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.     

Synthesis and stabilization of Au nanoparticles in colloidal solution using macroelectrolytes with sulfonic acid groups

Metal nanoparticles are obtained by different chemical reactions using reducing agents that are not environmentally friendly. This work report the synthesis of Au nanoparticles in colloidal solution using three monodisperse macroelectrolytes, with peripheral sulfonic acid groups bonded covalently, without toxic reducing agents. During the synthesis of Au nanoparticles were used the new macroelectrolytes as reducing and stabilizing agents in aqueous solution or ethylene glycol. The macroelectrolytes were synthesized using hexachlorocyclotriphosphazene as core, and o‐ or p‐aminobenzenesulfonic acid, obtaining acid macroelectrolytes with two and six sulfonic acid groups in ortho‐ position, and four sulfonic acid groups in para‐ position. The ultraviolet–visible (UV–vis) absorption spectroscopy and transmission electron microscopy study show that the macroelectrolytes with sulfonic acid groups in ortho‐ position are reducing agents for Au⁺⁺⁺ ions in colloidal solution and produced Au nanoparticles with anisotropic shapes, such as decahedrons and prisms. The macroelectrolyte with sulfonic acid groups in para‐ position is reducing agent for Au⁺⁺⁺ and produces quasispherical Au nanoparticles with sizes between 8 and 40 nm. The colloidal solutions with Au nanoparticles were stable by several months due to the protection of imine and sulfonic groups of macroelectrolytes on the Au nanoparticles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45888.     

Polyelectrolytes with tetrazole pendant groups useful in the stabilization of Au and Ag nanoparticles

Stabilization of metallic nanoparticles is a challenge of enormous dimensions because the nanosize nanoparticles are not stable by themselves and therefore they tend to coalesce, forming large agglomerates causing the loss of the properties of individual nanoparticles. In this work, we report the synthesis of polyelectrolytes with tetrazole groups useful as stabilizing agents of Au and Ag nanoparticles. The polyelectrolytes with tetrazole groups were synthetized from the appropriate starting materials with nitrile groups, which were successfully converted to the corresponding 1H‐tetrazole rings using 1,3‐dipolar cycloaddition with ammonium azide. These new materials were characterized by NMR and FT‐IR techniques and they were used for the stabilization of Au and Ag colloidal nanoparticles at room temperature, using sodium borohydride as reducing agent. Formation and stabilization processes of the nanoparticles were monitored by UV‐vis spectroscopy. Shape and size of nanoparticles were studied by TEM. The polyelectrolytes with tetrazole pendant group are suitable materials for synthesis and stabilization of gold nanoparticles, obtaining average sizes lower than 10 nm. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43773.     

Polymer mediated formation of corona-embedded gold nanoparticles in block polyelectrolyte micelles

Micelles having a hydrophobic core of poly(tert-butylstyrene) and a hydrophilic corona of poly(sodium sulfamate/carboxylate-isoprene) anionic polyelectrolyte, were formed through self-assembly of the diblock copolymer poly[tert-butylstyrene-b-sodium (sulfamate/carboxylate-isoprene)] (BS-SCI) in water. HAuCl₄, as the metal precursor, was preferentially dissolved and coordinated into the corona of the micelles. Au nanoparticles were formed within the corona block by subsequent reduction of Au³⁺ to Au⁰ without introducing any reducing agent, since the amine group of the corona block acts as both the reducing and stabilizing agent. The kinetics of the Au reduction reaction was followed by UV-vis spectroscopy by direct observation of the exact position and the intensity of the surface plasmon resonance band of created Au nanoparticles. The colloidal stability and structural response of the BS-SCI/Au nanohybrid was studied as a function of pH, ionic strength and temperature by dynamic light scattering (DLS). Additional information on the structure of the hybrid systems and the metal nanoparticle characteristics were gathered by UV-vis spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). Taking into account the polyelectrolyte nature and biocompatibility of the SCI corona of the BS-SCI/Au nanoassembly, the interactions with a model globular protein (lysozyme) were investigated, aiming at exploring the potential application of such hybrid colloids in protein assay protocols.     

