent for the synthesis of electroactive gold nanoplates

Highly crystalline, hexagonal and triangular nanoplates of gold are synthesized in high yield by a new wet chemical method using multifunctional molecules, Bismarck brown R (BBR) and Bismarck brown Y (BBY). This method involves a simple approach by keeping a mixture of aqueous HAuCl4 solution and BBR/BBY solution in presence of poly(vinyl pyrrolidone) for 24 h. These nanostructures show unprecedented electrochemical properties exhibiting surface confinement effect. The UV-visible (UV-vis) spectrum shows certain distinct features with absorptions at 300, 400, and 650 nm extending up to the near infrared region. Selected area electron diffraction patterns of these nanoparticles show highly oriented (111) crystal facets. X-ray diffraction analysis also confirms the predominant orientation in the (111) crystal planes with lattice constant approximately 4.07 angstroms of face-centered-cubic (fcc) gold. X-ray photoelectron (XP) and Fourier transform infrared (FTIR) spectroscopic analysis shows the presence of a fraction of reducing molecules as surface passivating agent either in the unreacted molecular state or as a mixture of reacted and unreacted product, which probably undergoes charge transfer with gold nanocrystals giving absorption at approximately 300 nm.     

烟草花叶病毒介导合成三角形金纳米片

利用碱处理烟草花叶病毒的生物还原性和辅助结构导向作用,在室温下以水为溶剂直接还原氯金酸制备出三角形金纳米片。采取透射电子显微镜（TEM）、高分辨透射电子显微镜（HRTEM）、选区电子衍射（SAED）和紫外-可见光谱仪（UV-Vis）等对所制备金纳米片的结构和性能进行了表征。结果显示,所制备三角形金纳米片为单晶,三角面为{111}晶面簇,边长在40 ~120 nm之间,厚度约为15 nm。该材料在可见光区有两个等离子共振吸收峰,在感光成像、生物检测和催化等领域具有很好的应用前景。     

Gold and silver nanorings formed at the air/water interface

Gold nanorings were prepared at the air/water interface through reduction of AuCl₄⁻ ions by UV-light irradiation or formaldehyde gas treatment at room temperature templated by thin films of phthalocyanine derivatives. Silver nanorings were produced at the air/water interface via reduction of Ag⁺ ions by UV-light irradiation templated by poly(9-vinylcarbazole) (PVK) thin films. These nanostructures were investigated by transmission electron microscopy (TEM), selective-area electron diffractometry (SAED), and high-resolution TEM (HRTEM). It was found that the gold nanorings are composed of close-packed nanoplates whose (1 1 0) crystal planes are parallel to the air/water interface; while silver rings are composed of nanoparticles. It is demonstrated that the ring-like aggregates formed by parallel linear supramolecules of the phthalocyanine derivatives and the ring-like structure of PVK supramolecules are responsible for the formation of the gold and silver nanorings, respectively.     

Synthesis and optical properties of triangular gold nanoplates with controllable edge length

Gold triangular nanoplates with a uniform size were synthesized by a simple seeds-growth method in a lamellar lyotropic liquid crystal (LLC) medium consisting of F127, n-C₄H₉OH and H₂O. The edge length of gold nanoplates can be adjusted from tens to several hundreds nanometers (and even a few micrometers) by varying the concentration of Au³⁺ and the seeds solution volume. The optical properties of the synthesized gold nanoplates were studied. The vis-NIR spectra of the synthesized gold nanoplates exhibited a good linear correlation between the in-plane plasmon resonance λ_max and the average edge length of the corresponding nanoplates.

     

Preparation of L-Alanine Crystals Containing Gold Nanoparticles

Amino acids provide useful foods, medicines, health foods, and nutritional supplements. We studied the morphology control of alanine, an amino acid. We also studied the effects of amino acid addition on the dispersion stability of gold nanoparticles. We then studied hybridization between alanine crystals and arginine-capped gold nanoparticles. Alanine crystal growth in a supersaturated alanine solution was found to increase linearly over time, and alanine crystal growth stopped as supersaturation decreased. Alanine crystals with arginine grew toward the c-axis because arginine was adsorbed onto the face (120) of alanine crystals. Absorption wavelengths of colloidal solutions changed for gold nanoparticles with arginine, suggesting that arginine was adsorbed onto gold nanoparticles. The change in alanine crystal morphology was the same for alanine crystals with arginine-capped gold nanoparticles in that it grew toward the c-axis. Alanine crystals contained arginine-capped gold nanoparticles toward the c-axis.     

Facile synthesis of concave gold nanoplates in hexagonal liquid crystal made of SDS/water system

Concave gold nanoplates are obtained in hexagonal liquid crystal (LLC) made of SDS (sodium dodecyl sulfate)/glycine/HAuCl(4) aqueous solution system where glycine plays the key role. All plates are single-crystals, characterized by {111} facets, with concave centers of regular hexagonal or triangular shapes, and with better electrocatalytic activity than gold nanoplates.     

Shape-controlled synthesis of gold icosahedra and nanoplates using Pluronic P123 block copolymer and sodium chloride

Gold icosahedra with an average diameter of about 600 nm were easily prepared by heating an aqueous solution of the amphiphilic block copolymer, poly(ethylene oxide)₂₀-poly(propylene oxide)₇₀-poly(ethylene oxide)₂₀ (Pluronic P123), and hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O) at 60 °C for 25 min. When sodium chloride (NaCl:HAuCl₄ molar ratio=10:1) was added to this aqueous solution, gold nanoplates were produced. The chloride ion was found to be a key component in the formation of the gold nanoplates by facilitating the growth of {111} oriented hexagonal/triangular gold nanoplates, because similar gold nanoplates were produced when LiCl or KCl was added to the aqueous solution instead of NaCl, while gold nanocrystals having irregular shapes were produced when NaBr or NaI was added.