Preparation and nanotribological properties of polyelectrolyte multilayers with in situ Au nanoparticles

Polyelectrolyte multilayers with in situ Au nanoparticles were prepared by alternate immersion of a substrate in poly(allylamine hydrochloride) (PAH)-AuCl₄⁻ complexes solution and poly(acrylic acid) solution for layer-by-layer self assemble process followed by reduction of the metal cations Au³⁺ through immersion into a fresh NaBH₄ solution. UV–vis spectrum, atomic force microscopy (AFM), X-ray photoelectron spectra (XPS), and transmission electron microscope (TEM) were used to confirm the construction of multilayers and synthesis of the Au nanoparticles. The nanotribological behaviors also have been studied using AFM. The polyelectrolyte multilayers with in situ Au nanoparticles exhibited a lower surface adhesion and friction force than the pure polyelectrolyte multilayers due to the nanoparticles improved the mutilayers surface structure and possess a good load-carrying capacity in nanoscale.     

Conjugated polymer mediated synthesis of nanoparticle clusters and core/shell nanoparticles

Two water soluble conjugated polymers, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ammonium ion stabilized poly(phenylene vinylene) (P2), are found to be able to reduce noble metal ions to zero-valent metals via a direct chemical deposition technique. Au nanoparticle clusters can be obtained through reduction of Au³⁺ ions by PEDOT:PSS and the electronic coupling between them can be controlled by HAuCl₄ concentration. Core/shell Ag/polymer nanostructures are prepared from reduction of Ag⁺ ions by P2, which have a ppb detection limit for 4-MBA using surface-enhanced Raman spectroscopy (SERS). This conjugated polymer mediated synthesis of metal nanoparticles may open a new avenue for fabricating nanomaterials and nanocomposites with tunable optical properties that are dominated by their structure and electronic coupling between nanoparticles.     

Biological synthesis of bimetallic Au/Ag nanoparticles using Persimmon (<Emphasis Type="Italic">Diopyros kaki</Emphasis>) leaf extract

Persimmon (Diopyros kaki) leaf extract was used for the synthesis of bimetallic Au/Ag nanoparticles. Competitive reduction of Au³⁺ and Ag⁺ ions present simultaneously in solution during exposure to Persimmon leaf extract leads to the formation of bimetallic Au/Ag nanoparticles. UV-visible spectroscopy was monitored as a function of reaction time to follow the formation of Au/Ag nanoparticles. The synthesized bimetallic Au/Ag nanoparticles were characterized with energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM images showed that large Au/Ag particles of 50–500 nm were formed with some cubic structure, while pure Ag particles obtained by reduction of only Ag+ ion were smaller with diameter of 15–90 nm and predominantly spherical. The atomic Ag contents of the bimetallic Au/Ag nanoparticles from EDS and XPS analysis were 36 and 71 wt%, respectively, suggesting that bimetallic Au core/Ag shell structure was formed by competitive reduction of Au³⁺ and Ag+ ions with Persimmon leaf extract. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.     

Polyhydrosilane Mediated Synthesis of One-Dimensional Gold Nanostructures

This work presents a solution-phase approach for the “one pot” synthesis of polysilane-gold nanorods. The process starts by the reduction of HAuCl₄ to Au^o with a solution of poly[diphenylsilane-co-methyl(H)silane] cooled to 4 °C. The formed small Au nanoparticles (5–15 nm diameter) serve further as seeds for the heterogeneous nucleation and anisotropic growth that takes place at 25 °C and yields crystalline needle-like polymer–gold nanostructures. The evolution of the small spherical nanoparticles to nanorods with length/width aspect ratios up to 10³ has been proved by UV–Vis spectroscopy, polarized light microscopy and AFM. Further insights on the growth mechanism were obtained by SEM, DLS and TEM.     

Dispersing multi-walled carbon nanotubes with water-soluble block copolymers and their use as supports for metal nanoparticles

Oxidized multi-walled carbon nanotubes (MWCNTs) were dispersed in aqueous and organic solvents by non-covalent modification with a double-hydrophilic block copolymer, poly(ethylene oxide)-b-poly [2-(N,N-dimethylamino)ethyl methacrylate] (PEO-b-PDMA). The PDMA segments were anchored onto the surface of the oxidized MWCNTs through multi-site zwitterionic interactions between the amino and the carboxyl groups while the PEO segments formed corona to promote the solubility of MWCNTs in different solvents. FT-IR and ¹H NMR spectroscopy gave structural information on the resulting composite, supporting the successful modification. Thermal gravimetric analysis showed that the grafting yield could reach 26%. UV/vis and transmission electron microscopy provided direct evidence for the individual dispersion. The resulting modified MWCNTs could find broad spectrum of applications. As an example, Au and Pt nanoparticles were attached on the sidewall of the modified MWCNTs by using the amino groups of PDMA segments.     

