Photochemical loading of metal nanoparticles on reduced graphene oxide sheets using phosphotungstate

Well-dispersed reduced graphene oxide (r-GO) sheets loaded with metal nanoparticles were produced in dimethylformamide (DMF). The r-GO suspension was prepared through the photocatalytic reduction of graphene oxide (GO) using a phosphotungstate as a homogeneous photocatalyst under UV irradiation. Immediately after UV lamp was turned off, the injection of precursors of Ag, Au, and Pd caused the rapid nucleation because photoreduced phosphotungstates as well as electrons stored in r-GO directly reduced metal ions. Furthermore, the r-GO sheets not only provided the nucleation sites but also prohibited the metal nanoparticles from agglomeration. As a result, relatively uniform-sized metal nanoparticles were formed on the r-GO sheets. With phosphotungstates and UV light irradiation, both GO and metal ions can be reduced to form the hybrids of Ag, Au, and Pd/r-GO as a suspension in DMF or an isolated paper sheet without using any toxic reagents.     

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.     

Graphene nanosheets-polypyrrole hybrid material as a highly active catalyst support for formic acid electro-oxidation

A novel electrode material based on graphene oxide (GO)-polypyrrole (PPy) composites was synthesized by in situ chemical oxidation polymerization. Palladium nanoparticles (NPs) with a diameter of 4.0 nm were loaded on the reduced graphene oxide(RGO)-PPy composites by a microwave-assisted polyol process. Microstructure analysis showed that a layer of coated PPy film with monodisperse Pd NPs is present on the RGO surface. The Pd/RGO-PPy catalysts exhibit excellent catalytic activity and stability for formic acid electro-oxidation when the weight feed ratio of GO to pyrrole monomer is 2:1. The superior performance of Pd/RGO-PPy catalysts may arise from utilization of heterogeneous nucleation sites for NPs and the greatly increased electronic conductivity of the supports.     

An efficient reduction route for the production of Pd–Pt nanoparticles anchored on graphene nanosheets for use as durable oxygen reduction electrocatalysts

Pt and Pd–Pt nanoparticles were anchored on reduced graphene oxide (RGO) with the aid of poly(diallyldimethylammonium chloride) (PDDA), where Pt and Pd ions were first attached to PDDA-functionalized graphene oxide sheets and the encased metal ions and graphene oxide were then reduced simultaneously by ethylene glycol. As supported by transmission electron microscopy, metal nanoparticles, of small particle size even at a high metal loading, were chemically attached to PDDA–RGO. X-ray diffraction indicates that the as-prepared Pd–Pt nanoparticles have a single-phase fcc structure and are principally alloys of Pd and Pt. Among the RGO-supported Pt and Pd–Pt catalysts, Pt nanoparticles anchored on PDDA–RGO exhibit the highest activity for the oxygen reduction reaction (ORR), and the ORR activity of the Pd–Pt alloy electrocatalysts increases with Pt content. All the catalysts demonstrate an enhanced ORR durability when PDDA is present; strongly suggesting that PDDA plays a crucial role in the dispersion and stabilization of the metal nanoparticles on RGO. The ORR activities of the Pd–Pt catalysts remain enhanced even after accelerated durability testing. The formation of a Pt-rich shell, as confirmed by X-ray photoelectron spectroscopy and CO stripping voltammetry, may account for the increased activity.     

Grafting polymer brushes on graphene oxide for controlling surface charge states and templated synthesis of metal nanoparticles

In this article, poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes were grafted onto graphene oxide (GO) sheet via noncovalent modification of pyrene terminated initiator and subsequent in situ surface‐initiated atom transfer radical polymerization (SI‐ATRP). The results of zeta‐potentials, dispersivity measurement as well as the permeability of cationic and anionic redox‐active probe molecules reveal that the as‐prepared GO/PDMAEMA composite exhibits zwitterionicity because of the presence of phenol hydroxyl, carboxyl, and amine groups and the charging state can be manipulated by controlling pH values. Furthermore, by ion exchange and in situ reduction, palladium and gold nanoparticles were successfully uploaded and the catalytic property of the uniformly distributed Pd‐Au nanoparticles on GO sheet was investigated. These results reported in this work may open primarily toward constructing a bridge among GO, charged polymer and metal nanoparticles and secondarily to represent a new strategy for uniformly depositing inorganic nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

