The synthesis and kinetic growth of anisotropic silver particles loaded on TiO2 surface by photoelectrochemical reduction method

Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO₂ films by photoelectrochemical reduction of Ag⁺ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO₂ film after UV irradiation in AgNO₃ solution is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO₂ film was obtained with the AgNO₃ concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO₂ films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO₂ films. The maximum growth rate of silver particles loaded on TiO₂ films can be up to 0.353 nm min⁻¹ among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO₂ is 1.751 × 10⁻³ min⁻¹.     

The synthesis of Ag/polypyrrole coaxial nanocables via ion adsorption method using different oxidants

Ag/polypyrrole (PPy) coaxial nanocables (NCs) were synthesized by an ion adsorption method. In this method, the pre-made Ag nanowires (NWs) were dispersed in the aqueous solution of copper acetate (Cu(Ac)₂), and the Cu²⁺ ions adsorbed onto the surface of Ag NWs can oxidize pyrrole monomers to polymerize into uniform PPy sheath outside Ag NWs after the Cu(Ac)₂-treated Ag NWs were re-dispersed in the aqueous solution of pyrrole. The morphology of NCs was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The relationship between the thickness of polymer sheath and the concentration of Cu(Ac)₂ was established. As Cu(Ac)₂ which served as the oxidant can also be replaced by AgNO₃ in this synthesis, the differences on the structure of polymer sheath caused by different oxidants were studied by surface-enhanced Raman scattering (SERS), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Comparing with the characterization results of Ag/PPy NCs synthesized using AgNO₃ as the oxidant which indicates the random arrangement of PPy chains at the interface between polymer sheath and Ag NWs, PPy chain oxidized by Cu²⁺ tends to show a relatively ordered conformation at the interface with the pyrrole rings identically taking the plane vertical to the surface of Ag NWs. In addition, although the main part of the polymer sheath was composed of PPy whatever kind of oxidant was used, the sheath of the NCs oxidized by Cu²⁺ is typical for the existence of Cu(I)–pyrrole coordinate structures with strong Cu(I)–N bond signal shown in XPS characterization.     

Optical and structural properties of CdS thin films grown by chemical bath deposition doped with Ag by ion exchange

In this work thin CdS films using glycine as a complexing agent were fabricated by chemical bath deposition and then doped with silver (Ag), by an ion exchange process with different concentrations of AgNO₃ solutions. The CdS films were immersed in silver solutions using different concentrations during 1 min for doping and after that the films were annealed at 200 °C during 20 min for dopant diffusion after the immersion on the AgNO₃ solutions. The aim of this research was to know the effects of different concentrations of Ag on the optical and structural properties of CdS thin films. The optical band gap of the doped films was determined by transmittance measurements, with the results of transmittance varying between 35% and 70% up to 450 nm in the electromagnetic spectra and the band gap varying between 2.31 and 2.51 eV depending of the silver content. X-ray photoelectron spectroscopy was used to study the influence of silver on the CdS:Ag films, as a function of the AgNO₃ solution concentration. The crystal structure of the thin CdS:Ag films was studied by the X-ray diffraction method and the film surface morphology was studied by atomic force microscopy. Using the ion exchange process, the CdS films’ structural, optical and electric characteristics were modified according to silver nitrate concentration used.     

Surface enhanced Raman scattering of nano diamond using visible‐light‐activated TiO2 as a catalyst to photo‐reduce nano‐structured silver from AgNO3 as SERS‐active substrate

In this work, we demonstrate nano‐structured silver particles photo‐reduced from silver nitride (AgNO₃) solution using visible‐light‐activated titanium dioxide (TiO₂), which can be a convenient and effective substrate for surface enhanced Raman spectroscopy (SERS) observation. Visible‐light‐activated carbon‐containing TiO₂ nanoparticles are applied to photo‐reduce and form nano‐structured silver from AgNO₃ upon visible‐light illumination. Photo‐reduced nano‐structured silver is used as an active substrate for SERS studies of TiO₂ as well as nano diamond and TiO₂. The photo reduction of AgNO₃ and SERS observation can be obtained by simultaneously using the same visible laser excitation. The coexistence of the anatase phase with small admixture of the rutile phase in the TiO₂ can be observed using SERS. The carbon structure in the carbon‐containing TiO₂ was determined to be sp² type carbon bonding by SERS. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of alternating current conduction mechanism in polypyrrole-magnesium ferrite hybrid nanocomposite through correlated barrier hopping model

