Small and uniform Pd monometallic/bimetallic nanoparticles decorated on multi-walled carbon nanotubes for efficient reduction of 4-nitrophenol

Pd and PdAu nanoparticles stabilized on multi-walled carbon nanotubes are synthesized by simple metal sputtering onto nanotubes dispersed in ionic liquids. The nanoparticles are as small as about 2 nm and possess bare surface without capping agents. The surface density of the nanoparticles can be controlled by tuning the sputtering conditions, while the sizes of the nanoparticles remain very similar. The supported Pd/PdAu nanoparticles are highly catalytically active for reduction of 4-nitrophenol, and an activity factor up to 205 s⁻¹ g⁻¹ is achieved. The PdAu bimetallic nanoparticles show superior catalytic performance than the Pd monometallic counterparts, indicating the synergistic effects of Pd and Au. The present approach has the merit of making alloyed nanocatalysts as simple as making corresponding elementary ones.     

Rapid preparation of noble metal nanocrystals via facile coreduction with graphene oxide and their enhanced catalytic properties

We present the facile preparation results of noble metal nanostructures induced by graphene via rapid coreduction by Ti(3+) at room temperature. Such a reduction of graphene oxide (GO) can be readily performed in solutions or on various substrates within seconds. High quality noble metal nanocrystals can be prepared by using graphene as the controlling agent at room temperature, including Rh, Au and Rh-Pt nanodendrites and Pd nanoparticles, showing the roles of graphene on tuning the growth behaviors of nanostructures. These surface clean Pd nanoparticles show high catalytic activity and selectivity in Suzuki and Heck coupling reactions.     

Preparation of uniform 2D ZnO nanostructures by the ionic liquid-assisted sonochemical method and their optical properties

Uniform 2D ZnO nanostructures were successfully synthesized by a sonochemical method, using 1,4-diazabicyclo[2.2.2]octane (DABCO) and imidazolium-based ionic liquids in water as the solvent after 30 min. The effects of ionic liquids as template on the morphology and size of nanostructures were investigated. The structural and optical properties of ZnO nanostructures were studied by using XRD, SEM and UV–visible. The characteristic results revealed that using ionic liquids in water not only prevents a drastic increase in the crystallite size of the zinc oxide species but also provides suitable conditions for the oriented growth of primary nanoparticles with nanosheet morphology. SEM revealed that using the longer alkyl chain at position-1 of DABCO or dicationic ionic liquids causes a uniform nanosheet and nanoleaf. A possible mechanism was proposed to explain the formation of ZnO nanostructures with nanosheet morphology. Also band gap variation with particle size was investigated.     

Controlled assembly of graphene shells encapsulated gold nanoparticles and their integration with carbon nanotubes

Controlled growth and uniform patterning of graphene/carbon shells encapsulated gold nanoparticles (GNPs) on silicon wafer or on high curvature carbon nanotubes (CNTs) is reported here. This was achieved by utilizing patterned gold nanoparticles with controlled sizes (∼30–600 nm) via gold film dewetting process. Surface-oxidized and patterned nanoparticles were used as sacrificial catalysts for the chemical vapor deposition (CVD) growth of graphene/carbon shells. The shell morphological evolution and thickness as well as surface migration of nanoparticles during the CVD process were studied as a function of the gold nanoparticles size. Reduced surface migration and coalescence was observed for gold nanoparticles after the CVD growth and this was attributed to the initial formation of graphene/carbon shells as well as stable dispersion of the dewetted gold nanoparticles. It is proposed that graphene/carbon shell growth was controlled by Ostwald’s ripening, surface gold oxide, and reducing CVD growth environment. Furthermore, complex heterostructures based on CNTs coated with GNPs were fabricated by dewetting Au films on CNTs and followed by surface oxidation and CVD growth steps. CNTs successfully survived multiple processing steps and selective growth of graphene shells around Au nanoparticles was achieved and studied using microscopic and spectroscopic methods.     

Graphene nano-cutting using biologically derived metal nanoparticles

We have developed a novel technique to cut graphene films using catalytic metal nanoparticles derived from ferritin, which is one of the proteins that contain a constant amount of Fe oxide in its inner core. For site-selective adsorption of ferritin molecules to sapphire surfaces that are partially covered with graphene films, two methods, dipping and spin-coating, were used. Graphene films were etched by the Fe-catalytic reaction with hydrogen gas at elevated temperatures. It was found that ferritin adsorption sites are controlled by graphene film edges, atomic steps of the sapphire substrate, and solution condition such as molecular concentration and ionic strength. We demonstrate that high density nanoribbons can be fabricated by using the uniformly-sized catalyst nanoparticles derived from ferritin and the aligned etching technique guided by the atomic structures of the substrate surface.     