钯/纳米石墨片复合材料的制备及其对甲醇的电催化性能

用改进的Hummers方法和机械剥离法制备纳米石墨片,以硼氢化钠为还原剂,采用一步法制备蠕虫状Pd纳米颗粒/纳米石墨片。结果表明这种新型的纳米石墨片的制备方法简单快速、温和高效。11.5 nm的Pd纳米颗粒能良好地分散在纳米石墨片上,且复合材料在碱性条件下对甲醇具有良好的催化活性和抗毒化性能,比相同条件下制备出的Pd负载在传统的改进Hummers方法制备的氧化石墨烯和商业炭黑Vulcan XC-72的催化性能更佳。     

Vacuum-assisted microwave reduction/exfoliation of graphite oxide and the influence of precursor graphite oxide

One-step synthesis of high quality graphene at gram-scale quantities is important for industrial applications, e.g. in electrochemistry for sensing and energy storage. Currently, thermal reduction/exfoliation of graphite oxide (GO) is a typical method of choice. However, it has the drawback of requiring specialized equipment for rapid thermal shock. A recent alternative method, microwave-assisted exfoliation, usually suffers from poor reduction of graphite oxide and thus low C/O ratios. Herein we show that vacuum-assisted microwave reduction/exfoliation of graphite oxide in a closed system leads to high C/O ratios and partial hydrogenation of graphene (2.6 at.% of H). Microwave irradiation of graphite oxide in vacuum leads to outgassing from GO and the creation of plasma which aids temperature distribution and hydrogenation. This plasma is quickly extinguished by further dramatic evolution of gases from GO and consequent pressure increase. We assess the influence of precursor graphite oxide, prepared by Hummers, Staudenmaier, and Hofmann methods, upon the materials properties of microwave exfoliated graphene. We show that microwave-exfoliated graphenes prepared from different graphite oxides show very fast heterogeneous electron transfer rates, with similar electrochemical behaviour to thermally reduced graphene oxide.     

一种具有温敏表面的氧化石墨烯负载钯催化剂的制备及催化性能

以过硫酸铵（APS）为引发剂,N-异丙基丙烯酰胺（NIPAM）为单体,在氧化石墨烯（GO）表面生长温敏高分子聚（N-异丙基丙烯酰胺）（PNIPAM）,获得复合载体GO-PNIPAM,并通过水相浸渍还原法制备具有温度敏感特性的Pd催化剂（Pd/GO-PNIPAM）。采用红外光谱、差示量热、热重、元素分析、透射电镜和电感耦合等离子原子发射光谱对复合载体GO-PNIPAM和Pd催化剂进行表征。结果表明,PNIPAM在GO上的接枝率约占60%。GO-PNIPAM显示出明显的温敏效应,其最低临界溶液温度约37℃。Pd/GO-PNIPAM上Pd纳米颗粒的平均粒径为(4.70±0.85)nm,远小于Pd/GO中Pd平均粒径(8.79±2.68)nm。因此,PNIPAM在GO上的接枝为金属纳米颗粒的沉积提供了大量的锚定位点,有助于金属纳米颗粒在其上的分散。Pd/GO-PNIPAM在高温下（80℃）肉桂醛（CAL）的选择性加氢反应中显示出优良的催化性能,初始转换频率（initial TOF）达192.3min^-1,高于GO负载Pd催化剂（Pd/GO,103.5min^-1）。Pd/GO-PNIPAM较高的Pd纳米颗粒分散性和高温下对CAL良好的吸附性能协同作用,导致其催化活性提高。     

Aqueous phase catalytic hydrodechlorination of 4-chlorophenol over palladium deposited on reduced graphene oxide

Palladium/reduced graphene oxide nanocomposites (Pd/RGO) are synthesized through the impregnation of polyvinyl-pyrrolidone-stabilized palladium nanoparticles on the surface of RGO sheets prepared from the reduction of graphene oxide in the presence of hydrogen gas. The Pd/RGO nanocomposites exhibited excellent catalytic property for the hydrodechlorination of 4-chlorophenol.     

