Plasmonic Properties and Size Programming: A Quantitative Study for Photosynthesized Gold Nanoparticles

A novel two‐component peak quantitative spectra deconvolution model is employed to elucidate the relationship between the plasmonic properties and the concentration‐dependent Au nanocrystals nucleation. The reactions with the initial concentration of starting reagent NaAuCl₄ from 0.75 mM to 0.1 mM are monitored. The peak area variation between component peak (b), large size nanoparticles (d ≥ 8.1 nm), and component peak (a), small size nanoparticles (d ≤ 8.0 nm), demonstrates that the initial concentration of NaAuCl₄ plays a decisive factor to determine the (b/a) ratio, i.e. the growth progresses of Au nanoparticles. If the initial concentration of NaAuCl₄ is higher than 0.2 mM, two independent growth progresses of Au nanoparticles are observed, and a continuous λ_max blue‐shift of surface plasmon absorption peak accompanied with the second growth progress is measured. On the other hand, in the reactions with the initial concentration of NaAuCl₄ lower than 0.2 mM, only one crystal growth progress of Au nanoparticles is shown, and the blue‐shift phenomenon of absorption peak induced by the second crystal growth progress no longer exists.     

Kinetics of the X-ray induced gold nanoparticle synthesis

Time resolved small angle scattering has been employed to follow the formation kinetics of gold nanoparticles from a solution of gold hydrochlorate and tris-sodium citrate at room temperature. While UV irradiation leads to a slow kinetics as observed by optical spectroscopy, the irradiation by the X-rays led to a reduction of the gold within a few minutes. The size and morphology evolution during the radiolytic formation of particles displays the initial nucleation phase and the growth kinetics, which exhibit very nonuniform behavior. They show that the electrostatics of the particle stabilization plays a pronounced role in the repulsive forces and transient clustering of particles.     

荧光碳点的合成及对酿酒酵母的毒性研究

以葡萄糖为碳源采用溶剂热法合成了荧光碳点。紫外吸收光谱、荧光光谱以及透射电镜照片表明,所合成的荧光碳点发光性能优异,分散性好,且无团聚现象。荧光碳点原溶液出现浓度淬灭现象,稀释60倍情况下荧光最强。以酿酒酵母为模型生物,考察了不同生长时期(调整期、对数期早期、对数期中期)的酿酒酵母与不同浓度的荧光碳点共培养后的生长曲线。结果表明,即使荧光碳点浓度在27.75 mmol.L-1条件下也没有影响酵母菌的生长曲线,可认为基本没有细胞毒性。比较了相同荧光强度下的荧光碳点与CdTe量子点对酿酒酵母的细胞毒性,结果表明荧光碳点的毒性显著低于量子点的毒性。     

UV/H2O2工艺湿法脱除燃煤烟气中NO的研究

在自行设计的内置紫外光-鼓泡器中，利用UV/H₂O₂高级氧化工艺湿法脱除燃煤烟气中的NO气体。主要对紫外光强度、H₂O₂初始浓度、NO初始浓度以及烟气总流量对NO脱除效率的影响进行了考察。研究结果表明，在实验范围内，NO脱除效率随着紫外光强度和H₂O₂初始浓度的增加而增加，但当达到一定值后，NO脱除效率的增加幅度均变得相对平缓；NO脱除效率随着NO初始浓度以及烟气总流量的增加呈近似线性减小。通过离子色谱对液相离子产物进行了定性与定量检测，并对NO中的氮元素进行了物料平衡计算，在此基础上对NO脱除路径与产物形态进行了理论分析。
     

纳米氧化锌粒子分散性对其吸收光谱的影响

在异丙醇中用氢氧化钠分别与醋酸锌及溴化锌反应制备了纳米氧化锌粒子. 分别用高分辨率电子显微镜及原位紫外吸收光谱测定了粒子大小及分布. 实验结果表明, 粒子的增大服从LSW (Lifshitz-Slyozov-Wagner)模型, 即粒子体积随老化时间线性增大；但粒子的分布不符合LSW模型, 这与他人的研究结果不一致. 用计算机数值模拟确定了纳米氧化锌分布函数对其紫外吸收光谱的影响, 发现在紫外吸收边附近光谱发生弯曲, 且随粒子分布标准方差(SD)的增大, 弯曲更显著, 引起紫外吸收光谱红移, 这将导致用吸收边计算氧化锌粒子大小时产生正误差. 就单分散(SD/γ<5%, γ是粒子的平均半径)纳米氧化锌而言, 这种正误差仅为2%, 但当粒子分布的SD/γ达到15%时, 所产生的正误差可高达15.1%.     

