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  1. #1
    Mustafa Umut Sarac's Avatar
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    Plasmonic Effect, Nano Particles of Gold, Silver, Copper and Best possible colorant

    Silver, gold, and copper colloids have been the major focus of interest because of their unique optical properties
    determined by the collective oscillations of electron density termed plasmons, which give rise to an intense absorption
    in the near UV–visible. Such strong absorption induces the brilliant color of these metal nanoparticles in colloidal
    dispersion
    . It is produced by the strong coupling of nanoparticles to the electromagnetic radiation of incident light,
    leading to a collective excitation of all of the free electrons in the particles. As illustrated in Figure 8, the movement
    of the electrons under the influence of the electronic field vector of the incoming light leads to a dipole excitation
    across the particle sphere, the positive polarization charge acting as a restoring force, which makes the electrons oscillate.
    Thus, the electron density within a surface layer, the thickness of which is about equal to the screening length
    of a few angstroms, oscillates, whereas the density in the interior of the particle remains constant [“surface plasmon”
    (SP)]. From one up to three SP bands may be observed, corresponding to three polarizability axes of the metallic
    nanoparticles. A prerequisite for the formation of an intense plasmon absorption band is that 12 (the imaginary part of the
    dielectric constant of the metal) is not too large [11]. Silver particles have the unique property that the excitation of the
    collective oscillation (plasmon absorption,  = 380 nm) and of the interband transitions ( = 320 nm) occur in separate
    wavelength regimes. The plasmon resonances possessed by gold and copper are in the visible (Au 520 nm; Cu 570 nm),
    however, these resonances are superimposed by interband transitions.
    In theory, the absorption spectra of metal particles smaller than the wavelength of incident light can be calculated
    on the basis of the Mie equation for nanoparticles whose metallic dielectric function is known and which
    are embedded in a medium of known dielectric constant [413–416]. The position and magnitude of the surface plasmon
    absorption band are intensively dependent on the size of the particles, the refractive index of the solvent,
    and the degree of aggregation. The surface plasmon resonance should shift slightly to high energy, and broaden
    somewhat as the particle size is decreased; meanwhile, the intensity of absorption decreases remarkably until it is essentially
    unidentifiable for crystallites of less than 2 nm effective diameter [417, 418]. For example, a symmetric and
    comparatively narrow absorption peak at a shorter wavelength is usually indicative of relatively small, monodisperse,
    and spherical metal nanoparticles. However, it has been demonstrated both theoretically [419–422] and experimentally
    [423, 424] that the SP resonances of the coinage metal nanoparticles depend much more sensitively on the particle
    shapes than on the sizes. Typically, in the case of gold nanorods, the absorption spectra are characterized by the
    dominant SPl band (at longer wavelength, ca. 620–900 nm), corresponding to longitudinal resonance and a much weaker
    transverse resonance than the SPt band (at shorter wavelength, ca. 520 nm).
    In general, for bimetallic Ag/Au nanoparticles, the absorption bands of alloys fall between the maxima of the
    respective constituent surface plasmon absorption bands, and core–shell structures manifest themselves in two distinct
    bands [413, 425]. Morphologies and absorption spectra of composite Ag/Au nanoparticles were, however, found
    to depend on the deposited metal atoms/surface ratio in a less than straightforward manner [426]. In contrast, several
    experimental results show that what is observed in the core– shell structured nanoparticles is only the plasmon absorption
    of pure metal of the core or shell constituent, probably due to particles deviating from the perfect core–shell model
    [427, 428]. The wavelength of the plasmon resonance of the nanoshells that are the other kind of colloidal particles,
    consisting of a small dielectric core covered by a thin metallic shell, can be tunable in the visible and near-infrared
    regions by varying the core/shell radii. This allows for the design of nanoshells with plasmon resonance across a spectral
    range from about 600 to 2500 nm [429]. The scattering from nanoshells adheres to the Mie scattering theory
    [429–431].
    The efficiency for the absorption and scattering of light by metal nanoparticles can surpass that of any molecular
    chromophore.
    In addition, both absorption and scattering properties can be considerably altered by surface
    modification or by electronic coupling between individual nanoparticles. Together with an expectional resistance
    to photodegeneration, such favorable optical features are stimulating the development of new applications in analytical
    chemistry and in photophysics, making metal colloids attractive components for diagnostic, electronic, and photonic
    devices.

