Deposition of gold nanoparticles on silica spheres by electroless metal plating technique

A previously proposed method for metal deposition with silver [Kobayashi et al., Chem. Mater. 13 (2001) 1630] was extended to uniform deposition of gold nanoparticles on submicrometer-sized silica spheres. The present method consisted of three steps: (1) the adsorption of Sn(2+) ions took place on surface of silica particles, (2) Ag(+) ions added were reduced and simultaneously adsorbed to the surface, while Sn(2+) was oxidized to Sn(4+), and (3) Au(+) ions added were reduced and deposited on the Ag surface. TEM observation, X-ray diffractometry, and UV-vis absorption spectroscopy revealed that gold metal nanoparticles with an average particle size of 13 nm and a crystal size of 5.1 nm were formed on the silica spheres with a size of 273 nm at an Au concentration of 0.77 M.     

Preparation of Silica Microspheres Containing Ag Nanoparticles

Two sol-gel fabrication processes were investigated to make silica spheres containing Ag nanoparticles: (1) a modified Stöber method for silica spheres below 1 m size, and (2) a SiO₂-film formation method on spheres of 3–;7 m size. The spheres were designed to incorporate silver nanoparticles of high ⁽³⁾ in a spherical optical cavity structure for the resonance effect. For the incorporation, interaction between [Ag(NH₃)₂]⁺ ion and Si-OH was important. In the Stöber method, the size of the silica spheres was determined by a charge balance of plus and minus ions on the silica surface. In the film formation method, the capture of Ag complex ion on the silica surface depended on whether the surface was covered with OH groups or not. After doping [Ag(NH₃)₂]⁺ into silica particles or SiO₂ films on the spheres, these ions w ere reduced by NaBH₄ to form silver nanoparticles. From plasma absorption at around 420 nm wavelength and TEM photographs of nanometer-sized silver particles, their formation inside the spherical cavity structures was confirmed.     

Synthesis and antibacterial property of hollow SiO2/Ag nanocomposite spheres

This paper presents a novel and facile method to fabricate hollow silica/sliver (SiO(2)/Ag) nanocomposite spheres. In this approach, the monodisperse hollow SiO(2) colloids bearing quantenary ammonium groups were prepared by dispersion polymerization combined sol-gel process and used as templates. The Ag(+) ions were first adsorbed onto the surfaces of the hollow SiO(2) beads via electrostatic interaction and then in situ reduced by the deprotonated silanol groups of the hollow SiO(2) beads, no extra reducing agents or catalysts were added during the reduction process. TEM, SEM and EDX analyses indicated that Ag nanoparticles were successfully deposited onto the surfaces of hollow SiO(2) beads. Some influencing parameters, such as the amount of quantenary ammonium groups in the inner wall of hollow SiO(2) colloids, Ag(+) ions concentration and reaction temperature, on the deposition of Ag nanoparticles onto SiO(2) colloids were investigated. Preliminary antibacterial tests indicated that these hollow nanocomposite spheres showed excellent antibacterial ability.     

聚苯乙烯/银纳米粒子复合微球的合成及催化性能

首先通过乳液聚合和浓硫酸酸化制备表面富含磺酸根的磺化聚苯乙烯(PS)微球(直径532 nm),再用其静电吸附[Ag(NH_3)_2]~+离子,最后采用聚乙烯吡咯烷酮还原表面吸附的[Ag(NH_3)_2]~+离子,得到了负载银纳米粒子的PS/AgNPs复合微球.采用扫描电子显微镜、透射电子显微镜、紫外-可见光谱、红外光谱和X射线衍射表征了PS/AgNPs复合微球,并考察了其对甲基蓝(MB)的催化性能.结果表明,Ag纳米粒子高度分散在磺化PS微球表面;该PS/AgNPs复合微球对催化转化MB有较高的催化活性,并可多次重复利用.本研究在催化降解有机污染物方面有一定的实用价值.     

Photochemical incorporation of silver quantum dots in monodisperse silica colloids for photonic crystal applications.

