One‐step synthesis of Pt@three‐dimensional graphene composite hydrogel: an efficient recyclable catalyst for reduction of 4‐nitrophenol

A Pt@three‐dimensional graphene (Pt@3DG) composite hydrogel with a unique porous nanostructure was prepared and used as an efficient, recyclable and robust catalyst for the reduction of 4‐nitrophenol to 4‐aminophenol under mild conditions. The influence of graphene architecture on catalytic activities was comparatively investigated by loading the same amount of Pt on reduced graphene oxide. Pt@3DG exhibits a very high catalytic activity owing to the three‐dimensional macroporous framework with high specific surface area, numerous activation sites and efficient transport pathways. Moreover, catalyst separation can be easily achieved by simple filtration, and the catalyst can be reused for at least five runs, maintaining its high catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Gold nanoparticles supported on three‐dimensional nitrogen‐doped graphene: an efficient catalyst for selective aerobic oxidation of hydrocarbons under mild conditions

The development of efficient and selective aerobic oxidation of alkylarenes to form more functional compounds by heterogeneously catalysed routes still presents a great challenge in the fine chemical industry and is a major research topic. In this work, gold nanoparticles supported on three‐dimensional nitrogen‐doped graphene‐based frameworks (Au NPs@3D‐(N)GFs) were successfully synthesized and found to have an impressive performance as bifunctional catalysts (nitrogen dopant as base and gold nanoparticles as active site) in the controlled oxidation of alkylarenes. The catalyst was found to be a simple bench top, stable, recyclable and selective catalytic system for the aerobic oxidation of various types of alkylarenes into their corresponding ketones at room temperature under environmentally friendly conditions with good yields and high selectivity. Copyright © 2015 John Wiley & Sons, Ltd.     

Buchwald‐Hartwig amination reaction of aryl halides using heterogeneous catalyst based on Pd nanoparticles decorated on chitosan functionalized graphene oxide

In this work, graphene oxide was functionalized with chitosan (GO‐Chit) followed by a simple approach for immobilization of palladium nanoparticles onto a chitosan grafted graphene oxide surface. The Pd‐nanocomposite (GO‐Chit‐Pd) was characterized using Transmission Electron Microscopy (TEM), Fourier transforms infrared spectroscopy (FT‐IR), and X‐ray diffraction (XRD) measurements. The catalytic activity of the prepared heterogeneous graphene oxide functionalized chitosan‐palladium (GO‐Chit‐Pd) was investigated in term of C‐N coupling reaction (Buchwald‐Hartwig amination reaction of aryl halides) yielding products of N‐arylamines. The easy purification, convenient operation, and environmental friendliness, combined with a high yield, render this method viable for use in both laboratory research and larger industrial scales. Studying the reusability of the catalyst in this work showed that it could be reused for five times without obvious loss in catalytic activity.     

CuO nanoparticles supported on three‐dimensional nitrogen‐doped graphene as a promising catalyst for thermal decomposition of ammonium perchlorate

In the present work, CuO nanoparticles grown on three‐dimensional nitrogen‐doped graphene‐based frameworks (CuO@3D‐(N)GFs) were synthesized using a two‐step method. After the synthesis of three‐dimensional nitrogen‐doped graphene, CuO nanoparticles were deposited on it, by adding cupric acetate followed by thermal treatment. Different analysis methods were used to characterize the products. The as‐prepared nanocomposite was used as a promising catalyst for thermal decomposition of ammonium perchlorate (AP) as one of the most common oxidizer in composite propellants. Differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) techniques were used to investigate the thermal decomposition of ammonium perchlorate. According to the DSC/TGA, high temperature decomposition of AP decreased to 111 °C in the presence of 4% CuO@3D‐(N)GFs and the total heat release (ΔH) from decomposition of AP increased to 1893 J g^?1 which is much more than 590 J g^?1 for pure AP.     

Electroless‐coated magnetic three‐dimensional graphene with silver nanoparticles used for the determination of pesticides in fruit samples

A new type of adsorbent composed of magnetic three‐dimensional graphene coated with silver nanoparticles was synthesized by an electroless technique and used in the magnetic solid‐phase extraction of selected pesticides (fenitrothion, chlorpyrifos, and hexaconazole) before gas chromatography with a micro‐electron capture detector. The adsorbent was characterized using Fourier‐transform infrared spectroscopy, X‐ray diffraction, vibrating sample magnetometry, and field‐emission scanning electron microscopy. The important extraction parameters such as pH, adsorbent dose, extraction time, and desorption conditions were investigated. Under the optimal conditions, the analytical figures of merit were obtained as: linear dynamic range of 0.1–5 ng/g with determination coefficients of 0.991–0.996; limit of detection of 0.07–0.13 ng/g; limit of quantification of 0.242–0.448 ng/g; and the intraday and interday relative standard deviations (C = 5 ng/g, n = 3) were 3.8–8.7 and 6.6–8.9%, respectively. The developed method was successfully applied for analysis of the selected pesticides in tomato and grape with extraction recoveries in the range of 72.8–109.6%.     