    from Noble Nano Particles

  2. #2
    Mustafa Umut Sarac's Avatar
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    Alsa Nanoparticle Colors

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  3. #3
    cliveh's Avatar
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    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  4. #4
    Mustafa Umut Sarac's Avatar
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    Zsolnay Silver Copper Nanoparticle Colors

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  5. #5
    Mustafa Umut Sarac's Avatar
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    Nanoparticles in Tiffany Glass

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  6. #6
    Mustafa Umut Sarac's Avatar
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    Collodial Gold

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    History

    Known since ancient times, the synthesis of colloidal gold was originally used as a method of staining glass. Modern scientific evaluation of colloidal gold did not begin until Michael Faraday's work of the 1850s.[8][9] A so-called Elixir of Life, a potion made from gold, was discussed, if not actually manufactured, in ancient times. Colloidal gold has been used since Ancient Roman times to colour glass intense shades of yellow, red, or mauve, depending on the concentration of gold, and in Hindu Chemistry, for various potions. In the 16th century, the alchemist Paracelsus claimed to have created a potion called Aurum Potabile (Latin: potable gold). In the 17th century the glass-colouring process was refined by Andreus Cassius and Johann Kunckel. In 1842, John Herschel invented a photographic process called Chrysotype (from the Greek word for gold) that used colloidal gold to record images on paper. Paracelsus' work is known to have inspired Michael Faraday to prepare the first pure sample of colloidal gold, which he called 'activated gold', in 1857. He used phosphorus to reduce a solution of gold chloride.

    For a long time the composition of the Cassius ruby-gold was unclear. Several chemists suspected it to be a gold tin compound, due to its preparation.[10][11] Faraday was the first to recognize that the color was due to the minute size of the gold particles.[12] In 1898 Richard Adolf Zsigmondy prepared the first colloidal gold in diluted solution.[13] Apart from Zsigmondy, Theodor Svedberg, who invented ultracentrifugation, and Gustav Mie, who provided the theory for scattering and absorption by spherical particles, were also interested in understanding synthesis and properties of colloidal gold.[7][14]
    [edit]
    Synthesis

    Generally, gold nanoparticles are produced in a liquid ("liquid chemical methods") by reduction of chloroauric acid (H[AuCl4]), although more advanced and precise methods do exist. After dissolving H[AuCl4], the solution is rapidly stirred while a reducing agent is added. This causes Au3+ ions to be reduced to neutral gold atoms. As more and more of these gold atoms form, the solution becomes supersaturated, and gold gradually starts to precipitate in the form of sub-nanometer particles. The rest of the gold atoms that form stick to the existing particles, and, if the solution is stirred vigorously enough, the particles will be fairly uniform in size.

    To prevent the particles from aggregating, some sort of stabilizing agent that sticks to the nanoparticle surface is usually added. They can be functionalized with various organic ligands to create organic-inorganic hybrids with advanced functionality.[8] It can also be synthesised by laser ablation.
    [edit]
    Turkevich method

    The method pioneered by J. Turkevich et al. in 1951 [15][16] and refined by G. Frens in 1970s,[17][18] is the simplest one available. Generally, it is used to produce modestly monodisperse spherical gold nanoparticles suspended in water of around 10–20 nm in diameter. Larger particles can be produced, but this comes at the cost of monodispersity and shape. It involves the reaction of small amounts of hot chlorauric acid with small amounts of sodium citrate solution. The colloidal gold will form because the citrate ions act as both a reducing agent, and a capping agent.

