Electrochemical preparation and characterization of gold-polyaniline core-shell nanocomposites on highly oriented pyrolytic graphite

A simple electrochemical method for the in situ preparation of homogeneously dispersed gold-polyaniline core/shell nanocomposite particles with controlled size on the highly oriented pyrolytic graphite(HOPG)was demonstrated.The HOPG surface was modified preferentially by covalent bonding of a two-dimensional 4-aminophenyl monolayer employing diazonium chemistry.AuCl4 -ions were attached to the Ar-NH2 termination and reduced electrochemically.This results in the formation of Au nuclei that could be further grown into gold nanoparticles.The formation of polyaniline as the shell wrap of Au nanoparticle was established by localized electro-polymerization.These core-shell nanocomposites prepared were characterized by AFM and cyclic voltammetry.The results show that the gold-polyaniline core-shell composites on HOPG have a mean particle size of 100 nm in diameter and the polyaniline shell thickness is about 15 nm.     

In-situ chemical synthesis route for a fiber shaped gold-polyaniline nanocomposite

A facile synthesis route is described for the preparation of a gold-polyaniline nanocomposite material by polymerization of aniline hydrochloride using HAuCl4 as the oxidant. It was found that the oxidative polymerization of aniline hydrochloride leads to the formation of polyaniline with a fiber-like morphology, while the concomitant reduction of HAuCl₄ results in the formation of gold nanoparticles of diameter 2–7 nm. The gold nanoparticles were highly dispersed and stabilized throughout the polyaniline fibers while being in intimate contact with the polymer. The combination formed a uniform metal-polymer composite material.     

A novel formation process of polyaniline micro-/nanofiber network on solid substrates

By a chemical oxidative polymerization of aniline on solid substrates treated with Au nanoparticles (Au-NPs) deposition and 4-aminothiophenol (ATP) modification, polyaniline (PANI) fibers were obtained in micro-/nanosize with two-dimensional network structures. The observation by laser scanning microscopy (LSM) indicated that the formation of PANI fibrous network occurred during the drying process rather than the polymerization. It was suggested the ATP modification on Au-NPs deposited substrate resulted in an inhomogeneous grafting of solution-formed PANI on the solid substrates, which self-aggregated to the fibrous network structure with the evaporation of water due to interchain interactions. The influence of polymerization conditions on the formation of fibrous network and the conducting property of the prepared film were discussed. Results from the gas sensing of the as-prepared PANI sensor upon exposure to NH₃ confirmed that the sensitivity and responding rapidity was improved greatly by the PANI 2D fibrous network structure. Especially, a rapid response in resistance change on NH₃ with low concentration indicated that the developed method in this work can be used to fabricate highly sensitive PANI gas sensors.     

Fabrication and characteristics of spindle Fe2O3@Au core/shell particles

The fabrication and characteristics of spindle Fe2O3@Au core/shell particle were investigated, and the effect of the core/shell nanoparticles as the surface enhanced Raman spectroscopy (SERS)-active substrates was studied. By using the seed-catalyzed reduction technique, anisotropic Fe2O3@Au core/shell particles with spindle morphology were successfully prepared. The Fe2O3 particles with spindle morphology were initially prepared as original cores. The Au nanoparticles of 2 nm were attached onto the Fe2O3 particles through organosilane molecules. Uniform Au shell formed onto Fe2O3 core modified by Au nanoparticles through the in-situ reduction of HAuCl4. The shell thickness was controlled through regulating the concentration of HAuCl4 solution. The results of TEM, XRD and UV-vis characterization show that the core/shell particles with the original shape of the Fe2O3 particles are obtained and these surfaces are covered by Au shell completely. The surface enhanced Raman spectrum of the probe molecules adsorbed on these core/shell substrates is strong and the intensity is enhanced with the increase of the thickness of Au shell or the aspect ratio of particles. The spindle Fe2O3@Au core/shell particles exhibit optimum (SERS) activity.     

Gold nanoparticles–polyaniline composite material: Synthesis,structure and electrical properties

Gold nanoparticles–polyaniline composite materials were synthesised and their structure and electrical properties were analised. Different stabilizing agents were used resulting in the formation of nanoparticles with sizes within 5–10 nm. The best results were obtained when the composite material was obtained during the polymerization of the anilinium salt in the presence of the mixture composed by dodecyl benzene sulfonic acid and 2-mercaptoethanesulfonic acid stabilized gold nanoparticles. Electrical properties of this composite material demonstrated the formation of Schottky barriers between polyaniline and gold particles, an essential property for its use in bio-inspired complex information handling materials.     