Early stages of ZnS nanoparticle growth studied by in-situ stopped-flow UV absorption spectroscopy.

The early stages of ZnS nanoparticle growth from supersaturated solution are investigated in situ by stopped-flow UV absorption spectroscopy with a time resolution of 1.28 ms. A model for data analysis is suggested which makes it possible to study both the average particle radius and the concentration. The average radii lie in the sub-nanometer range. During the first 40 ms, growth is predominantly governed by ripening.     

Effects of abiotic stressors on synthesis of the mycosporine-like amino acid shinorine in the Cyanobacterium Anabaena variabilis PCC 7937

In the present investigation we show that the cyanobacterium Anabaena variabilis PCC 7937 produces a single mycosporine-like amino acid (MAA), shinorine (retention time = 2.3 min and absorption maximum at 334 nm) when isolated and purified by HPLC. Although there was significant induction of MAA synthesis from its initial value under 395 or 320 nm cutoff filters, MAA induction was significantly more pronounced in samples covered with 295 nm cutoff filters after 72 h of exposure. Heat as a stress factor had no effect on MAA induction with or without UV radiation. In contrast, salt and ammonium treatment had synergistic effects with UV stress. MAA synthesis was also induced by salt and ammonium in a concentration-dependent manner without UV stress in samples covered with 395 nm cutoff filters. The results indicate that MAAs may have other functions in addition to photoprotection in this organism.     

Preparation of nanosized gold particles in a biopolymer using UV photoactivation

Gold nanoparticles have been prepared by UV photoactivation in the presence of a biopolymer, sodium alginate. The particles are characterized by UV-vis spectra and TEM studies. Both particle size and the UV-visible absorption peak are dependent on the sodium alginate concentration. The effects of various other parameters such as change of light source, cell material of the reaction chamber, heating effect, irradiation time, and HAuCl4 concentration are studied. The particles are spherical and in situ stabilized by the biopolymer. The method is very simple and reproducible.     

Photostability of Octyl‐P‐Methoxy Cinnamate in O/W Emulsions and in SLNs Vehicled in the Emulsions

The photochemical degradation of the sunscreen p‐octyl‐methoxy‐cinnamate (OMC) was studied in different media: Finsolv TN (a fluid ester), O/W emulsion and gel‐emulsion. OMC photolysis was performed using an UVB lamp and the degradation kinetic was studied in presence of various initial concentration of the active. The study was performed comparing the naked to the SLNs form of the active and the experiments were monitored with HPLC/UV‐VIS apparatus. Results suggest that lower is the concentration of the UVB sunscreen in the formulations more pronounced is its photodegradation rate. In all the cases the inglobation of OMC into SLNs leads to an over additive UV‐blocking effect.     

纳米AgBr乳剂的制备及其紫外吸收光谱的研究

通常人们把粒径1~100 nm之间的金属、半导体、氧化物及各种化合物的粒子或者粒子的集合体称为纳米粒子。近年来的纳米粒子化学和物理的迅速发展已经证实:随着原子或分子簇尺寸的减小,表面原子的比例逐渐增大,粒子表现了与块状材料不同的特性,其粒子显示出以“量子尺寸效应”为主的特点,特性表现出种种异常^[1,2]。     

粒径可控纳米CeO_2的微乳液法合成

以十六烷基三甲基溴化铵(CTAB)/正丁醇/正辛烷/硝酸铈(Ce(NO3)3)水溶液(氨水)所形成的反相微乳液体系合成CeO2前驱体,利用热重(TG)和X射线衍射(XRD)分析方法确定了得到纳米CeO2的适宜焙烧温度为550℃,CeO2前驱体经550℃焙烧后得到纳米CeO2.采用XRD、透射电镜(TEM)、紫外-可见(UV-Vis)分光光度计等表征手段分别对纳米CeO2的晶形、形貌、粒径及紫外吸收性质进行了表征,该纳米CeO2粒子具有立方晶型结构,分散性较好、粒径范围为5-18nm.考察了微乳液中正辛烷与正丁醇质量比、Ce(NO3)3浓度对纳米CeO2粒径的影响,结果表明:利用微乳液法,通过改变微乳液中正辛烷与正丁醇质量比、Ce(NO3)3浓度能够对纳米CeO2粒径进行有效控制;纳米CeO2的粒径均随着正辛烷与正丁醇质量比和Ce(NO3)3浓度的增大而减小.同时,对不同条件下制得的纳米CeO2的紫外吸收性质进行了考察.     