Facile solid-state synthesis of Ag/graphene oxide nanocomposites as highly active and stable catalyst for the reduction of 4-nitrophenol

A facile solid-state synthetic route was used to fabricate graphene oxide (GO) decorated with Ag nanoparticles. Ag/GO nanocomposites were prepared by reducing silver acetate with ascorbic acid in the presence of GO at ambient conditions. The characterization results showed that Ag nanoparticles with an average diameter of ~ 50 nm were well dispersed on the surface of GO nanosheets. Moreover, an application of the obtained Ag/GO nanocomposites as a catalyst in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol by NaBH₄ was demonstrated. The Ag/GO nanocomposites exhibited high activity and stability for the catalytic reduction of 4-NP.     

Pt修饰的Pd/石墨烯纳米复合材料的制备及对乙二醇氧化反应的电催化活性

以氧化石墨(GO)和Pd(NO₃)₂为原料,通过化学还原法制备Pd纳米粒子-石墨烯(Pd/G)纳米复合材料,然后以H₂PtCl₆作为Pt前体,在Pd纳米粒子的表面恒电位沉积Pt,制备不同Pt负载量的Pd/G(Pt-Pd/G)电极.利用场发射扫描电镜(FE-SEM)、透射电镜(TEM)和X射线能谱仪(EDX)对材料的微观结构进行了表征和分析.结果显示石墨烯上的金属粒子分散均匀,平均粒径约7.2nm.电化学测试结果显示Pt-Pd/G电极对乙二醇电化学氧化反应具有良好的催化性能.当纳米粒子的Pt:Pd原子百分比为1:42时,其反应峰电流密度分别为Pd/G和Pt/G电极的3.0倍和2.7倍.少量的Pt沉淀可显著改进Pd/G电极的催化活性.本研究采用的修饰方法简单,修饰效果明显,可应用于其他金属纳米复合材料的异金属修饰.     

Multiscale patterning of graphene oxide and reduced graphene oxide for flexible supercapacitors

A simple and facile method for multiscale, in-plane patterning of graphene oxide and reduced graphene oxide (GO–rGO) was developed by region-specific reduction of graphene oxide (GO) under a mild irradiation. The UV-induced reduction of graphene oxide was monitored by various spectroscopic techniques, including optical absorption, X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD), while the resultant GO–rGO patterned film morphology was studied on optical microscope, scanning electron microscope (SEM), and atomic force microscope (AFM). Flexible symmetric and in-plane supercapacitors were fabricated from the GO–rGO patterned polyethylene terephthalate (PET) electrodes to show capacitances up to 141.2 F/g.     

The use of graphite oxide to produce mesoporous carbon supporting Pt, Ru, or Pd nanoparticles

Mesoporous carbon having platinum, ruthenium or palladium nanoparticles on exfoliated graphene sheets were produced from graphite oxide (GO) and metal complexes. The Pt included carbon was made by heating of the intercalation compound including tetraammineplatinum (II) chloride monohydrate. Samples having Ru or Pd are producible by heating in nitrogen gas atmosphere using hexaammineruthenium (III) chloride or tetraamminepalladium (II) chloride monohydrate instead of Pt complex. The particle sizes of platinum, ruthenium, and palladium were, respectively, 1-3, 1-2, and 3-7 nm. The platinum- or palladium-containing sample showed catalytic activity for oxygen reduction.     

Graphite Oxide as a Novel Host Material of Catalytically Active Pd Nanoparticles

Graphite oxide (GO) was utilized as a novel host material for Pd nanoparticles of controlled crystallite size. Immobilization of the Pd nanoparticles from a stable Pd sol in GO resulted in the formation of organophilic Pd–GO, a layer-structured material, which was characterized by ICP-AES, XRD and TEM. Pd–GO proved to be a highly active and stereoselective catalyst in liquid-phase alkyne hydrogenations under mild conditions.     

Large-scale synthesis of graphene by the reduction of graphene oxide at room temperature using metal nanoparticles as catalyst

A simple chemical approach has been developed for the synthesis of graphene through a mild reduction of graphene oxide (GO) using metal nanoparticles as the catalyst for the hydrolysis reaction of NaBH₄ at room temperature. The morphology and structure of the graphene were characterized with atomic force microscopy and transmission electron microscopy. The reduction process and quality of graphene were followed and examined by UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. By this method, graphene can be prepared in large quantity without using toxic reducing agents such as hydrazine or its derivatives, making it environmentally benign. The reaction is conducted under mild conditions (room temperature), resulting in the formation of fewer defects. The method can be easily scaled up and the metal catalyst can be recycled.     

