Oxidizing metal ions with graphene oxide: the in situ formation of magnetic nanoparticles on self-reduced graphene sheets for multifunctional applications
Yuhua XueHao ChenDingshan YuShuangyin WangMichal YardeniQuanbin DaiMingming GuoYong LiuFan LüJia QuLiming Dai
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Fe2+ cations in FeCl2 or FeSO4 were oxidized by graphene oxide, leading to an in situ deposition of Fe3O4 nanoparticles onto the self-reduced graphene oxide (rGO) sheets. The resultant Fe3O4/rGO sheets were demonstrated to possess interesting magnetic and electrochemical properties attractive for a large variety of potential applications.Keywords:
Oxidizing agent
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Graphene is a novel two dimensional material with exceptional properties. Chemical vapor deposition of graphene on metal substrates is widely used to prepare high quality graphene film. However, the graphene films need to be transferred to oxide substrates for device applications. A chemical vapor deposition approach for direct growth of graphene films on zinc oxide was demonstrated in the present investigation. Raman spectra were used to characterize the grown graphene films. The impact of the growth temperature, time and gas flow ratio on the layer number and crystallite size of graphene was investigated.
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As a three-dimensional porous structure made of two-dimensional graphene building blocks, graphene foam, has gained enormous attention in recent years. Such graphene foam integrates graphene sheets into macroscopic structures meanwhile inheriting most of the fascinating intrinsic properties of graphene. Together with its ultralow density, high porosity and flexibility, graphene foam has been proposed in many applications, such as supercapacitors, microwave shielding, electrochemical sensing and lithium-ion batteries. In this paper, three-dimensional graphene foams were synthesized by low pressure chemical vapor deposition. The obtained graphene foams were characterized by scanning electron microscopy and Raman spectroscopy. The results show that nickel foam surface was fully covered by graphene. The Raman spectra show that most graphene were multilayer, but monolayer and bilayer graphene were also found in some areas. In addition to this, it was also found that the synthesized graphene has very small D peak, indicating high quality of the synthesized graphene.
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In this study, a graphene electrode showed that the uniform Ag particles on the graphene surface uniformly. The Ag-coated graphene electrode exhibited superior electrochemical properties to the crude graphene. The chemical composition analysis of graphene electrode was confirmed by X-ray photoelectron spectroscopy. The synthesized materials were characterized by XRD. Ag particles are introduced to the graphene surface as a function of the applied current. A half cell of the Ag-coated graphene electrode is fabricated to examine the electrochemical performance, such as the charge-discharge behaviors, cyclic voltammetry, and specific capacitance. As a result, the electrochemical performance of the Ag-coated graphene electrode is two times higher than that of the crude graphene electrode.
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Graphene is a carbon material that presents special properties. Usually, graphene is obtained by chemical or thermal reduction of graphene oxide. The graphene grown by chemical vapor deposition on metal foam substrates lead to obtaining of graphene structures with ultralow density, high surface area, high mechanical strength, electrical conductivity, and optical transparency, suitable for different applications. In this paper, we synthesized graphene by using nickel and copper foams as substrate in a CVD process with methane as carbon source. Different deposition times were used. The graphene grown on metal foams were investigated by SEM, XRD and Raman spectroscopy in order to make a comparative study.
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최근 스마트폰, 태블릿, 노트북 PC 같은 모바일 기기의 경우, 경량화 및 박형화에따라 기기의 두께가 감소하면서 내부의 프로세서로부터 발생되는 열을 방출하기위한 해결 방법에도 제한이 발생하고 있다. 그 중 Graphite sheet 는 높은 면방향의 열전도도 및 낮은 두께방향의 열전도도로 인해 프로세서의 열을 빠르게 주변으로 확산시키면서도 사용자로 열이 전달되는 것을 줄일 수 있어 모바일 기기의 방열 solution으로서 주로 사용되고 있다. 다만, 기계적인 강도가 약하고 취성이 커서이에 대한 해결이 요구되고 있는 실정이다. 이에 대한 대체재로서 Graphene을 이용한 방열 Sheet의 개발이 활발해지고 있다. 하지만 CVD Graphene의 경우 가격적인 문제가 있고, Graphene nanoplate 와 같은 분말형태의 Graphene 을 이용하여 Cu foil 등에 코팅하여 제조하는 경우, 열적인 특성이 기대에 못미치고 있다.본 연구에서는 rGO(reduced graphene oxide) 형태의 Graphene sheet 를 제조하면서 Silver nanoparticle 을 Graphene 용액내에 분산시켜 코팅하여 그 특성을 평가하였다. 평가 방법은 Laser flash 법을 사용한 열전도도 평가와 함께 Thermal Transient Method 를 이용한 열저항을 평가하여 실제 방열구조에서의 접촉저항에 의한 방열 효과 변화도 함께 확인할 수 있었다.
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Combining adsorption with electrochemical oxidation has been shown to be effective for the removal and oxidation of dissolved and dispersed organic contaminants from water, using a graphite flake adsorbent. In order to increase the adsorption capacity, we have investigated the use of graphene based adsorbents, which have high specific surface area combined with electrochemical activity. We have prepared and tested reduced graphene oxide (RGO), graphene foam and graphene metal oxide composite materials. RGO offer significantly higher adsorptive capacity than graphite flake. Similarly graphene foam was found to have a high adsorption capacity, although the adsorption kinetics were poor due to the slow diffusion of conatminants into the foam pores. A graphene foam would be more readily separated from the treated water and further work is planned to determine whether a flow through treatment process can be used to overcome the slow adsorption kinetics. However, during electrochemical oxidation, the structural integrity of the foam was compromised after only 1 or 2 cycles, presumably due to oxidation of the graphene. A graphene / iron oxide composite was preapred with ferromagnetic characteristics to enable separation from the treated water. The adsorption capcity was slightly reduced, but the electrochemcial regeneration performance was good. Oxidation of graphene remains a challenge, and work is ongoing to explore the use of graphene / titanium dioxide composites. The TiO2 will catalyse the organic oxidation and may also protect the graphene from oxidation.
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Hybrid nanopaper-like thin films with a graphene oxide (GO) layer sandwiched by two functionalized graphene (GP-SO3H) layers were successfully prepared from oxidized graphene and benzene sulfonic modified graphene. The hybrid graphene-graphene oxide-graphene (GP-GO-GP) nanopapers showed combination of high mechanic strength and good electrical conductivity, leading to desirable electromagnetic interference shielding performance, from the GP-SO3H layers, and superior gas diffusion barrier provided by the GO layer. These GP-GO-GP nanopapers can be readily coated onto plastic and composite substrates by thermal lamination and injection molding for various industrial applications such as fuel cell and natural gas containers.
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