We developed a novel method to fabricate nanocomposite monodisperse SiO2 spheres (approximately 100 nm) containing homogeneously dispersed Ag quantum dots (approximately 2 to 5 nm). The inclusion morphology is controlled through the timing of the photochemical reduction of silver ions during hydrolysis of tetraethoxysilane in a microemulsion. Depending on the timing, Ag quantum dots can be directed to different annuli within the SiO2 spheres, as well as onto the SiO2 sphere surfaces. The embedded Ag quantum dots show a plasmon resonance absorption band at 438 nm. These Ag@SiO2 particles have significant surface charge and readily self-assemble into crystalline colloidal array (CCA) photonic crystals which Bragg-diffract light in the visible region. The magnitude of the plasmon resonance absorption depends on the CCA Bragg diffraction condition. The negative dielectric constant of the silver nanoparticles may be decreasing the silica-silver nanodot composite refractive index below that of the water medium. We may be observing an analogue of the Borrmann effect previously observed in X-ray scattering, where the incident and diffracted electric field standing wave becomes localized in regions of small CCA crystal absorption.     

Controlling the hydrophobicity of submicrometer silica spheres via surface modification for nanocomposite applications

We control the hydrophobicity of submicrometer silica spheres by modifying their surface with -CH3, -CH=CH2, -(CH2)(2)CH3, -CH2(CH2)(4)CH2-, -C(6)H(5), -(CH2)(7)CH3, and -(CH2)(11)CH3 groups through a modified one-step process. The scanning electron microscopy (SEM), quasi-elastic light scattering (QELS), UV-visible spectra, nitrogen sorption, and water vapor adsorption methods are used to characterize the particles. The SEM micrographs of the particles demonstrate that the modified particles are uniformly spherical, monodisperse, and well-shaped with the particle size ranging from 130 to 149 nm depending on the modified organic groups. In aqueous solution, the particles modified with phenyl groups have an obvious UV absorption peak at around 210 nm, whereas the other modified particles and unmodified particles do not have any UV-visible absorption peaks. There exist obvious differences in the amount of water vapor adsorbed depending on the type of surface functional groups of the modified particles. Compared with the unmodified particles, the modified particles have a lower water vapor adsorption because of the improved hydrophobicity of the particle surface. As a potential application, we prepared polystyrene/SiO2 nanocomposites by blending polystyrene with the synthesized particles. Water contact angle measurements show that the surface of the composite prepared with the modified particles are more hydrophobic. Confocal microscopy demonstrates that the particles are less agglomerated in the nanocomposite as the particles become more hydrophobic. These comprehensive experimental results demonstrate that the hydrophobicity of the particles can be easily controlled by surface modification with different organosilanes through a modified one-step process.     

Synthesis of contiguous silica-gold core-shell structures: critical parameters and processes

A direct process for preparing contiguous gold shells (15-25 nm thick) over amorphous silica spheres (200 nm) is described. In this method, gold seeds are synthesized from HAuCl(4) in a dilute NaOH solution using deposition-precipitation with subsequent metallization by sodium borohydride (NaBH(4)). The ease of dispersing gold nanocrystals on spheres of bare silica and spheres after grafting with ammonia was studied as a function of pH (4-8), reaction temperature (65-96 degrees C), and time (5-30 min). Additional parameters requiring optimization included the quantity of NaBH4 and the HAuCl(4) in K(2)CO(3) solution to silica volume ratio. The evolution of gold nanocrystal growth was monitored by transmission electron microscopy, and the bathochromic shift of ultraviolet-visible absorption was correlated with shell perfection and thickness.     

Reactivity of ammonia ligands of the antitumor agent cisplatin: a unique dodecanuclear Pt4,Pd4,Ag4 platform for four cytosine model nucleobases

