Synthesis of silver nanoplates by two-dimensional oriented attachment

Synthesis of silver nanoplates was studied in the modified polyol method, where the nucleation and seed stage occurred in a poly(ethylene glycol) (PEG)-water mixture solution, and the growth stage happened in the PEG environment. The morphological evolution of nanoplates was characterized using UV, SEM, and TEM. Interestingly, plane nanostructures with unusual jagged edges were finally formed in our modified polyol method. Using TEM, we observed the medium state of fusion between two nanoplates, resulting in generating unusual jagged edges. Therefore, a novel two-dimensional oriented attachment occurred in our modified polyol method, which involves smaller nanoplates as the building blocks. Further control experiments showed that the presence of water could break this kinetic preferred reactivity, leading to the formation of nanoparticles.     

Facile synthesis of gold nanoplates by thermally reducing AuCl_4~- with aniline

We herein report a one-step,wet-chemical approach to synthesizing gold nanoplates in large quantities via the AuCl_4~-thermal reduction process by aniline,without introducing additional capping agent or suffactant.It is found that the reduction kinetics of AuCl_4~-is greatly altered by varying the initial molar ratio of aniline to AuCl_4~-.Moreover,further investigation reveals that the in- situ formed polyaniline could serve effectively as a capping agent to preferably adsorb the{111}facets of gold crys...     

Thiol-frozen shape evolution of triangular silver nanoplates

The structural and optical stability of nanoparticles directly influences their applications. The shape evolution of silver nanoplates synthesized in the presence of bis(2-ethylhexyl) sulfosuccinate (AOT) could be effectively frozen using thiols in aqueous solution. These thiols (e.g., 1-hexanethiol, 1-octanethiol, 1-dodecanethiol, and 1-hexadecanethiol) exhibit stronger surface affinity on the silver crystalline surfaces. This is evidenced from both the unchanged shape/size of nanoplates and their unshifted plasmon resonances in optical absorption. To quantitatively explain the thiol-frozen shape evolution mechanism of silver nanoplates at molecular scale, molecular dynamics simulation was performed. The results show that these thiols exhibit larger interaction energies than AOT molecules on the silver atomic surfaces and hence freeze the shape evolution of silver nanoparticles. This thiol-frozen strategy would not only be useful for stabilizing nanoparticles but would also allow the introduction of a wide range of surface chemical functionalities to the nanoparticles for potential applications in nanosensors.     

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.

     

Room-temperature reaction of laser-photolytically generated Te nanosols with silver

KrF laser photolysis of diphenyl ditelluride in 2-propanol yields a stable solution of tellurium nanosols, which reacts with immersed Ag sheets to yield thin silver telluride films. The nanosols were identified by UV–vis spectroscopy and the films were characterized by electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis. It is revealed that the films are mostly amorphous and contain small contributions of cubic as well as monoclinic Ag₂Te structures. The procedure provides the first example of the fast formation of silver telluride thin films by reaction between the elements in inert solvent at room-temperature.     

Ultrasonic-assisted synthesis of monodisperse single-crystalline silver nanoplates and gold nanorings

A simple sonochemical route was developed for the crystal growth of uniform silver nanoplates and ringlike gold nanocrystals in a N,N-dimethylformamide solution. The platelike structures were generated from the selective growth on different crystal planes in the presence of poly(vinylpyrrolidone) and the ultrasonic-assisted Ostwald ripening processes. The silver nanoplates in solution served as the templates for the synthesis of ringlike gold crystals via a displacement reaction. Both the silver nanoplates and gold nanorings were highly oriented single crystals with (111) planes as the basal planes.     

Triangular silver nanoplates: Properties and ultrasensitive detection of miRNA

Triangular silver nanoplates (TSNPs) have been functionalised with probe strand miRNA that is complementary in part to the target nucleic acid, miR-132-3p, that is associated with neuroblastoma. These TSNPs were immobilised in gold microcavities via complementary miRNA hybridisation and can give plasmonic enhancement of the Raman response. Optimum enhancement can be achieved by using different excitation wavelengths and changing the distance between the nanoplate and the surface of the cavity. As silver is electrocatalytically active to the reduction of hydrogen peroxide, these probe-functionalised TSNPs can be used in a miRNA assay where a linear response was obtained for target concentrations from 100 fM to 1 μM target concentration, with a current generated of 100 μA.     

