Characterization of SiO2/Ag composite particles synthesized by in situ reduction and its application in electrically conductive adhesives

In the study, SiO₂/Ag composite particles with silver coating onto the surface of silica have been successfully prepared via a novel and facile approach (Oxidation–Reduction Method). In this approach, the SiO₂ particles were first modified with 3-ammoniatriethoxysilane (APTES) and glyoxalic acid (GA) through two-step reaction, the aldehyde group (CHO) were anchored onto the surfaces of silica spheres via electrostatic attraction, these [Ag(TEA)₂]⁺ ions in the solution were then reduced by the CHO and coated onto the surface of silica to obtain SiO₂/Ag composite particles. The effects of the reaction conditions on silver content and synthetic mechanism had also been discussed. The structure, morphology and optical properties of the SiO₂/Ag composite particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results showed the surface of SiO₂ was surrounded by pure silver nanoparticles, and the silver nanoparticles had face-centered-cubic structure, the SiO₂/Ag composite particles with core–shell morphology and special optical properties. And the small content SiO₂/Ag composite particles applied in electrically conductive adhesives (ECAs) improved the electrical bulk resistivity and tensile shear strength.     

Alternative method for preparation of CdS/epoxy resin nanocomposite

Hybrid composites of CdS nanoparticles embedded in epoxy resin matrixes have been prepared by co-precipitate method and characterized. Epoxy resin acted as the matrix for the formation of nano CdS particles in the reaction system and kept them from agglomerating. The resulting viscous orange liquid could be cured with normal curing agent. The result of XRD, UV and TEM analysis reveals that the CdS particles are in nano size and dispersed in epoxy resin matrix homogeneously.     

Spark plasma sintering of silicon nitride using nanocomposite particles

The spark plasma sintering (SPS) of silicon nitride (Si₃N₄) was investigated using nanocomposite particles composed of submicron-size α-Si₃N₄ and nano-size sintering aids of 5 wt% Y₂O₃ and 2 wt% MgO prepared through a mechanical treatment. As a result of the SPS, Si₃N₄ ceramics with a higher density were obtained using the nanocomposite particles compared with a powder mixture prepared using conventional wet ball-milling. The shrinkage curve of the powder compact prepared using the mechanical treatment was also different from that prepared using the ball-milling, because the formation of the secondary phase identified by the X-ray diffraction (XRD) method and liquid phase was influenced by the presence of the sintering aids in the powder compact. Scanning electron microscopy (SEM) observations showed that elongated grain structure in the Si₃N₄ ceramics with the nanocomposite particles was more developed than that using the powder mixture and ball-milling because of the enhancement of the densification and α-β phase transformation. The fracture toughness was improved by the development of the microstructure using the nanocomposite particles as the raw material. Consequently, it was shown that the powder design of the Si₃N₄ and sintering aids is important to fabricate denser Si₃N₄ ceramics with better mechanical properties using SPS.     

Preparation of gold-silica heterogeneous nanocomposite particles by alcohol-reduction method

Au-silica heterogeneous nanocomposite particles were prepared by novel preparation strategy involving alcohol-reduction method using 3-aminopropyltrimethoxysilane (APTMS) as a binder between silica surface and Au nanoparticles, and using PVP as a stabilizer for Au nanoparticles. The evolution of morphology of composite particles was investigated with increasing reaction time at different Au precursor concentrations of 100 ppm and 250 ppm using UV-vis spectrophotometer and TEM. It is shown that the size of immobilized Au particles on silica surface can be controlled with the variation of reaction rate via adjusting Au precursor concentration and reaction time, but the high concentration of Au precursor hinders the immobilization of well-defined Au nanoparticles due to the slow reduction rate of Au precursor. On the basis of experimental results, the role of APTMS and PVP on the formation of composite particles and the effect of Au precursor concentration on the morphological evolution of composite particles are briefly discussed.     

Facile carbothermal reduction approach to hybrid platinum-carbon nanotubes composite for electrocatalytic oxidation of ethanol

We have provided an effective, environmentally benign approach for the synthesis of hybrid platinum-carbon nanotubes (Pt-CNTs) composite via a CNTs-guided carbothermal reduction. The materials were characterized by transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results revealed that CNTs acted as both support and reducing agent, and therefore the Pt nanoparticles with an average particle size of 3.5 nm could uniformly disperse onto the surface of CNTs. Moreover, as-fabricated Pt-CNTs exhibited the enhanced electrocatalytic activity and stability for ethanol oxidation in both acidic and alkaline media, in comparison to that prepared by electrochemical deposition. This approach greatly enlarges the practical application areas of hybrid Pt-CNTs composite materials.     