The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis-[Pt(NH(3))(2)(1-MeC-N3)(H(2)O)](2+) (6; 1-MeC: 1-methylcytosine), with the electrophile [Pd(en)(H(2)O)(2)](2+) (en: ethylenediamine) at pH approximately 6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1-MeC(-)-N3,N4 and OH bridges, namely cis-[Pt(NH(3))(2)(1-MeC(-)-N3,N4)(OH)Pd(en)](2+). Upon addition of excess Ag(+) ions, conversion takes place to form a thermodynamic product, which, according to (1)H NMR spectroscopy and X-ray crystallography, is dominated by a mu-NH(2) bridge between the Pt(II) and Pd(II) centers. X-ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt(II), four Pd(II), and four Ag(+) entities: [{Pt(2)(1-MeC(-)-N3,N4)(2)(NH(3))(2)(NH(2))(2)(OH)Pd(2)(en)(2)Ag}(2){Ag(H(2)O)}(2)](NO(3))(10) 6 H(2)O (10) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by mu-NH(2) groups (between Pt and Pd centers), mu-OH groups (between pairs of Pt atoms), and metal-metal donor bonds (Pt-->Ag, Pd-->Ag). The four 1-methylcytosinato ligands, which are stacked pairwise, as well as the four NH(3) ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2') of 10 are labile in solution and show the expected behavior of Ag(+) ions in water, that is, they are readily precipitated as AgCl by Cl(-) ions. The resulting pentanuclear complex [Pt(2)Pd(2)Ag(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(4)7 H(2)O (11) largely maintains the structural features of one half of 10. The other two Ag(+) ions (Ag1, Ag1') of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt(2)Pd(2)AgCl(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(3)4.5 H(2)O (12), obtained from 10 with excess NaCl, displays a Cl(-) anion bound to the Ag center (2.459(3) A) and is thus a rare case of a crystallized "AgCl molecule".     

Magic sized ZnS quantum dots as a highly sensitive and selective fluorescence sensor probe for Ag+ ions

A green and simple chemical synthesis of magic sized water soluble blue-emitting ZnS quantum dots (QDs) has been accomplished by reacting anhydrous Zn acetate, sodium sulfide and thiolactic acid (TLA) at room temperature in aqueous solution. Refluxing of this mixture in open air yielded ZnS clusters of about 3.5 nm in diameter showing very strong and narrow photoluminescence properties with long stability. Refluxing did not cause any noticeable size increment of the clusters. As a result, the QDs obtained after different refluxing conditions showed similar absorption and photoluminescence (PL) features. Use of TLA as a capping agent effectively yielded such stable and magic sized QDs. The as-synthesized and 0.5 h refluxed ZnS QDs were used as a fluorescence sensor for Ag(+) ions. It has been observed that after addition of Ag(+) ions of concentration 0.5-1 μM the strong fluorescence of ZnS QDs was almost quenched. The quenched fluorescence can be recovered by adding ethylenediamine to form a complex with Ag(+) ions. The other metal ions (K(+), Ca(2+), Au(3+), Cu(2+), Fe(3+), Mn(2+), Mg(2+), Co(2+)) showed little or no effect on the fluorescence of ZnS QDs when tested individually or as a mixture. In the presence of all these ions, Ag(+) responded well and therefore ZnS QDs reported in this work can be used as a Ag(+) ion fluorescence sensor.     

Coordination structures of the silver ion: infrared photodissociation spectroscopy of Ag(+)(NH(3))(n) (n = 3-8)

Infrared (IR) spectra are measured for Ag(+)(NH(3))(n) with n = 3-8 in the NH-stretch region using photodissociation spectroscopy. The spectra of n = 3 and 4 exhibit absorption features only near the frequencies of the isolated NH(3), indicating that every NH(3) molecule is coordinated individually to Ag(+). For n >or= 5, the occupation of the second shell is evidenced by lower-frequency features characteristic of hydrogen bonding between NH(3) molecules. Density functional theory and MP2 calculations are carried out in support of the experiments. A detailed comparison of the experimental and theoretical IR spectra reveals the preference for a tetrahedral coordination in the n = 5 and 6 ions. Likewise, most of the features observed in the spectra of n = 7 and 8 can be assigned to isomers containing a tetrahedrally coordinated inner shell as the basic structural motif. These results signify that the ammonia-solvated Ag(+) ion has a propensity toward a coordination number of four and the resulting tetrahedral Ag(+)(NH(3))(4) complex forms the central core of further solvation process.     

