The Influence of Surface-Modification Technology on the Spectral Characteristics of Hydrophilic CdSe/ZnS Nanoparticles upon Interaction with Polyelectrolytes

The spectral and kinetic characteristics of CdSe/ZnS nanoparticles (NPs) surface-modified with cysteamine by two different methods are considered upon interaction with polyelectrolytes. With the use of steady-state and time-resolved fluorescence spectroscopies, it is shown that the fluorescence intensity and stability of NPs in the presence of polyelectrolytes depend on the surface-modification method. It is found that hydrophilic NPs obtained at the interface between two immiscible liquids (chloroform–water) are more resistant to aggregation.     

微波辐射法制备水溶性CdTe量子点及其光谱学研究

用半胱胺作为稳定剂,采用微波辐射加热的方法快速合成了水溶性的CdTe量子点。吸收光谱和荧光光谱表明所合成的量子点具有优异的发光性能。透射电子显微镜(TEM)和X射线粉末衍射(XRD)表征了量子点的结构和粒径分布。通过荧光发射光谱研究了反应温度、加热时间和配体浓度对量子点晶体生长速度的影响。反应温度提高或稳定剂半胱胺的浓度减小,纳米晶体的生长速度加快。在一定温度下,随着反应时间的延长,量子点发射波长发生红移。与传统的水相回流方法相比微波加热制备水溶性的CdTe量子点具有反应速度快、得到的量子点尺寸分布均匀、半峰宽较窄和量子产率较高等特点。     

Enhancement of the fluorescence of triphenylmethane dyes caused by their interaction with nanoparticles from β-diketonate complexes

We have studied the absorption and fluorescence spectra of Malachite Green and Crystal Violet in aqueous and alcoholic-aqueous solutions in which nanoparticles from Ln(III) and Sc(III) diketonates are formed at concentrations of complexes in a solution of 5–30 μM. We have shown that, if the concentrations of the dyes in the solution are lower than 0.5 μM, dye molecules are incorporated completely into nanoparticles or are precipitated onto their surface. The fluorescence intensity of these incorporated and adsorbed Malachite Green and Crystal Violet molecules increases by several orders of magnitude compared to the solution, which takes place because of a sharp increase in the fluorescence quantum yields of these dyes and at the expense of the sensitization of their fluorescence upon energy transfer from β-diketonate complexes entering into the composition of nanoparticles. We have shown that, if there is no concentration quenching, the values of the fluorescence quantum yield of the Crystal Violet dye incorporated into nanoparticles and adsorbed on their surface vary from 0.06 to 0.13, i.e., are close to the fluorescence quantum yield of this dye in solid solutions of sucrose acetate at room temperature. The independence of the fluorescence quantum yield of Crystal Violet on the morphology of nanoparticles testifies to a high binding constant of complexes and the dye. The considerable fluorescence quantum yields of triphenylmethane dyes in nanoparticles and sensitization of their fluorescence by nanoparticle-forming complexes make it possible to determine the concentration of these dyes in aqueous solutions by the luminescent method in the range of up to 1 nM.     

Preparation and characterization of AgI nanoparticles with controlled size,morphology and crystal structure

AgI nanoparticles were prepared by solution-based routes using water-soluble anionic or cationic polyelectrolytes as capping agents. Depending on the polyelectrolytes, AgI nanoparticles with well-defined morphology, size, and phase compositions were obtained: the use of poly(sodium 4-styrenesulfonate) (PSS) resulted in AgI nano-rods of β-AgI in wurtzite structure (2H); with poly(acrylic acid sodium salt) (PAS) truncated-tetrahedron shaped γ-AgI nanoparticles (nanotetrahedra) in zinc-blende structure (3C) were obtained; by employing poly(diallyldimethylammonium chloride) (PDADMAC) plate-like AgI nanoparticles (nano-plates) consisting of unusual polytype phases of AgI (7H and 9R) were formed. Macroscopically unstable γ-AgI and 7H and 9R phases could be stabilized in the form of nanocrystalline powders. They transform reversibly into the high temperature α-AgI phase and exhibit unusually high ionic conductivity and substantially smaller transformation enthalpy values compared to the macroscopic β-AgI.     

