One-Stage Synthesis of Gold Hydrosol with Nanoparticles of Desired Shape

The effect of borohydride concentration on the synthesis of gold nanoparticles in solutions of chloroauric acid, cetyltrimethylammonium bromide, and ascorbic acid in the absence of seeds has been studied systematically. Variations in the concentration of NaBH₄ allow one to obtain particles of different sizes and shapes. A method has been developed for the one-stage synthesis of large pentagonal gold rods (the average length and thickness are 550 ± 135 and 71.2 ± 11.6 nm, respectively) with a high yield using borohydride in an ultra-low (≤5 × 10^–8 mol/L) concentration. The resulting particles have been characterized using optical spectroscopy, scanning and transmission electron microscopy (including high-resolution technique), and electron diffraction.     

Fabrication of silver nanoparticles in pH responsive polymer microgel dispersion for catalytic reduction of nitrobenzene in aqueous medium

Copolymer microgels based on N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) have been synthesized by free radical emulsion polymerization using N,N-methylenebisacrylamide (BIS) as a cross-linker. Synthesized microgels were characterized by Fourier transform infrared spectroscopy (FTIR). Then silver nanoparticles were fabricated in the synthesized microgels by in-situ reduction of AgNO₃ with NaBH₄. The formation of silver nanoparticles was confirmed by UV–Vis spectroscopy. The pH sensitivity of the copolymer microgels was investigated using dynamic light scattering technique (DLS). Hydrodynamic radius of P (NIPAM–MAA) microgels increases with increase in pH of the medium at 25°C. Surface plasmon resonance wavelength (λ_SPR) of silver nanoparticles increases with increase in hydrodynamic radius due to change in pH of the medium. The catalytic activity for the reduction of nitrobenzene (NB), an environmental pollutant, into aniline was investigated by UV–Vis spectroscopy in excess of NaBH₄ using hybrid microgels as catalyst. The value of apparent rate constant (k_app) of the reaction was calculated using pseudo first order kinetic model and it was found to be linearly related to the amount of catalyst. The results were compared with literature data. The system was found to be an effective catalyst for conversion of NB into aniline.     

Gold nanoparticles anchored onto the magnetic poly(ionic‐liquid) polymer as robust and recoverable catalyst for reduction of Nitroarenes

Gold nanoparticles supported on poly ionic‐liquid magnetic nanoparticles (MNP@PIL@Au) were synthesized by reduction of HAuCl4 with sodium borohydride. The synthesized catalyst was characterized using by AAS, TEM, FT‐IR, EDS, TGA and XRD techniques. The performance of the synthesized catalyst was investigated in the reduction of nitroarenes with NaBH₄. The reaction was carried out for various nitroarenes in water and mild conditions with high yields. The catalyst selectivity for the reduction of nitro group in the presences of other functional groups such as halides and alkynes was fairly well. The recycling of the catalyst was done 8 times without any significant loss of its catalytic activity.     

Homogeneous Palladium Nanoparticles Surface Hosts Catalyzed Reduction of the Chromophoric Azo (–N=N–) Group of Dye,Acid Orange 7 by Borohydride in Alkaline Media

In alkaline media, well‐characterized gelatin‐stabilized palladium (GPd) nanoparticles catalyze the reduction of the azo group containing pollutant dye, Acid Orange 7 (AO7) by sodium borohydride (NaBH₄) to 1‐amino‐2‐napthol and sulfanilic acid. Kinetic observations and detailed FTIR studies suggests that the reaction follows Langmuir–Hinshelwood kinetic model, where during the reaction both AO7 and borohydride are adsorbed on the GPd surface. Plots of lnk_o versus ln[AO7] or ln[NaBH₄] show that the order of reaction with respect to AO7 and NaBH₄ remains almost same over different molar ratios of [NaBH₄]/[AO7]. The catalyzed reaction shows an initial induction period (t₀) due to a surface‐restructuring process of GPd nanoparticles, and (1/t₀) can be defined as the rate of surface restructuring. The activation energy of the catalyzed reaction and energy of the surface‐restructuring process of GPd are estimated as 22 ± 3 and 25 ± 7 kJ M^?1, respectively.     

Palladium nanoparticles supported on mesoporous natural phosphate: An efficient recyclable catalyst for nitroarene reduction

We report the preparation of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) using a wetness impregnation method. The prepared catalyst was characterized using various techniques. Furthermore, the reduction and preparation of the palladium nanoparticles was followed using UV–visible spectra. Based on the Scherrer equation, the crystallite size of the as‐synthesized palladium nanoparticles was 10.88 nm. The performance of the synthesized catalyst was investigated in the reduction of 4‐nitrophenol as a model substrate to 4‐aminophenol using NaBH₄ as a hydrogen source. Moreover, catalytic reduction of various nitroarenes was studied and monitored using UV–visible spectroscopy and gas chromatography. The Pd@NP catalyst showed a high activity for the selected reaction and could be recycled.     