Synthesis and characterization of large colloidal cobalt particles

Large colloidal environmentally stable silica-coated cobalt particles were synthesized by combining the sodium borohydride reduction in aqueous solution and the St?ber method. Low size polydisperse cobalt spheres with an average size of 95 nm were synthesized by using a borohydride reduction method and were subsequently coated with a thin layer of silica by means of hydrolysis and condensation of tetraethylorothosilicate (TEOS) in an aqueous/ethanolic solution. The large uniform cobalt spheres consist of smaller metallic Co clusters, explaining the superparamagnetic behavior of the spheres. The particles were investigated by transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM).     

Silver nanoparticles: green synthesis and their antimicrobial activities

This review presents an overview of silver nanoparticles (Ag NPs) preparation by green synthesis approaches that have advantages over conventional methods involving chemical agents associated with environmental toxicity. Green synthetic methods include mixed-valence polyoxometallates, polysaccharide, Tollens, irradiation, and biological. The mixed-valence polyoxometallates method was carried out in water, an environmentally-friendly solvent. Solutions of AgNO(3) containing glucose and starch in water gave starch-protected Ag NPs, which could be integrated into medical applications. Tollens process involves the reduction of Ag(NH(3))(2)(+) by saccharides forming Ag NP films with particle sizes from 50-200 nm, Ag hydrosols with particles in the order of 20-50 nm, and Ag colloid particles of different shapes. The reduction of Ag(NH(3))(2)(+) by HTAB (n-hexadecyltrimethylammonium bromide) gave Ag NPs of different morphologies: cubes, triangles, wires, and aligned wires. Ag NPs synthesis by irradiation of Ag(+) ions does not involve a reducing agent and is an appealing procedure. Eco-friendly bio-organisms in plant extracts contain proteins, which act as both reducing and capping agents forming stable and shape-controlled Ag NPs. The synthetic procedures of polymer-Ag and TiO(2)-Ag NPs are also given. Both Ag NPs and Ag NPs modified by surfactants or polymers showed high antimicrobial activity against gram-positive and gram-negative bacteria. The mechanism of the Ag NP bactericidal activity is discussed in terms of Ag NP interaction with the cell membranes of bacteria. Silver-containing filters are shown to have antibacterial properties in water and air purification. Finally, human and environmental implications of Ag NPs to the ecology of aquatic environment are briefly discussed.     

Preparation of uniform Au@SiO2 particles by direct silica coating on citrate-capped Au nanoparticles

Preparation of Au@SiO₂ particles by direct silica coating on three different sized citrate-capped Au nanoparticles (17, 25 and 33 nm) with Stöber method was investigated in this work. It was found that the uniformity of the resulting Au@SiO₂ particles was related to both the sizes of the Au nanoparticles and the concentration of citrate during the particle synthesis. When the citrate concentration during the particle synthesis was low, the 25 and 33 nm Au nanoparticles could be well dispersed in the Stöber system, thus resulting the formation of uniform Au@SiO₂ particles containing single core. However, small Au nanoparticles (17 nm) were identified to show poor stability in the Stöber system even under low citrate concentration, the silica coating must be performed in a pre-hydrolyzed Stöber system to get the uniform Au@SiO₂ particles. This approach was also applicable to citrate capped Ag nanoparticles. After removal of the excess citrate in the Ag prepared by citrate reduction, uniform Ag/SiO₂ particles containing single core colloids could also be prepared by the direct silica coating.     

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on St?ber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).     

纳米银掺杂二氧化硅复合颗粒的制备及表征

0引言金属纳米颗粒因其粒子尺寸小(1￣100nm),比表面积大,表面原子数多,表面能和表面张力随粒径的下降急剧增大而具有量子尺寸效应[1]、小尺寸效应[2]、表面效应[3]及宏观量子隧道效应[4]等,从而出现了不同于常规固体的新奇特性,如:光学性质、磁性质以及电磁学性质[5],使其在催化、信息存储及非线性光学等领域展示了广阔的应用前景[6]。虽然制备金属纳米颗粒的方法有很多[6],但是由于纳米尺寸的金属颗粒具有较高的表面能,容易发生聚集,所以如何保持其稳定性依旧是比较困难的问题。随着纳米科技的发展,人们正尝试用各种方法来解决这个问题:如…     