Micelles of polyisobutylene-block-poly(methacrylic acid) diblock copolymers and their water-soluble interpolyelectrolyte complexes formed with quaternized poly(4-vinylpyridine)

The micellization of ionic amphiphilic diblock copolymers, polyisobutylene-block-poly(methacrylic acid) (PIB-b-PMAA), with a constant degree of polymerization of the non-ionic block and various degrees of polymerization of the polyelectrolyte block was examined in aqueous media by means of fluorescence spectroscopy using pyrene as a polarity probe. The molar values of the critical micellization concentration (cmc) were found to be around 2×10⁻⁶ mol/l, being nearly independent of the length of the polyelectrolyte block as well as pH (in the range 6-9) and ionic strength (≤0.5 M NaCl) while the specific cmc values varied from 20 to 100 mg/l. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) experiments provided evidence that aggregation numbers and hydrodynamic radii of the formed copolymer micelles are sensitive to variations of pH and ionic strength, indicating that these micelles might be ‘dynamic’ rather than ‘frozen’ ones. It was also shown by means of a combination of turbidimetry, analytical ultracentrifugation, fluorescence spectroscopy, SANS, and DLS that the formed copolymer micelles mixed with a strong cationic polyelectrolyte, poly(N-ethyl-4-vinylpyridinium bromide) at charge ratio Z=[+]/[−] not exceeding a certain critical value Z_M<1, generate peculiar water-soluble micellar complex onion-like species, each containing a two-phase hydrophobic nucleus and a hydrophilic corona. The nucleus consists of a PIB core and a shell assembled from the fragments of water-insoluble interpolyelectrolyte complex. The corona is formed by the excess fragments of poly(sodium methacrylate) blocks not involved in complexation with poly(N-ethyl-4-vinylpyridinium bromide).     

The role of cationic Au and nonionic Au species in the low-temperature water–gas shift reaction on Au/CeO2 catalysts

The roles of cationic and nonionic Au species in the water–gas shift (WGS) reaction on Au/CeO₂ catalysts were studied by comparing the reaction behavior of a cyanide leached catalyst, after removal of the Au nanoparticles by cyanide leaching, with that of non-leached catalysts, following the technique introduced by Q. Fu et al. [Science 301 (2003) 935]. Using rate measurements as well as in situ spectroscopic and structure-sensitive techniques, we found that based on the Au mass balance, cyanide leaching removed all Au except for ionic Au³⁺ species, and that leaching resulted in a pronounced decay of the catalyst mass normalized activity to 1–25% of that of a non-leached catalyst. The extent of the activity loss strongly depended on the post-treatment of the leached catalyst. Both the catalyst treatment after leaching and, in particular, the WGS reaction resulted in considerable reformation of Au⁰ species by thermal decomposition of Au oxides (Au³⁺) and subsequent nucleation and growth of very small Au⁰ aggregates and metallic Au⁰ nanoparticles, as indicated by Au(4f) signals at 85.9 eV (Au³⁺), 84.0–84.6 eV (up-shifted signal of small Au⁰ aggregates), and 84.0 eV (metallic Au⁰). In this work, correlations between ionic and nonionic Au species and between total WGS activity and activity for the formation/decomposition of bidentate formate species are evaluated, and the role of the respective Au species in the WGS reaction on Au/CeO₂ catalysts is discussed.     

Polyelectrolytes with sulfonate groups obtained by chemical modification of chitosan useful in green synthesis of Au and Ag nanoparticles

Usually the metal nanoparticles are obtained by different chemical reactions that are not environmentally friendly. This paper describes the synthesis of two polyelectrolytes with sulfonate groups in ortho‐position and in ortho‐ and para‐positions, which were obtained by chemical modification of chitosan. They were used in the green synthesis of Au and Ag nanoparticles by colloidal method in aqueous solution. Polyelectrolytes were used as reducing agents of Au³⁺ and Ag⁺ ions and as stabilizing agents of Ag and Au nanoparticles. The hydroxyl and imine groups in the polyelectrolytes are reducing agents of Au³⁺ and Ag⁺ ions while the sulfonate groups and the polymer backbone stabilized Au and Ag nanoparticles. Polyelectrolyte 1, which has sulfonate group in ortho‐position, favors the obtaining of anisotropic Au nanoparticles with an average size of 19 nm. While the polyelectrolyte 2, with two sulfonate groups in the ortho‐ and para‐positions, yielded quasi‐spherical Au nanoparticles with an average size of 14 nm. In general, Ag nanoparticles stabilized with both polyelectrolytes, show quasi‐spherical forms with good control in size. Finally, both polyelectrolytes have the ability to protect the Au and Ag nanoparticles allowing obtaining colloidal solutions that are stable for several months. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45240.     

