Green synthesis of gold and silver nanoparticles using gallic acid: catalytic activity and conversion yield toward the 4-nitrophenol reduction reaction

In the present report, gallic acid was used as both a reducing and stabilizing agent to synthesize gold and silver nanoparticles. The synthesized gold and silver nanoparticles exhibited characteristic surface plasmon resonance bands at 536 and 392 nm, respectively. Nanoparticles that were approximately spherical in shape were observed in high-resolution transmission electron microscopy and atomic force microscopy images. The hydrodynamic radius was determined to be 54.4 nm for gold nanoparticles and 33.7 nm for silver nanoparticles in aqueous medium. X-ray diffraction analyses confirmed that the synthesized nanoparticles possessed a face-centered cubic structure. FT-IR spectra demonstrated that the carboxylic acid functional groups of gallic acid contributed to the electrostatic binding onto the surface of the nanoparticles. Zeta potential values of ?41.98 mV for the gold nanoparticles and ?53.47 mV for the silver nanoparticles indicated that the synthesized nanoparticles possess excellent stability. On-the-shelf stability for 4 weeks also confirmed that the synthesized nanoparticles were quite stable without significant changes in their UV–visible spectra. The synthesized nanoparticles exhibited catalytic activity toward the reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. The rate constant of the silver nanoparticles was higher than that of the gold nanoparticles in the catalytic reaction. Furthermore, the conversion yield (%) of 4-nitrophenol to 4-aminophenol was determined using reversed-phase high-performance liquid chromatography with UV detection at 254 nm. The silver nanoparticles exhibited an excellent conversion yield (96.7–99.9 %), suggesting that the synthesized silver nanoparticles are highly efficient catalysts for the 4-nitrophenol reduction reaction.     

Fluorescence Modulation of Acridine and Coumarin Dyes by Silver Nanoparticles

Silver nanoparticles were synthesized by chemical reduction of silver ions by sodium borohydride in the presence of poly-(N)-vinyl-2-pyrrolidone in solution of short chain alcohols. The nanoparticles are stable in 2-propanol, and the average diameter of the Ag colloid obtained in this solvent is about 6 nm. The photophysical properties of acridinium and coumarin dyes in 2-propanol are affected by the presence of silver nanoparticles. The interaction of silver nanoparticles with acridinium derivative leads to a spectral change of its intramolecular charge transfer (ICT) absorption band. The dye emission increases suddenly with the initial addition of the Ag metal nanoparticles, but at a high concentration of the colloid, static fluorescence quenching occurs with a progressive decrease of the fluorescence efficiency. Amino coumarin fluorescence is only quenched by the silver nanoparticles in solution.     

Silver Nanoparticle Based Analysis of Aminoglycosides

Colorimetric silver nanoparticle sensor was developed for determination of aminoglycosides in milk. Silver nanoparticles were synthesized by using sodium borohydride as reducing agent and sodium dodecyl sulfate as stabilizer. Yellow color of silver turned into orange and red in proportion to the concentrations of analytes. Quantitative analyses were performed by using decrease in absorbance of silver nanoparticles at 394 nm. Linear ranges were 20–60 ng mL^?1, 23–60 ng mL^?1, and 60–100 ng mL^?1 for gentamicin, tobramycin, and amikacin, respectively. The method was optimized in terms of pH, ionic strength, and time. This simple and validated method was applied to milk samples and pharmaceutical preparations.     

Synthesis and photophysical study of silver nanoparticles stabilized by unsaturated dicarboxylates

Solution-phase synthesis of nanometer-sized silver particles is reported by sodium borohydride reduction of AgNO_3. Two isomeric dicarboxylates (sodium maleate and sodium fumarate) have been used as stabilizing agents. The dicarboxylate-stabilized silver nanoparticles are characterized by UV-vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and fourier transform infrared (FT-IR) spectroscopy. A qualitative comparison is made between the UV-vis spectral characteristic of the SPR band and the simulated curve obtained from modified Mie's theory. Silver nanoparticles prepared using these two isomeric dicarboxylates show intense fluorescence in the visible region. DFT with hybrid functional (B3LYP)-based frequency (IR) calculation of both the dicarboxylates and the respective nanoparticles are in good agreement with the experimental IR frequency. On the basis of this calculation a model has been proposed for the stabilization of silver nanoparticles by these two isomeric dicarboxylate anions.     