LaAlO3 hollow spheres: synthesis and luminescence properties

Nearly monodisperse LaAlO(3) hollow spheres are synthesized by a novel precursor thermal decomposition method. Spherical colloids of capsulelike precursors with uniform diameters of 273 ± 35 nm have been synthesized by a solvothermal method. These spherical colloids could convert to LaAlO(3) hollow spheres with diameters of 166 ± 26 nm by a thermal decomposition process. The thermal transformation process from the precursors to LaAlO(3) was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and the Fourier transform infrared spectroscopy (FT-IR). By the doping of various lanthanide ions (Sm(3+), Eu(3+), and Tb(3+)), the emission luminescence of lanthanide-doped LaAlO(3) hollow microspheres can be tuned from red to green. In particular, these luminescent LaAlO(3) hollow spheres can be well dispersed in polar solvents such as the ethanol and water, which broadens the range of potential applications of these hollow spheres. The UV-vis absorption spectra show energy absorption at 211, 223, and 313 nm corresponding to the host lattice absorption and charge-transfer transitions. The results are in good agreement with the peaks observed in the excitation spectra.     

Ag-PVA和Ag-PVA/TiO2复合超薄膜的制备及性能研究

用3种方法制备了银纳米粒子-聚乙烯醇复合体系,其中用加热还原法所得体系中Ag纳米粒子的尺寸较大(15nm),其表面等离子体共振吸收峰较宽,最大吸收波长位于420nm;用室温硼氢化钠还原法得到的复合体系的吸收峰蓝移至409nm,且峰形较窄,Ag纳米粒子的平均粒径为8.7nm;低温NaBH4还原法所得体系吸收峰进一步蓝移至397nm,此时Ag纳米粒子粒径最小(3.5nm).将室温还原法所得Ag-PVA复合体系旋涂成膜,所得薄膜光滑、透明、均匀性好,该法适用于制备多层薄膜,以调控薄膜的厚度和光谱性质.将Ag-PVA复合体系与钛酸四丁酯(Ti(O_nBu)₄)的乙醇溶液交替旋涂得到Ag-PVA/TiO₂有机/无机复合薄膜.紫外-可见吸收光谱研究表明,随着Ag-PVA层数的增加,薄膜的表面等离子体共振吸收强度呈线性增加,但是TiO₂层数的增加对吸收光谱没有明显影响.Ag-PVA/TiO₂有机/无机复合薄膜将金属纳米粒子、有机高分子与无机半导体材料结合在一起,这种多层纳米结构在光电、催化功能薄膜等方面具有潜在的应用前景.     

三维有序大孔SiO2中的纳米银

A multi-step process was used for preparation of three-dimensionally ordered macroporous (3DOM) SiO2, in which fully accessible Ag nanoparticles are incorporated. The method involves the processes of assembly of polystyrene colloidal crystal, preparation of 3DOM SiO2, and incorporation of Ag nanoparticles within 3DOM SiO2 through in situ Tollens‘ reaction. XRD, SEM and EDXS determination show that the Ag particles deposited on the macroporous walls in nano dimension. The results indicate that lower concentration of silver ammoniate and for-maldehyde in the solution is favorable for forming a very narrow size distribution and uniform shape of nanoparticles. However, the higher the concentration of the solution and the more the loading times, the larger the possibility to form un-uniform particles. Ag nanoparticles can be sintered into larger and spheral particles by calcination at 600℃, but can resist sintering owing to their high dispersivity when loading amount is small. The study provided a simple approach to tailor Ag/3DOM SiO2 composite materials with desired morphology and size of Ag particles within the macropores.     

Synthesis and characterization of silica-silver core-shell composite particles with uniform thin silver layers

Silica-silver core-shell composite particles with uniform thin silver layers were successfully synthesized by a facile and one-step ultrasonic electrodeposition method. By electrolysis of the slurry consisting of preformed silica spheres and silver perchlorate without any additives, the homogenous composite particles can be prepared. The average size of single silver crystals in the composite is about 12 nm and the thickness of silver layer is 14±2 nm. Moreover, the continuity of Ag distribution, the surface roughness and the thickness of silver layer are controllable by adjusting the current density (I), the concentration of electrolyte (C) and the reaction time (t). Optical properties of the composite particles with different silver content were also investigated.     

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.