    Recently, the evolution of the spherical gold nanoparticles in the Turkevich reaction has been elucidated. Interestingly, extensive networks of gold nanowires are formed as a transient intermediate. These gold nanowires are responsible for the dark appearance of the reaction solution before it turns ruby-red.[19]

    To produce larger particles, less sodium citrate should be added (possibly down to 0.05%, after which there simply would not be enough to reduce all the gold). The reduction in the amount of sodium citrate will reduce the amount of the citrate ions available for stabilizing the particles, and this will cause the small particles to aggregate into bigger ones (until the total surface area of all particles becomes small enough to be covered by the existing citrate ions).
    [edit]
    Brust method

    This method was discovered by Brust and Schiffrin in early 1990s,[20] and can be used to produce gold nanoparticles in organic liquids that are normally not miscible with water (like toluene). It involves the reaction of a chlorauric acid solution with tetraoctylammonium bromide (TOAB) solution in toluene and sodium borohydride as an anti-coagulant and a reducing agent, respectively.

    Here, the gold nanoparticles will be around 5–6 nm.[21] NaBH4 is the reducing agent, and TOAB is both the phase transfer catalyst and the stabilizing agent.

    It is important to note that TOAB does not bind to the gold nanoparticles particularly strongly, so the solution will aggregate gradually over the course of approximately two weeks. To prevent this, one can add a stronger binding agent, like a thiol (in particular, alkanethiols), which will bind to gold, producing a near-permanent solution. Alkanethiol protected gold nanoparticles can be precipitated and then redissolved. Some of the phase transfer agent may remain bound to the purified nanoparticles, this may affect physical properties such as solubility. In order to remove as much of this agent as possible the nanoparticles must be further purified by soxhlet extraction.
    [edit]
    Perrault Method

    This approach, discovered by Perrault and Chan in 2009,[22] uses hydroquinone to reduce HAuCl4 in an aqueous solution that contains gold nanoparticle seeds. This seed-based method of synthesis is similar to that used in photographic film development, in which silver grains within the film grow through addition of reduced silver onto their surface. Similarly, gold nanoparticles can act in conjunction with hydroquinone to catalyze reduction of ionic gold onto their surface. The presence of a stabilizer such as citrate results in controlled particle growth. Typically, the nanoparticle seeds are produced using the citrate method. The hydroquinone method complements that of Frens,[17][18] as it extends the range of monodispersed spherical particle sizes that can be produced. Whereas the Frens method is ideal for particles of 12-20 nm, the hydroquinone method can produce particles of at least 30-250 nm.
    [edit]
    Sonolysis

    Another method for the experimental generation of gold particles is by sonolysis. In one such process based on ultrasound, the reaction of an aqueous solution of HAuCl4 with glucose,[23] the reducing agents are hydroxyl radicals and sugar pyrolysis radicals (forming at the interfacial region between the collapsing cavities and the bulk water) and the morphology obtained is that of nanoribbons with width 30 -50 nm and length of several micrometers. These ribbons are very flexible and can bend with angles larger than 90°. When glucose is replaced by cyclodextrin (a glucose oligomer) only spherical gold particles are obtained suggesting that glucose is essential in directing the morphology towards a ribbon.
    [edit]
    Block Copolymer-mediated Method

    An economical, environmentally benign and fast synthesis methodology for gold nanoparticles using block copolymer has been developed by Sakai et al. [3]. In this synthesis methodology, block copolymer plays the dual role of a reducing agent as well as a stabilizing agent. The formation of gold nanoparticles comprises three main steps: reduction of gold salt ion by block copolymers in the solution and formation of gold clusters, adsorption of block copolymers on gold clusters and further reduction of gold salt ions on the surfaces of these gold clusters for the growth of gold particles in steps, and finally its stabilization by block copolymers. But this method usually has a limited yield (nanoparticle concentration) which does not increase with the increase in the gold salt concentration. Recently, Ray et al. demonstrated that the presence of an additional reductant (trisodium citrate) in 1:1 molar ratio with gold salt enhances the yield by manyfold [4].
    Last edited by Mustafa Umut Sarac; 11-09-2012 at 06:07 PM. Click to view previous post history.