N-vinyl pyrrolidone promoted aqueous-phase dehydrogenation of formic acid over PVP-stabilized Ru nanoclusters

In this work, we fabricated the poly(N-vinyl-2-pyrrolidone)(PVP)-stabilized ruthenium(0) nanoclusters by reduction of RuCl_3 using different reducing agents, and studied their catalytic activity in hydrogen generation from the decomposition of formic acid.It was demonstrated that N-vinyl-2-pyrrolidone(NVP), which is a monomer of PVP, could promote the reaction by coordination with Ru nanoparticles. The Ru nanoparticles catalyst reduced by sodium borohydride(NaBH_4) exhibited highest catalytic activity for the decomposition of formic acid into H_2 and CO_2. The turnover of numenber(TOF) value could reach 26113 h~(–1) at 80 °C. We believe that the effective catalysts have potential of application in hydrogen storage by formic acid.     

A High-Performance Catalytic and Recyclability of Phyto-Synthesized Silver Nanoparticles Embedded in Natural Polymer

The present work deals with phytogenic synthesis of Ag NPs in the natural polymer alginate as support material using Aglaia elaeagnoidea leaf extract as a reducing, capping, and stabilizing agent. Ag nanoparticles embedded in alginate were characterized using UV–Vis absorption spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy techniques and selected area electron diffraction techniques. The formation of AgNPs embedded in the polymer was in spherical shape with an average size of 12 nm range has been noticed. The prepared embedded nanoparticles in polymer were evaluated as a solid heterogeneous catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) and methylene blue to leuco methylene blue in the liquid phase using sodium borohydride (NaBH₄) as reducing agent. The silver nanoparticles embedded polymer exhibited extraordinary catalytic efficacy in reduction of 4-NP to 4-AP and the rate constant is 0.5054 min^?1 at ambient conditions. The catalyst was recycled and reused up to 10 cycles without significant loss of catalytic activity. The preparation of Ag–CA composite was facile, stable, efficient, eco-friendly, easy to recycle, non-toxic, and cost effective for commercial application.     

Cellulose/silver nanoparticles composite microspheres: eco-friendly synthesis and catalytic application

Cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated. Porous cellulose microspheres, fabricated from NaOH/thiourea aqueous solution by a sol–gel transition processing, were served as supports for Ag NPs synthesis by an eco-friendly hydrothermal method. The regenerated cellulose microspheres were designed as reducing reagent for hydrothermal reduction and also micro-reactors for controlling growth of Ag NPs. The structure and properties of obtained composite microspheres were characterized by Optical microscopy, UV–visible spectroscopy, WXRD, SEM, TEM and TG. The results indicated that Ag NPs were integrated successfully and dispersed uniformly in the cellulose matrix. Their size (8.3–18.6?nm), size distribution (3.4–7.7?nm), and content (1.1–4.9?wt%) were tunable by tailoring of the initial concentration of AgNO₃. Moreover, the shape, integrity and thermal stability were firmly preserved for the obtained composite microspheres. The catalytic performance of the as-prepared cellulose/Ag composite microspheres was examined through a model reaction of 4-nitrophenol reduction in the presence of NaBH₄. The composites microspheres exhibited good catalytic activity, which is much high than that of hydrogel/Ag NPs composites and comparable with polymer core–shell particles loading Ag NPs.     

Electrospun nickel nanoparticles@poly(vinylidene fluoride-hexafluoropropylene) nanofibers as effective and reusable catalyst for H2 generation from sodium borohydride

Nickel nanoparticles (Ni NPs) supported on Poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers (PVDF-HFP NFs) were successfully synthesized through electrospinning and in-situ reduction of Ni²⁺ salts into the surface of PVDF-HFP NFs to form metallic Ni NPs@PVDF-HFP NFs. Different percentages of nickel acetate tetrahydrate (NiAc) (10 %, 20 %, 30 %, 40 % wt.) based PVDF-HFP. The formation of tiny metallic Ni NPs @PVDF-HFP membrane NFs was demonstrated using standard physiochemical techniques. Nanofibers membranes have demonstrated good catalytic activity in H₂ production from sodium borohydride (NaBH₄). The sample composed of 40 %wt Ni showed the highest catalytic activity compared to the other formulations. Whereas 103 mL of H₂, from the hydrolysis of 1.34 mmol NaBH₄, was produced using 40 wt% NiAc compared to 68 mL, 81 mL, and 93 mL for 10 wt%, 20 wt%, and 30 wt% NiAc, respectively, in 60 min at 25 °C. The hydrogen generation has been enhanced with an increase in the Nanofibers membrane amount and reaction temperature. The latter results in a low activation energy (23.52 kJ mol^?1). The kinetics study revealed that the reaction was pseudo-first-order in sodium borohydride concentration and catalyst amount. Furthermore, the catalyst exhibits satisfactory stability in the hydrolysis process for ten cycles. Because of its easy recyclability, the introduced catalyst has a wide range of potential applications in the generation of H₂ from sodium borohydride hydrolysis.     

