Synthesis of gold nanoparticles decorated on sulfonated three‐dimensional graphene nanocomposite and application as a highly efficient and recyclable heterogeneous catalyst for Ullmann homocoupling of aryl iodides and reduction of p‐nitrophenol

Gold nanoparticles were decorated onto sulfonated three‐dimensional graphene (3DG‐SO₃H) through spontaneous chemical reduction of HAuCl₄ by 3DG‐SO₃H. This nanocomposite exhibited excellent catalytic activity for the synthesis of symmetric biaryls via the Ullmann homocoupling of aryl iodides in an aqueous medium. Additionally, this nanocomposite was used as a catalyst for the reduction of p‐nitrophenol to p‐aminophenol. The catalyst could be used more than six times successively without significant deactivation.     

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.     

Pd‐Cu alloy nanoparticle supported on amine‐terminated ionic liquid functional 3D graphene and its application on Suzuki cross‐coupling reaction

Well distributed Pd‐Cu bimetallic alloy nanoparticles supported on amine‐terminated ionic liquid functional three‐dimensional graphene (3D IL‐rGO/Pd‐Cu) as an efficient catalyst for Suzuki cross‐coupling reaction has been prepared via a facile synthetic method. The introduction of IL‐NH₂ cations on the surface of graphene sheets can effectively avoid the re‐deposition of graphene sheets, allowing the catalyst to be reused up to 10 cycles. The addition of Cu not only saves cost but also ensures high catalytic efficiency. It is worthy to note that the catalyst 3D IL‐rGO/Pd_2.5Cu_2.5 can efficiently catalyze the Suzuki cross‐coupling reaction with the yield up to 100% in 0.25 h, almost one‐fold higher than that by the pristine IL‐rGO/Pd_2.5 catalyst (52%). The Powder X‐Ray Diffraction (XRD), combining energy dispersive X‐ray spectroscopy (EDS) mapping results confirm the existence and distribution of Pd and Cu in the bimetallic nanoparticles. The transmission electron microscopy (TEM) reveals the nanoparticle size with an average diameter of 3.0 ± 0.5 nm. X‐ray photoelectron spectroscopy (XPS) analysis proved the presence of electron transfer from Cu to Pd upon alloying. Such alloying‐induced electronic modification of Pd‐Cu alloy and 3D ionic liquid functional graphene with large specific surface area both accounted for the catalytic enhancement.     

Two‐Dimensional Metal‐Organic Layers for Electrochemical Acceptorless Dehydrogenation of N‐Heterocycles

The catalytic acceptorless dehydrogenation (CAD) is an attractive synthetic route to unsaturated compounds because of its high atomic efficiency. Here we report electrochemical acceptorless dehydrogenation of N‐heterocycles to obtain quinoline or indole derivatives using metal‐organic layer (MOL) catalyst. MOL is the two‐dimensional version of metal‐organic frameworks (MOF), and it can be constructed on conductive multi‐walled carbon nanotubes via facile solvothermal synthesis to overcome the conductivity constraint for MOFs in electrocatalysis. TEMPO‐OPO₃^2? was incorporated into the system through a ligand exchange with capping formate on the MOL surface to serve as the active catalytic centers. The hybrid catalyst is efficient in the organic conversion and can be readily recycled and reused.     

高活性、可循环的Pt-Cu@3D石墨烯复合催化剂的制备和催化性能

A composite hydrogel consisting of well-dispersed Pt-Cu nanoparticles (NPs) supported on three-dimensional (3D) graphene (Pt-Cu@3DG) was successfully prepared by mild chemical reduction. The 3D interconnected macroporous structure of the graphene framework not only possesses large specific surface area that allows high metal loadings, but also facilitates mass transfer during the catalytic reaction. The Pt-Cu bimetallic alloy NPs show good catalytic activity compared with Pt NPs and reduce the content of Pt NPs used, thereby lowering costs. The morphology and composition of the Pt-Cu@3DG composite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). The catalysis studies indicate that the resulting composites can be used as an efficient, inexpensive, recyclable, and stable catalyst for the reduction of 4-nitrophenol to 4-aminophenol under mild conditions.     