Polyelectrolytes based on poly(<Emphasis Type="Italic">p</Emphasis>-acryloyloxybenzaldehyde) with arsonic acid groups useful in the colloidal synthesis of silver nanoparticles

Several methods have been developed for synthesis of Ag nanoparticles. However, Ag nanoparticles are unstable materials, and they tend to agglomerate losing their properties. Polymers are commonly employed for the stabilization of Ag nanoparticles in colloidal solutions. Polymers with ionic groups such polyelectrolytes can stabilize metallic nanoparticles through electrostatic and steric effects. In this work we employed poly(p-acryloyloxybenzaldehyde) and their derivates containing arsonic acid groups in ortho and para positions as reducing and stabilizing agents in the synthesis of Ag nanoparticles. Polyelectrolytes containing arsonic acid groups in ortho position were better reducing agents than the poly(p-acryloyloxybenzaldehyde) and the polyelectrolyte with arsonic acid group in para position, leading to the reduction of Ag⁺ ions in short reaction time. The polyelectrolyte with arsonic acid groups in para position was the best stabilizing agent leading to obtaining Ag nanoparticles with the smallest average size.     

Size-Controlled Synthesis of Colloidal Gold Nanoparticles at Room Temperature Under the Influence of Glow Discharge

Highly dispersed colloidal gold (Au) nanoparticles were synthesized at room temperature using glow discharge plasma within only 5 min. The prepared Au colloids were characterized with UV–visible absorption spectra (UV–vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) equipped with an energy dispersion X-ray spectrometer (EDX). UV–vis, XPS and EDX results confirmed that Au³⁺ ions in HAuCl₄ solution could be effectively reduced into the metallic state at room temperature with the glow discharge plasma. TEM images showed that Au nanoparticles were highly dispersed. The size of colloidal Au nanoparticles could be easily tuned in the nanometer range by adjusting the initial concentration of HAuCl₄ solution. Moreover, the as-synthesized Au colloids (d _av = 3.64 nm) exhibited good catalytic activity for glucose oxidation. The nucleation and growth of colloidal Au particles under the influence of the plasma was closely related with the high-energy electrons generated by glow discharge plasma.     

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.     

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.     

ETS-10 Supported Au Nanoparticles for Solvent-Free Oxidation of 1-Phenylethanol with Oxygen

Abstract  

Au nanoparticles (NPs) were uniformly dispersed on ETS-10 titanosilicate using the cation exchange procedure and [Au(NH₃)₄](NO₃)₃ complex as the gold source. [Au(NH₃)₄]³⁺ cations were first introduced inside ETS-10 micropores, ligands were then released, Au³⁺ was reduced to Au⁺ forming electron-deficient Au clusters, and finally aggregation to Au NPs occurred. In comparison to the incipient-wetness and deposition–precipitation methods, the ion-exchange led to greater activity of the Au NPs in the oxidation of 1-phenylethanol by oxygen.     

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.     

Fabrication of polyoxometallate-modified gold nanoparticles and their utilization as supports for dispersed platinum in electrocatalysis

The usefulness of Keggin-type anions (PMo₁₂O₄₀³⁻) as both reducing, capping and activating agents during synthesis of polyoxometallate-modified gold nanoparticles is demonstrated here. Fabrication of gold nanoparticles stabilized with monolayer-type films of inorganic polyoxometallates (e.g. phosphododecamolybdates), Au-PMo₁₂, was achieved by treating an aqueous solution of gold precursor (HAuCl₄) with a solution of the partially reduced heteropolyblue molybdate. The choice of temperature strongly affected morphology and size of the resulting Au nanoparticles. The presence of strongly adsorbed molybdate-agents on surfaces of gold nanoparticles was evident from the independent infrared (FTIR by reflectance) and voltammetric experiments. Interfacial polymolybdate anions on Au prevent the particle agglomeration and support formation of the stable colloidal Au-PMo₁₂ solutions. They are colored due to existence of the plasmonic effect. The Au-PMo₁₂ nanoparticles typically had 30–40 nm diameters, and they were used as supports or carriers for dispersed catalytic platinum nanoparticles (of ca. 7–8 nm diameters). Polyoxometallates (PMo₁₂O₄₀³⁻) existing on gold surfaces could also interact with neighboring platinum centers thus acting as “linking” agents facilitating dispersion of Pt nanoparticles. Further, the phosphomolybdate adsorbates (on Au supports) are also likely to activate Pt sites (e.g. by providing reactive hydroxy groups) towards more efficient electrocatalytic oxidation of ethanol both under voltammetric and chronoamperometric conditions.     