Manganese(III) porphyrin anchored onto multiwall carbon nanotubes: An efficient and reusable catalyst for the heterogeneous reduction of aldehydes and ketones

Reduction of a variety of carbonyl compounds with NaBH₄, using Mn-porphyrin, meso-tetrakis(4-hydroxyphenyl)porphyrinatomanganese(III), supported onto functionalized multiwall carbon nanotubes has been investigated. The heterogeneous catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis spectroscopy. The amount of catalyst loading on the nanotubes was determined by atomic absorption spectroscopy. Thermogravimetric analysis (TGA) demonstrated that the nanocatalyst was thermally stable to almost 300 °C, exhibiting high thermostability of the catalyst over a broad range of temperatures. This heterogeneous catalyst proved to be an efficient catalyst in the aerobic reduction of various aldehydes and ketones with NaBH₄. In the presence of the nanocatalyst, NaBH₄ can readily reduce a variety of aldehydes in good to excellent yields (50–100%) and ketones in excellent yields (100%) to their corresponding alcohols. The separation of the catalyst is very simple and economic. Also, FTIR spectra after four successive cycles showed that the catalyst was strongly anchored to the nanotubes.     

Preparation of nano-silver-supported activated carbon using different ligands

In this study, we investigated the effect of water soluble ligands [i.e., sodium borohydride (NaBH₄), polyvinyl alcohol, glucose and galactose] on the preparation of nano-silver-supported activated carbon (AC). Ligand-stabilized Ag nanoparticle dispersion characteristics were also compared with those of ligand-free Ag nanoparticles. The nanoparticle distribution was investigated using a scanning electron microscope (SEM) which enabled a qualitative analysis of ligand-dependent nanoparticle adsorption onto AC. Silver nanoparticles with average sizes ranging from 7 to 20 nm were synthesized with different coatings. In particular, silver nanoparticles reduced and stabilized by NaBH₄ were found to have a dense and homogenous dispersion of sizes in the range of 100–400 nm on the AC surface. These particles also seemed to remain on the AC surface after rinsing with water. The distribution of silver nanoparticles prepared in the presence of NaBH₄/PVA was not as good as the one prepared with NaBH₄. Their aggregate size varied from 300 to 600 nm on the AC surface and particles greater than 500 nm were eliminated from the AC surface upon rinsing with water. Glucose- and galactose-stabilized silver nanoparticles did not display an extensive adsorption and their adsorption seemed to be poor. However, glucose-stabilized silver nanoparticles could still be detectable to some extent after rinsing, while galactose-stabilized ones could not. Antimicrobial studies showed that all silver-containing carbons studied in this study inhibit bacterial growth and act as bacteriostatic agents.     

Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe3O4@polyaniline composites as a highly efficient,magnetically separable and atom‐economical catalyst for reduction of nitrobenzenes

The preparation of Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe₃O₄@polyaniline composites is reported. Fe₃O₄ nanoclusters were first synthesized through the solvothermal method and then the SiO₂ shell was coated on the Fe₃O₄ surface via a sol–gel process. To prepare Fe₃O₄@SiO₂@polyaniline composites, polyvinylpyrrolidone was first grafted on to the surface of Fe₃O₄@SiO₂ composites and subsequently polymerization of aniline was carried out via an ultrasound‐assisted in situ surface polymerization method. Selective etching of the middle SiO₂ layer was then accomplished to obtain the yolk–shell Fe₃O₄@polyaniline composites. The approach uses polyaniline (PANI) conductive polymer as a template for the synthesis of Ni@Pd core–shell nanoparticles. The catalytic activity of the synthesized yolk–shell Fe₃O₄@PANI/Ni@Pd composite was investigated in the reduction of o‐nitroaniline to benzenediamine by NaBH₄, which exhibited conversion of 99% in 3 min with a very low content of the catalyst. Transmission electron microscopy, X‐ray photoelectron spectroscopy, TGA, X‐ray diffraction, UV–visible, scanning electron microscopy, X‐ray energy dispersion spectroscopy and FT‐IR were employed to characterize the synthesized nanocatalyst. Copyright © 2014 John Wiley & Sons, Ltd.     