Heterogenized peroxopolyoxotungstate catalyst on the surface of clicked magnetite‐graphene oxide nanocomposite: Magnetically recoverable epoxidation catalyst

A new heterogeneous catalyst for the epoxidation of olefins was prepared by immobilization of peroxophosphotungstate anions on the surface of clicked magnetite‐graphene oxide as magnetically recoverable support. To prepare the heterogeneous catalyst, the clicked magnetite‐graphene oxide support was prepared by thiolene click reaction of thiol functionalized graphene oxide with vinyl modified magnetite nanoparticles. The tailored support was then modified with aminopropyl groups followed by electrostatic interaction with peroxophosphotungstate anions to achieve the desired heterogeneous catalyst. Characterization of the catalyst was performed by various physicochemical methods which confirmed the successful immobilization of peroxopolyoxotungstate species on the surface of clicked magnetite‐graphene oxide. Catalytic activity of the catalyst revealed its high catalytic activity and selectivity in the epoxidation of various olefins in the presence of H₂O₂ as green oxidant. This heterogeneous catalyst can be magnetically reused several times without significant loss of activity and selectivity.     

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.     

Pd‐ Dithizone grafted onto magnetic nanoparticles and study of its catalyticactivity in C‐C and C‐N coupling reactions

In this paper, we report a simple, facile and efficient method for the synthesis of Fe₃O₄/SiO₂‐DTZ‐Pd. The immobilized palladium was an efficient catalyst without addition of phosphine ligands for Stille, Heck and N‐arylation reactions. This method has some advantages such as high yields and easy work up of products. In addition, the catalyst can be recovered using a magnet and reused several times without significant loss of its catalytic activity. This catalyst was characterized by various physico‐chemical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and inductively coupled plasma (ICP).     

Mn(III)‐salan/graphene oxide/magnetite nanocomposite as a highly selective catalyst for aerobic epoxidation of olefins

A nanocomposite was synthesized using carbon‐coated Fe₃O₄ nanoparticle‐decorated reduced graphene oxide as a convenient and efficient supporting material for grafting of a manganese–reduced Schiff base (salan) complex via covalent attachment. The nanocomposite was characterized using X‐ray diffraction, Fourier transform infrared and diffuse reflectance UV–visible spectroscopies, inductively coupled plasma atomic emission spectrometry and scanning electron microscopy. It was evaluated as a catalyst for the aerobic epoxidation of olefins in acetonitrile in combination with a sacrificial co‐reductant (isobutyraldehyde). The catalytic performance of the heterogeneous system of the Mn–salan complex is superior to that of the homogeneous one. The catalyst activity strongly depends on the reaction temperature and nature of the solvent. The epoxide yield increases with the nucleophilic character of the olefin. The nanocomposite performs well as an epoxidation catalyst for electron‐rich and conjugated olefins. It can be recovered from the reaction medium by magnetic decantation and reused, maintaining good catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

High Catalytic Activity of Nitrogen and Sulfur Co‐Doped Nanoporous Graphene in the Hydrogen Evolution Reaction

Chemical doping has been demonstrated to be an effective way to realize new functions of graphene as metal‐free catalyst in energy‐related electrochemical reactions. Although efficient catalysis for the oxygen reduction reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co‐doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt‐free HER catalyst, 2D MoS₂. The interplay between the chemical dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis.     

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.     

Bottom‐Up Fabrication of a Sandwich‐Like Carbon/Graphene Heterostructure with Built‐In FeNC Dopants as Non‐Noble Electrocatalyst for Oxygen Reduction Reaction