Optical properties of monodispersed silver nanoparticles produced via reverse micelle microemulsion

Silver nanoparticles produced by the sodium borohydride reduction of silver nitrate were stabilized by means of 1-dodecanethiol providing sulfur atom. (n-Dodecyl) trimethylammonium bromide (DTAB), which was used as a phase transfer agent in two-phase system involving water and toluene, played a significant role in the formation of monolayer-protected silver nanoparticles. These nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible absorption spectroscopy (UV-vis), FT-IR spectra and fluorescence. The results indicate that the system is monodispersed and leads to the self-assembly of silver nanoparticles into 0-D quanta-dot arrays.     

银胶溶液pH值对结晶紫的表面增强拉曼光谱增强效果的影响

通过NaBH4还原AgNO3制得银溶胶, 分析了结晶紫溶液表面增强拉曼光谱随银胶溶液pH值减小而逐渐减弱的机理。其原因是当加入酸改变银胶溶液pH值时, 在静电力作用下H+聚集在粗糙且存在偶电层(Ag+─负吸附质)的银胶表面, 使胶体中存在的表面等离子体共振吸附态的光吸收源随着H+浓度的增加逐渐减弱。并且H+与结晶紫的竞争作用又使结晶紫与银颗粒之间的吸附数量减少, 最终使结晶紫SERS强度随着pH值减小而逐渐减弱。我们测得银胶溶液的紫外──可见吸收光谱吸收峰强度随着pH值减小而逐渐减弱, 证明了分析的正确性。     

Synthesis of biomacromolecule-stabilized silver nanoparticles and their surface-enhanced Raman scattering properties

In this work, water soluble silver nanoparticles stabilized by biomacromolecule, were produced through using an aqueous solution of silver nitrate with Bovine Serum Albumin (BSA) under different reducing agents (such as sodium borohydride, hydrazine, N,N-dimethyl formamide) at the room temperature, where BSA provided the main function to form monodispersed silver nanoparticles. UV–vis spectroscopy, Fluorescence spectra, TEM and HR-TEM are used to characterize the BSA-capped silver nanoparticles under different condition. The results show that the formed silver nanoparticles have different size and morphology under the three different reducing agents. Moreover, the fluorescence intensity of BSA was drastically quenched in presence of Ag nanoparticles from the results of fluorescence spectra. Furthermore, the surface-enhanced Raman scattering effects of the formed silver nanoparticles were also displayed and we made a comparison under three different reducing agents.     

Preparation and properties of nano-sized Ag and Ag2S particles in biopolymer matrix

Silver (Ag) and silver sulfide (Ag₂S) nanoparticles were synthesized in a sago starch matrix. The resulting nanocomposites were investigated using structural, optical and thermal methods. XRD spectra of the nanocomposites confirmed the presence of nanostructured silver (cubic phase) and silver sulfide (monoclinic phase) in the matrix. TEM micrographs showed that the nanoparticles are mostly spherical in shape. Analyzes of the optical properties of the silver nanocomposite aqueous dispersions/solutions of various concentrations were carried out. The results and the theoretical considerations suggested that at high concentrations there is a release of silver nanoparticles from the composite in the water environment. Further dilution produces homogeneous solution in which silver nanoparticles are capped with starch macromolecules. TGA analysis revealed reduced thermal stability of the nanocomposites with respect to pure starch matrix.     

Raman study of oxidation-reduction dispersion of silver

We have examined the process of redox dispersion of silver, using a solution simultaneously containing an oxidizing agent (potassium ferricyanide) and a reducing agent (sodium borohydride). We have studied the changes over time in the Raman spectra of the indicated solution when no silver particles are present and when such particles are added to the solution. We have established that the silver particles have a catalytic effect on the reaction between potassium ferricyanide and sodium borohydride, kinetically slowed down in alkaline medium. The original silver particles (1–20 μm) undergo redox dispersion as a result, and Ag particles are formed with sizes 1–10 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 182–186, March–April, 2006.     

Raman spectra of benzoic acid enhanced by the silver nanoparticles of various sizes

Using sodium borohydride as the reducing agent and polyvinyl pyrrolidone (PVP, MW = 10 000) as the stabilizer, we obtained silver nanoparticles of various diameters (8–78 nm) from silver nitrate aqueous solutions in the concentration range from 0.001 to 0.1 M. The surface‐enhanced Raman scattering (SERS) from benzoic acid's ring‐breathing mode at 1003 cm⁻¹ was detected from its dilute solutions (∼10⁻² M) doped with these silver nanoparticles under 488‐nm laser excitation. The observed size dependences of SERS intensities fit quite well with those calculated by Schatz's theoretical model for spherical silver nanoparticles. The only exception occurred with the smallest particles (8 nm), possibly due to the failure of Maxwell's electromagnetic theory used in this model. Copyright © 2009 John Wiley & Sons, Ltd.     

Diagnostics of aqueous colloids of noble metals by extinction modeling based on mie theory

Two-factor dependences of the maximum and half-width of a surface plasmon resonance band on both the average diameter of nanoparticles and the scatter in their particle-size distributions were defined for colloidal silver and gold aqueous solutions based on modeling the extinction effectiveness factor by Mie theory. The obtained three-dimensional surfaces determined the shape of calibration curves used to define the average particle diameters and the scatter in their particle-size distributions from measurements of the maximum and half-width of the surface plasmon resonance band in spectra of the silver and gold colloidal solutions. The calibration curves were correlated with experimental samples of aqueous ultradispersed media containing silver and gold nanoparticles.     

质子酸功能化离子液体中银纳米颗粒的制备及其光学性能研究

以质子酸功能化离子液体1-丁基-3-甲基咪唑磷酸二氢盐([Bmim]H₂PO₄)为反应介质和表面活性剂,采用简单的化学还原法制备了具有形状各向异性的块状银纳米颗粒。通过X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)吸收光谱等一系列手段对其结构、形貌及光吸收特性进行了表征。结果表明,所制备的银纳米块具有立方结构,其平均横向尺寸约为30 nm,在硅片上自组装形成密堆积结构的多层膜。以1,2-二(4-吡啶基)乙烯(BPE)作为探针分子,研究所制备银纳米颗粒的表面增强拉曼散射(SERS)活性。结果表明所制的银纳米颗粒是较好的SERS基底,具有良好的增强效果,痕检能力及稳定性。对BPE分子的最低检测浓度可低至10-9mol·L-1,而且保存了90天后,其检测灵敏度没有显著的降低。     

金银纳米粒子的电化学性质及联苯胺的SERS研究

采用柠檬酸钠还原氯金酸,硼氢化钠还原硝酸银分别制备了较小粒径的金、银纳米粒子。运用紫外可见吸收光谱(UV-Vis)、扫描电子显微镜(SEM)、循环伏安法(CV)对金、银纳米粒子进行了表征。结果表明：所得金、银纳米粒子粒径分别约为16和10 nm,并能以亚单层形式组装于导电玻璃(ITO)表面;CV图显示金、银纳米粒子分别有一对不对称的氧化还原峰,而且纳米粒子的浓度对其氧化还原电位存在一定的影响。采用自组装方法,以联苯胺为偶联分子, 在粗糙金基底表面构筑了金/银纳米粒子的双层有序结构。表面增强拉曼光谱研究表明, 在有序金银纳米粒子组装体中偶联分子的拉曼散射得到了增强。     

Synthesis and characterization of silver nanoparticles: effect on phytopathogen <Emphasis Type="Italic">Colletotrichum gloesporioides</Emphasis>

Colloidal silver nanoparticles were synthesized by reducing silver nitrate solutions with glucose, in the presence of gelatin as capping agent. The obtained nanoparticles were characterized by means of UV–Vis spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The response surface methodology (RSM) was also used to determine the influence of the variables on the size of the nanoparticles. The antifungal activity of the silver nanoparticles was evaluated on the phytopathogen Colletotrichum gloesporioides, which causes anthracnose in a wide range of fruits. The UV–Vis spectra indicated the formation of silver nanoparticles preferably spherical and of relatively small size (<20 nm). The above-mentioned was confirmed by TEM, observing a size distribution of 5–24 nm. According to RSM the synthesis variables influenced on the size of the silver nanoparticles. By means of FTIR spectroscopy it was determined that gelatin, through their amide and hydroxyl groups, interacts with nanoparticles preventing their agglomeration. The growth of C. gloesporioides in the presence of silver nanoparticles was significantly delayed in a dose dependent manner.     

AOT微乳体系中纳米银的可控合成及其紫外-可见光谱研究

在以琥珀酸二异辛酯磺酸钠(AOT)为表面活性剂、环己烷为连续相形成的W/O型微乳体系中,用增溶于微乳液水核中的AgNO₃为银源、水合肼为还原剂制备了纳米银溶胶,利用UV-Vis光谱分析了AgNO₃的浓度、AOT的浓度、还原剂的种类和水与表面活性剂的物质的量比(W)等参数对形成粒子数量及平均粒径的影响,为纳米银粒子的可控合成和纳米银的UV-Vis光谱解析提供了新的依据。研究表明,适当增大AgNO₃的浓度,有利于形成粒径较小的纳米银粒子;W值增大,形成粒子的平均粒径和粒子数量明显增加。和NaBH₄相比,水合肼在反胶束中的溶解性能较好,有利于微乳液反胶束中Ag+的还原。增大AOT的浓度,在一定范围内胶束对反应物的增溶能力增强,胶束的半径也相应减小,有利于形成数量较多、平均粒径较小的纳米银粒子。     

甲基橙溶液的pH值对纳米银荧光增强效应的影响

研究了甲基橙溶液的pH对纳米银荧光增强效应的影响.当pH 1.5和2.1时,纳米银对溶液的吸收光谱影响甚小.当pH 3.1时,吸收峰蓝移26 nm,且强度明显降低.当pH值在3.8～8.2范围时,不仅吸收峰蓝移而且在426～456 nm出现宽吸收带.在任何pH值的甲基橙溶液中加入纳米银,S2→S0跃迁荧光发射带强度下降,但下降比率受pH值影响不大;S1→S0跃迁荧光发射带强度增强,其增强比率受pH值影响较大.当pH 2.1时,荧光增强比率最大;当pH 4.8时,荧光增强比率最小.分析认为,pH值对甲基橙溶液光谱性质的影响与不同pH值条件下甲基橙分子结构的改变以及分子在纳米银粒子表面不同的吸附方式、介质环境等因素相关,尤其与甲基橙分子与纳米银粒子间的距离密切相关.     

憎水性金属纳米粒子及其LB膜的制备与光谱表征

用油酸钠和十四烷基硫醇作为稳定剂,制备了高度单分散的疏水性银和金纳米溶胶。考察了单粒子层的π－Ａ曲线并建造了纳米粒子的ＬＢ膜。通过紫外可见光谱讨论了纳米粒子的分散状态,由红外光谱结果讨论了纳米粒子表面有机吸附层的状态。     

A fluorescence spectroscopy study of traditional Chinese medicine Angelica

By measuring the fluorescence spectra of Chinese medicine (CM) Angelica water solutions with different concentrations from 0.025 to 2.5 mg/mL, results showed that the fluorescence intensity was proportional to the concentration. Through fluorescence spectra of Angelica solution under different pH values, results indicated coumarin compounds were the active ingredients of Angelica. We also observed fluorescence quenching of the Angelica solution in the presence of spherical silver nanoparticles with radius of 12 nm. Keeping a certain value for the volume of the silver nanoparticles, the fluorescence intensity at 402 nm was linearly proportional to the Angelica in the range of 1–3 mg/mL.     

Spectral manifestation of surface plasmon resonance of silver nanoparticles upon interaction with water-soluble metalloporphyrins

Absorption and resonant light-scattering spectra of nanoparticles (NPs) of silver, and their complexes with water-soluble Cu(II)-5,10,15,20-tetrakis(4-N-methylpyridinium)-porphyrin (CuTMpyP4) and Fe(II)-5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (FeTSPP) have been compared. It is shown that in the presence of cationic CuTMpyP4, the band of surface plasmon resonance in the absorption and resonant scattering spectra of silver NPs is shifted to the long-wavelength region that is associated with the agglomeration of the particles caused by the Coulomb attraction between the silver particles and the porphyrin molecules. Addition of anionic FeTSPP to the silver NP solution does not lead to any spectral changes. The observed effect of silver-NP association induced by the cationic porphyrin can be used to develop an optical method for the detection of nanoparticles in solutions.     

Optical transmission of dielectric layers with metallic nanoparticles inhomogeneously distributed over the sample thickness

Dielectric layers with silver nanoparticles in the bulk, synthesized by the vacuum evaporation of metal onto viscous-flow softened polymer substrates are analyzed. New materials with a nonuniform distribution of nanoparticles over the sample thickness are obtained. Optical characteristics of the composition layers are calculated from the transmission spectra. To calculate the optical spectra, a model of a multilayered plane-parallel film structure is considered. Functions of dielectric constants of separate composition layers are determined using the Bruggeman theory of effective medium. A qualitative agreement between the experimental and simulated optical spectra is achieved taking into account nonuniform distribution of metal nanoparticles over the composition material thickness.