An advanced electrocatalyst with exceptional eletrocatalytic activity via ultrafine Pt-based trimetallic nanoparticles on pristine graphene

It has been a great challenge to directly deposit uniform metal particles onto pristine graphene due to its low surface energy and chemical inertness. Without any surfactant or functionalization, we have developed a unique synthesis of high-quality PtRuNi trimetallic nanoparticles supported on pristine graphene via a simple but effective supercritical route. Due to excellent wettability between supercritical carbon dioxide and the carbon surface, ultrafine metal particles are uniformly and firmly anchored on the graphene sheets. While well retaining its intrinsic structure and outstanding electronic conductivity, the pristine graphene with well-dispersed PtRuNi trimetallic nanoparticles shows significantly improved catalytic activity towards methanol oxidation, which is at least ten times higher than those of the commercial Pt/C and homemade Pt/XC-72 catalysts. The resulting trimetallic hybrid also exhibits high stability as compared to Pt and PtRu/pristine graphene composites and the reduced graphene oxide counterparts. In principle, the supercritical method can be applied to other metal nanoparticles in fabrication of high-performance graphene-based nano-catalysts.     

石墨烯复合功能材料及其在重金属离子检测的电化学研究与应用

石墨烯(GR)是典型的单原子碳纳米材料,具有独特的二维共辄平面结构,其高活性的比表面积和突出的导电性能,在电催化和敏感材料制备领域已得到广泛的应用。氧化石墨烯(GO)作为GR的前驱体,存在大量的含氧官能团,具有良好的水溶分散性。大量GO含氧官能团的介入会破坏其K-7T共辘结构,导致其电学性能变差。GO通过化学、水热合成或直接电化学还原方法可有效修复其共辄平面结构,得到导电性良好的还原氧化石墨烯(rGO),即GR.单组分的GR材料在实际应用中仍存在某些局限性,如电学活性相对较弱,与其它材料加工复合性能较差等。将GR、G O材料与其它功能材料进行复合,可进一步改善复合物的物理或化学性能,如分散性、加工修饰和电催化活性等。综述了石墨烯材料与金属及其氧化物纳米粒子、聚合物、掺杂原子、导电离子液体、碳纳米材料等功能材料复合后,能形成可调控的微结构,具有改性的化学性质和协同发挥的电学效应,表现出显著的电子传递能力及其功能性作用。论述了GR功能化修饰的复合材料作为敏感界面,构筑基于重金属离子检测的电化学生物传感器,可以实现对Pb2+,Hg2+,C『+等多种重金属离子的同时或分别检出,提出了GR复合制备材料的纳米结构特征、功能修饰作用对于提高传感器的电催化活性和选择性性能等方面的应用,并对该研究领域进行了总结与展望。     

Template-free synthesis of large anisotropic gold nanostructures on reduced graphene oxide

The morphologies/dimensions of Au nanostructures can be tailored by merely controlling the reduction degree of graphene oxide surface. Au nanoparticles, long Au nanowires, and semicircular-shaped Au nanoplates are in situ synthesized on slightly, moderately, and highly reduced graphene oxide films respectively, without the need of any templating agent.     

Self-assembled high aspect ratio gold nanostar/graphene oxide hybrid nanorolls

Owing to their unique properties and potential applications in nanoelectronics, graphene and its derivatives have received extensive attention over the last decade. Noble metal nanostructures, on the other hand, enable the confinement and manipulation of light at the nanoscale. Integration of nanocarbons and plasmonic nanostructures is expected to result in synergistic optoelectronic properties that can potentially revolutionize the design and fabrication of optoelectronic devices. In this letter, we demonstrate a simple self-assembly approach to achieve synergistic ensemble of plasmonic gold nanostars and graphene oxide. Gold nanostars are directly nucleated and grown on the surface of graphene oxide by in situ reduction method producing differential surface charged hybrid macroanionic sheets, which are then kinetically rolled and simultaneously assembled into high aspect ratio hybrid nanorolls by means of the interplay of kinetics and graphene–gold interactions.     

A general strategy for synthesis of metal oxide nanoparticles attached on carbon nanomaterials

We report a general strategy for synthesis of a large variety of metal oxide nanoparticles on different carbon nanomaterials (CNMs), including single-walled carbon nanotubes, multi-walled carbon nanotubes, and a few-layer graphene. The approach was based on the π-π interaction between CNMs and modified aromatic organic ligands, which acted as bridges connecting metal ions and CNMs. Our methods can be applicable for a large variety of metal ions, thus offering a great potential application.     