Bacterial kinetics-controlled shape-directed biosynthesis of silver nanoplates using Morganella psychrotolerans

We show for the first time that by controlling the growth kinetics of Morganella psychrotolerans, a silver-resistant psychrophilic bacterium, the shape anisotropy of silver nanoparticles can be achieved. This is particularly important considering that there has been no report that demonstrates a control over shape of Ag nanoparticles by controlling the growth kinetics of bacteria during biological synthesis. Additionally, we have for the first time performed electrochemistry experiments on bacterial cells after exposing them to Ag(+) ions, which provide significant new insights about mechanistic aspects of Ag reduction by bacteria. The possibility to achieve nanoparticle shape control by using a "green" biosynthesis approach is expected to open up new exciting avenues for eco-friendly, large-scale, and economically viable shape-controlled synthesis of nanomaterials.     

Green and controllable fabrication of nanocrystals from ionic liquids

Nanocrystals are of great value in delivering poorly soluble drugs as a technique enables enhanced dissolution and bioavailability. The bottom-up technique allows better control of particle properties. However, the commonly used organic solvents are hazardous to environment and operators, and always lead to large particle size and wide size distribution due to failure on controlling the nucleation and crystal growth. The situation is exacerbated in scale-up production. Therefore, in the proof-of-concept study, we evaluated the feasibility of green and controllable fabrication of drug nanocrystals by using biocompatible ionic liquids (ILs) as solvents. Choline based ILs (Ch-ILs) were synthesized via metathesis reactions. Pure paclitaxel nanocrystals of high quality were obtained from Ch-ILs with surface tension higher than 42 mN/m. The sizes were below 250 nm, while the polydispersity indexes were lower than 0.25. Compared with ethanol, choline lactate is superior in controlling the size of the nanocrystals in scale-up production, where the drug concentration was increased by 6 times. The underlying mechanism may be due to the high viscosity and low surface tension of the ILs, which are supposed to benefit homogeneous and burst nucleation. Ch-ILs can be recycled from the process and recovery rate reached 91.1%. Moreover, the applicability of the green technique was validated in a wider range of model drugs and Ch-ILs. In conclusion, ILs are potent solvents in bottom-up technique for green and controllable fabrication of nanocrystals.     

Monitoring the shape evolution of silver nanoplates: a marker study

Out of the frame: A marker study using gold frames was designed to reveal that silver nanoplates undergo a shape transition during their seeded growth from triangular to circular to hexagonal plates before ultimately returning to triangular structures with an orientation 180° relative to that of the original triangular seeds (see picture, the original gold triangular frame is visible at the center of the silver nanoplate).     

Preparation of silver nanocrystals in the presence of aniline

The preparation and characterization of silver nanocrystals by chemical reduction of silver ions in the presence of aniline using hydrazine monohydrate (N(2)H(4).H(2)O) or sodium citrate as the reducing agent are described. A high yield of aniline-derivatized hexagonal silver nanoparticles is obtained by the reduction of Ag(2)SO(4) with N(2)H(4).H(2)O. An alternative strategy is the reduction of Ag(+) by citrate in the presence of aniline, by which the size and morphology of the Ag nanocrystals can be controlled to a certain degree by changing the concentration ratio of aniline to Ag(+). It is believed that the amount of aniline added in the starting solutions for the preparation influences the morphology of the Ag nanoparticles. In addition, the long Ag nanorods with a high mean aspect ratio are prepared in the presence of aniline at a low concentration or o-anisidine.     