Formation and Deposition of Langmuir-Blodgett Films with Thiol-Stabilized CdTe Nanoparticles

Incorporation of the thiol-stabilized CdTe nanoparticles into mono- and multilayer films produced by Langmuir-Blodgett (LB) technique was investigated using “pressure-area” isotherms, Quartz Crystal Microbalance, FTIR, UV/Vis absorption and photoluminescence spectroscopy. LB films were formed from cationic (octadecyltrinonylammonium iodide—ODTNA) and anionic (behenic acid) surfactants. Both noticeable increase of limiting surface area of behenic acid monolayer and simultaneous decrease of film strength have been established when the aqueous solution of CdTe nanoparticles was used as a subphase. LB films deposition on solid substrates depends on the type of stabilizing ligands (1-thioglycerol or 2-mercaptoethanol) for CdTe nanoparticles. Optical absorption and photoluminescence properties of the films obtained from behenic acid monolayers that has thioglycerol-stabilized CdTe nanoparticles incorporated into them acquire the same properties as the size-quantized CdTe nanoparticles. The bonding of the cadmium ions, that released as a result of a partial dissociation of ligand-stabilized CdTe nanoparticles with carboxylic group, is considered to be responsible for the incorporation in case of behenic acid surfactant, and in case of ODTNA the incorporation proceeds by means of a weak “nanoparticle-LB matrix” interaction.     

Structures of some surfactant—polyelectrolyte complexes

Structures of complexes formed in aqueous solutions by some anionic polyelectrolytes (double and single stranded (ds and ss) DNA, poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS)) with a cationic surfactant system consisting of cetyltrimethylammonium bromide (CTAB) and sodium 3-hydroxy-2-naphthoate (SHN) have been determined using small angle X-ray diffraction. All complexes are found to have a two-dimensional (2-D) hexagonal structure at low SHN concentrations. Analysis of the diffraction data shows that the ds DNA—CTAB complex has an intercalated structure, with each DNA strand surrounded by three cylindrical micelles. On increasing SHN concentration, DNA—CTAB—SHN complexes exhibit a hexagonal-to-lamellar transition, whereas PVS complexes show a hexagonal → centered rectangular → lamellar transition. PSS complexes show yet another sequence of structures. These results indicate the significant influence of the chemical nature of the polyelectrolyte on the structure of the complexes.     

Ultrathin self-assembled polyelectrolyte multilayer membranes

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes for alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability. Received 4 September 2000     

蓝光锆（Ⅳ）配合物的合成及光致发光性能研究

合成了一系列蓝光锆（Ⅳ）配合物 Cl[Zr（NN）（DBM）₃]（DBM=二苯甲酰基甲烷,NN=1,10-邻菲罗啉 1;2,9-二甲基-1,10-邻菲罗啉 2;4,4'-二甲基-2,2'-联吡啶 3;1-乙基-2-（1-萘基）-1H-咪唑-4,5-f-1,10-邻菲罗啉4）,以波长为355 nm的紫外光激发,4个配合物的最大发射峰均位于445 nm左右,半峰宽只有36~45 nm。在相同的测试条件下,配合物 1 的蓝光发射强度最大,量子效率最高,其原因是结构刚性强,能够有效地减少非辐射跃迁造成的能量损失。而且,配合物 1~3 的热稳定性很好,分解温度均在200℃以上,可以用于制作有机发光器件,不会在器件的制作过程中发生分解。     

Visible luminescence enhancement methods in SiGe/Si heterostructures

The possibility of increasing the photoluminescence signal of Si1?xGex/Si quantum wells in the visible spectral range due to a change in the conduction band structure and the interaction of many-body states with plasma oscillations of metal nanoparticles is studied. The sample band structure was controlled using a uniaxial strain of ～10?4. It is found that such an approach allows an increase in the emission intensity of biexcitons in the quantum well (x = 9%) by a factor of 2.4 at a temperature of 5 K. Metal nanoparticles deposited on the sample surface with a protective layer thickness of 20 nm allowed us to increase the luminescence intensity of quantum wells approximately by a factor of 2.7.     

Casimir-Lifshitz quantum state of superhydrophobic black-silicon surfaces manufactured by a metal-assisted hierarchical nano-microtexturing process

We investigated superhydrophobic Si nanosurfaces similar to the lotus leaf by performing a hierarchical nanotexturing process on micropyramidal Si surfaces. The process was carried out using a metal-assisted chemical etching process based upon the deposition of Ag nanoparticles. The hierarchical micro-nanosurfaces showed a superhydrophobic character with contact angles of approximately 134～150°. The photon tunnelling also provides a strong light absorption as a black Si. The surface-light emission from broad and sharp photoluminescence was observed in the wavelength ranges of 414.7～440 and 509～516.2?nm. The field-induced tunnelling current on nanosurface shows the formation of quantum surface states. From the analyses of Casimir-Lifshitz quantum state of a photon in vacuum, the superhydrophobic behaviour of water droplet is closely related to the nanosurface and the nanoporous cavity shows the absorption of terahertz energy. Si nanosurface shows the broadband absorption in the spectral range of 800～900 cm^?1 corresponding to the energy range of 99.2～111.6?meV with 24～27 THz.     