Preparation and characterization of polyaniline nanoparticles synthesized from DBSA micellar solution

Chemical oxidative polymerization of aniline was performed in a micellar solution of dodecylbenzene sulfonic acid (DBSA, anionic surfactant) to obtain conductive nanoparticles with enhanced thermal stability and processability. DBSA was used to play both the roles of surfactant and dopant. The polymerization kinetics and optimum polymerization conditions were determined by UV–VIS spectra. The optimum molar ratio of oxidant to aniline was 0.5 and DBSA content was the most important factor in the formation of polyaniline (PANI) salt. The polymerization rate was increased with increasing DBSA concentration. The reaction model was proposed on the basis of the roles of DBSA. The electrical conductivity varied with the molar ratio of DBSA to aniline and the highest conductivity of particles was 24 S/cm. The layered structure due to PANI backbone separated by long alkyl chains of DBSA was observed and it seems to facilitate the electrical conduction. The doping level of particle was fairly high and was dependent on the preparative conditions. The average size of the PANI particles determined by Guinier plot of small-angle X-ray scattering (SAXS) measurement was 20–30 nm, which was well coincidence with scanning electron microscopy (SEM) results     

Synthesis and characterization of the core–shell Au covered LSMO manganite magnetic nanoparticles

In this work we report the synthesis and characterization of the nanomagnetic perovskite Sr manganites covered with Au shells having different thickness. La_2/3Sr_1/3MnO₃ (LSMO) manganite nanoparticles were first prepared by a sol–gel procedure. The LSMO manganite nanoparticles were chemically covered with gold to produce the core–shell samples. TEM, HRTEM and atomic emission spectroscopy techniques were used to determine the morphology and structure of the LSMO@Au nanoparticles. The bare LSMO nanoparticles have a mean diameter of around 4.4 nm while LSMO@Au nanoparticles have mean diameters between 7.15 and 4.8 nm depending on the gold quantity involved in the capping process. XRD studies show that both core and shell systems have the expected crystalline structure. The formation of the core–shell structure is sustained by the shift of the plasmon resonance wavelength maximum observed in the UV–vis absorbtion spectra of the LSMO@Au samples depending on the gold concentration. The magnetization versus applied magnetic field of the bare LSMO nanoparticles and LSMO@Au samples shows no hysteresis loop indicating the superparamagnetic behavior of these systems. The analysis of the temperature dependences of FC and ZFC magnetizations shows that for all the samples the axial anisotropy energy barriers are increased due to the magnetic dipolar interactions between neighbor nanoparticles.     

In-situ polymerized polyaniline films: 3. Film formation

Polyaniline films were produced on glass surface immersed in the reaction mixture during the oxidative polymerization of aniline. Glass supports placed in the reaction mixture at the start of the oxidation were gradually removed during the reaction. The thickness of polyaniline films produced on glass, assessed by optical absorption, was followed as a function of reaction time. The progress of polymerization was monitored by temperature changes. In another experiment, glass supports were successively inserted into the polymerization mixture. The formation of polyaniline films on glass, which had been already pre-coated with polyaniline, was also investigated. The proposed model of film formation is based on the concept of the primary and secondary nucleation. Oligoaniline cation radicals adsorbed on the glass surface nucleate the primary growth of polyaniline film, the secondary nucleation occurs on the produced polyaniline layer.     

Silk fibroin fibers supported with high density of gold nanoparticles: fabrication and application as catalyst

Silk fibroin (SF) fibers were modified with sulfonated polyaniline and, via an in situ redox technique, a high density of gold (Au) nanoparticles were supported directly on the surface of the fiber. The morphology, formation, and application of the as-prepared product, Au/SPANI-modified SF composite fiber, were investigated. By controlling the concentration of HAuCl₄, the density of Au nanoparticles on the composite fiber could be effectively adjusted. It is suggested that sulfonated polyaniline contributes to the generation of a high density of Au nanoparticles supported on the SF fibers. The composite fiber exhibited good activity when taking the reduction of p-nitrophenol as a model reaction.     

The structure change-induced morphology transition of polyaniline in 1.6-hexanediol aqueous and acid-free solutions: From submicron-spheres to nanofibers

This study shows that the polymerization of aniline monomers in 1.6-hexanediol aqueous and acid-free solutions can produce three-dimensional (3D) polyaniline submicron-spheres and one-dimensional (1D) nanofibers at different reaction stages through a morphology transition process. Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units in the initial reaction stage, producing polyaniline submicron-spheres with a diameter of ～400 nm. The hydrogen bonds between 1.6-hexanediol molecules and polyaniline chains serve as the driving force for the polyaniline chains to construct submicron-spheres. However, as the reaction proceeds, the solution acidity increases and the initially formed phenazine-like segments function as the nucleate for the free aniline monomers to polymerize through para-coupling linkage. This process forms polyaniline samples with a structure consisting of a core of phenazine-like units and a shell of para-linked units. In this stage, the newly formed para-linked aniline units exhibit an intrinsic tendency to transit the polyaniline morphology from submicron-spheres into nanofibers. These results indicate that a change in polyaniline structure during the polymerization process can produce different micro/nanostructures at different reaction stages. This finding provides a practical route for the further design and synthesis of different polyaniline micro/nanostructures.     

