Monodisperse Sandwich‐Like Coupled Quasi‐Graphene Sheets Encapsulating Ni2P Nanoparticles for Enhanced Lithium‐Ion Batteries

In this report, sandwiched Ni₂P nanoparticles encapsulated by graphene sheets are first synthesized by directly encapsulating functional units in graphene sheets instead of fabricating separate graphene sheets and then immobilizing the functional components onto the generated surfaces. In this strategy, we use low‐cost, sustainable and environmentally friendly glucose as a carbon source and NiNH₄PO₄ ? H₂O nanosheets as sacrificial templates. This unique structure obtained here cannot only prevent the nanoparticles from aggregation or loss but also enhance the electronic conductivity compared to the independent nanoparticles. Furthermore, the novel sandwich‐like Ni₂P/C can be applied in plenty of fields, especially in electrical energy storage. In this paper, a series of electrochemical tests of the sandwich‐like Ni₂P/C are carried out, which demonstrate the excellent cyclic stability and rate capacity for lithium‐ion batteries.     

Microwave‐Induced In Situ Synthesis of Zn2GeO4/N‐Doped Graphene Nanocomposites and Their Lithium‐Storage Properties

Zn₂GeO₄/N‐doped graphene nanocomposites have been synthesized through a fast microwave‐assisted route on a large scale. The resulting nanohybrids are comprised of Zn₂GeO₄ nanorods that are well‐embedded in N‐doped graphene sheets by in situ reducing and doping. Importantly, the N‐doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn₂GeO₄ nanorods, thereby effectively relieving the volume‐expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as‐formed Zn₂GeO₄/N‐doped graphene nanocomposite exhibits high capacity (1463 mAh g^?1 at a current density of 100 mA g^?1), good cyclability, and excellent rate capability (531 mAh g^?1 at a current density of 3200 mA g^?1). Its superior lithium‐storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn₂GeO₄ nanorods are well‐stabilized by the high electronic conduction and flexibility of N‐doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary‐oxide‐based composites as high‐performance electrode materials that involve structural conversion and transformation.     

Identification of Catalytic Sites for Oxygen Reduction in Metal/Nitrogen‐Doped Carbons with Encapsulated Metal Nanoparticles

The development of metal‐N‐C materials as efficient non‐precious metal (NPM) catalysts for catalysing the oxygen reduction reaction (ORR) as alternatives to platinum is important for the practical use of proton exchange membrane fuel cells (PEMFCs). However, metal‐N‐C materials have high structural heterogeneity. As a result of their high‐temperature synthesis they often consist of metal‐N_x sites and graphene‐encapsulated metal nanoparticles. Thus it is hard to identify the active structure of metal‐N‐C catalysts. Herein, we report a low‐temperature NH₄Cl‐treatment to etch out graphene‐encapsulated nanoparticles from metal‐N‐C catalysts without destruction of co‐existing atomically dispersed metal‐N_x sites. Catalytic activity is much enhanced by this selective removal of metallic nanoparticles. Accordingly, we can confirm the spectator role of graphene‐encapsulated nanoparticles and the pivotal role of metal‐N_x sites in the metal‐N‐C materials for ORR in the acidic medium.     

Nanostructured Fe2O3–graphene composite as a novel electrode material for supercapacitors

Nanostructured Fe₂O₃–graphene composite was successfully fabricated through a facile solution-based route under mild hydrothermal conditions. Well-crystalline Fe₂O₃ nanoparticles with 30–60?nm in size are highly encapsulated in graphene nanosheet matrix, as demonstrated by various characterization techniques. As electrode materials for supercapacitors, the as-obtained Fe₂O₃–graphene nanocomposite exhibits large specific capacitance (151.8?F?g^?1 at 1?A?g^?1), good rate capability (120?F?g^?1 at 6?A?g^?1), and excellent cyclability. The significantly enhanced electrochemical performance compared with pure graphene and Fe₂O₃ nanoparticles may be attributed to the positive synergetic effect between Fe₂O₃ and graphene. In virtue of their superior electrochemical performance, they will be promising electrode materials for high-performance supercapacitors applications.     

Graphene-encapsulated Fe3O4 nanoparticles with 3D laminated structure as superior anode in lithium ion batteries

Fe₃O₄–graphene composites with three‐dimensional laminated structures have been synthesised by a simple in situ hydrothermal method. From field‐emission and transmission electron microscopy results, the Fe₃O₄ nanoparticles, around 3–15 nm in size, are highly encapsulated in a graphene nanosheet matrix. The reversible Li‐cycling properties of Fe₃O₄–graphene have been evaluated by galvanostatic discharge–charge cycling, cyclic voltammetry and impedance spectroscopy. Results show that the Fe₃O₄–graphene nanocomposite with a graphene content of 38.0 wt % exhibits a stable capacity of about 650 mAh g^?1 with no noticeable fading for up to 100 cycles in the voltage range of 0.0–3.0 V. The superior performance of Fe₃O₄–graphene is clearly established by comparison of the results with those from bare Fe₃O₄. The graphene nanosheets in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe₃O₄.     

Fabrication of magnetically separable palladium–graphene nanocomposite with unique catalytic property of hydrogenation

One step solvothermal route has been developed to prepare a well dispersed magnetically separable palladium–graphene nanocomposite, which can act as a unique catalyst against hydrogenation due to the uniform decoration of palladium nanoparticles throughout the surface of the magnetite–graphene nanocomposite and hence can be reused for several times. In addition to catalytic activity, palladium nanoparticles also facilitate the formation and homogeneous distribution of magnetite (Fe₃O₄) nanoparticles onto the graphene surfaces or else an agglomerated product has been obtained after the solvothermal reduction of graphene oxide in presence of Fe³⁺ alone.     

A Designed TiO2/Carbon Nanocomposite as a High‐Efficiency Lithium‐Ion Battery Anode and Photocatalyst

Herein, a peapod‐like TiO₂/carbon nanocomposite has successfully been synthesized by a rational method for the first time. The novel nanostructure exhibits a distinct feature of TiO₂ nanoparticles encapsulated inside and the carbon fiber coating outside. In the synthetic process, H₂Ti₃O₇ nanotubes serve as precursors and templates, and glucose molecules act as the green carbon source. With the alliciency of hydrogen bonding between H₂Ti₃O₇ and glucose, a thin polymer layer is hydrothermally assembled and subsequently converted into carbon fibers through calcinations under an inert atmosphere. Meanwhile, the precursors of H₂Ti₃O₇ nanotubes are transformed into the TiO₂ nanoparticles encapsulated in carbon fibers. The achieved unique nanocomposites can be used as excellent anode materials in lithium‐ion batteries (LIBs) and photocatalytic reagents in the degradation of rhodamine B. Due to the synergistic effect derived from TiO₂ nanoparticles and carbon fibers, the obtained peapod‐like TiO₂/carbon cannot only deliver a high specific capacity of 160 mAh g^?1 over 500 cycles in LIBs, but also perform a much faster photodegradation rate than bare TiO₂ and P25. Furthermore, owing to the low cost, environmental friendliness as well as abundant source, this novel TiO₂/carbon nanocomposite will have a great potential to be extended to other application fields, such as specific catalysis, gas sensing, and photovoltaics.     

An efficient way to functionalize graphene sheets with presynthesized polymer via ATNRC chemistry

Graphene nanosheets offer intriguing electronic, thermal and mechanical properties and are expected to find a variety of applications in high‐performance nanocomposite materials. The great challenge of exfoliating and dispersing pristine graphite or graphene sheets in various solvents or matrices can be achieved by facilely and properly chemical functionalization of the carbon nanosheets. Here we reported an efficient way to functionalize graphene sheets with presynthesized polymer via a combination of atom transfer nitroxide radical coupling chemistry with the grafting‐onto strategy, which enable us to functionalize graphene sheets with well‐defined polymer synthesized via living radical polymerization. A radical scavenger species, 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), was firstly anchored onto ? COOH groups on graphene oxide (GO) to afford TEMPO‐functionalized graphene sheets (GS‐TEMPO), meanwhile, the GO sheets were thermally reduced. Next, GS‐TEMPO reacted with Br‐terminated well‐defined poly(N‐isopropylacrylamide) (PNIPAM) homopolymer, which was presynthesized by SET‐LRP, in the presence of CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine to form PNIPAM‐graphene sheets (GS‐PNIPAM) nanocomposite in which the polymers were covalently linked onto the graphene via the alkoxyamine conjunction points. The PNIPAM‐modified graphene sheets are easily dispersible in organic solvents and water, and a temperature‐induced phase transition was founded in the water suspension of GS‐PNIPAM. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Flexible Magnetic Nanoparticles–Reduced Graphene Oxide Composite Membranes Formed by Self‐Assembly in Solution

A facile and robust route for the pre‐synthesized Fe₃O₄ nanoparticles (NPs) exclusively assembled on both sides of reduced graphene oxide (RGO) sheets with tunable density forming two‐dimensional NPs composite membranes is developed in solution. The assembly is driven by electrostatic attraction, and the nanocomposite sheets display considerable mechanical robustness, such as it can sustain supersonic and solvothermal treatments without NPs falling off, also, can freely float in solution and curl into a tube. The obtained two‐dimensional composite grain membranes exhibit superparamagnetic behavior at room temperature but responds astutely to an external magnetic field. In addition, these magnetic composite membranes show an enhanced absorption capability for microwaves. The grain sheets are attractive for biomedical, sensors, environmental applications and electric‐magnetic devices benefited from large surfaces, high magnetization moment, and superparamagnetic properties. The effective integration of oxide nanocrystals on RGO sheets provides a new way to design semiconductor–carbon nanocomposites for nanodevices or catalytic applications.     

Fabrication of Fe‐Doped LiCoO2 Sandwich‐Like Nanocomposites as Excellent Performance Cathode Materials for Lithium‐Ion Batteries

In this article, the two‐layer sandwiched graphene@LiFe_0.2Co_0.8O₂ nanoparticles (SG@LFCO) have been prepared and investigated as high‐rate and long‐life cathode materials for rechargeable lithium‐ion batteries. The materials possess a high‐surface area (267.1 m² g^?1) and lots of void spaces. By combining various favorable conditions, such as Fe doping, coating graphene, and designing novel morphology, the as‐prepared materials deliver a specific capacity of 115 mAh g^?1 at 10 C. At the 0.1 C cycling rate, the capacity retention of 97.2 % is sustained after 250 cycles and a coulombic efficiency of around 97.6 % is obtained.     

Label‐free Electrochemical Aptasensor for Carcino‐embryonic Antigen Based on Ternary Nanocomposite of Gold Nanoparticles,Hemin and Graphene

In this report, a label‐free electrochemical aptasensor for carcino‐embryonic antigen (CEA) was successfully developed based on a ternary nanocomposite of gold nanoparticles, hemin and graphene nanosheets (AuNPs‐HGNs). This nanocomposite was prepared by decorating gold nanoparticles on the surface of hemin functionalized graphene nanosheets via a simple wet‐chemical strategy. The aptamer can be assembled on the surface of AuNPs‐HGNs/GCE (glassy carbon electrode) through Au‐S covalent bond to form the sensing interface. Hemin absorbed on the graphene nanosheets not only acts as a protective agent of graphene sheets, but also as an in situ probe base on its excellent redox properties. Gold nanoparticles provide with both numerous binding sites for loading CEA binding aptamer (CBA) and good conductivity to promote the electron transfer. The current changes, which are caused by CEA specifically binding on the modified electrode, are exploited for the label‐free detection of CEA in a very rapid and convenient protocol. Therefore, the method has advantages of high sensitivity, wide linear range (0.0001–10 ng mL^?1), low detection limit (40 fg mL^?1) and attractive specificity. The results illustrate that the proposed label‐free electrochemical aptasensor has a potential application in the biological or clinical target analysis for its simple operation and low cost.     