Silicon nanowire arrays-induced graphene oxide reduction under UV irradiation

This paper reports on efficient UV irradiation-induced reduction of exfoliated graphene oxide. Direct illumination of an aqueous solution of graphene oxide at λ = 312 nm for 6 h resulted in the formation of graphene nanosheets dispersible in water. X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, atomic force microscopy (AFM) and electrochemical measurements (cyclic voltammetry and electrochemical impedance spectroscopy) suggest a restoration of the sp(2) carbon network. The results were compared with graphene nanosheets prepared by photochemical irradiation of a GO aqueous solution in the presence of hydrogenated silicon nanowire (SiNW) arrays or silicon nanowire arrays decorated with silver (SiNW/Ag NPs) or copper nanoparticles (SiNW/Cu NPs). Graphene nanosheets obtained by illumination of the GO aqueous solution at 312 nm for 6 h in the presence of SiNW/Cu NPs exhibited superior electrochemical charge transfer characteristics. This is mainly due to the higher amount of sp(2)-hybridized carbon in these graphene sheets found by XPS analysis. The high level of extended conjugated carbon network was also evident by the water insoluble nature of the resulting graphene nanosheets, which precipitated upon photochemical reduction.     

A green approach for the reduction of graphene oxide nanosheets using non-aromatic amino acids

A simple and green chemistry approach for the preparation of reduced graphene oxide nanosheets through the reduction of graphene oxide (GO) using non-aromatic and thiol-free amino acids as the reductant was successfully demonstrated. l-Aspartic acid and valine amino acids were used as models to prove that the reduction method is generic to other amino acids. The significance of the proposed method is that it eliminates the use of toxic and harmful chemicals to humans and the environment, which makes it compatible for the large-scale production of graphene. Reduced GO nanosheets showed good stability in aqueous dispersions due to the strong electrostatic repulsion on the graphene surface. Structural studies confirmed the deoxygenation of GO from the loss of hydroxyl, carbonyl and epoxy groups, and preparation of graphene sheets between 20 and 70 nm suitable for broad biomedical applications.     

Microwave-assisted one-pot synthesis of metal/metal oxide nanoparticles on graphene and their electrochemical applications

An effective synthesis strategy of hybrid metal (PtRu)/metal oxide (SnO₂) nanoparticles on graphene nanocomposites is developed using a microwave-assisted one-pot reaction process. The mixture of ethylene glycol (EG) and water is used as both solvent and reactant. In the reaction system for the synthesis of SnO₂/graphene nanocomposite, EG not only reduces graphene oxide (GO) to graphene, but also results in the formation of SnO₂ facilitated by the presence of a small amount of water. On the other hand, in the reaction system for preparation of PtRu/graphene nanocomposites, EG acts as solvent and reducing agent for reduction of PtRu nanoparticles from their precursors and reduction of graphene from graphene oxide. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) characterizations confirm the feasibility of the microwave-assisted reaction system to simultaneously reduce graphene oxide and to form SnO₂ or PtRu nanoparticles. The as-synthesized SnO₂/graphene hybrid composites show a much higher supercapacitance than the pure graphene, and the as-prepared PtRu/graphene show much better electrocatalytic activity for methanol oxidation compared to the commercial E-TEK PtRu/C electrocatalysts.     

Surface plasmon resonance-induced visible light photocatalytic reduction of graphene oxide: using Ag nanoparticles as a plasmonic photocatalyst

The present communication reports on the first preparation of reduced graphene oxide (rGO) via surface plasmon resonance (SPR)-induced visible light photocatalytic reduction of GO with the use of Ag nanoparticles (AgNPs) as a plasmonic photocatalyst in the presence of an electron donor (ED).     

Hydrazine-reduction of graphite- and graphene oxide

We prepared hydrazine-reduced materials from both graphite oxide (GO) particles, which were not exfoliated, and completely exfoliated individual graphene oxide platelets, and then analyzed their chemical and structural properties by elemental analysis, XPS, TGA, XRD, and SEM. Both reduced materials showed distinctly different chemical and structural properties from one another. While hydrazine reduction of graphene oxide platelets produced agglomerates of exfoliated platelets, the reduction of GO particles produced particles that were not exfoliated. The degree of chemical reduction of reduced GO particles was lower than that of reduced graphene oxide and the BET surface area of reduced GO was much lower than that of reduced graphene oxide.