High‐performance non‐noble electrocatalysts for oxygen reduction reaction (ORR) are the prerequisite for large‐scale utilization of fuel cells. Herein, a type of sandwiched‐like non‐noble electrocatalyst with highly dispersed FeN_x active sites embedded in a hierarchically porous carbon/graphene heterostructure was fabricated using a bottom‐up strategy. The in situ ion substitution of Fe³⁺ in a nitrogen‐containing MOF (ZIF‐8) allows the Fe‐heteroatoms to be uniformly distributed in the MOF precursor, and the assembly of Fe‐doped ZIF‐8 nano‐crystals with graphene‐oxide and in situ reduction of graphene‐oxide afford a sandwiched‐like Fe‐doped ZIF‐8/graphene heterostructure. This type of heterostructure enables simultaneous optimization of FeN_x active sites, architecture and interface properties for obtaining an electron‐catalyst after a one‐step carbonization. The synergistic effect of these factors render the resulting catalysts with excellent ORR activities. The half‐wave potential of 0.88 V vs. RHE outperforms most of the none‐noble metal catalyst and is comparable with the commercial Pt/C (20 wt %) catalyst. Apart from the high activity, this catalyst exhibits excellent durability and good methanol‐tolerance. Detailed investigations demonstrate that a moderate content of Fe dopants can effectively increase the intrinsic activities, and the hybridization of graphene can enhance the reaction kinetics of ORR. The strategy proposed in this work gives an inspiration towards developing efficient noble‐metal‐free electrocatalysts for ORR.     

Facile fabrication of magnetic MoO2–Salen‐modified graphene‐based catalyst for epoxidation of alkenes

A facile, green and efficient method for the immobilization of MoO₂–Salen onto graphene hybridized with glucose‐coated magnetic Fe₃O₄ nanoparticles is proposed to fabricate a magnetic organic–inorganic hybrid heterogeneous RGO/Fe₃O₄@C‐Salen‐MoO₂ catalyst for the epoxidation of cyclooctene and geraniol using tert ‐butyl hydroperoxide or H₂O₂ as oxidant. Carbon‐coated Fe₃O₄ can improve the stability and add functional ─OH groups on the surface of Fe₃O₄. The fabricated composite exhibited good performance due to good dispersion of MoO₂–Salen active sites. The catalyst can be easily separated from the reaction system using a permanent magnet and used three times without significantly losing its catalytic activity and selectivity.     

Iridium‐Catalyst‐Based Autonomous Bubble‐Propelled Graphene Micromotors with Ultralow Catalyst Loading

A novel concept of an iridium‐based bubble‐propelled Janus‐particle‐type graphene micromotor with very high surface area and with very low catalyst loading is described. The low loading of Ir catalyst (0.54 at %) allows for fast motion of graphene microparticles with high surface area of 316.2 m² g^?1. The micromotor was prepared with a simple and scalable method by thermal exfoliation of iridium‐doped graphite oxide precursor composite in hydrogen atmosphere. Oxygen bubbles generated from the decomposition of hydrogen peroxide at the iridium catalytic sites provide robust propulsion thrust for the graphene micromotor. The high surface area and low iridium catalyst loading of the bubble‐propelled graphene motors offer great possibilities for dramatically enhanced cargo delivery.     

A new strategy to design a graphene oxide supported palladium complex as a new heterogeneous nanocatalyst and application in carbon–carbon and carbon‐heteroatom cross‐coupling reactions

The palladium nanoparticles were successfully stabilized with an average diameter of 6–7 nm through the coordination of palladium and terpyridine‐based ligands grafted on graphene oxide surface. The graphene oxide supported palladium nanoparticles were thoroughly characterized and applied as an efficient heterogeneous catalyst in carbon–carbon (Suzuki‐Miyaura, Mizoroki‐Heck coupling reactions) and carbon–heteroatom (C‐N and C‐O) bond‐forming reactions. The catalyst was simply recycled from the reaction mixture and was reused consecutive four times with small drop in catalytic activity.     

Heck and oxidative boron Heck reactions employing Pd(II) supported amphiphilized polyethyleneimine‐functionalized MCM‐41 (MCM‐41@aPEI‐Pd) as an efficient and recyclable nanocatalyst