Advantaging Synergy Photocatalysis with Graphene‐Related Carbon as a Counterpart Player of Titania

The enhancement of photocatalytic activity of TiO₂ can be made either by promoting absorption efficiency of photon energy or by reducing recombination losses of photogenerated charge carriers, for which fabrication of nanocomposite structure with carbon materials is an optional selection. Among various nanocarbons, graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) are more favorable as the counterpart materials because they can provide availability of both obverse and reverse surface, thus doubling effective sites for adsorption, loading of nanoparticles, and interfacial interaction with the loaded nanoparticles. Composition of G/GO with titania, therefore, is a hopeful strategy for achieving synergy or cooperative effect in photocatalysis. In this personal account, we focus on the background and methodology of several soft chemical approaches that we have utilized up to date to fabricate nanocomposites of G/GO and titania, aiming to shed light on the importance of designing of nanocomposite structure for enhancing photocatalysis. In addition, we emphasize the role of interfacial interaction between carbon and titania by exemplifying a hybridized photocatalyst based on inexpensive biomass‐derived carbon sphere (CS), and demonstrate that it is a crucial influential factor underlying an enhanced visible light photocatalysis. CS can be a better selection as a counterpart component than G/GO, whose core‐shell composing structure with titania (TiO₂@CS) can efficiently induce charge transfer so as to achieve a much higher photocatalytic performance under visible light illumination as compared to the composite of rGO and titania.     

Multilevel Coupled Hybrids Made of Porous Cobalt Oxides and Graphene for High-Performance Lithium Storage

Metal oxide coupling with carbon materials holds great promise for lithium storage. Herein, multilevel coupled cobalt oxide–graphene (CoO/CO₃O₄–G) hybrids were fabricated by in situ assembly of Co hydroxide precursors and a calcination process. The oxygen-containing functional groups on the graphene surface act as bridging sites and tend to bond with Co²⁺ ions, effectively modifying the morphology and structure of the Co species. The as-obtained CoO/CO₃O₄–G hybrids are composed of unique CoO/CO₃O₄ porous nanoparticles uniformly anchored on graphene sheets, as confirmed by a series of characterization analyses. Benefiting from these structural characteristics, the CoO/CO₃O₄–G hybrids used as an anode can deliver a high capacity of about 1080 mA h g⁻¹ reversibly at 0.1 Ag⁻¹ in the voltage range between 3.0 and 0.01 V, which is remarkably superior to that of the CoO hexagonal sheets in the absence of graphene. The high reversible capacity of the CoO/CO₃O₄–G hybrids is retained at elevated current densities, for example, a capacity of approximately 455 mA h g⁻¹ can be achieved at a current rate as high as 4 A g⁻¹, indicative of its potential for high-performance lithium-ion batteries.     

Palladium Nanoparticles Bonded to Two‐Dimensional Iron Oxide Graphene Nanosheets: A Synergistic and Highly Reusable Catalyst for the Tsuji–Trost Reaction in Water and Air

Low cost, high activity and selectivity, convenient separation, and increased reusability are the main requirements for noble‐metal‐nanocatalyst‐catalyzed reactions. Despite tremendous efforts, developing noble‐metal nanocatalysts to meet the above requirements remains a significant challenge. Here we present a general strategy for the preparation of strongly coupled Fe₃O₄ and palladium nanoparticles (PdNPs) to graphene sheets by employing polyethyleneimine as the coupling linker. Transmission electron microscopic images show that Pd and Fe₃O₄ nanoparticles are highly dispersed on the graphene surface, and the mean particle size of Pd is around 3 nm. This nanocatalyst exhibits synergistic catalysis by Pd nanoparticles supported on reduced graphene oxide (rGO) and a tertiary amine of polyethyleneimine (Pd/Fe₃O₄/PEI/rGO) for the Tsuji–Trost reaction in water and air. For example, the reaction of ethyl acetoacetate with allyl ethyl carbonate afforded the allylated product in more than 99 % isolated yield, and the turnover frequency reached 2200 h^?1. The yield of allylated products was 66 % for Pd/rGO without polyethyleneimine. The catalyst could be readily recycled by a magnet and reused more than 30 times without appreciable loss of activity. In addition, only about 7.5 % of Pd species leached off after 20 cycles, thus rendering this catalyst safer for the environment.     

PtPd-nanoparticles supported by new carbon materials

Nanocomposites based on PtPd nanoparticles with chemical ordering like disordered solid solution on surface of multilayer graphene have been prepared through thermal shock of mechanically obtained mixture of double complex salt [Pd(NH₃)₄][PtCl₆] and different carbon materials–exfoliated graphite, graphite oxide and graphite fluoride. An effect of original carbon precursors on formation of PtPd bimetallic nanoparticles was studied using X-ray absorption spectroscopy (XAFS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was shown that the distribution of bimetallic nanoparticles over the multilayer graphene surface as well as the particles size distribution is controlled by the graphene precursors. For all nanocomposites, the surface of the nanoparticles was found to be Pd-enriched. In case when the thermal exfoliated graphite and graphite oxide were used as the graphene precursors a thin graphitized layer covered the nanoparticles surface. Such a graphitized layer was not observed in the nanocomposite, which used the fluorinated graphite as the precursor.     

Optimal TiO2–Graphene Oxide Nanocomposite for Photocatalytic Activity under Sunlight Condition: Synthesis,Characterization, and Kinetics

TiO₂–graphene oxide nanocomposites have been fabricated by the sol–gel technique for degradation of a typical cationic dye solution. The prepared photocatalysts were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric‐differential analyses, Brunauer–Emmett–Teller surface area measurement, and scanning and transmission electron microscopy. In addition, the photocatalytic activities of samples were evaluated by degradation of methylene blue aqueous solution under the sunlight irradiation. The change in color of solution was evaluated by the UV–vis spectroscopy, and the maximum photocatalytic decoloration (94%) was achieved within 60 min, which exceeded that of pure anatase under the same conditions. The results show that the nanocomposite containing 9.0 wt% of graphene oxide has the superior photocatalytic performance to either single‐phase anatase or other composites containing different amounts of graphene oxide. The experimental degradation data obtained from the batch tests were analyzed by a modified kinetic model, which predicted the performance with higher regression coefficients and lower relative errors. The distribution of TiO₂ nanoparticles (<20 nm) on graphene oxide sheets is proposed to be the efficient factor in the homogeneous degradation of dye which can concomitantly improve the photocatalytic activity.     

Preparation of magnetic CoFe2O4-functionalized graphene sheets via a facile hydrothermal method and their adsorption properties

Magnetic CoFe₂O₄-functionalized graphene sheets (CoFe₂O₄-FGS) nanocomposites have been synthesized by hydrothermal treatment of inorganic salts and thermal exfoliated graphene sheets. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that cobalt ferrite nanoparticles with sizes of 10-40 nm are well dispersed on graphene sheets. OH⁻ was recognized as a tie to integrate the inorganic salts with the graphene sheets, which made reaction started and developed on the surface of graphene sheets and formed cobalt ferrite nanoparticles on graphene sheets. The adsorption kinetics investigation revealed that the adsorption of methyl orange from aqueous solution over the as-prepared CoFe₂O₄-FGS nanocomposites followed pseudo-second-order kinetic model and the adsorption capacity was examined as high as 71.54 mg g⁻¹. The combination of the superior adsorption of FGS and the magnetic properties of CoFe₂O₄ nanoparticles can be used as a powerful separation tool to deal with water pollution.     

