Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core–shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal–metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theo...

Photoemission mechanism of water-soluble silver nanoclusters: ligand-to-metal-metal charge transfer vs strong coupling between surface plasmon and emitters.

In this work, a simple one-step method of silver nanoparticle (NPs) preparation with controlled size is introduced. Silver NPs were prepared by reduction of [Ag(NH3)2]+ complex cation by d-maltose in the presence of low concentrations (1 × 10–10 mol/L to 1 × 10–7 mol/L) of high-molecular-weight poly(acrylic acid) (PAA). This modification of the reduction reaction results in managing of the prepared silver nanoparticles’ size in the range from 28 nm (the reaction system without PAA) to 77 nm (system with the highest used PAA concentration). The presence of poly(acrylic acid) influences both nucleation process and also the subsequent stage of nanoparticle growth. The rate of nuclei formation by homogeneous nucleation is affected by PAA due to the formation of the strong complex with silver ions which results in a prolongation of the initiation phase of the reduction process proportionally to PAA concentration. The formation of the adsorption layer of PAA on the surface of the emerging silver nuclei prevents...

Polyacrylate-Assisted Size Control of Silver Nanoparticles and Their Catalytic Activity

Silver nanoparticles are synthesized by the reduction of metal salt solutions from sodium borohydride in a microfluidic chip. The influence of different operating conditions on silver particle diameter, morphology, size distribution, and elemental compositions has been investigated. The results demonstrated that ethylenediaminetetraacetic acid (EDTA) serving as a complexant significantly affected the particle size of synthesized silver nanoparticles. An increase in the silver nanoparticle mean diameter was observed with decreasing NaBH4/AgNO3 molar concentration ratios, and increasing fluid flow rates.

Droplet synthesis of silver nanoparticles by a microfluidic device

Symmetrical silver phosphate (Ag3PO4) crystals with porous structure were grown by a facile controllable route in aqueous solution. The Ag3PO4 crystals have a cubic-type structure and the morphologies are distinctive under different conditions. The crystals had high purity, were well-crystallized and were free of secondary phases by powder X-ray diffraction, IR, Raman spectra, scan electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). It is interesting that the different crystal faces of the crystals have high physical–chemical–biological activity and large surface areas, so as to act as high activity micro-reactors (HAMs). The HAMs can effectively improve the photocatalytic activity and bacteriostatic activity of the Ag3PO4 crystals. Furthermore, we proposed a possible growth mechanism and detailed morphology transformation process of Ag3PO4 crystals with different properties.

Controlled synthesis of silver phosphate crystals with high photocatalytic activity and bacteriostatic activity

In this paper, the influence of variable molar ratios between reducing and loading agents (1:100, 1:50, 1:20, 1:10, 1:5, 1:2, 1:1, 2:1) and between protective and loading agents (0.3:1, 0.75:1, 1.5:1, 3:1, 7.5:1, 30:1, 75:1) in the synthesis of silver nanoparticles by chemical reduction has been evaluated to obtain multicolor nanoparticles with a high stability in time. The protective agent poly(acrylic acid, sodium salt) (PAA) and reducing agent dimethylaminoborane (DMAB) play a key role in the formation of the resultant color. Evolution of the optical absorption bands of the silver nanoparticles as a function of PAA and DMAB molar ratios made it possible to confirm the presence of silver nanoparticles or clusters with a specific shape. The results reveal that a wide range of colors (violet, blue, green, brown, yellow, red, orange), sizes (from nanometer to micrometer), and shapes (cubic, rod, triangle, hexagonal, spherical) can be perfectly tuned by means of a fine control of the PAA and DMAB molar concentrations.

/pdf/effect-of-both-protective-and-reducing-agents-in-the-285u9rf933.pdf

Effect of both protective and reducing agents in the synthesis of multicolor silver nanoparticles.

A new tool is presented to control formation of Ag nanoparticles. Small amounts of silver ions were added to dilute solutions of long-chain sodium polyacrylates (NaPA). Four NaPA samples covering a...

Controlled formation of ag nanoparticles by means of long-chain sodium polyacrylates in dilute solution.

Mixtures of a calix[4]arene and a naphthyridine derivative dissolved in 1,2-dichlorobenzene form thermoreversible aggregates. The aggregation process was followed by means of time-resolved multiangle light scattering at two different mixing ratios, 1:3 and 1:4, yielding a detailed record of the relative mass, the radius of gyration, and the particle scattering function of the growing aggregates. On the basis of these data, a conclusive model of the structure is presented for the developing aggregates: monomers aggregate to wormlike filaments which form branching points. Formation of branching points proceeds in a frequency and distribution which is similar to the polycondensation of ABC monomers toward non-randomly branched macromolecules (Burchard, W. Macromolecules 1977, 10, 919-927). Thus, aggregation results in hyperbranched-like particles with striking analogies to the polymerization of glucose to amylopectin.

Formation of branched calixarene aggregates-a time-resolved static light scattering study.

Time resolved structure analysis of growing β-amyloid fibers

Selbstbau eines digitalen Low‐Cost‐Fotometers für den Chemieunterricht

Experimental and theoretical investigations on the ultrafast photoinduced decomposition of three tert-butyl peroxides of general structure R−C(O)O−O−tert-butyl with R = phenyloxy, benzyl, or naphthyloxy in solution are presented. Photoinduced O−O bond scission occurs within the time resolution (200 fs) of the pump−probe experiment. The subsequent dissociation of photochemically excited carbonyloxy radicals, R−CO2, has been monitored on a picosecond time scale by transient absorption at wavelengths between 290 and 1000 nm. The measured decay of R−CO2 is simulated via statistical unimolecular rate theory using molecular energies, geometries, and vibrational frequencies obtained from density functional theory (DFT) calculations. The results are compared with recent data for tert-butyl peroxybenzoate (R = phenyl). While benzoyloxy radicals exhibit nanosecond to microsecond lifetimes at ambient temperature, insertion of an oxygen atom or a methylene group between the phenyl or naphthyl chromophore and the CO2 ...

Ultrafast Decarboxylation of Carbonyloxy Radicals: Influence of Molecular Structure

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