Development and characterisation of a novel composite electrode material consisting of poly(3,4-ethylenedioxythiophene) including Au nanoparticles

Composite material consisting of poly(3,4-ethylenedioxythiophene) (PEDOT), including Au nanoparticles encapsulated by N-dodecyl-N,N-dimethyl-3-ammonium-1-propanesulphonate (SB12) is synthesised by constant-current method on ITO glass, in aqueous medium, leading to an electrode coating. The synthesis process is followed by UV-vis spectroelectrochemistry, both in normal-beam and in parallel-beam configurations. Under the same experimental conditions PEDOT is also synthesised by electropolymerisation only in the presence of LiClO₄ supporting electrolyte, as well in solutions also containing SB12. The data relative to the electrosynthesis of the three materials are compared. The composite material based on the conductive polymer matrix including Au nanoparticles has been characterised by SEM, TEM, ICP, Raman and UV-vis spectroscopies. The behaviour of the three different electrode coatings with respect to p-doping process has been studied by conventional electrochemical techniques and by potentiostatic and potentiodynamic UV-vis spectroelectrochemical methods. Conclusions are drawn out about the effect of the presence of the surfactant and of Au nanoparticles on the electrochemical properties of the electrode system.     

Polyelectrolytes with sulfonic acid groups useful in the synthesis and stabilization of Au and Ag nanoparticles

Two novel polyelectrolytes were obtained by chemical modification of poly(4-acryloyloxybenzaldehyde) using o- and p-aminophenylsulfonic acid, the characterization shows a chemical modification of 24.38 and 63.33%, respectively. The study shows that the polyelectrolyte with sulfonic acid in para position reduces metal ions more rapidly than polyelectrolyte in ortho position. The obtained nanoparticles of Au and Ag were characterized by ultraviolet–visible absorption spectroscopy (UV–vis) and transmission electron microscopy. The results showed that these ionic polymers are not only capable of reducing gold and silver ions, but also can stabilize the nanoparticles in the colloidal solutions. With these polymers, the process of metallic ions reduction is very slow and they lead to the production of Au and Ag nanoparticles with quasi-spherical shapes which are stable in colloidal solutions for several months. The advantage of the method used here is that the reduction can be realized in water at room temperature.     

Water-soluble polyelectrolyte complexes formed by poly(diallyldimethylammonium chloride) and poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly(N,N-dimethylacrylamide) copolymers

The formation of polyelectrolyte complexes (PECs) between the cationic homopolymer poly(diallyldimethylammonium chloride) (PDADMAC) and the anionic graft copolymers poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly(N,N-dimethylacrylamide) (P(NaA-co-NaAMPS)-g-PDMAM) was studied in aqueous solution in comparison with the PECs formed between PDADMAC and the graft copolymer backbone poly(sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate). The turbidimetric study of the PECs formed revealed that associative phase separation is prevented when the anionic polyelectrolyte is grafted with the nonionic hydrophilic poly(N,N-dimethylacrylamide) side chains. The PECs are formed through a charge neutralisation process and they adopt a compact structure, as shown by conductivity and viscometry measurements respectively. The water-insoluble PEC core seems to be stabilised by a hydrophilic PDMAM corona, leading to the formation of nanoparticles with a hydrodynamic radius of some decades of nanometers as determined by quasi-elastic light scattering measurements.     

Preparation and electrochemical properties of gold nanoparticles containing carbon nanotubes-polyelectrolyte multilayer thin films

Multi-walled carbon nanotubes (MWCNT)/polyelectrolyte (PE) hybrid thin films were fabricated by alternatively depositing negatively charged MWCNT and positively charged (diallyldimethylammonium chloride) (PDDA) via layer-by-layer (LbL) assembly technique. The stepwise growth of the multilayer films of MWCNT and PDDA was characterized by UV–vis spectroscopy. Scanning electron microscopy (SEM) images indicated that the MWCNT were uniformly embedded in the film to form a network and the coverage density of MWCNT increased with layer number. Au nanoparticles (NPs) could be further adsorbed onto the film to form PE/MWCNT/Au NPs composite films. The electron transfer behaviour of multilayer films with different compositions were studied by cyclic voltammetry using [Fe(CN)₆]^3−/4− as an electrochemical probe. The results indicated that the incorporation of MWCNT and Au NPs not only greatly improved the electronic conductivity of pure polyelectrolyte films, but also provided excellent electrocatalytic activity towards the oxidation of nitric oxide (NO).     