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.     

Laser-induced photoprocesses in solutions and films of the CdSe/ZnS nanoparticles

The photophysical properties of solutions and films with relatively high concentrations of CdSe/ZnS nanoparticles are studied in the presence of the visible laser irradiation in a wide range of power densities. The short-wavelength wing detected in the photoluminescence spectra of the solutions of quantum dots is due to the selective laser excitation of small-size nanoparticles. A comprehensive analysis of the anti-Stokes photoluminescence of the nanoparticles in solutions and films indicates the thermal mechanism of this phenomenon. The dimensional quantization effect, narrow spectra, and a relatively high luminescence yield are retained in the films with a high nanoparticle concentration. The luminescence spectra of the films remain unchanged when the laser flux density increases to 1 × 10⁶ W/cm². The effect of the laser radiation on the nanoparticle films is studied at the flux densities exceeding the damage threshold (5 × 10⁶–1 × 10⁹ W/cm²).     

ZnO纳米晶/巯基乙酸复合膜的荧光特性

用自组装方法将巯基乙酸(MPA)与ZnO纳米晶薄膜(ZDF)通过共价键偶联到一起,形成纳米晶／巯基乙酸复合膜(ZDF／MPA)。采用发光光谱和XPS电子能谱技术,研究了ZDF／MPA的荧光特性以及它们之间的能量传递机制。研究发现ZDF／MPA中ZnO自由激子发光和束缚激子发光强度随着巯基乙酸的浓度增大而分别呈现不同的非线性减弱关系,当巯基乙酸达到一定的浓度量时,ZnO荧光完全消失。研究表明：ZnO纳米薄膜与MPA之间能够发生成键作用,并且在成键之后发生了能量传递。     

The influence of cysteamine and counterion concentrations on the properties of CdSe/ZnS quantum dots

The influence of the cysteamine surfactant concentration on the stability of CdSe/ZnS nanoparticles (NPs) solubilized by this compound at the phase interface between two immiscible liquids is considered. The steady-state and time-resolved fluorescence spectroscopy data show that the fluorescence quantum yield of cysteamine-coated NPs and their stability to aggregation in a potassium phosphate buffer are determined by the balance between the concentrations of surfactant in the aqueous phase and hydrophobic NPs in the nonpolar phase (chloroform, toluene, etc.). It is found that the brightest and most stable hydrophilic NPs can be obtained by completely coating them by cysteamine molecules without a surfactant deficit or excess in the reaction at the phase interface.     

Study of surface and solution properties of gemini-conventional surfactant mixtures and their effects on solubilization of polycyclic aromatic hydrocarbons

The aqueous solubility enhancement of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene and pyrene by micellar solutions of single gemini surfactant hexanediyl-1,6-bis(dimethylcetylammonium bromide) (G6) and its mixtures with cationic cetyltrimethylammonium bromide (CTAB), anionic sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and nonioinic polyoxyethylene (20) cetyl ether (Brij 58) have been investigated. Above the cmc, maximum solubilization occurs in the Brij 58 surfactant micelles whereas the solubilization is least in presence of AOT. The PAHs are solubilized synergistically in mixed gemini-conventional surfactant solutions, which is attributed to the formation of mixed micelles, their lower cmc values, and the increase of the solvents' molar solubilization ratios or micellar partition coefficients because of the lower polarity of the mixed micelles.     

Characterization of ZnS nanoparticles synthesized by co-precipitation method

ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible(UV-Vis)absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect.The photoluminescence spectrum of Zn S nanoparticles shows a blue visible spectrum.     

Size controlled synthesis of semiconductor nanocrystals in a continuous-flow mode microcapillary reactor

A microcapillary reactor with 320 μm inner diameter was utilized for CdSe nanoparticle synthesis. The influence of the reaction temperature and flow rate of precursors on the size and size distribution of prepared CdSe nanoparticles was systematically studied. The as-prepared nanoparticles exhibit sharp excitonic absorption and photoluminescence peak (FWHM 30 nm) with a quantum-yield around 10–40%. The microcapillary reactor was also used for CdSe/ZnS core-shell nanoparticle synthesis in continuous-flow mode. The quantum yield of the core-shell nanoparticles was found to be considerably influenced by the reactor temperature and have a close correlation with the thickness of ZnS shell under growth. An optimized quantum yield up to 70% was obtained for the CdSe/ZnS core-shell nanoparticles.     