  7. #7
    Mustafa Umut Sarac's Avatar
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    Colloidal Silver

    Ag nanoparticles are easily prepared by conventional
    chemical reduction methods. The citrate (Turkevich
    method) [229, 255, 256] and NaBH4 [255, 257–259] reduction
    method are the two standard chemical preparation
    routes. The synthesis of silver nanoparticles in AOT reverse
    micelles by mixing AOT reverse micellar solutions at the
    same water content containing Ag(AOT) and N2H4 or
    NaBH4 offers a stable Ag colloidal solution and facile control
    of particle size [260]. Following the treatment by a
    size-selected precipitation process, nearly monodispersed Ag
    nanoparticles are accessible [261, 262]. Shape-controllable
    synthesis is always a challenging subject in nanoparticle
    preparation. This is, without exception, for the synthesis of
    silver nanoparticles. An amazing result of the shape control
    of Ag nanoparticles was reported by Mirkin and co-workers
    recently [263]. In the presence of bis(p–sulfonatophenyl)
    phenyl–phosphine dihydrate dipotassium salt (BSPP) (as a
    stabilizing agent), they observed that large quantities of
    silver nanoprisms evolve from the initial spherical nanoparticles
    through the fluorescent light irradiation. The
    production of Ag nanoprisms lies in the light-induced ripening
    process in which the small nanoprisms act as seeds, and
    then grow as the small spherical nanocrystals are digested, as
    shown in Figure 2. Most recently, one arresting experiment
    shows that triangular Ag nanoprisms are obtained by boiling
    AgNO3 in N,N–dimethyl formamide (a powerful reducing
    agent against Ag+ ions) in the presence of PVP [264]. The
    optimal experimental conditions are chosen ([AgNO3 =
    0022 M, [PVP = 006 mM) so that a large population of
    (mainly) triangular, and in general polygonal, nanoprisms
    are formed in solution. Another attractive experiment shows
    that truncated triangular Ag nanoplates can be synthesized
    in large quantities through a seed-mediated growth (by
    reduction of Ag+ ions with ascorbic acid on silver seeds
    in a basic solution) in the presence of highly concentrated
    micelles of CTAB [115, 265]. It is noticeable that, in these
    cases, the optical properties of Ag nanoprisms or triangular
    nanoplates varied in contrast to that of spheroidal Ag nanoparticles.
    An intensive in-plane dipole resonance absorption
    peaks at 550–675 nm, which gives a red- or blue-colored
    colloidal solution. Another breakthrough in the shape control
    of Ag nanoparticles was achieved by Xia and co-workers
    [266]. They fabricated monodisperse Ag nanocubes in large
    quantities by reducing silver nitrate with ethylene glycol in
    the presence of PVP. Here, the concentration of AgNO3
    was high enough (0.25 M), and the molar ratio between the
    repeating unit of PVP and AgNO3 was kept at 1.5. Meanwhile,
    the presence of PVP and its molar ratio (in terms
    of repeating unit) relative to silver nitrate both played key
    roles in the determination of the geometric shape and size of
    the product. The generated single-crystalline Ag nanocubes
    were characterized by a slightly trunctated shape bounded by
    {100}, {110}, and {111} facets. Other techniques, including
    pulsed laser irradiation [21, 267],  irradiation [68], pulsed
    sonoelectrochemistry [58, 268], and ultraviolet irradiation
    [117], have proven to be efficient methods to control the
    shapes of Ag nanoparticles.

  8. #8
    Rick A's Avatar
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    blah-blah-blah......
    Rick A
    Argentum aevum
    BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"

  9. #9
    Mustafa Umut Sarac's Avatar
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    ...

  10. #10
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    Quote Originally Posted by Rick A View Post
    blah-blah-blah......
    I find it quite interesting.
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

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