Synthesis and Microstructural Investigations of Organometallic Pd(II) Thiol-Gold Nanoparticles Hybrids

In this work the synthesis and characterization of gold nanoparticles functionalized by a novel thiol-organometallic complex containing Pd(II) centers is presented. Pd(II) thiol, trans, trans-[dithiolate-dibis(tributylphosphine)dipalladium(II)-4,4′-diethynylbiphenyl] was synthesized and linked to Au nanoparticles by the chemical reduction of a metal salt precursor. The new hybrid made of organometallic Pd(II) thiol-gold nanoparticles, shows through a single S bridge a direct link between Pd(II) and Au nanoparticles. The size-control of the Au nanoparticles (diameter range 2–10 nm) was achieved by choosing the suitable AuCl₄ ⁻/thiol molar ratio. The size, strain, shape, and crystalline structure of these functionalized nanoparticles were determined by a full-pattern X-ray powder diffraction analysis, high-resolution TEM, and X-ray photoelectron spectroscopy. Photoluminescence spectroscopy measurements of the hybrid system show emission peaks at 418 and 440 nm. The hybrid was exposed to gaseous NO _x with the aim to evaluate the suitability for applications in sensor devices; XPS measurements permitted to ascertain and investigate the hybrid –gas interaction.     

Biofabrication of gold nanoparticles and its biocompatibility in human breast adenocarcinoma cells (MCF-7)

In this paper, a simple and environmentally friendly method for synthesis of gold nanoparticles (AuNPs) using culture supernatant of Bacillus flexus as reductants and stabilizers is reported. The prepared AuNPs were characterized by various analytical techniques. UV–visible spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) results confirmed that Au³⁺ ions reduced into Au⁰. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the chemical surface structure of AuNPs. TEM images showed the size and morphology of AuNPs. Moreover, the toxicity studies suggested that AuNPs were neither toxic nor inhibitory to human breast cancer cells (MCF-7).     

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) (PAA-PS-PIB-PS-PAA) block copolymers were prepared using a combination of quasiliving carbocationic and atom transfer radical polymerization (ATRP) techniques. Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymer macroinitiators with targeted molecular weights and high degrees of chain end functionality (F_n>1.7) were prepared by quasiliving carbocationic polymerization of isobutylene followed by sequential addition of styrene. Poly(tert-butyl acrylate-b-styrene-b-isobutylene-b-styrene-b-tert-butyl acrylate) (PtBA-PS-PIB-PS-PtBA) pentablock terpolymers with targeted molecular weights and low polydispersities (PDIs) were synthesized from the PS-PIB-PS macroinitiators via ATRP of tBA using either a Cu(I)Cl/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2-(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. Deprotection of the tert-butyl groups using trifluoroacetic acid at 25 °C resulted in the formation of PAA-PS-PIB-PS-PAA pentablock terpolymers. Comonomer composition of the final terpolymers, determined by ¹H-NMR spectroscopy, was very close to theoretical.     

Characterization of Au/MnO x /TiO2 for Photocatalytic Oxidation of Carbon Monoxide

The Au/MnO _x /TiO₂ catalyst was used for the photocatalytic oxidation of carbon monoxide. The catalytic activity of Au/MnO _x /TiO₂ with low concentration of manganese (3–7 mol%) was much higher than that of Au/TiO₂. The surface of Au/MnO _x /TiO₂ was characterized by XPS and Raman spectroscopy. While the main state of manganese in 13.8 mol% MnO _x /TiO₂ was Mn⁴⁺ species, Mn³⁺ was the dominant species in the samples with below 6.5 mol% manganese. Raman spectroscopy revealed that the interaction between the MnO _x and TiO₂ form Mn–O–Ti species in which the state of manganese was Mn³⁺. The Au particles also interacted with both MnO _x and TiO₂ to modify the surface of them. In the case of the Au species, low loading of manganese produced the metallic Au⁰ and perimeter interfacial Au^δ+, whereas high loading showed the coexistence of three components which were metallic Au⁰, perimeter interfacial Au^δ+, and oxidic Au³⁺. The catalytic active component was the metallic Au⁰ and perimeter interfacial Au^δ+ species, which were dispersed on TiO₂ and Mn³⁺/TiO₂.     