Synthesis of silver/silica nanocomposites anchored by polymer via in situ reduction

Silver/silica nanocomposites were synthesized by in situ reduction of silver salt and anchorage of the formed silver nanoparticles to silica nanospheres using a polymer anchor. Synthesis conditions including reductants, anchor polymers, and surfactants were determined. The successful formation of the nanocomposites was governed by the reduction of silver nitrate in citrate aqueous solution by sodium borohydride and adsorption onto polyvinylpyrrolidone coated silica nanospheres. The size and structure of the nanocomposites were observed by light scattering measurement and scanning electron microscopy, respectively. Optical properties of the nanocomposites were determined by UV-visible absorption spectra.     

Fe-Ni/NiFe_2O_4纳米复合颗粒的制备与磁性研究

结合共沉淀法和氢气还原法成功制备出FeNi/NiFe2O4纳米复合颗粒,所制备的纳米复合颗粒包含NiFe2O4和Fe-Ni合金,其中Fe-Ni合金具有体心立方和面心立方两种结构。用XRD和TEM对所得样品进行结构分析。用SQUID测量样品在室温时的磁滞回线,发现Fe-Ni/NiFe2O4纳米复合颗粒的矫顽力和饱和磁化强度与制备态NiFe2O4纳米颗粒相比随着退火时间的增加呈现出逐渐增加的趋势。为了进一步研究所制备的纳米复合颗粒的磁性特征,测量退火时间相同而退火温度不同的两个样品在零磁场冷却(ZFC)和带磁场冷却(FC)条件下的M-T曲线。     

Facile photoreductive synthesis of silver nanoparticles for antimicrobial studies

In the present work, silver nanoparticles stabilized with L-Cysteine (L-Cys) were synthesized based on the one-pot green process by UV irradiation, in which L-Cysteine acts as biological capping agent. The composition and morphological characteristics of the L-Cys capped AgNPs has been ascertained by different techniques such as UV–vis, FL, XRD, TEM, EDX, FTIR and CD analysis. The results demonstrated the formation of spherical nanoparticles of pure Ag° coated with L-Cys. The antibacterial tests on L-Cys capped AgNPs were performed, exerting effective antimicrobial activity both against E. coli and S. aureus, with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 21.9 μg/mL and 175 μg/mL, respectively. Considering this simple and green process, the approach may facilitate new approaches to the manufacture of AgNPs-based antibacterial agent.     

Single-step synthesis of MWCNT/ZnO nanocomposite using co-chemical vapor deposition method

Single-step synthesis of MWCNT and ZnO nanocomposite was conducted by co-chemical vapor deposition method. Electron microscopic analysis revealed that the fabricated nanostructures consisted of MWCNTs with a diameter of 60-70 nm which were coated with ZnO nanoparticles with an average size of 20-30 nm. The growth of ZnO nanoparticles took place after the formation of MWCNTs. EDS and XRD analyses could confirm the high crystallinity of ZnO deposited on the MWCNT surface. In comparison with pristine MWCNTs and ZnO nanoparticles, the UV absorption of MWCNT/ZnO nanocomposite was changed through modification with ZnO nanoparticles.     

Functional properties of ceramic-Ag nanocomposite coatings produced by magnetron sputtering

In recent years, the use of nanocomposite materials to functionalize surfaces has been investigated, taking advantage of the complementary properties of the nanocomposite constituents. Among this family of materials, ceramic-Ag coatings have been widely studied due to the large variety of functionalities that silver possesses and the possibility of tuning the coating’s practical features by selecting the proper matrix to support this noble metal. Therefore, this review focuses on the effects of silver nanoparticles on the functional properties of ceramic-Ag nanocomposites. The chemistry, structure, morphology and topography of the coatings are analyzed with respect to the changes produced by the silver nanoparticles’ distribution, amount and sizes and by altering production process variables. To offer a clear understanding of the functionalities of these materials, the optical, electrical, mechanical, tribological, electrochemical and biological properties reported in the last decade are reviewed, focusing on the ability to tune such properties by modifying the silver distribution, morphology and composition. In particular, the surface plasmon resonance, self-lubricating ability and antibacterial effect of silver are covered in detail, establishing their correlation with factors such as silver diffusion, segregation and ionization.     