Fe3O4 – Glutathione stabilized Ag nanoparticles: A new magnetically separable robust and facile catalyst for aqueous phase reduction of nitroarenes

The heterostructured Ag nanoparticles decorated Fe₃O₄ Glutathione (Fe₃O₄‐Glu‐Ag) nanoparticles (NPs) were synthesized by sonicating glutathione (Glu) with magnetite and further surface immobilization of silver NPs on it. The ensuing magnetic nano catalyst is well characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA). The prepared Fe₃O₄‐Glu‐Ag nanoparticles have proved to be an efficient and recyclable nanocatalyst with low catalyst loading for the reduction of nitroarenes and heteronitroarenes to respective amines in the presence of NaBH₄ using water as a green solvent which could be easily separated at the end of a reaction using an external magnet and can be recycled up to 5 runs without any significant loss in catalytic activity. Gram scale study for the reduction of 4‐NP has also being carried out successfully and it has been observed that this method can serve as an efficient protocol for reduction of nitroarenes on industrial level.     

Facile and green solvothermal synthesis of palladium nanoparticle-nanodiamond-graphene oxide material with improved bifunctional catalytic properties

We developed a selective solvothermal synthesis of palladium nanoparticles on nanodiamond (ND)–graphene oxide (GO) hybrid material in solution. After the GO and ND materials have been added in PdCl₂ solution, the spontaneous redox reaction between the ND–GO and PdCl₂ led to the creation of nanohybrid Pd@ND@GO material. The resulting Pd@ND@GO material was characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectrometry, scanning electronic microscopy (SEM), and atomic absorption spectrometry methods. The Pd@ND@GO material has been used for the first time as a catalyst for the reduction for 2-nitrophenol and the degradation of methylene blue in the presence of NaBH₄. GO plays the role of 2D support material for Pd nanoparticles, while NDs act as a nanospacer for partly preventing the re-stacking of the GO. The Pd@ND@GO material can lead to high catalytic activity for the reduction reaction of 2-nitrophenol and degradation of methylene blue with 100% conversion within ~15 s for these two reactions even when the content of Pd in it is as low as 4.6 wt%.     

Hydrophilic polymer supported nanoparticles prepared from samarium trichloride and lanthanum trichloride in liquid-phase

Nanoparticles were obtained by the reaction of SmCl₃·6H₂O with sodium borohydride (NaBH₄) in the presence of sodium polyacrylate (PAA) with average molecular weight of 5,100 as a capping polymer. The resulting colloidal solution was placed on a Cu grid and characterized by transmission electron microscope (TEM) measurement, which clearly indicated the generation of nanoparticles. The reaction of LaCl₃ with NaBH₄ in the presence of PAA led to preparation of lanthanum nanoparticles, similarly as samarium nanoparticles.     

Preparation of poly(styrene‐b‐N‐isopropylacrylamide) micelles surface‐linked with gold nanoparticles and thermo‐responsive ultraviolet–visible absorbance

Poly(styrene‐b‐N‐isopropylacrylamide) (PSt‐b‐PNIPAM) with dithiobenzoate terminal group was synthesized by reversible addition‐fragmentation‐transfer polymerization. The dithiobenzoate terminal group was converted into thiol terminal group with NaBH₄, resulting thiol‐terminated PSt‐b‐PNIPAM‐SH. After PSt‐b‐PNIPAM‐SH assembled into core‐shell micelles in aqueous solution, gold nanoparticles were in situ surface‐linked onto the micelles through the reduction of gold precursor anions with NaBH₄. Thus, temperature responsive core/shell micelles of PSt‐b‐PNIPAM surface‐linked with gold nanoparticles (PSt‐b‐PNIPAM‐Au micelles) were obtained. Transmission Electron Microscopy revealed the successful linkage of gold nanoparticles and the dependence of the number of gold nanoparticles per micelle on the molar ratio of HAuCl₄ to thiol group of PSt‐b‐PNIPAM. Dynamic Light Scattering analysis demonstrated thermo‐responsive behavior of PSt‐b‐PNIPAM‐Au micelles. Changing the temperature of PSt‐b‐PNIPAM‐Au micelles led to the shrinkage of PNIPAM shell and allowed to tune the distance between gold nanoparticles. Ultraviolet–visible (UV–vis) spectroscopy clearly showed the reversible modulation of UV–vis absorbance of PSt‐b‐PNIPAM‐Au micelles upon heating and cooling. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5156–5163, 2007     