Selective reduction of aromatic nitro compounds over recyclable hollow fiber membrane‐supported Au nanoparticles

Guanidylated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (GPPO) hollow fiber membrane (HFM) supported Au nanoparticles are prepared by a simple adsorption‐reduction of Au³⁺ with sodium borohydride as a reducing agent and polyvinyl pyrrolidone as a dispersant. The novel heterogeneous catalyst shows high catalytic activity for the reduction of various aromatic nitro compounds in an aqueous medium at room temperature and can be easily reused for several runs, for example, for the reduction of nitrobenzene, the yield reaches up to 92% even after 10 cycles, indicating the potential application of GPPO HFM as a catalysts support material for sustainable chemistry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41268     

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.     

Powder XRD analysis and catalysis characterization of ultra-small gold nanoparticles deposited on titania-modified SBA-15

Ultra-small gold nanoparticles (0.8–1 nm) are successfully deposited on titania-modified SBA-15 via a deposition–precipitation method. A comparison of experimental X-ray diffraction (XRD) patterns with theoretical ones shows that gold exists as Au³⁺ and Au⁰ in the as-synthesized and reduced catalyst, respectively. The XRD analyses also suggest that Au nanoparticles are more developed along the 〈1 1 1〉 direction forming a raft-type structure. Z-contrast transmission electron microscopy analyses indicate that the ultra-small gold nanoparticles are uniformly dispersed on the surface of the substrate. The material is found to possess high catalytic activity for low-temperature CO oxidation.     

Enhanced carbon monoxide oxidation activity over gold–ceria nanocomposites

The composites with nanosized gold loaded in nanoporous ceria were prepared on a large scale by a facial and environment-benign sol–gel process. These materials were characterized by XRD, ICP, BET, UV–vis absorption, XPS, HRTEM and EDX. The main factors such as size and surface state of the Au and defect in the ceria could be adjusted by acid treatment of the composites in ascorbic acid solution to improve the activity and decrease the content of noble metal Au in the materials. Enhanced catalytic activities were obtained for the CO oxidation reaction over the catalysts due to the small crystal sizes with narrow size distributions of gold nanoparticles, a large amount of defects in the nanoporous ceria support, as well as a high ratio of Au³⁺/Au⁰ in the nanocomposites.     

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.     

Enhanced carbon monoxide oxidation activity over gold–ceria nanocomposites

The composites with nanosized gold loaded in nanoporous ceria were prepared on a large scale by a facial and environment-benign sol–gel process. These materials were characterized by XRD, ICP, BET, UV–vis absorption, XPS, HRTEM and EDX. The main factors such as size and surface state of the Au and defect in the ceria could be adjusted by acid treatment of the composites in ascorbic acid solution to improve the activity and decrease the content of noble metal Au in the materials. Enhanced catalytic activities were obtained for the CO oxidation reaction over the catalysts due to the small crystal sizes with narrow size distributions of gold nanoparticles, a large amount of defects in the nanoporous ceria support, as well as a high ratio of Au³⁺/Au⁰ in the nanocomposites.     

Ceria-zirconia supported Au as highly active low temperature Water-gas shift catalysts

Au/CeZrO₄ catalysts have shown very low temperature activity for the WGS reaction. Characterisation of the as-prepared catalysts shows Au is present primarily as isolated Au³⁺ atoms. It has been found that a higher proportion of Au³⁺ present in the as-prepared catalyst leads to a higher WGS activity, although under reaction conditions reduction to Au⁰ is observed. Use of TPR and iso-thermal H₂O re-oxidation has shown that Au reacts with H₂O at lower temperatures than an equivalent Pt/CeZrO₄ catalyst, indicating that H₂O activation is key in the onset of low temperature WGS activity.     