Gold nanoparticles supported on thiol‐functionalized reduced graphene oxide as effective recyclable catalyst for synthesis of tetrahydro‐4H‐chromenes in aqueous media

Gold nanoparticles supported on thiol‐functionalized reduced graphene oxide (AuNPs@RGO‐SH) were found to be a biocompatible, stable, recyclable heterogeneous catalyst. The catalysts were characterized by field emission scanning electron microscopy (FE‐SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT‐IR), thermal gravimetric analysis (TGA), and X‐ray diffraction spectroscopy (XRD). The obtained catalyst was used in synthesis of tetrahydro‐4H‐chromenes in aqueous media with excellent yields. The catalysts could be easily separated from the reaction mixture and recovered several times without a significant loss of activity.     

Synthesis of 5‐substituted 1H‐tetrazoles using a recyclable heterogeneous nanonickel ferrite catalyst

An efficient method was developed for the [2 + 3] cycloaddition of sodium azide with nitriles to afford 5‐substituted 1H‐tetrazoles using nanonickel ferrite (NiFe₂O₄) as an effective heterogeneous catalyst in dimethylformamide. The main advantages of this method are high yields, simple methodology and easy work‐up. The catalyst can be recovered and reused for several cycles with predictable activity. Copyright © 2015 John Wiley & Sons, Ltd.     

PdCo bimetallic nanoparticles supported on three‐dimensional graphene as a highly active catalyst for Sonogashira cross‐coupling reaction

PdCo bimetallic nanoparticles (NPs) were decorated over three‐dimensional graphene (3DG) in a facile manner by reducing palladium chloride and cobalt chloride in the presence of ethylene glycol as reducing, stabilizing and dispersing agent. The PdCo NPs–3DG nanocomposite was characterized using Raman, X‐ray photoelectron and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction and transmission electron microscopy. The obtained catalyst can act as an efficient catalyst for Sonogashira cross‐coupling reactions in aqueous media.     

Functionalized graphene oxide supported copper (I) complex as effective and recyclable nanocatalyst for one‐pot three component synthesis of 1,2,3‐triazoles

Efficient, one pot three‐component reaction of alkyl halides, sodium azide with terminal alkynes can be catalyzed by functionalized graphene oxide with copper(I) under thermal conditions. A series of 1,4‐disubstituted 1,2,3‐triazoles were obtained by this one‐pot strategy. The catalyst was prepared and characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), emission scanning electron microscopy (FE‐SEM) and energy dispersive X‐ray (EDX). The catalyst can be reused at least five times without significant deactivation.     

A practical and highly efficient synthesis of densely functionalized nicotinonitrile derivatives catalyzed by zinc oxide‐decorated superparamagnetic silica attached to graphene oxide nanocomposite

Zinc oxide‐decorated superparamagnetic silica attached to graphene oxide (Fe₃O₄/SiO₂/PTS‐GO‐ZnO), as a novel nanocomposite, was designed, and its core‐shell structure was appropriately characterized by different spectroscopy or microscopy methods and thermal techniques as well as measuring of its porosity and magnetic properties. The catalytic activity of Fe₃O₄/SiO₂/PTS‐GO‐ZnO, as a reusable heterogeneous catalyst, was investigated for efficient one‐pot multi‐component synthesis of medicinally important functionalized 2‐amino‐6‐(2‐oxo‐2H‐chromen‐3‐yl)‐4‐arylnicotinonitrile derivatives. The significant features of the present procedure are mild reaction conditions, low loading of the catalyst, high to quantitative yields of the desired products, avoiding the use of toxic heavy metals or solvents, simple isolation and purification of the products, and stability as well as reusability of the catalyst after at least six consecutive runs.     

A novel ternary GO@SiO2‐HPW nanocomposite as an efficient heterogeneous catalyst for the synthesis of benzazoles in aqueous media

A new solid acid catalyst, consisting of 12‐phosphotungstic heteropoly acid (HPW) supported on graphene oxide/silica nanocomposite (GO@SiO₂), has been developed via immobilizing HPW onto an amine‐functionalized GO/SiO₂ surface through coordination interaction (GO@SiO₂‐HPW). The GO@SiO₂‐HPW nanocomposite was characterized by Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and powder X‐ray diffraction (XRD). The prepared nanocomposite could be dispersed homogeneously in water and further used as a heterogeneous, reusable, and efficient catalyst for the synthesis of benzimidazoles and benzothiazoles by the reaction of 1,2‐phenelynediamine or 2‐aminothiophenol with different aldehydes.     