The preparation of Ag/mesoporous silica by direct silver reduction and Ag/functionalized mesoporous silica by in situ formation of adsorbed silver

Mesoporous silica (MS) with large pores and thiol functionalized mesoporous silica (TFMS) were synthesized. ²⁹Si MAS NMR confirmed the functionalization of MPTMS on the surface of mesoporous silica. Silver nanoparticles were prepared by two methods: (1) direct reduction of Ag⁺ ions with NaBH₄ in aqueous AgNO₃ solution containing MS, (2) in situ reduction of Ag⁺ ions adsorbed on TFMS with NaBH₄. The characteristics of products from both methods were compared using SAXRD, TEM, and N₂ adsorption-desorption. Ag nanoclusters were mostly confined and dispersed in the channels of the TFMS and their sizes were under 6 nm. However, Ag nanoparticles on the MS formed outside the mesoporous channels rather than within them.     

A simple method for the quantification of molecular decorations on silica particles

A simple, rapid quantitative approach to determining attachment density on silica nanoparticles has been demonstrated using attenuated total reflectance Fourier transform infrared spectroscopy and verified by thermogravimetric analysis. A very high attachment of approximately 5 attachments per nm² has been achieved through photoinduced thiol–ene click reaction of 11-bromo-1-undecene with a thiol functionalized silica nanoparticle formed from mercaptopropyltrimethoxysilane as the sole precursor. Attachment density with concentration of alkene and reaction time is shown to be highly nonlinear and appears to be limited by accessability of thiols on the surface of the particle. This method opens the opportunity to form nanoparticles with controlled functionality including multifunctional particles, which have been produced in this work.     

Facile route to preparation of positively charged GO using poly (diallyldimethylammoniumchloride)

Abstract

In the present study, positively charged graphene oxide (GO) was prepared by a simple method under mild reaction conditions. The samples were characterized via Zeta potential, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and Scanning electron microscope. The results showed that GO was successfully modified by Poly (diallyldimethylammoniumchloride) (PDDA). The obtained sample (PDDA-GO) still had a lamellar structure; however, it clearly presented wavy wrinkles appearance in the surface microscopy morphology. When the ratio of GO to PDDA was 1:13, the fabricated PDDA-GO sheets possessed a high positive charge value and a good dispersion in water. Also, to study the interaction between PDDA and GO in PDDA-GO, GTA modified GO was selected as a comparative experiment. The Fourier transform infrared spectroscopy, UV/vis spectroscopy, and Fluorescence spectroscopy results indicate that the π-π interactions played a leading role in the process of PDDA modified GO sheets. While the electrostatic interactions played an inferior role in the same process.     

Preparation of silica–silver heterogeneous nanocomposite particles by one-pot preparation strategy using polyol process: Size-controlled immobilization of silver nanoparticles

The size-controlled immobilization of silver nanoparticles onto the silica surface was carried out through one-pot process involving polyol process for the first time. Thiol groups were employed as a chemical protocol to make a binding bridge between silver nanoparticle and silica surface. The size of immobilized silver nanoparticles was controlled by reaction temperature and time at two different concentrations of silver nitrate: 1000 and 10,000 ppm. This one-pot process involving polyol process can simplify the conventional complex reaction process to control the size of immobilized metal nanoparticles. Also, this research can contribute to the immobilization of the other metals onto the inorganic supports and to the control of the size of immobilized metal particles.     

Complexes of Cu(II) with polyvinyl alcohol as precursors for the preparation of CuO/SiO<Subscript>2</Subscript> nanocomposites

Cupric oxide (CuO) nanoparticles have been prepared in amorphous SiO₂ matrix using a novel variant of sol-gel technique. The method is based on the polycondensation of a silica source (sodium silicate) in the presence of an aqueous solution containing complex of Cu(II) with polyvinyl alcohol (CuPVA). After gelation, polymeric complexes containing several thousands Cu atoms each are incorporated into the silica network forming a precursor, which is then annealed in oxygen to get rid of organic components. The formation of CuO nanoparticles was confirmed by electron diffraction studies. The size of nanoparticles can be controlled by varying [Cu²⁺]/[PVA] ratio in the precursor. Thus prepared CuO/SiO₂ nanocomposites are characterized by high specific surface area as measured by capillary adsorption of nitrogen, suggesting their possible use in catalysis. Received: 10 February 2000 / Reveiwed and accepted: 20 March 2000     

Synthesis of silver nanoparticles using N 1, N 2-diphenylbenzamidine by microwave irradiation method

Silver nanoparticles have been prepared under microwave irradiation from a solution of silver nitrate in the presence of N ¹,N ²-diphenylbenzamidine (DPBA) or simply amidine without any stabilizing agent. Different morphologies of silver colloids with charming colors could be obtained using N ¹,N ²-diphenylbenzamidine (DPBA). The structures of silver colloids were determined by TEM. UV-Vis spectroscopy was used to follow the reaction process and to characterize the optical properties of the resultant silver colloids. The influence of unconventional reducing agent on the morphology of silver was investigated.     