Au nanocolloids as recyclable quasihomogeneous metal catalysts in the chemoselective hydrogenation of α,β-unsaturated aldehydes and ketones to allylic alcohols

In the catalytic hydrogenation of α,β-unsaturated aldehydes and ketones, highly selective allylic alcohol formation can be achieved by application of Au⁰ nanocolloids dispersed in amide solvents. The polyvinylpyrrolidone protected Au⁰ nanoparticles prefer CO reduction over CC saturation and act as chemoselective quasihomogeneous metal catalysts in the hydrogenation of trans-2-butenal (crotonaldehyde), 2-methyl-2-propenal (methacrolein), 4-methyl-3-penten-2-one (mesityl oxide) and 3-methyl-3-penten-2-one. An extensive solvent screening revealed the superiority of amides as media for both synthesis and application of the Au⁰ nanocolloids. In comparison with the widely used alcohol solvents, amides offer enhanced colloidal stability for the Au⁰ nanosol and increased hydrogenation chemoselectivity. Control over the Au⁰ cluster formation provided the opportunity to investigate the size-dependency of the catalytic performance and to determine the optimum gold cluster size for a maximization of the allylic alcohol yields. The most successful Au⁰ clusters, with a typical diameter of 7 nm and synthesized in N,N-dimethylformamide, lead to a crotyl alcohol selectivity of 73% at 93% crotonaldehyde conversion and a 58% allylic alcohol yield in the hydrogenation of mesityl oxide at a molar substrate/Au catalyst ratio of 200. Analogous Pt⁰ and Ru⁰ sols are more active than the Au⁰ nanosols, but substantially less chemoselective for allylic alcohols. The Au⁰ nanocolloids can be recycled efficiently by ultrafiltration over custom-made, cross-linked polyimide membranes. In the recycling experiments the gold nanodispersion was well retained by the solvent-resistant ultrafiltration membranes and the performance of the colloidal gold catalyst was satisfactorily preserved in successive hydrogenation runs.     

AuNPs composites of gelatin hydrogels crosslinked by ferrocene-containing polymer as recyclable supported catalysts

To fabricate a recyclable supported catalyst based on gold nanoparticles (AuNPs) and gelatin hydrogel (HG) composites, a ferrocene (Fc)-containing tetrablock copolymer [P(NCHO-b-NFc-b-NTEG-b-NCHO)] was used as both reducing and stabilizing agents for AuNPs and as a crosslinker for HG. First, the effects of Fc-containing polymers, including homopolymer PNFc and copolymer P(NCHO-b-NFc-b-NTEG-b-NCHO), and different solvent systems on the morphology and aggregation of AuNPs were examined by using ultraviolet–visible spectroscopy, transmission electron microscopy, and dynamic light scattering. Second, two strategies (blending and soaking) were applied to prepare different AuNPs/HG composites ( AuNPs-HG ), and their structure and properties were studied by using various techniques including scanning electron microscopy, X-ray diffraction, and thermogravimetry. Finally, the catalytic performance and reusability of AuNPs-HG-1 (via blending) and AuNPs-HG-2 (via soaking) were evaluated utilizing the model catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH₄. Results indicated that P(NCHO-b-NFc-b-NTEG-b-NCHO) dissolved in N,N-dimethylformamide was the optimal reductant and stabilizer to prepare AuNPs. The in situ reduction of Au^III ions to Au⁰ particles was very essential for the fabrication of AuNPs-HG in terms of hydrogel pore size, Au⁰ distribution and immobilization stability, and hydrogel thermal stability. Due to the stronger interactions among AuNPs, P(NCHO-b-NFc-b-NTEG-b-NCHO), and gelatin molecules in the blending strategy, AuNPs-HG-1 showed better mechanical stability and catalytic performance and more reusing cycles than AuNPs-HG-2 . This work highlights the design and fabrication of robust recyclable supported AuNP catalyst by using eco-friendly Fc-containing HGs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48653.