Nonenzymatic H2O2 Electrochemical Sensor Based on SnO2‐NPs Coated Polyethylenimine Functionalized Graphene

This paper demonstrated using polyethylenimine (PEI)‐functionalized graphene (Gr) incorporating tin oxide (SnO₂) hybrid nanocomposite as a platform for nonenzymatic H₂O₂ electrochemical sensor. The results of UV‐vis spectroscopy and X‐ray diffraction (XRD) confirmed the simultaneous formation of tin oxide (SnO₂) nanocomposite and reduction of graphene oxide (GO). Transmission electron microscopy (TEM) images showed a uniform distribution of nanometer‐sized tin oxide nanoparticles on the grapheme sheets, which could be achieved using stannous chloride (SnCl₂) complex instead of tin oxide as precursor. The electrochemical measurements, including cyclic voltammetry (CV) and amperometric performance (I‐t), showed that the PEI‐functionalized Gr supported SnO₂ (SnO₂‐PEI‐Gr) exhibited an excellent electrocatalytic activity toward the H₂O₂. The corresponding calibration curve of the current response showed a linear detection range of 9×10⁻⁶∼1.64×10⁻³ mol L⁻¹, while the limit of detection was estimated to be 1×10⁻⁶ mol L⁻¹. Electrochemical studies indicated that SnO₂ and functionalized Gr worked synergistically for the detection of H₂O₂.     

Synthesis of a nanocomposite containing a water‐soluble polythiophene derivative and gold nanoparticles

This paper reports on a facile method for synthesizing gold nanoparticles (AuNps) with diameter around 5 nm encapsulated with water‐soluble polythiophene sulfonate poly[2‐(3‐thienyl)ethyloxy‐4‐butylsulfonate] sodium salt (PTS) and their physical–chemical characterization. The synthesis of hybrid materials of polythiophene derivatives and gold nanoparticles is a way to improve the polymer properties, mainly in application for chemical and optical sensing platforms. The AuNps were prepared by reducing gold salt with acid aqueous sodium citrate by the Turkvich method in the presence of PTS, and both PTS and citrate helped to stabilize the AuNps. The suspensions of AuNp:PTS presented good chemical and photostability for long period of storage. The nanoparticles encapsulated with the polymer presented smaller diameters than those obtained using only sodium citrate, according to scanning electron microscopy images. The AuNps obtained were used for fabrication LbL films with commercial chitosan, which were characterized by impedance spectroscopy measurements. The results showed that the charge transfer resistance values (R_ct) decrease as the average diameter of the AuNps decreases and the proportion of PTS increases in the nanocomposite. Such increase of the nanocomposite conductivity, given by the low values of R_ct, indicates that the novel film architecture developed is promising for chemical sensing applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1245–1254     

One‐pot synthesis of magnetic palladium–NiFe2O4–graphene oxide composite: an efficient and recyclable catalyst for Heck reaction

A magnetically separable NiFe₂O₄@GO–Pd composite (GO = graphene oxide) was successfully prepared by a facile one‐pot hydrothermal strategy. This new kind of hybrid material was fully characterized using powder X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Structural characterizations confirmed the formation of NiFe₂O₄ and Pd nanocrystals, and the close anchoring between nanoparticles and GO sheets. Additionally, the as‐prepared NiFe₂O₄@GO–Pd nanocomposite was effectively employed in the palladium‐catalyzed Heck reaction in an ethanol–water system as a green solvent. The catalyst was completely recoverable with the simple application of an external magnetic field and with no obvious loss of catalytic activity even after six repeated cycles. Copyright © 2016 John Wiley & Sons, Ltd.