Studies on photocatalytic performance and photodegradation kinetics of zinc oxide nanoparticles prepared by microwave-assisted sol–gel technique using ethylene glycol

ZnO nanoparticles with an average particle size of 27 nm were fabricated using a microwave-assisted sol–gel method in the presence of ethylene glycol. The nanoparticles were characterized by X-ray diffraction, Monshi’s equation, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The band gap energy of the nanoparticles was measured to be 3.27 eV by UV–Vis absorption and reflection spectroscopy. Photocatalytic activity of the synthesized nanoparticles was assessed by degrading nitrophenol in aqueous solution under UV-C irradiation. The effects of initial nitrophenol concentration, amount of photocatalyst, and of pH on the photodegradation process were investigated. Degradation samples were analyzed by UV–Vis spectroscopy. Nitrophenol was removed by 98 % within 240 min. The degradation kinetics were studied and fitted well to pseudo-first-order and Langmuir–Hinshelwood models.     

Rapid dissolution of vitamin E by using sodium N-lauroylsarcosinate ionic surfactant

Vitamin E is widely used in pharmaceutical, food and cosmetic preparations. This paper discusses methods of preparing a vitamin E emulsion by using sodium N-lauroylsarcosinate (SNLS) ionic surfactant. The amount of vitamin E dissolved in water was analyzed by turbidity and UV absorption measurements. The emulsion droplet size was determined by laser light scattering. Microemulsions with small particle size and high resistance to oxidation in air can be obtained by solubilizing vitamin E in SNLS solution. The dissolution is rapid and the surfactant solution has high solubilization power. At 0.7% surfactant concentration, the saturation value is 1 g vitamin E per gram of surfactant. The micellar dissociation concentration (MDC) of the surfactant can be estimated from a vitamin saturation—surfactant concentration curve. Dissolution mechanisms at different surfactant concentrations are interpreted by use of the MDC and CMC (critical micellar concentration) concepts.     

Influence of pH variation on structural,optical, and superparamagnetic behavior of Ni-doped ZnO (X=0.02) using a solvothermal method

Zn1-xNixO nanoparticles at a concentration (2%) with pH variation (4, 5, 8 and 9) are successfully synthesized using the solvothermal method. ZnO nanoparticle has a hexagonal wurtzite structure when synthesized at acidic and basic conditions. In pH, the solution is calculated from 4 to 9 by the composed addition of NaOH and HCl. The structural properties are studied from XRD and TEM. The average particle size is found to be 13.2 nm using the Debye Scherrer formula and optical properties are analyzed through UV–Visible, FTIR, & PL. From the absorption spectra, it is observed that the bandgap energy is inversely proportional to the particle size. UV–Vis and PL are used to study the optical behavior of the samples. The magnetic behavior of Zn1-xNixO exhibit changing behavior from paramagnetic to superparamagnetic structure with increases in their pH values.     

Molecular orientation in electrodeposited polypyrrole films

The molecular arrangement in electrodeposited polypyrrole films was studied by means of linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K absorption edges of carbon and nitrogen. It has been found that the change of the exciting radiation incidence from normal to grazing leads to an increase in the intensity of π*-related resonances with simultaneous decrease in the intensity of σ*-related resonances in the spectra. Similar changes in the spectra measured for both absorption edges indicate a pronounced conjugation of π-bonds in the polypyrrole chains in the grown films. Preferential in-plane orientation of pyrrole rings relative to the substrate surface is observed for all the deposited films. The linear dichroism is more pronounced at the initial stages of deposition (2D growth) than at later stages characterized by “cauliflower”-like morphology of the grown film.     

Phthalocyanine nanoparticle formation in supersaturated solutions

Self-organization of molecules in solution is an important natural and synthetic process, in particular for the preparation of nanomaterials. However, the mechanism of growth for solution-based nanoparticle formation is not always well understood. We present results that clarify these mechanisms in solutions of magnesium phthalocyanine in which the self-organization is induced by addition of a miscible nonsolvent. From simultaneous measurements of the sizes of the growing nanoparticles by photon correlation spectroscopy and the molecular concentration by absorption and fluorescence spectroscopy, we have found that the particles do not grow by molecular diffusion to the surfaces. These results suggest the importance of unstable clusters in the growth process. We also observed a strong dependence of the particle size on the initial concentration which we attribute to effects of the curvature of the solubility curve.     

Synthesis and Optical Properties of Mn2+-Doped ZnS Nanoparticles in Solutions and Coatings

Mn2+-doped ZnS nanoparticles with different Mn-doping concentrations stabilized by hydroxypropyl cellulose (HPC) have been synthesized in ethanolic solutions and coatings. Their optical and structural properties have been characterized by means of UV-vis spectroscopy, luminescence spectroscopy, high resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS). Solutions and coatings exhibit a strong luminescence at 590 nm when excited with UV light showing that Mn2+ is incorporated into the ZnS nanoparticles. The highest luminescence intensity is obtained with an Mn2+ concentration of 2 mol%. HRTEM and SAXS investigations show that the particles are crystalline and are 3 ± 0.5 nm in size. Irradiation of the coatings with UV light leads to a photochemical oxidation of the particles, as shown by the decreasing absorption of the coating with irradiation time and a blue shift of the absorption maximum. Furthermore, the luminescence intensity first strongly increases and then decreases completely with UV-irradiation time. Both phenomena can be explained by the photochemical oxidation of the particles.     

The kinetics of growth of semiconductor nanocrystals in a hot amphiphile matrix

The first comprehensive study on the kinetics of nanocrystal growth in a hot amphiphile medium is presented. An example is given with CdSe semiconductor nanocrystals grown after the injection of precursor (a mixture of Cd- and Se-reagents) in concentrated tri-octylphosphine oxide matrix (heated to more than 300 degrees C). The particle size distribution is reconstructed as a function of time from the absorption and photoluminescence spectra collected during the synthesis process. For this purpose a new expression is used relating the exciton energy due to quantum confinement with the nanocrystal radius. The growth kinetics is considered as a two-stage process in order to describe the time variation of nanoparticle size. During the first stage, called reaction-limited growth, the size of initial nucleus rapidly increases due to a sort of surface reaction exhausting the precursor in the nanoparticle vicinity. The growth in such conditions favors also a remarkable narrowing of the size distribution. The nanocrystal develops further on account of a slow precursor transfer from a distant space driven by the concentration gradient--classical diffusion-limited growth. The width of size distribution also increases proportional to the average particle size. Any growth will stop after the precursor concentration reaches a minimum value defining the limit for the final nanocrystal size in a batch. Solving the kinetic equations for the growth rate in each case of kinetics derives analytical expressions for the mean radius and variance of size distribution. Then the respective expressions are matched in a uniform solution valid during the entire synthesis. The theoretical model is in a good quantitative agreement with the experimental data for independent syntheses. Important characteristic scales of the processes (time-constant and length) and microscopic parameters of the reacting system (interfacial energy and reaction rate constant) are estimated from the data. It turns out that the fast reaction-limited growth is important to obtain well-defined nanocrystals of high optical quality by using less energy, time and consumable. However, to make them reproducibly uniform one should control also the ultra-fast nucleation process preceding the nanocrystal growth, which is still unknown. Nevertheless, our current findings allow the conceptual design of a new continuos-flow reactor for the manufacturing of a large amount of uniform nanocrystals.     

Growth of uncapped, subnanometer size gold clusters prepared via electroporation of vesicles

Electric-field-induced transient pore formation (electroporation) in synthetic unilamellar vesicles is utilized for the preparation of subnanometer size uncapped gold quantum dots. With the precursor AuCl4(-) placed in the aqueous bulk solution and the reducing agent BH4(-) originally entrapped in the vesicles' compartments, the redox reaction--that occurs in the bulk--is initiated by the opening of transient pores in the vesicles' bilayers. The absence of caps permits (i) continued growth of the Au clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. The normally rapid self-aggregation of Au atoms is slowed to the time scales of hour and week by their adsorption at the exterior surface of the vesicles. The UV spectra exhibit novel, time-dependent, oscillating red and blue shifts of the characteristic absorption band, which can be attributed to the evolution of cluster size transiently halting at magic aggregation numbers corresponding to Au2, Au8, Au20, and Au34. Subsequent growth is associated with a monotonic red shift of the absorption band up to the characteristic surface plasmon absorption at 520 nm.     

Capillary electrophoretic study of green fluorescent hollow carbon nanoparticles

CE coupled with laser‐induced fluorescence and UV absorption detections has been applied to study the complexity of as‐synthesized green fluorescent hollow carbon nanoparticles (HC‐NP) samples. The effects of pH, type, and concentration of the run buffer and SDS on the separation of HC‐NP are studied in detail. It is observed that phosphate run buffer is more effective in separating the HC‐NP and the optimal run buffer is found to be 30 mM phosphate and 10 mM SDS at pH 9.0. The CE separation of this HC‐NP is based on the difference in size and electrophoretic mobility of HC‐NP. Some selected HC‐NP fractions are collected and further characterized by UV‐visible absorption and photoluminescence (PL) spectroscopy, MS, and transmission electron microscopy. The fractionated HC‐NP show profound differences in absorption, emission characteristics, and PL quantum yield that would have been otherwise misled by studying the complex mixture alone. It is anticipated that our CE methodology will open a new initiative on extensive studies of individual HC‐NP species in the biomedical, catalysis, electronic, and optical device, energy storage, material, and sensing field.