Temperature dependence of photoluminescence of semiconductor quantum dots upon indirect excitation in a SiO2 dielectric matrix

The processes of excitation and relaxation of confined excitons in semiconductor quantum dots upon indirect high-energy excitation have been considered. The temperature behavior of photoluminescence of quantum dots in a SiO₂ dielectric matrix has been described using a model accounting for the process of population of quantum-dot triplet states upon excitation transfer through mobile excitons of the matrix. Analytical expressions that take into account the two-stage and three-stage schemes of relaxation transitions have been obtained. The applicability of these expressions for analyzing fluorescence properties of semiconductor quantum dots has been demonstrated using the example of silicon and carbon nanoparticles in the thin-film SiO₂ matrix. It has been shown that the complex character of the temperature dependences of the photoluminescence upon indirect excitation can be an indication of a multistage relaxation of excited states of the matrix and quantum dots. The model concepts developed in this study allow one to predict the form of temperature dependences of the photoluminescence for different schemes of indirect excitation of quantum dots.

     

Luminescence of Nile red as indicator of composition of nanoparticles from diketonate complexes of trivalent metals

We study the sensitization of fluorescence of Nile red in nanoparticles formed in aqueous solutions of complexes of Al, In, Sc, and Lu with DBM, DBM, and phen and of complexes of In with MBTA and phen. We show that, at concentrations of Nile red of 2–50 nM and complexes of 10–30 μM, the fluorescence intensity of Nile red in aqueous solutions increases by 1.5–2 orders of magnitude compared to its fluorescence in H₂O. We find that, at these concentrations of Nile red in solutions of complexes Al, the dye is completely contained in nanoparticles from these complexes. We show that Nile red molecules are inhomogeneously distributed in nanoparticles from complexes and, upon the completion of the formation of nanoparticles, dye molecules tend to be localized in regions of nanoparticles formed from diketonate complexes M(diketone)₃phen (M is Lu or In) and Al(DBM)₃. Upon the localization of Nile red in these regions, the maximum of its fluorescence spectrum shifts toward ∼600 nm and, upon the penetration of Nile red into nanoparticles from Sc complexes, the shift of the maximum of its fluorescence spectrum compared to the spectrum in water does not exceed 10 nm. The shifts of the spectra are collated with the ability of ions to form diketonate and hydroxy diketonate complexes. We demonstrate that the fluorescence of Nile red is efficiently sensitized, not only upon its penetration into nanoparticles formed from complexes, but also upon its adsorption on the nanoparticle surface when Nile red molecules are introduced in solutions of already formed nanoparticles.     

Degree of Flocculation and Interparticles Charges of Conditioned Municipal Activated Sludge using Mixed Polymers

The present research work focuses on a new conditioning and flocculation mechanism of municipal fresh activated sludge using a dual polymer system combining cationic and anionic polyelectrolytes. Various pairs of three different types of polyelectrolytes, low molecular weight cationic polyacrylamide (CPAM-10), high molecular weight cationic polyacrylamide (CPAM-80) and an anionic polyacrylamide (APAM-30), were selected, being used either individually or as cationic-anionic pairs. The results of use of the dual systems indicated that using mixed polymers for conditioning gave lower turbidity with better settling when compared to that of using individual pure polymers. The mixed polymers improved the sludge volume index (SVI) by 62%. The zeta potentials of the supernatant and solid-like samples of conditioned activated sludge were measured. Slight increases in zeta potential, from –12 to –9, of the mixed polymers for all supernatants were observed. On the other hand, zeta measurements showed that the sludge solid-like particles retained their negative charges despite the addition of the individual cationic polymers in the mixture. This phenomenon was explained in terms of the addition of the polyelectrolytes attracting, primarily, the carboxylic groups of the fine suspended sludge particles, while hydrogen bonds between the larger sludge particles resulted in attraction in accordance with the Van der Waals mechanism, and both attractions caused an immediate dewatering that led to flocculation, but with low compactness. As a result of retaining negative charges on the large sludge particles, dissolved metals were partially attracted, causing reduction in conductivities of the supernatants of 10% to 15% for all pairs. Rheological tests showed that the formed flocs had low shear stress resistances, ranging between 0.2 and 0.4 Pa, and weak flocs strength.