Graphene‐mesoporous anatase TiO2 nanocomposite: A highly efficient and recyclable heterogeneous catalyst for one‐pot multicomponent synthesis of benzodiazepine derivatives

The potential to bias chemical reaction pathways is a significant goal for physicists and material researchers to design revolutionary materials. Recently, two‐dimensional materials have appeared as a promising candidate for exploring novel catalyst activity in organic reaction. In this context, herein we report an easy and efficient synthesis of substituted benzodiazepines in high yields through the graphene‐based mesoporous TiO₂ nanocomposite (Gr@TiO₂ NCs) catalyst. To validate the merits of the Gr@TiO₂ NCs as a catalyst, we have also designed TiO₂ nanoparticle (NPs) under similar conditions. Successful comprehension realization of Gr@TiO₂ NCs and TiO₂ NPs were concluded from the XRD, SEM, HR‐TEM, EDS elemental mapping, FT‐IR, Raman, UV–Vis and TGA analysis. Gr@TiO₂ NCs has the propitious catalyst performance (~98%) over the TiO₂ NPs (~77%), which could be scrutinized in terms of graphene support toward the TiO₂ NPs and enable the large contact area between graphene and TiO₂ NPs. Incorporated graphene maintaining TiO₂ as a catalytically active and attracting electron to site isolation, as well as protecting TiO₂ from oxidative degradation during the reaction. Moreover, the role of graphene is suggested to prolonged reaction duration, yield and unaltered throughout the reaction because of the π‐π interaction between graphene and TiO₂ NPs. Additionally, the catalyst is recycled by filtration and reprocessed six times without having a significant loss in its catalytic activity.     

Copper nanoparticles supported on 2‐methoxy‐1‐phenylethanone‐functionalized MCM‐41: An efficient and recyclable catalyst for one‐pot three‐component C–S coupling reaction of aryl halides with benzyl bromide and thiourea

An environmentally friendly copper‐based catalyst supported on 2‐methoxy‐1‐phenylethanone‐functionalized MCM‐41 was prepared and characterized by Fourier transform‐infrared, transmission electron microscopy, field emission‐scanning electron microscopy, X‐ray diffraction and inductively coupled plasma techniques. The catalyst was applied for the one‐pot three‐component C–S coupling reactions of aryl halides with benzyl bromide and thiourea under aerobic conditions to afford the corresponding coupled products in good yields in water. The catalyst could be recovered and recycled five times. These results prove 2‐methoxy‐1‐phenylethanone‐functionalized MCM‐41 supported Cu (II) complex was not leached during the reaction. Also it shows the correct heterogeneous nature of the catalyst.     

An efficient heterogeneous cross‐coupling of aryl iodides with diphenylphosphine catalyzed by copper (I) immobilized in MCM‐41

The heterogeneous cross‐coupling reaction of aryl iodides with diphenylphosphine was achieved in toluene at 115 °C in the presence of 10 mol% of phenanthroline‐functionalized MCM‐41‐supported copper (I) complex (Phen‐MCM‐41‐CuI) with Cs₂CO₃ as base, yielding various unsymmetric triarylphosphines in good to excellent yields. This protocol can tolerate a wide range of functional groups and does not need the use of expensive additives or harsh reaction conditions. This heterogeneous Cu (I) catalyst exhibited the same catalytic activity as homogeneous CuI/Phen system, and could easily be recovered by a simple filtration of the reaction solution and recycled up to seven times without significant loss of activity.     

In situ synthesis of silver nanoparticles on densely amine‐functionalized polystyrene: Highly active nanocomposite catalyst for the reduction of methylene blue

In this contribution, polystyrene (PS) bearing nitrogen‐rich ligands as chelation moieties for both Ag⁺ ions and Ag⁽⁰⁾ nanoparticles was prepared through successive chemical modifications of native PS including nitration (treatment with HNO₃/H₂SO₄), reductive amination (treatment with SnCl₂/HCl), Michael addition of methyl acrylate, and grafting of ethyelenediamine. The as‐synthesized PS derivative was further used to support silver nanoparticles through initial chelation of the silver nanoparticle ions precursor and subsequent chemical in situ reduction with sodium borohydride. Chemical structure of the PS derivatives was confirmed after each synthesis step by using complementary characterization methods including infrared and energy‐dispersive X‐ray spectroscopies, elemental analysis, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The catalytic activity of the PS‐EAD/AgNP nanocomposite was demonstrated using the reduction of methylene blue to leucomethylene blue, as a model reaction. The reaction was monitored by UV‐vis spectrophotometry and achieved with an excess of sodium borohydride allowing for a pseudo‐first‐order analysis of the kinetic reaction parameters. Quantitative reduction of the methylene blue was obtained upon successive catalytic cycles with a rate constant value of 0.4016 minute^?1.     