Photochemical synthesis of bimetallic Au-Ag nanoparticles with "core-shell" type structure by seed mediated catalytic growth

The colloidal Au core/Ag shell structure composite nanoparticles were synthesized in PEG-acetone solution by photochemical route. The monodispersed Au nanoparticles with average diameter of 3.9 nm were used as growth seeds. The optical property of colloids and the sizes of composite nanoparticles were characterized when the molar ratio of Au to Ag ranges from 4 : 1 to 1 : 4. The results show that a composite nanoparticle structure similar to strawberry shape is formed at the molar ratio of Au to Ag from 4 : 1 to 1 : 1; the composite nanoparticles consisting of a core of Au and shell of Ag were generated at the 1: 4 molar ratio, having a striking feature of forming interconnected network structure.     

Self-assembled necklace-like polyaniline nanochains from elliptical nanoparticles

High quality necklace-like polyaniline nanochains assembled by elliptical nanoparticles have been synthesized in chitosan aqueous solution by a facile dispersion polymerization method. The synthetic procedure is very simple and easy to scale up. The necklace-like nanochains coated by a layer of chitosan are typical doped polyaniline in its emeraldine salt form, which is easy to form stable polyaniline dispersion in water. Open-circuit potential measurements show that the rate of polymerization of aniline has a substantial decrease due to the steric effects of chitosan. The synthetic parameters, such as reaction times, and the concentrations of chitosan, aniline, and dopant acid, have profound influences on the sizes and morphologies of polyaniline nanostructures. A new self-assembly process of elliptical nanoparticles has been proposed for the formation of necklace-like polyaniline nanochains with fluctuant diameters, which is different from that of other one-dimensional polyaniline nanostructures including nanofibers and nanotubes.     

The polymerization of aniline in polystyrene latex particles

Polystyrene latex particles were swollen with aniline and subsequently exposed to ammonium peroxydisulfate solution. The polyaniline membrane was produced at the particle interface and separated both reactants. The electrons from aniline monomer are transferred to oxidant molecules through conducting polyaniline membrane. The aniline and peroxydisulfate thus react without the need to physically meet. Polyaniline gradually penetrated inside latex particle, in contrast to core–shell morphology obtained in classical coating of latex particles with polyaniline.     

Fabrication of modified-poly(divinylbenzene)/Au core–shell structure

A novel PDVB/Au core–shell structure was prepared by the chemical reduction of a gold–phenanthroline complex on the surface of a poly(divinylbenzene) (PDVB) cores (2–4 μm). The PDVB cores were synthesized by precipitation polymerization, and the surface was modified by introducing thiol and sulfonic acid groups. The modified surface structure was examined by FT-IR, XPS and EDS and the degree of sulfonation was measured according to its ion exchange capacity (IEC, 5.72 meq/g). The modified PDVB cores were immersed in a solution of a gold–phenanthroline complex and subsequently reduced to form gold nanoseeds. These were further grown in a solution of HAuCl₄ and NH₂OH to form gold nanoshells. The effects of the functional groups on the PDVB cores on fabrication of the core–shell structure were carefully examined. SEM and XPS were used to characterize the gold nanoshells. The presence of the functional groups could be of great assistance for the gold shell formation.     

Preparation of poly(N-vinylcarbazole) (PVK) nanoparticles by emulsion polymerization and PVK hollow particles

PVK nanoparticles were obtained by oil-in-water emulsion polymerization of N-vinylcarbazole (VCz). VCz is a white crystalline material with a melting point of 65 °C, which is an unsuitable monomer for conventional emulsion polymerization because of its crystallinity. However, we could successfully synthesize PVK nanoparticles by emulsion polymerization from VCz solution with organic solvent. And then, we found that the concentration of VCz influenced the particle size. PVK hollow particles were also obtained by etching of PMMA core from PMMA/PVK core–shell particles, and the size of a hollow particle was enlarged by two times compared with a core–shell particle due to the swelling process. PVK nanoparticles were probed by UV–vis absorption and fluorescence spectrometers, and hollow particles were characterized by FT-IR spectra. Both of them were confirmed by TEM, and the light-scattering instrument.     

Facile one-step route to polyaniline–silver nanocomposite particles and their application as a colored particulate emulsifier

Polyaniline–silver nanocomposites were synthesized in the form of colloidal particles by the facile one-step aqueous chemical oxidative dispersion polymerization of aniline using silver nitrate as an oxidant and poly(vinyl alcohol) as a colloidal stabilizer. Aniline monomer was oxidized by silver ions, yielding polyaniline and elemental Ag simultaneously. The synthesized nanocomposite particles were colloidally stable over 2 years and transmission electron microscopy studies indicated the production of spherical, plate and rod-shaped polyaniline–silver nanocomposite particles with a silver core–polyaniline shell morphology. The conductivity of a pressed pellet of the nanocomposite particles using the conventional four-point probe technique was 1.4 × 10^?2 S/cm at 25 °C. The nanocomposite particles behaved as a ‘colored’ particulate emulsifier for the stabilization of transparent oil-in-water emulsions.     

Fabrication and thermal degradation behavior of polystyrene nanoparticles coated with smooth polyaniline

Electrically conductive core–shell polyaniline/polystyrene (PAn/PS) nanoparticles were synthesized in the presence of different surfactants. PS core particles were prepared in microemulsion system and further coated with PAn by using in situ polymerization method. The core–shell structure of PAn/PS nanocomposite was determined by scanning electron microscopy (SEM) and FTIR measurement. Differential scanning calorimetry (DSC) and thermo gravimetric analyzer (TGA) were used to investigate the thermal stability and thermal degradation behavior of PS and PAn-coated PS particles. Both DSC and TGA curves revealed that the coating of a thin PAn layer on the surface of PS can drastically increase the thermal stability of PS matrix. TGA isothermal degradation data illustrate that the activation energy of the PAn/PS particle is larger than PS particle.     

Emulsion polymerization of aniline with ionic dispersants containing ionic poly(vinylpyridinium methanesulfonate) segments

Ionic polymer prepared from acid–base interaction between methanesulfonic acid (MSA) and poly(4-vinylpyridine) (P4VP) or poly(styrene-co-4-vinylpyridine) (PS-P4VP) was served as dispersant for the emulsion polymerization of aniline. Dependent on the dispersants (as P4VP(MSA) or PS-P4VP(MSA)) used, the maximum amounts of polyaniline incorporated without premature precipitation during polymerization are different. A 3 wt.% of aniline in relative to P4VP(MSA) dispersant resulted in precipitation during polymerization; however, the aniline/PS-P4VP(MSA) ratio can reach 10 wt.% without the undesired precipitation if PS-P4VP(MSA) was used as dispersant. The inner PS block in PS-P4VP(MSA) can serve as a stabilizer to prevent the expansion of the outer P4VP(MSA) block and provided a more stable micelle system as compared with the aniline/P4VP(MSA) system. Spherical particles of different sizes were observed in products of low polyaniline contents (<3 wt.%). With increasing polyaniline contents, the conductive polyaniline phases tended to aggregated and separated from the dispersant matrix.     

不同壳层厚度Au@SiO_2的表面增强拉曼效应

通过电偶置换反应制备了尺寸在30~35 nm的结晶性良好的Au纳米颗粒,并成功在其表面包覆了不同厚度的Si O2壳层,利用TEM、HRTEM和UV-Vis对样品的结构和形貌进行了表征,并以罗丹明6G(R6G)为探针分子,对Au@SiO_2复合粒子的表面增强拉曼散射(SERS)效应进行了研究。结果显示,相对于Au纳米颗粒,Au@SiO_2复合粒子显著提高了拉曼信号的质量和检测的灵敏度,且Si O2壳层厚度对其SRES效应影响显著,壳层厚度为2 nm的复合粒子对R6G分子的检测极限可达10~(-7)mol/L。     

Optical and electrical transport properties of polyaniline–silver nanocomposite

Polyaniline–silver nanocomposite has been synthesized successfully by the chemical oxidative polymerization of aniline with ammonium peroxydisulphate as an initiator in presence of negatively charged silver nanoparticles. Silver nanoparticles are prepared by standard citrate reduction method. TEM, SEM, XRD, FTIR, TGA, DSC, optical absorption and photoluminescence studies are done for the morphological, structural, thermal and optical characterization of the polyaniline nanocomposite. From the TEM and SEM image, it is observed that nanoparticles are well dispersed in the polyaniline matrix. XRD pattern shows that polyaniline is amorphous, but peaks present in XRD pattern in polymer nanocomposites are for silver nanoparticles. TGA and DSC results show that polyaniline silver nanocomposite is more crystalline and more thermally stable. A surface plasmon absorption band is obtained from the optical absorption at 380 nm, which indicates that silver nanoparticles are present in the polyaniline matrix. The optical band gap of nanocomposite decreases with increasing content of silver nanoparticles. An enhancement in photoluminescence has been observed in polyaniline–silver nanocomposite than that in pure polyaniline. The electrical conductivity of polyaniline–silver nanocomposite increases with increase in silver nanoparticle content than that of pure polyaniline. This is a simple way by which optical and electrical properties of polyaniline may be enhanced by doping with suitable nanoparticles.