Transformation of silver nanospheres into triangular nanoplates through a photoinduced process

Triangular silver nanoplates exhibit excellent optical and catalytic properties in many fields, such as catalysts, sensors and bio-medicine. In this paper, triangular nanoplates were generated just in the presence of sodium citrate through a light-induced ripening process, which were converted from spherical silver nanoparticles by reducing silver nitrate with sodium borohydride. By using UV–Vis spectroscopy, particle size analyzer, transmission electron microscopy (TEM) and Ag⁺ concentration analysis, the effects of precursors during the preparation of triangular nanoplates were systematically investigated and the optimal experimental conditions were determined. Based on density functional theory (DFT), the adsorption energies of citrate ion, malate ion and tartronate ion on Ag (1 1 1), (1 1 0) and (1 0 0) were calculated. In addition, theoretical calculations coupled with experimental observations showed that citrate ion as capping agent could more preferentially bind to Ag (1 1 1) and thus blocked Ag (1 1 1) while only allowing extensive growth along the lateral direction. This well explains sodium citrate is an efficient agent in preparing triangular silver nanoplates.     

Dissolution-recrystallization mechanism for the conversion of silver nanospheres to triangular nanoplates

A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH(4) reduction of AgNO(3) in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O(2)/Cl(-) etching of the Ag nanospheres and the reduction of the released Ag(+) by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag(0) atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).     

导电聚吡咯纳米线的电化学无模板法可控合成与表征

以β-萘磺酸(NSA)为掺杂剂,采用电化学无模板法制备了聚吡咯(PPy)纳米线.研究了NSA浓度、吡咯(Py)单体浓度及反应温度对PPy纳米线形貌的影响.分别采用场发射扫描电子显微镜(FE-SEM)和拉曼光谱对PPy纳米线的结构形貌和化学结构进行了表征.结果表明,利用电化学无模板法可得到中空的PPy纳米线;NSA浓度会影响PPy纳米线的取向性;增大Py单体浓度,可制得圆锥状PPy纳米线;低温有利于合成形状细长、紧密堆积的PPy纳米线.PPy纳米线形貌受游离Py浓度及Py-NSA胶束数量影响,通过调节NSA浓度、Py浓度及反应温度改变游离Py浓度及Py-NSA胶束数量,可制得不同形貌的PPy纳米线.     

A novel shape-selective fabrication of nanostructured silver

A novel protection-reduction technique is developed for the preparation of silver nanoparticles, nanorods and wheatear-like supramolecular nanostructures at room temperature using silver potassium cyanide [KAg(CN)2] as a silver source, vitamin C (Vc) as a reducing agent and polyvinylpyrrolidone (PVP) as a protecting agent. The concentration of KAg(CN)2, the mole ratios of PVP/Vc and KAg(CN)2/Vc have significant effects on the formation and growth of these novel nanostructures. This method may be extended to prepare novel nanostructures of other metals.     

Surface-enhanced Raman scattering studies on aggregated silver nanoplates in aqueous solution

Four different sizes of citrate-protected silver nanoplates with the corresponding in-plane dipole resonance band at 530, 619, 778, and 858 nm, respectively, are synthesized for surface-enhanced Raman scattering (SERS) study. Their aggregation behaviors are monitored by use of UV-vis spectroscopy. During the aggregation process, a marked red shift of the in-plane dipole resonance of silver nanoplates is observed, whereas other resonance modes of them only have small alterations in the site or intensity. Aggregated silver nanoplates can serve as active SERS substrates with an enhancement factor of about 4.5 x 10(5) using 2-aminothiophenol as a probing molecule. The SERS performance of silver nanoplates is even superior to the commonly used Lee-Meisel silver colloid, making them very attractive for SERS applications.     

Preparation of reagent indicator papers with silver triangular nanoplates for chemical analysis

An impregnation method to prepare reagent indicator papers with silver triangular nanoplates (TNPs) is developed. The conditions for obtaining modified papers (type of paper, method for applying TNPs, and drying conditions) allowing for an acceptably uniform distribution of the TNPs are chosen. The spectral characteristics of the prepared materials are studied. The presence of an intense TNP surface plasmon resonance band in the diffuse reflectance spectra of the modified papers, which is linearly related to the content of the TNPs in the samples, as well as the lability of its position and shape in the presence of some substances, gives rise to the prospects of using the prepared materials as test-tools in chemical analysis.