Magnetic GO‐PANI decorated with Au NPs: A highly efficient and reusable catalyst for reduction of dyes and nitro aromatic compounds

Due to the high activity of Au nanoparticles (NPs) for various reactions, many researchers have tried to develop heterogeneous catalysts in order to prevent irreversible agglomeration of Au NPs. Herein, magnetic graphene oxide modified with polyaniline (PANI) was used as a support for Au NPs that brings together advantages including: uniform dispersal of the catalyst in water,alarge surface area related to the graphene oxide; easy electron transfer in chemical reactions and good attachment of Au NPs to the support associated with PANI; and finally facile recovery in the presence of a magnetic field. Catalytic reduction of different analytes (Congo red, methylene blue, rhodamine B and 4‐nitro phenol) was evaluated in the presence of NaBH₄ and the results show high catalytic activity of the catalyst. The catalyst was thoroughly characterized using various methods including FTIR, XRD, XPS, FE‐SEM and HRTEM analyses while its catalytic activity was evaluated via reduction of different analytes.     

Ligandless heterogeneous palladium: an efficient and recyclable catalyst for Suzuki‐type cross‐coupling reaction

A mild and efficient ligand‐free Suzuki‐type cross‐coupling reaction of benzoyl chlorides and arylboronic acids catalyzed by heterogeneous Pd/C was developed. Benzoyl chlorides undergo cross‐coupling with electronically diverse arylboronic acids to give biaryl ketones in excellent yield, under aqueous media and optimum temperature. The application of 3 mol% of 10 wt% Pd/C to the cross‐coupling delivers utmost efficiency, and could be reused up to many consecutive cycles without any loss in activity. This method proceeds under aqueous media and a recyclable catalytic system, offering an environmentally benign alternative to the existing protocols. Copyright © 2014 John Wiley & Sons, Ltd.     

Fe3O4/MIL‐101(Fe) nanocomposite as an efficient and recyclable catalyst for Strecker reaction

A highly porous metal‐organic framework, MIL‐101(Fe), was prepared by a solvothermal method in the presence of amino‐modified Fe₃O₄@SiO₂ nanoparticles, in order to achieve Fe₃O₄/MIL‐101(Fe) nanocomposite, which was characterized by XRD, FT‐IR, SEM, TEM, BET, and VSM. This hybrid magnetic nanocomposite was employed as heterogeneous catalyst for α‐amino nitriles synthesis through three‐component condensation reaction of aldehydes (ketones), amines, and trimethylsilyl cyanide in EtOH, at room temperature. The recoverability and reusability was admitted for the heterogeneous magnetic catalyst; no significant reduction of catalytic activity was observed even after five consecutive reaction cycles.     

Comparative study of amphiphilic hyperbranched and linear polymer stabilized organo‐soluble gold nanoparticles as efficient recyclable catalysts in the biphasic reduction of 4‐nitrophenol

A series of organo‐soluble spherical gold nanoparticles (AuNPs) were prepared through the reduction of HAuCl₄ by NaBH₄ in the presence of amphiphilic hyperbranched polymers that had a hydrophilic hyperbranched polyethylenimine core and a hydrophobic shell formed by many palmitamide (C16) chains. For comparison, the corresponding linear polymeric analog derived from linear polyethylenimine was also used to prepare the organo‐soluble AuNPs. The obtained AuNPs were characterized by transmission electron microscopy. It was found that higher feed ratio of polymer to HAuCl₄ and utilization of polymers with higher C16 density usually resulted in smaller AuNPs with relatively lower polydispersity. Except of the polymer having the pronounced low molecular weight, the molecular weight and the morphology of the amphiphilic polymers had almost no obvious effect on the size of the formed AuNPs. These organo‐soluble AuNPs could be used as efficient catalysts for the biphasic catalytic reduction of 4‐nitrophenol by NaBH₄. Their apparent rate coefficients had correlation with the molecular weight of the used amphiphilic polymers, but were less relevant to the morphology of these polymers. These organo‐soluble AuNPs could be conveniently recovered and reused many times. The morphology of the capping polymers had obvious effect on the lifetime of the AuNPs catalysts in the catalytic reduction of 4‐nitrophenol. Except of the pronounced low molecular weight hyperbranched polymer, the other hyperbranched ones with relatively high molecular weight rendered the AuNPs to have bigger turnover number values than their linear analog. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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.