A novel nanocatalyst was developed based on covalent surface functionalization of MCM‐41 with polyethyleneimine (PEI) using [3‐(2,3‐Epoxypropoxy)propyl] trimethoxysilane (EPO) as a cross‐linker. Amine functional groups on the surface of MCM‐41 were then conjugated with iodododecane to render an amphiphilic property to the catalyst. Palladium (II) was finally immobilized onto the MCM‐41@PEI‐dodecane and the resulted MCM‐41@aPEI‐Pd nanocatalyst was characterized by FT‐IR, TEM, ICP‐AES and XPS. Our designed nanocatalyst with a distinguished core‐shell structure and Pd²⁺ ions as catalytic centers was explored as an efficient and recyclable catalyst for Heck and oxidative boron Heck coupling reactions. In Heck coupling reaction, the catalytic activity of MCM‐41@aPEI‐Pd in the presence of triethylamine as base led to very high yields and selectivity. Meanwhile, the MCM‐41@aPEI‐Pd as the first semi‐heterogeneous palladium catalyst was examined in the C‐4 regioselective arylation of coumarin via the direct C‐H activation and the moderate to excellent yields were obtained toward different functional groups. Leaching test indicated the high stability of palladium on the surface of MCM‐41@aPEI‐Pd as it could be recycled for several runs without significant loss of its catalytic activity.     

Synthesis,characterization and application of graphene palladium porphyrin as a nanocatalyst for the coupling reactions such as: Suzuki‐Miyaura and Mizoroki‐Heck

The palladium(II)‐coordinated 5,10,15,20‐tetrakis‐(4‐hexyloxyphenyl)‐porphyrin as a macrocyclic palladium complex was covalently grafted to the surface of graphene oxide (denoted as GO‐CPTMS@Pd‐TKHPP). GO‐CPTMS@Pd‐TKHPP was characterized using microscopic and spectroscopic techniques for confirmation of functionalization. The synthesized catalyst was checked in the Suzuki‐Miyaura and the Mizoroki‐Heck coupling reactions. The catalyst is very easy to handle, environmentally safe and economical. Also, this catalytic system shows high catalytic activity and the yields of the products are excellent. Moreover, the suggested catalyst was reusable for five runs with no significant decrease in catalytic activity.     

A Phytic Acid Induced Super‐Amphiphilic Multifunctional 3D Graphene‐Based Foam

Surfaces with super‐amphiphilicity have attracted tremendous interest for fundamental and applied research owing to their special affinity to both oil and water. It is generally believed that 3D graphenes are monoliths with strongly hydrophobic surfaces. Herein, we demonstrate the preparation of a 3D super‐amphiphilic (that is, highly hydrophilic and oleophilic) graphene‐based assembly in a single‐step using phytic acid acting as both a gelator and as a dopant. The product shows both hydrophilic and oleophilic intelligence, and this overcomes the drawbacks of presently known hydrophobic 3D graphene assemblies. It can absorb water and oils alike. The utility of the new material was demonstrated by designing a heterogeneous catalytic system through incorporation of a zeolite into its amphiphilic 3D scaffold. The resulting bulk network was shown to enable efficient epoxidation of alkenes without prior addition of a co‐solvent or stirring. This catalyst also can be recovered and re‐used, thereby providing a clean catalytic process with simplified work‐up.     

Application of biosynthesized palladium nanoparticles (Pd NPs) on Rosa canina fruit extract‐modified graphene oxide as heterogeneous nanocatalyst for cyanation of aryl halides

A green palladium (Pd)‐based catalyst supported on Rosa canina fruit extract‐modified graphene oxide [Pd nanoparticles (NPs)/reduced graphene oxide (RGO)‐Rosa canina] hybrid materials has been used as a recoverable and heterogeneous nanocatalyst for cyanating aryl halides using K₄[Fe (CN)₆] as the resource of cyanide. The nitriles were achieved in good to high yield, and the catalyst can be recovered and reused for up to seven cycles with no remarkable decrease in its catalytic activity.     

Cu(II) immobilized on Fe3O4–diethylenetriamine: A new magnetically recoverable catalyst for the synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and oxidative coupling of thiols

Cu(II) immobilized on Fe₃O₄–diethylenetriamine was designed as a new, inexpensive and efficient heterogeneous catalyst for the synthesis of 2,3‐dihydroquinazolin‐4(1H )‐ones and the oxidative coupling of thiols. The structure of the nanomagnetic catalyst was comprehensively characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, X‐ray diffraction and atomic absorption spectroscopy. Simple preparation of the catalyst from commercially available materials, high catalytic activity, simple operation, high yields, use of green solvents, easy magnetic separation and reusability of the catalyst with unaltered activity make our protocol a green and feasible synthetic strategy.