Controllable coverage of chemically modified graphene sheets with gold nanoparticles by thermal treatment of graphite oxide with N,N-dimethylformamide

We describe a simple chemical method to reduce and functionalize graphite oxide by reaction with dimethylformamide under controlled heating. Our experiments suggest that the reaction conditions assist the decomposition of the solvent to produce dimethylamine molecules that can react with the oxygen-rich functional groups covering the surface of the exfoliated layers of graphene, therefore generating chemically modified graphene (CMG). These N-functionalities have been next used as anchoring points for the grafting of Au nanoparticles. Given that the functionalization extent can be controlled with the temperature and reaction time, our approach can be considered as a straightforward route for the controlled decoration of CMG layers with gold nanoparticles.     

The microwave-assisted ionic liquid nanocomposite synthesis: platinum nanoparticles on graphene and the application on hydrogenation of styrene

The microwave-assisted nanocomposite synthesis of metal nanoparticles on graphene or graphite oxide was introduced in this research. With microwave assistance, the Pt nanoparticles on graphene/graphite oxide were successfully produced in the ionic liquid of 2-hydroxyethanaminium formate [HOCH₂CH₂NH₃][HCO₂]. On graphene/graphite oxide, the sizes of Pt nanoparticles were about 5 to 30 nm from transmitted electron microscopy (TEM) results. The crystalline Pt structures were examined by X-ray diffraction (XRD). Since hydrogenation of styrene is one of the important well-known chemical reactions, herein, we demonstrated then the catalytic hydrogenation capability of the Pt nanoparticles on graphene/graphite oxide for the nanocomposite to compare with that of the commercial catalysts (Pt/C and Pd/C, 10 wt.% metal catalysts on activated carbon from Strem chemicals, Inc.). The conversions with the Pt nanoparticles on graphene are >99% from styrene to ethyl benzene at 100°C and under 140 psi H₂ atmosphere. However, ethyl cyclohexane could be found as a side product at 100°C and under 1,520 psi H₂ atmosphere utilizing the same nanocomposite catalyst.     

Fabrication of hybrids based on graphene and metal nanoparticles by in situ and self-assembled methods

In this work, we developed two novel strategies to attach metal nanoparticles (Au and Ag) to the surface of graphene nanosheets, in which graphene oxide was first modified by the linking molecule (3-mercaptopropyl)triethoxysilane and then subjected to different treatments including in situ and self-assembled techniques. The synthesis processes and the resulting hybrids were investigated by ultraviolet-visible measurements, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that both approaches could effectively immobilize metal nanoparticles onto a graphene surface, and that better distribution and size control of metal nanoparticles were obtained by the self-assembled method. Moreover, we prepared poly(vinylidene fluoride)/graphene-Ag nanocomposites by a solution blending method. The AC conductivity of the resulting nanocomposites could be increased significantly when the loading amount of graphene-Ag was only 2 wt%. We expect that such graphene-metal nanoparticle hybrids may be potentially useful in composite reinforcement, sensors, and electronic devices.     

Nanocomposites of size-controlled gold nanoparticles and graphene oxide: formation and applications in SERS and catalysis

In this paper, we describe the formation of Au nanoparticle-graphene oxide (Au-GO) and -reduced GO (Au-rGO) composites by noncovalent attachment of Au nanoparticles premodified with 2-mercaptopyridine to GO and rGO sheets, respectively, viaπ-π stacking and other molecular interactions. Compared with in situ reduction of HAuCl4 on the surface of graphene sheets that are widely used to prepare Au-GO composites, the approach developed by us offers well controlled size, size distribution, and morphology of the metal nanoparticles in the metal-GO nanohybrids. Moreover, we investigated surface enhanced Raman scattering (SERS) and catalysis properties of the Au-graphene composites. We have demonstrated that the Au-GO composites are superior SERS substrates to the Au NPs. Similarly, a comparative study on the catalytic activities of the Au, Au-GO, and Au-rGO composites in the reduction of o-nitroaniline to 1,2-benzenediamine by NaBH4 indicates that both Au-GO and Au-rGO composites exhibit significantly higher catalytic activities than the corresponding Au nanoparticles.     

Small Reduced Graphene Oxides for Highly Efficient Oxygen Reduction Catalysts

We demonstrated highly efficient oxygen reduction catalysts composed of uniform Pt nanoparticles on small, reduced graphene oxides (srGO). The reduced graphene oxide (rGO) size was controlled by applying ultrasonication, and the resultant srGO enabled the morphological control of the Pt nanoparticles. The prepared catalysts provided efficient surface reactions and exhibited large surface areas and high metal dispersions. The resulting Pt/srGO samples exhibited excellent oxygen reduction performance and high stability over 1000 cycles of accelerated durability tests, especially the sample treated with 2 h of sonication. Detailed investigations of the structural and electrochemical properties of the resulting catalysts suggested that both the chemical functionality and electrical conductivity of these samples greatly influence their enhanced oxygen reduction efficiency.     