Water‐Soluble Gold Nanoparticles: From Catalytic Selective Nitroarene Reduction in Water to Refractive Index Sensing

Water‐soluble gold nanoparticles (Au NPs) stabilized by a nitrogen‐rich poly(ethylene glycol) (PEG)‐tagged substrate have been prepared by reduction of HAuCl₄ with NaBH₄ in water at room temperature. The morphology and size of the nanoparticles can be controlled by simply varying the gold/stabilizer ratio. The nanoparticles have been fully characterized by TEM, high‐resolution (HR) TEM, electron diffraction (ED), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis, powder XRD, and elemental analysis. The material is efficient as a recyclable catalyst for the selective reduction of nitroarenes with NaBH₄ to yield the corresponding anilines in water at room temperature. Furthermore, the potential ability of the Au NPs as a refractive index sensor owing to their localized surface plasmon resonance (LSPR) effect has also been assessed.     

Incorporation of surface-derivatized gold nanoparticles into electrochemically generated polymer films

Stable colloidal solutions of gold nanoparticles surface-derivatized with a thiol monolayer have been prepared using two-phase (water–nitrobenzene) reduction of AuCl₄⁻ by sodium borohydride in the presence of 2-mercapto-3-n-octylthiophene (MOT). This kind of surface-functionalized gold nanoparticles can be easily incorporated into the poly(3-octylthiophene) (POT) films on electrode in the process of electrochemical polymerization leading to POT–gold nanoparticle (POT–Au) composite films. Scanning probe microscopy (SPM) and X-ray photoelectric spectroscopy (XPS) have been employed to characterize the surface-derivatized particles and the resulting films. The method of incorporation of nanoparticles into polymer by surface-derivatization and in situ polymerization can also be employed to prepare many other polymer–nanoparticle compostie materials.     

An efficient and easily retrievable dip catalyst based on silver nanoparticles/chitosan-coated cellulose filter paper

Re-use of a catalyst is an important task, which is usually achieved by loading it on easily separable supports such as magnetic substrates. However, we demonstrate here the process of easy and fast catalyst separation from a reaction medium by loading it onto an economically feasible and microscopically high surface substrate of filter paper (FP) made up of cellulose microfibers as catalyst support. To achieve the goal, we coated chitosan (CH) on filter paper (CH-FP) to impart a high affinity of the substrate for metal ion absorption. AgNO₃ dissolved in water with a 0.1 M concentration was used as the Ag ion carrier solution, and CH-FP strips with known rectangular dimensions were submerged into it for the metal ion absorption. The metal ion-laden CH-FP strips were dip treated with sodium borohydride (NaBH₄) aqueous solution to prepare Ag-nanoparticle loaded CH-FP (Ag/CH-FP). X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the formation of the Ag/CH-FP hybrid. Ag/CH-FP morphology was examined through scanning electron microscopy analysis, which showed the presence of Ag nanoparticles attached to the cellulose microfibers. The prepared Ag/CH-FP was employed as a dip catalyst for the degradation of nitroarene compounds of 2-nitophenol (2-NP) and 4-nitrophenol (4-NP) by NaBH₄. Remarkably, the rate constants for 4-NP and 2-NP were 3.9 × 10^?3 and 1.7 × 10^?3 s^?1, respectively. In addition, we discussed the ease of the catalyst retrievability from the reaction mixture and its re-usability.     

Concentration Dependent Catalytic Activity of Glutathione Coated Silver Nanoparticles for the Reduction of 4-Nitrophenol and Organic Dyes

In the present study, we have synthesized glutathione modified silver nanoparticles (GSH-AgNPs) in aqueous medium and are characterized by absorption, high resolution transmission electron microscope (HR-TEM), selective area electron diffraction (SAED) pattern, dynamic light scattering (DLS), Zeta potential and Fourier transform infrared (FT-IR) spectroscopic measurements. Catalytic activity of GSH-AgNPs has been evaluated for the reduction reactions of 4-nitrophenol (4-NP), methylene blue (MB dye) and eosin Y (EY dye) in presence of sodium borohydride including the effect of catalyst concentration on the catalytic activity. Furthermore, the rate constants of reduction reactions are determined, which are linearly enhanced upon increasing the concentrations of GSH-AgNPs. It is explored that reduction reactions such as 4-NP, organic dyes by NaBH₄ in the presence of catalyst follow a pseudo first order kinetics. The catalytic reduction of 4-NP and organic dyes proceed with a faster rate even in the presence of nanomolar concentration of catalyst.