Optical and morphological characterisation of a silver nanoparticle/fluorescent poly(phenylenethynylene) composite for optical biosensors

Thiol silver nanoparticles prepared by the phase transfer method have been mixed with a fluorescent poly(phenylenethynylene) sequenced with dithioester-diethylsulfide moieties in order to develop a nanocomposite for its possible application in optical biosensors for the detection and attack of fungi such as Paecilomyces variotii. Films have been prepared by dipping technique and characterized by AFM, XPS, UV-Visible and fluorescence spectroscopy. Optical Absorption properties of the nanocomposite are similar to those of the polymer with an absorption tail in the visible which supports the presence of silver nanoparticles. Despite the lack of fluorescence of the nanoparticles, the composite emits in the yellow green region and the intensity of the fluorescence of the nanocomposite film decreases after the immersion in the culture thus permitting the detection of the fungus by this technique. The fungus can be deposited on films of both the polymer and nanocomposite, nevertheless only in the latter case, an attack on mycelium is observed revealing the fungicidal effect of silver nanoparticles in the nanocomposite.     

Facile preparation and electrochemical characterization of graphene/ZnO nanocomposite for supercapacitor applications

Graphene/ZnO nanocomposites were successfully synthesized by microwave-assisted method. The structure, morphology, optical and composition of the obtained samples were characterized using XRD, FT-IR, laser Raman, UV–Vis spectroscopy and XPS analysis. XRD analysis confirmed the presence of graphene/ZnO nanocomposite. FE-SEM image reveals that the homogenous distribution of ZnO nanoparticles on the graphene nanosheets. The electrochemical properties of the graphene/ZnO electrodes were analyzed by cyclic voltammetry and impedance spectroscopy. The results confirmed that the incorporation of ZnO nanoparticles enhanced the capacitive performance of graphene electrode. Graphene/ZnO nanocomposite electrode showed higher capacitance value of 109 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M KCl solution as compared to the graphene electrodes. These results demonstrated the importance and great potential of graphene based composites in the development of high-performance energy-storage systems.     

A new two-phase system for the preparation of nearly monodisperse silver nanoparticles

Nearly monodisperse silver nanoparticles were prepared in a two-phase water-cyclohexane system. Aqueous silver nitrate was reduced by the product of the reaction of aqueous hydrazine with benzyl aldehyde in cyclohexane to form, in the presence of oleic acid, cyclohexane-soluble silver nanoparticles. The silver nanoparticles were examined by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The nanoparticles are relatively monodisperse (diameter less than 6 nm) and have good stability in cyclohexane due to the oleic acid adsorbed on their surfaces. These silver nanoparticles were successfully assembled into a powder with a face-centered-cubic structure by slow evaporation of the solvent. With some change in particle size, these silver nanoparticles could be transferred from cyclohexane to water by the addition of cetyltrimethylammonium bromide.     

A Prussian blue route to nitrogen-doped graphene aerogels as efficient electrocatalysts for oxygen reduction with enhanced active site accessibility

Developing high-performance nonpredous-metal electrocatalysts for the oxygen reduction reaction (ORR) is crudal for a variety of renewable energy conversion and storage systems.Toward that end,rational catalyst design principles that lead to highly active catalytic centers and enhanced active site accessibility are undoubtedly of paramount importance.Here,we used Prussian blue nanoparticles to anchor Fe/Fe3C species to nitrogen-doped reduced graphene oxide aerogels as ORR catalysts.The strong interaction between nanosized Fe3C and the graphitic carbon shell led to synergistic effects in the ORR,and the protection of the carbon shell guaranteed stability of the catalyst.As a result,the aerogel electrocatalyst displayed outstanding activity in the ORR on par with the state-of-the-art Pt/C catalyst at the same mass loading in alkaline media,good performance in acidic media,and excellent stability and crossover tolerance that rivaled that of the best nonprecious-metal ORR electrocatalysts reported to date.