In the present work, both polypyrrole (PPy) and optimized polypyrrole–magnesium ferrite (PPy-MgFe₂O₄) hybrid nanocomposite were synthesized separately by simple oxidative chemical polymerization method and then structurally characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The FTIR spectrum of the composite showed the presence of characteristic absorption bands of both PPy and MgFe₂O₄ in the composite confirming interfacial interaction of PPy with MgFe₂O₄. That this interaction is not affected by crystalline behaviour of predominant MgFe₂O₄ particles but that MgFe₂O₄ has embedded in PPy matrix was confirmed by XRD studies. Agglomerated granular spherical morphology of the composite was confirmed by SEM studies. Decrease in AC conductivity of the composite as compared to PPy due to the formation of interfacial heterojunction barrier between p-type PPy and n-type MgFe₂O₄ was confirmed experimentally and well supported theoretically by calculating binding energy, hopping distance and density of states at Fermi level of PPy and the composite as per CBH model.     

Microbial synthesis of silver nanoparticles by Bacillus sp.

A silver resistant Bacillus sp. was isolated through exposure of an aqueous AgNO₃ solution to the atmosphere. Silver nanoparticles were synthesized using these airborne bacteria (Bacillus sp.). Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analyses confirmed that silver nanoparticles of 5–15 nm in size were deposited in the periplasmic space of the bacterial cells; a preferable cell surface location for the easy recovery of biogenic nanoparticles.     

UV-induced synthesis,characterization and formation mechanism of silver nanoparticles in alkalic carboxymethylated chitosan solution

The silver nanoparticles (AgNPs) were synthesized in an alkalic aqueous solution of silver nitrate (AgNO₃)/carboxymethylated chitosan (CMCTS) with ultraviolet (UV) light irradiation. CMCTS, a water-soluble and biocompatible chitosan derivative, served simultaneously as a reducing agent for silver cation and a stabilizing agent for AgNPs in this method. UV–vis spectra and transmission electron microscopy (TEM) images analyses showed that the pH of AgNO₃/CMCTS aqueous solutions, the concentrations of AgNO₃ and CMCTS can affect on the size, amount of synthesized AgNPs. Further by polarized optical microscopy it was found that the CMCTS with a high molecular weight leads to a branch-like AgNPs/CMCTS composite morphology. The diameter range of the AgNPs was 2–8 nm and they can be dispersed stably in the alkalic CMCTS solution for more than 6 months. XRD pattern indicated that the AgNPs has cubic crystal structure. The spectra of laser photolysis of AgNO₃/CMCTS aqueous solutions identified the early reduction processes of silver cations (Ag⁺) by hydrated electron formed by photoionization of CMCTS. The rate constant of corresponding reduction reaction was 5.0 × 10⁹ M⁻¹ s⁻¹.     

Preparation and characterization of conducting polymer/silver hexacyanoferrate nanocomposite

In this work, we present an alternative route to prepare silver hexacyanoferrate(II)/polyaniline (PANI) composite thin films. Differently from the electrochemical method, used to synthesize the conducting polymer film on a electrode surface, this new chemical route makes use of dialysis membrane as a solid support to synthesize the silver hexacyanoferrate(III) compound, and subsequently uses this composite membrane as oxidizing agent to polymerize the aniline monomer. The spectroscopic (UV-vis and IR region) and electrochemical characterization (cyclic voltammetry) indicates that the polymeric composite remains optically active and conductive. The X-ray analysis shows that the composite membrane/Ag₃[Fe_III(CN)₆] has an crystalline structure that can be assigned to the Ag₃[Fe_III(CN)₆] structure, and after reaction with aniline solution it became less crystalline. Additionally the SEM measurements shown that the reaction of silver ions with hexacyanoferrate(III) across the membrane results in a well defined and aliened Ag₃[Fe_III(CN)₆] crystals and when this crystalline compound reacts with aniline monomer silver wire of 100 nm of diameter by 6 μm longer are formed together with the conducting polymer polyaniline/Ag_x[Fe_II(CN)₆] composite.     

Preparation and photoelectrochemical performance of Ag/graphene/TiO2 composite film

By dipping-lifting in sol-gel solution and reducing process, the graphene/TiO₂ composite film on the glass plate was first prepared. Then, the Ag/graphene/TiO₂ composite film was fabricated by interface reaction with AgNO₃ and N₂H₄·H₂O on the surface of graphene/TiO₂ composite film. The characterization results show that the uniform porous TiO₂ film is made up of the anatase crystal, and the Ag/graphene/TiO₂ composite film is constructed by doping or depositing graphene sheets and Ag nanoparticles on the surface of TiO₂ film. The photoelectrochemical measurement results indicate that the Ag/graphene/TiO₂ composite film has an excellent photoelectrochemical conversion property.     

Preparation and dispersive mechanism of highly dispersive ultrafine silver powder

Using ascorbic acid as the reducing agent, AgNO₃ as the source of Ag, the ultrafine silver powder was prepared by liquid-phase reduction method. The optimal conditions to prepare the ultrafine silver powder were obtained by studying the effects of following factors, such as the selection of dispersant, the doses of dispersant and pH, on the dispersibility of silver powder under other constant conditions. The pure ultrafine silver powder with quasi-spherical shape and mean size of 1.15 μm was synthesized under the optimal conditions of polyvinyl alcohol (PVA) as disperser, PVA/AgNO₃ mass ratio of 4:100 and pH 7 while maintaining other conditions exactly in the same circumstances, such as AgNO₃ concentration of 0.20 mol L⁻¹, ascorbic acid concentration of 0.15 mol L⁻¹ and reaction temperature of 40 °C. The ultrafine silver powder was characterized by SEM and XRD. And a PVA dispersive mechanism for preparing highly dispersive ultrafine silver powder, proved by the ultraviolet spectra, is that PVA absorbed on the surface of silver particles by coordination bond preventing the silver particles from diffusion and aggregation. In addition, the steric effect may help to reduce aggregation.     

Synthesis and characterisation of polypyrrole–indium phosphide composite film

Polypyrrole (PPy)–indium phosphide (InP) composite material was electrochemically prepared by the incorporation of InP into a PPy matrix during electrochemical synthesis (cycling) under magnetic stirring from the acetonitrile/LiClO4 electrolyte containing the Py and InP particles. The PPy–InP composite material was designed to explore new approaches to improve light-collection efficiency in polymer photovoltaic. The samples were characterised by cyclic voltammetry, impedance spectroscopy measurement, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV–visible and photoelectrochemical measurements. It was observed that the photocurrent of the composites was higher than that of the single PPy films and increased with InP concentration. The study showed that the presence of InP particles in the polymeric film improves the optical and the photovoltaic properties of PPy and give information on the use possibility of these films for photovoltaic cells' application.     

One-step synthesis of silver nanoparticles in an aqueous solution and their antibacterial activities

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented in this research. In the synthesis, an amino-terminated hyperbranched polymer (HBP-NH₂) was applied as a stabilizer and a reductant. The syntheses, performed at various initial AgNO₃ concentrations (0.28–0.56 g/l) in a 2 g/l HBP-NH₂ aqueous solution, produced silver colloid nanoparticles having average sizes from 3 to 30 nm with narrow size distributions. The formation of silver colloid nanoparticles was characterized by Fourier Transform Infrared Spectrophotometry (FTIR), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), UV/Visible Absorption Spectrophotometry, and X-ray Diffraction (XRD) measurements. The results indicated that both particle size and the UV absorption are strongly dependent on the initial AgNO₃ concentrations. The silver colloid nanoparticles, prepared with a 0.35 g/l AgNO₃ aqueous solution in the presences of 2 g/l HBP-NH₂, showed good antibacterial activities against Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). A very low concentration of nano-silver (as low as 3.0 ug/ml Ag) also gave excellent antibacterial performance.     

Highly Water‐Dispersible,Highly Conductive,and Biocompatible Polypyrrole‐Coated Silica Particles Stabilized and Doped by Chondroitin Sulfate

Currently available methods to prepare conducting polymers‐coated colloidal substrates for biomedical applications need to be improved because they involve the use of toxic reagents and tend to result in aggregated products with diminished conductivity. The work herein describes for the first time a facile strategy for preparing highly water‐dispersible, highly conductive, and biocompatible polypyrrole‐coated silica core–shell (SiO₂@PPy) particles using only chondroitin sulfate (CS), a biologically derived polymer, as the stabilizer and dopant. The CS preadsorbed onto silica surface serves as a template to control the confined growth of the PPy shell and doping of in situ polymerized PPy shell. The thickness of the PPy shell can be tuned from 8 to 17 nm by varying the CS preadsorbed amount. Increasing the thickness of the adsorbed CS layer can control the deposition of thinner PPy shells on an SiO₂ core surface to provide highly water‐dispersible SiO₂@PPy particles. Moreover, CS‐doped SiO₂@PPy particles exhibit conductivities as high as 5.3 S cm^?1. The conductivity of the particles depends on the PPy mass loading and the doping level of the PPy shell. Furthermore, the SiO₂@PPy particles exhibit good biocompatibility and therefore have potential applications in biomedicine.     