Colloidal gel from amphiphilic heteroarm polyelectrolyte stars in aqueous media

We report on the gelation capability of polystyrene/poly(2-vinyl pyridine) amphiphilic heteroarm polyelectrolyte stars in acidic salt-free aqueous media. The star polymers associate through hydrophobic interactions, by retraction of the stretched arms under no interdigitation conditions, in the dilute regime forming colloidal soft nanoparticles comprising about 6 stars, At concentrations significantly higher than the hydrodynamic overlap concentration (c > 40c^∗), the crowding of the colloidal nanoparticles drives a jamming transition, leading to a colloidal gel. The intermediate overlap regime (c^∗ < c < 40c^∗) is characterized by a significant compaction of the polyelectrolyte entities prior interdigitation and jamming.     

Synthesis of pH‐ and temperature‐responsive chitosan‐graft‐poly[2‐(N,N‐dimethylamino) ethyl methacrylate] copolymer and gold nanoparticle stabilization by its micelles

Novel pH‐ and temperature‐responsive chitosan‐graft‐poly[2‐(N,N‐dimethylamino)ethyl methacrylate] (chitosan‐g‐PDMAEMA) copolymers were successfully synthesized by homogeneous atom transfer radical polymerization (ATRP) under mild conditions. Chitosan macroinitiator was prepared by phthaloylation of amino groups of chitosan and subsequent acylation of hydroxyl groups of chitosan with 2‐bromoisobutyryl bromide. The copolymers were obtained by ATRP of 2‐(N,N‐dimethylamino)ethyl methacrylate and they can self‐assemble into stable micelles in water. Hybrid micelles with a PDMAEMA corona incorporating gold nanoparticles (Au NPs) were prepared in situ via the reduction of HAuCl₄ with NaBH₄. The pH and temperature responses of the copolymer micelles and hybrid micelles were characterized using UV‐visible spectroscopy and dynamic laser light scattering. The morphology of the micelles was observed using transmission electron microscopy and atomic force microscopy. The PDMAEMA corona of the micelles acts as the ‘nanoreactor’ and the ‘anchor’ for the in situ formation and stabilization of Au NPs. Therefore, the spatial distribution of Au NPs within the micelles can be tuned by varying the temperature and pH value. Copyright © 2010 Society of Chemical Industry     

Poly(N-tert-butyl acrylamide-b-N-acryloylmorpholine) amphiphilic block copolymers via RAFT polymerization: Synthesis, purification and characterization

Amphiphilic block copolymers consisting of two poly(acrylamide) derivative blocks have been synthesized via the reversible addition fragmentation chain transfer (RAFT) polymerization process with a hydrophobic block, poly(N-tert-butyl acrylamide), poly(TBAm), and a non-ionic hydrophilic one, poly(N-acryloylmorpholine), poly(NAM). Both polymerization orders, poly(TBAm-b-NAM) and poly(NAM-b-TBAm), were compared in terms of conversion and control over molecular weights (MW). Purification of the block copolymers was carried out via several methods in order to optimize their subsequent characterization. ¹H NMR analysis resulted in an accurate determination of the second block MW whereas determination of the CMC by the pendant drop method confirmed the ability of the poly(TBAm-b-NAM) block copolymers to self-assemble into micelles in aqueous phase.     

Design of novel poly(methyl vinyl ether) containing AB and ABC block copolymers by the dual initiator strategy

A new set of block copolymers containing poly(methyl vinyl ether) (PMVE) on one hand and poly(tert-butyl acrylate), poly(acrylic acid), poly(methyl acrylate) or polystyrene on the other hand, have been prepared by the use of a novel dual initiator 2-bromo-(3,3-diethoxy-propyl)-2-methylpropanoate. The dual initiator has been applied in a sequential process to prepare well-defined block copolymers of poly(methyl vinyl ether) (PMVE) and hydrolizable poly(tert-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA) or polystyrene (PS) by living cationic polymerization and atom transfer radical polymerization (ATRP), respectively. In a first step, the Br and acetal end groups of the dual initiator have been used to generate well-defined homopolymers by ATRP (resulting in polymers with remaining acetal function) and living cationic polymerization (PMVE with pendant Br end group), respectively. In a second step, those acetal functionalized polymers and PMVE-Br homopolymers have been used as macroinitiators for the preparation of PMVE-containing block copolymers. After hydrolysis of the tert-butyl groups in the PMVE-b-ptBA block copolymer, PMVE-b-poly(acrylic acid) (PMVE-b-PAA) is obtained. Chain extension of the AB diblock copolymers by ATRP gives rise to ABC triblock copolymers. The polymers have been characterized by MALDI-TOF, GPC and ¹H NMR.