Solution-Based, High-Yield Synthesis of Cobalt-Doped Zinc Oxide Nanorods

Transition metal cobalt-doped zinc oxide (ZnO) nanorods with room-temperature ferromagnetism have been rationally fabricated by a facile solution-based route. The synthesis just involves hydrolyses and condensation processes, which allow the growth of transition metal-doped ZnO nanostructures at a high yield, low cost, and mild temperatures. The morphology of the products can be controlled by tuning the reaction conditions such as precursors, solvents, and reaction time. The nanorods show room-temperature ferromagnetic behavior using C₂₀H₃₇NaO₇S as a surfactant. The origin of the ferromagnetism is also discussed.     

Engineering multi-dimensional nanocarbons with enhanced electrochemical activity as high-performance bifunctional electrocatalyst

Environment-friendly metal-free electrocatalysts with high performance and stability are highly desirable for energy conversion and storage instead of noble metal materials. Here we report a three dimensional carbon-based porous aerogel as a bifunctional electrocatalyst by combining carbon nanostructures of various dimensionalities such as carbon onions, carbon nanotubes and graphene oxide. Notably, this all-carbon composite without any transition-metal or heteroatom doping exhibits excellent performance towards both oxygen evolution and oxygen reduction reactions. Our characterizations reveal that the enhancement can be ascribed to the porous-rich structure and large specific surface areas in the integrated nanocarbons architectures. This strategy represents a step toward the design of all-carbon bifunctional catalysts with high performance and low cost.     

A surface-enhanced Raman spectroscopy study of thin graphene sheets functionalized with gold and silver nanostructures by seed-mediated growth

We describe a simple method for decorating graphene (1–5 layers) with Au and Ag nanostructures (nanoparticles, nanorods, and nanoplates). We deposit graphene electrostatically from highly-oriented pyrolytic graphite onto Si/SiO₂ surfaces functionalized with (aminopropyl)trimethoxysilane and grow the metal nanostructures by a seed-mediated growth method from hexanethiolate-coated Au monolayer-protected cluster “seeds” that are attached to graphene by hydrophobic interactions. Scanning electron microscopy reveals the selective growth of Au or Ag nanostructures on the graphene surface. In the case of Au, the low pH 2.8 growth solution causes etching of the graphene and formation of scroll-like structures. For Ag, the high pH 9.3 solution does not seem to affect the graphene. Raman spectroscopy is consistent with the graphene morphology and reveals that the presence of Au and Ag nanostructures increases the Raman scattering from the graphene by a factor of about 45 and 150, respectively. This work demonstrates a simple method for decorating graphene with noble metal nanostructures that may have interesting optical, electronic, and chemical properties for applications in nanoelectronics, sensing, and catalysis.     

Glucose sensing,photocatalytic and antibacterial properties of graphene–ZnO nanoparticle hybrids

A simple and efficient approach was developed to uniformly decorate graphene nanosheets with zinc oxide (ZnO) nanoparticles. A single source precursor, zinc benzoate dihydrazinate complex, has been used for the in situ generation of ZnO nanoparticles onto graphene at a relatively low temperature, 200 °C. Physico chemical analyses such as X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy revealed that ZnO nanoparticles were finely dispersed on the surface of graphene. ZnO–graphene hybrids were further characterized by Raman spectroscopy and ultraviolet visible spectroscopy and room-temperature photoluminescence. The materials exhibited excellent photocatalytic activity as evident from the degradation of methylene blue in ethanol under UV irradiation. An electrochemical glucose biosensor was fabricated by immobilization of glucose oxidase on the ZnO–graphene hybrids. This biosensor showed improved sensitivity towards glucose as compared to graphene. Also, the hybrids showed significant antibacterial activity against E. coli, gram negative bacteria. This simple and economical preparation strategy may be extended for the preparation of other graphene-based hybrids.     

Exfoliated graphene sheets decorated with metal/metal oxide nanoparticles: Simple preparation from cation exchanged graphite oxide

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au–Gr and Ag–Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu–Gr and Co–Gr) existed as a metal oxide. Most Ni particles in Ni–Gr were metal, but the surfaces of large particles were partly oxidized, producing a core–shell structure. The Ag–Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag–Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment.