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.     

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.     

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.     

Synthesis and characterization of nanostructured Ag on porous titania

In this work, porous titania was prepared on bulk Ti by chemical oxidation, and then nanostructured silver (Ag) was deposited on titania surface by ion beam sputtering. After annealing treatment, Ag/TiO₂ composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that a nano-porous titania layer with mean pore size of 150 nm and thickness of 1 μm was formed by chemical oxidation at 80 °C for 45 min. There were three Ag species (Ag (0), Ag (1+), and Ag (2+)) on composites surface after annealing treatment, and metallic Ag content achieved maximum value with annealing temperature of 500 °C in air. Ag showed high thermal stability being partly attributed to the inhibiting the diffusion of Ag by the underlying porous titania.     

Deposition and wettability of silver nanostructures on Si(1 0 0) substrate based on galvanic displacement reactions

A new route for silver electroless deposition on Si(1 0 0) substrate is developed based on the galvanic displacement process. The basic electroless bath contains NaF and AgNO₃ with different concentrations. The morphologies of electrolessly deposited silver nanostructures, including silver nanowires and nanoparticles, are strongly dependent on the electrolyte composition. Adding an excess dosage of polyvinylpyrrolidone into the basic electrolyte yields final silver films of porous structures composed by multitudinous Ag nanoparticles. The porous silver films possess the surface hydrophobic property after the modification with n-dodecanethiol. Unidirectional wetting and spreading of a water droplet are also demonstrated on the patterned porous Ag films.     

Synthesis of porous hollow silica spheres using polystyrene-methyl acrylic acid latex template at different temperatures

Porous hollow silica spheres were prepared by using polystyrene-methyl acrylic acid latex as a template and cetyltrimethylammonium bromide as a wall structure-directing agent starting from tetraethoxysilane. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-infrared spectroscopy (FT-IR) and nitrogen adsorption/desorption were used to characterize the hollow silica spheres. When silica-coated latex composites were prepared at room temperature, hollow silica spheres with micropores in the walls were formed after removing the latex templates by calcination. When silica-coated latex composites were aged at a higher temperature of 150 °C, intact mesoporous hollow silica spheres were formed after calcination treatment.     

Preparation of poly(?-caprolactone)-based polyurethane nanofibers containing silver nanoparticles

In this study, poly(?-caprolactone)-based polyurethane (PCL-PU) nanofibers containing Ag nanoparticles for use in antimicrobial nanofilter applications were prepared by electrospinning 8 wt% PCL-PU solutions containing different amounts of AgNO₃ in a mixed solvent consisting of DMF/THF (7/3 w/w). The average diameter of the pure PCL-PU nanofibers was 560 nm and decreased with increasing concentration of AgNO₃. The PCL-PU nanofiber mats electrospun with AgNO₃ exhibited higher tensile strength, tensile modulus, and lower elongation than the pure PCL-PU nanofiber mats. Small Ag nanoparticles were produced by the reduction of Ag⁺ ions in the PCL-PU solutions. The average size and number of the Ag nanoparticles in the PCL-PU nanofibers were considerably increased after being annealed at 100 °C for 24 h. They were all sphere-shaped and evenly distributed in the PCL-PU nanofibers, indicating that the PCL-PU chains stabilized the Ag nanoparticles well.     

Electroless deposition of silver on synthesized calcite via surface modification

Metallic silver was deposited on the surface of synthesized calcite via a simple electroless deposition method. Calcite with cubic morphology was prepared first by homogeneous precipitation and it was subsequently surface modified using ammonium oxalate. The electroless deposition was carried out using formaldehyde as the reducing agent and silver nitrate as the silver source. Both calcite and the silver deposited calcite were characterized by different techniques. Surface modification of calcite with ammonium oxalate is necessary for the deposition of silver and the size of the deposited silver particles could be controlled by changing the deposition parameters such as concentration of the reagents and the deposition time. Lower concentration of silver ions (e.g. 0.01 M AgNO₃) and shorter deposition times (e.g. 30 min) lead to the formation of silver nanoparticles on calcite.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

In-situ formation of silver nanoparticles stabilized by amphiphilic star-shaped copolymer and their catalytic application

Silver nanoparticles (Ag NPs) were prepared via in situ reduction of silver nitrate (AgNO₃) using polymeric micelles as nanoreactors without any additional reductant. The micelles were constructed from the amphiphilic star-shaped copolymer composed of poly(?-caprolactone) (PCL) segment, 2-(dimethylamino)ethyl methacrylate (DMAEMA or DMA) units and oligo(ethylene glycol)monomethyl ether methacrylate (OEGMA or OEG) units. The Ag NPs stabilized by those star-shaped copolymers were characterized using UV-vis spectrum, DLS, TEM and FTIR. It confirmed that PDMAEMA exhibited the reducing property unless pH was above 7. The Ag NPs were sphere-like with a diameter of 10-20 nm, which was independent of the architecture of the copolymer and AgNO₃ concentration. Furthermore, the catalytic activity of these Ag NPs was investigated by monitoring the reduction of p-nitrophenol (4-NP) by NaBH₄. The result showed that the Ag NPs formed by coordination reduction can be effectively applied in catalytic reaction.     

Preparation of titania hollow spheres by catalyst-free hydrothermal method and their high thermal stabilities

TiO₂ hollow spheres have been prepared by hydrothermal method using carbon spheres as hard templates based on template-directed deposition and calcination in order to remove templates. The morphology and structure of samples were systematically characterized by using various techniques, including XRD, zeta analyzer, SEM, TEM, DRS and FTIR. In this approach, the anatase phase was retained for temperatures up to 900 °C. Moreover, negative charged titania is deposited onto the negative charged surface of carbon spheres, which is proved by nanoparticle size analyzer. Therefore, a possible formation mechanism of TiO₂ hollow spheres was proposed. TiO₂ hollow spheres calcined at 550 °C exhibited the superior photocatalytic activity for the degradation of Rhodamine B, 2.9 times greater than that of Degussa P25. Furthermore, thermal stability of TiO₂ hollow spheres was examined. Fortunately, we found that hollow structures could still be visible distinctly after calcining at 900 °C.     

Electrochemical synthesis of Ag nanoparticles supported on glassy carbon electrode by means of p-isopropyl calix[6]arene matrix and its application for electrocatalytic reduction of H2O2

The silver nanoparticles were prepared on the glassy carbon (GC) electrode, modified with p-iso propyl calix[6]arene, by preconcentration of silver ions in open circuit potential and followed by electrochemical reduction of silver ions. The stepwise fabrication process of Ag nanoparticles was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared Ag nanoparticles were deposited with an average size of 70 nm and a homogeneous distribution on the surface of electrode. The observed results indicated that the presence of calixarene layer on the electrode surface can control the particle size and prevent the agglomeratione and electrochemical deposition is a promising technique for preparation of nanoparticles due to its easy-to-use procedure and low cost of implementation. Cyclic voltammetry experiments showed that Ag nanoparticles had a good catalytic ability for the reduction of hydrogen peroxide (H₂O₂). The effects of p-isopropyl calix[6]arene concentration, applied potential for reduction of Ag⁺, number of calixarene layers and pH value on the electrocatalytic ability of Ag nanoparticles were investigated. The present modified electrode exhibited a linear range from 5.0 × 10⁻⁵ to 6.5 × 10⁻³ M and a detection limit 2.7 × 10⁻⁵ M of H₂O₂ (S/N = 3) using amperometric method.     

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.     

Spatially controlled dissolution of Ag nanoparticles in irradiated SiO2 sol-gel film

In this paper, we report the spatially controlled dissolution of silver nanoparticles in irradiated SiO₂ sol-gel films. The Ag nanoparticles have been formed in the sol-gel solution before the film deposition by adding Triton and ascorbic acid and also after the film deposition using a heat treatment at 700 °C for few minutes or at 550 °C for 6 h in reducing atmosphere. Using a spectrometer, a new view white light interferometer and a micro-thermal analyzer, we demonstrate that the silver nanoparticles can be dissolved using a continuous black ray UV lamp or with a near-infrared (NIR) femtosecond laser, due to a significantly increase in the local temperature. We confirm that the micro-thermal analyzer can be used as a new tool to study the dissolution of metallic nanoparticles in thin film if located at the surface of the films.     

Fabrication of superhydrophobic surfaces on zinc substrates

Stable superhydrophobic surfaces were fabricated on the zinc substrates through simple silver replacement deposition process with the modification of octadecyl mercaptan. The effects of reaction conditions on the surface morphology and wettability of the prepared surfaces were carefully studied. The results show that the fabrication of a best superhydrophobic surface depends largely on the moderate reactant concentration. When the concentration of AgNO₃ solution was 2 mmol/L, the zinc substrate was covered by a dendritic outline structure. Aggregated silver nanoparticles were formed on the substrate in accordance with some certain laws, exhibiting great surface roughness. The typical hierarchical micro-nanostructures, flower-like structures and porous structures also could be found from the SEM images. The maximal water contact angle (CA) value of about 161 ± 2°, and the minimal sliding angle (SA) of about 2° were obtained under the same reaction condition.     

Electromagnetic and microwave absorption properties of Fe3O4 magnetic films plated on hollow glass spheres

Magnetic hollow spheres of low density were prepared by plating Fe₃O₄ magnetic films on hollow glass spheres using ferrite plating. The complex permeability and permittivity of spheres–wax composites were measured in the range of 2–18 GHz. The complex permeability and permittivity increased, and the dielectric and magnetic losses were improved as the volume fraction of the magnetic spheres in the composites increased from 60% to 80%, which also resulted in a great improvement of microwave absorption properties. For composites with volume fraction 80%, its magnetic resonance frequency was at about 13 GHz and it appeared three loss peaks in the calculated reflection loss curves; the bandwidth less than −10 dB was almost 4 GHz which was just in the Ku-band frequencies (12–18 GHz) and a minimum reflection loss of −20 dB was obtained when the thickness was 2.6 mm; the microwave absorbing properties were mainly due to the magnetic loss. The results showed that the magnetic spheres composites were good and light microwave absorbers in the Ku-band frequencies.     

Synthesis of hollow ferrite nanospheres for biomedical applications

Hollow ferrite spheres of 220-340 nm diameter were synthesized at 60 °C as multi-functionalized magnetic carriers which are potentially applicable both as drug delivery systems (DDS) and hyperthermia treatment. We found that SH and OH groups on the silica template spheres enabled the fabrication of continuous ferrite shells of 20-30 nm in thickness. Transmission electron microscopy and energy-dispersive spectroscopy revealed that the templates were dissolved by a NaOH solution, yielding hollow particles exhibiting saturation magnetization of 78 emu/g. The results suggested that the ferrite shells are porous and the pores work as pathway for releasing drugs from the hollow particle inside.     

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.     

Spatially defined silver mirror reaction on a micropatterned aldehyde-terminated self-assembled monolayer

A simple microfabrication technique for silver (Ag) based on spatially defined silver mirror reaction using a photolithographically micropatterned aldehyde (CHO)-terminated self-assembled monolayer (SAM) is proposed. First, both a Si substrate covered with native oxide and a quartz glass plate were exposed to a vapor of triethoxysilylundecanal (TESUD) diluted with absolute toluene for 3 h at 403 K. This vapor phase treatment produced a 1.2-nm-thick TESUD-SAM with a flat, homogeneous surface. Several samples were then photolithographically micropatterned using an excimer lamp radiating 172 nm vacuum ultraviolet light, and subsequently employed as templates for area-selective electroless Ag plating. Optical microscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed that Ag metal was preferentially deposited on the CHO-terminated regions, resulting in the formation of well-ordered Ag microstructures composed of rectangular 5 μm × 25 μm features. The CHO terminal groups of the TESUD-SAM were found to be effective in reducing Ag ionic species at the solid/liquid interface.     

Self assembly of SiO2-encapsulated carbon microsphere composites

SiO₂ was firstly coated onto the surface of carbon microspheres (CMSs) using tetraethyl orthosilicate (TEOS) as precursor by Stöber method. Then SiO₂-encapsulated CMS (CMS@SiO₂) composites were self-assembled by vertical deposition, in which the effects of deposition temperature and suspension concentration on the quality of self-assembling film were investigated. Morphologies and structures of the samples were characterized by field emission scanning electron microscopy, Fourier transformation infrared spectrometry, X-ray diffraction and thermogravimetry. The results show that uniform CMS@SiO₂ composites with good mono-dispersion were prepared by St?ber method with 0.5 g of CMSs, 2 mL of TEOS, 30 mL of ammonia and 12 h of reaction time, the CMSs-based films with ordered and denser structure were prepared by vertical deposition using CMS@SiO₂ composites as monodipersion spheres under suspension concentration of 1 wt% and deposition temperature of 50 °C. The ultraviolet-visible absorption measurement shows that the absorbance of CMS@SiO₂ composite films grew steadily with increasing suspension concentration.