A novel method of nanocrystal fabrication based on laser ablation in liquid environment

Metal nanoparticles can be prepared by a novel technique that consists of the laser ablation of a solid target immersed in a water solution of a metal salt. Silicon was chosen as the most adequate target to synthesize silver and gold nanoparticles from a water solution of either AgNO₃ or HAuCl₄. The influence of both the silver nitrate concentrations and the irradiation time of the Si target on the optical properties of the Au and Ag nanoparticles have been investigated. The crystalline nature of the metal nanoparticles has been determined by X-ray diffraction (XRD). Average size and particle size distribution have been measured by means of TEM. The absorbance spectra show the characteristic band of the surface resonant plasmon of silver and gold nanoparticles.     

A novel method for synthesis of colloidal silver nanoparticles by arc discharge in liquid

This paper presents a novel, inexpensive and one-step approach for synthesis of silver nanoparticles (Ag NPs) using arc discharge between titanium electrodes in AgNO₃ solution. The resulting nanoparticles were characterized using UV–Vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Silver nanoparticles of 18 nm diameter were formed during reduction of AgNO₃ in plasma discharge zone. Optical absorption spectroscopy of as prepared samples at 15 A arc current in AgNO₃ solution shows a surface plasmon resonance around 410 nm. It was found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. SEM images exhibit the increase of reduced nanoparticles in 6 min arc duration compared with 1 min arc duration. TEM image of the sample prepared at 6 min arc duration shows narrow size distribution with 18 nm mean particle size. Antibacterial activities of silver nanoparticles were investigated at the presence of Escherichia coli (E-coli) bacteria.     

Preparation and study of complex self-assembled film as a super-thin barrier on silver

A self-assembled monolayers (SAMs) of (3-mercaptopropy) trimethoxysilane (3-MPT) chemisorbed on silver surface was chemically modified by 1-octadecanethiol (C₁₈H₃₇SH) (to form self-assembled mixed-monolayer (SAMM)) and the co-polymer of N-vinylcarbazole and methyl methacrylate ester to form complex self-assemblied film (CSAF). The combinative state of interface between SAMs (or SAMM) and co-polymer were characterized by dynamic mechanical thermal analysis (DMTA). The thickness of film on Ag was characterized by X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) measurements in 10% NaOH aqueous solution with the silver surface and covered with film indicated that 3-MPT SAMs modified with C₁₈H₃₇SH and then with co-polymer have higher capability against oxidation.     

Dynamic templating role of polynaphtalene sulphonate in the formation of silver nanocrystals in aqueous solution

We have used time resolved small angle X-ray scattering (SAXS) for investigating the early stages of the formation of crystalline colloidal Ag particles by AgNO₃ reduction with ascorbic acid in an aqueous acidic solution of a polynaphthalene sulphonate polymer (Daxad). In order to exploit the polymer role in silver crystallization, the measurements have been performed at different polymer concentrations. Data analysis suggests that the nucleation and growth of primary particles of about 20 nm in diameter, occurring in a surface-fractal arrangement of the dynamic polymeric template, is assisted by the development of long range spatial correlations. These correlations could be a sign of polymer-induced liquid fluctuations as intermediate precursors of Ag crystallization.     

Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach

Abstract  The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl₄ is greater than the AgNO₃ at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum. The case of low concentration of extract with HAuCl₄ offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal- or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state. Graphical abstract  Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent. The rate of bioreduction of AgNO₃ is lower than the HAuCl₄ at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration of phyllanthin with AgNO₃ and HAuCl₄.      

Synthesis of hollow silver spheres using poly-(styrene-methyl acrylic acid) as templates in the presence of sodium polyacrylate

Hollow silver spheres were successfully prepared by reducing AgNO₃ with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO₃ and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150 °C for 3 h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran.