We observed a drastic increase in density of states. The article is focused on the study of the optical properties of inkjetprinted graphene oxide go layers by spectroscopic ellipsometry. Graphene hybrid sio2 hierarchical dual network aerogel. Thermal contact resistance between graphene and silicon dioxide z. Recently, graphene oxide go has drawn extensive attentions in cement and concrete fields due to its unique features. Despite being applied as graphene precursor, go along with other carbon nanostructures have been labeled. However, if the nanostructured layers are formed on metallic iron substrates, the thermal annealing leads to the formation of gradient oxide layers consisting of wustite feo, magnetite fe 3 o 4. Effect of thermal annealing on the heat transfer properties. Thermal annealing of graphene to remove polymer residues. For preparing highquality graphene, hightemperature annealing was shown to be necessary and the layers of rgo expanded due to the release of cox gases. Valenceband electronic structure evolution of graphene. Here, a new and effective methodology of preparing nitrogen. Rapid thermal exfoliationreduction of graphite oxide is a fast and easy method among the oxidationreduction approaches for graphene synthesis. Effect of thermal annealing on the heat transfer properties of.
Highconcentration boron doping of graphene nanoplatelets by simple thermal annealing and their supercapacitive properties. Here, we investigated the bulk electrical conductivity of reduced graphene oxide rgo powders depending on the applied pressure and additional thermal annealing. Rapid thermal exfoliationreduction of graphite oxide is a fast and easy method among the oxidationreduction approaches for graphene. Furthermore, when graphene based materials are interacting with the surrounding environment, e. Effect of thermal annealing on the electrochemical capacitive. We show that a combination of highresolution in situ xray photoemission and xray absorption spectroscopies offer a powerful. Probing the thermal deoxygenation of graphene oxide using.
Monolayer graphene is obtained by mechanical exfoliation using scotch tapes. In this research, we firstly demonstrated that graphene can be obtained with a surface area of 550 to 700 m2 g. No change of the coating properties is required during this process. Electrophoretic deposition and thermal annealing of a. Degree of oxygen functionalization was controlled by annealing temperatures, and an electronic structure evolution was monitored using realtime ultraviolet photoelectron spectroscopy. Here, we report the results of a fundamental study on the remarkable conversion between n and ptype reduced graphene oxide rgo with changes in the thermal annealing temperature. Understanding the thermal reduction of graphene oxide go is important for graphene exfoliation, and chemical and morphological modi.
Furthermore, when graphenebased materials are interacting with the surrounding environment, e. C required to reduce the graphene oxide go films leads to high manufacturing costs and restricts its broader application in thermal management applications. Mild annealing enables more ordered laminar channels than high thermal annealing process. Highconcentration boron doping of graphene nanoplatelets by. As an example, the thermal conductivity of graphene was reported to decreases from about 20005000 w m1. Electrical measurements of thermally reduced graphene oxide. Dames1,a 1department of mechanical engineering, university of california, riverside, california 92521, usa 2department of physics and astronomy, university of california, riverside, california 92521, usa received 19 august 2009. The general approach to the synthesis of nitrogendoped graphene ng, such as chemical vapor deposition cvd performed in gas phases, requires transitional metal catalysts which could contaminate the resultant products and thus affect their properties. At the beginning of graphene history go was only a simple and cheap step for preparation of single and multilayer graphene films and bulk structures by reduction. We also did the test to compare the tga of reduced graphene oxide and graphite 94 oxide in air, as shown in fig.
For the onestep thermal annealing graphene, the heat graphite oxide in air heat one step thermal annealed graphene in air a. Herein, we report a highperformance, lowtemperature reduced graphene oxidemagnetic carbon. Due to its unique optical and electrical properties, go can be used as, for example, a transparent and flexible electrode material in organic and printed electronics. Remarkable conversion between n and ptype reduced graphene. Mechanical and thermal properties of graphene oxide filled. The gob 2 o 3 mixture was annealed at various temperatures to systematically control the efficiency of boron doping and the degree of reduction of go. Spectroscopic ellipsometry was used to characterize the optical response of the. Only the spectra for annealing temperature of 2008c and above were analyzed in this study due to the possible charging effect for graphene oxide go is important for graphene exfoliation, and chemical and morphological modi. Thermal contact resistance between graphene and silicon. The degree of reduction of the rgo powders was controlled by varying the thermal annealing temperature. Jan 28, 2019 graphene oxide go is useful and promising material for graphene based applications in electronic, optics, chemistry, energy storage, and biology.
Synthesis of the igraphene graphene oxide go was purchased from tianjin plannano co. Graphene exhibits unique structure which has a two dimensional single layered made of carbon. Jul 18, 2016 additionally, to give a clear evolution from the graphene oxide liquid crystal to longrange ordered graphene fibers, a structure evolution model has been built. Physical properties investigation of reduced graphene. Graphene oxide go was employed as the sizing agent for continuous carbon fiber cf tows by an electrophoretic deposition and subsequent thermal annealing. This paper reports on the thermal properties of reduced graphite oxide rgo flakes, studied by means of scanning thermal microscopy sthm. Switch on the high thermal conductivity of graphene paper. High temperature reduction process increases thermal. Thermal annealing of graphene monolayers transferred from cu to sio2si substrate has been investigated to. The influence of thermal annealing to remove polymeric. Graphene films have attracted much attention as a heat dissipation material due to their unique thermal transfer behavior that exceeds that the performance of graphite. Go was first chemically reduced with hydrazine to substantially increase the formation of c c bonds and simultaneously decrease the atomic oxygen concentration. We provide a systematic study of rta of graphene transistors with four different contact metals, cu, ag, au, and pd. Effect of annealing on doping of graphene with molybdenum.
Jun 14, 2018 graphene has outstanding properties that make it an auspicious material for many applications. It is possible only in the case when t max is smaller than the. Thermal treatment or chemical reducing agent is an efficient method to reduce graphene oxide go to graphene dubin et al. Graphene has outstanding properties that make it an auspicious material for many applications. Thermal reduction of graphene oxide 75 where d 002 is the thickness of crystallite here, gp thickness, k is a constant dependent on the crystallite shape 0. Despite the recent developments in graphene oxide due to its importance as a host precursor of graphene, the detailed electronic structure and its evolution during the thermal reduction remain largely unknown, hindering its potential applications. The high defect density in graphene is reflected by r 2d22526 cm 1. Thermal annealing an overview sciencedirect topics.
This work presents the production of graphene oxide go via the langmuirblodgett process and the subsequent restoration of single layer graphene flakes slgf via the chemical reduction, and thermal annealing of the go. Here, we investigated the bulk electrical conductivity of reduced graphene oxide rgo powders depending on. Go could also react with the hydrated ions and has an important impact on the. Comparing effects of thermal annealing and chemical. We report valence band electronic structure evolution of graphene oxide go upon its thermal reduction. Bardhan1,2, sefaattin tongay3, junqiao wu3,angelam. Scalable enhancement of graphene oxide properties by thermally driven phase transformation priyank v.
For an improved mechanistic understanding of the e. The general approach to the synthesis of nitrogendoped graphene ng, such as chemical vapor deposition cvd performed in gas phases, requires transitional metal catalysts which could contaminate the resultant products and thus affect. Remarkable conversion between n and ptype reduced graphene oxide on varying the thermal annealing temperature. The go sheets were tightly coated and covalently attached to cf surfaces. The process of graphene transfer generally involves a polymer support. Electrophoretic deposition epd is believed to be an effective and versatile approach for this purpose. To allow for the use of graphene in various nanoelectronic applications, the methods for the largescale production of graphene with controllable electrical properties need to be developed. Highlightsmild thermal annealing was proved effective for preparing rgo nanofiltration membrane. Only the spectra for annealing temperature of 2008c and above were analyzed in this study due to the possible charging effect for thermal reduction of graphene oxide 75 where d 002 is the thickness of crystallite here, gp thickness, k is a constant dependent on the crystallite shape 0. The strategy employed in this work was to modify graphene oxide go prior to thermal annealing so as to provide a more efficient structure for quaternary n doping. Jan 28, 2014 graphene oxide is being used in energy, optical, electronic and sensor devices due to its unique properties. The electronic and chemical properties of graphene can be modulated by chemical doping foreign atoms and functional moieties.
Grossman1 chemical functionalization of graphene is promising for a variety of nextgeneration technologies. Recent advances in effective reduction of graphene oxide for. Nitrogen doping significantly improves the electrochemical properties of graphene. Mild annealing reduced graphene oxide membrane for. The high thermal conductivity and stability, outstanding mechanical properties, and low weight make graphene suitable for many applications in the realm of thermal management, especially in high integration systems. Catalystfree synthesis of nitrogendoped graphene via. Water and salt transport mechanism in mrgo and hrgo was.
Among various methods used for the reduction of graphene oxide go into a purer form of graphene, the thermal reduction method provides a simpler, safer, and economic alternative, compared to other techniques. The further studies revealed the substantial structure imperfection of graphene oxide. Valenceband electronic structure evolution of graphene oxide. It can be proved that thermal annealing is an efficient way to fabricate highstrength graphene fibers. Graphene oxide go has been accepted as a costeffective source for scaleup amount of graphene, the controllable assembly of which towards functional structure e. Raman spectra of the annealed graphene show both the 2d. Valence band electronic structure evolution of graphene oxide.
However, unlike its counterpart graphene the thermal transport properties of. The electrical conductivity of graphene powders is critical for their uses in fabricating highperformance devices or materials. This leads to the formation of three acoustic a and 3 n 3 3 optical o phonon modes. The scientists stress the potential of using this method for. Thermal conductivity of freestanding reduced graphene oxide. It was found that the charge carriers in rgo for temperatures of 300450 c and 800 c are electrons ntype, whereas for temperatures of 450800 c. Interfacemediated extremely low thermal conductivity of graphene aerogel yangsu xie a, shen xu a, zaoli xu a, hongchao wu a, cheng deng a, xinwei wang a, b, a 2010 black engineering building, department of mechanical engineering, iowa state university, ames, ia 50011, usa. It is found that the hightemperature annealing dramatically increases the inplane thermal conductivity, k, of the. Enhancement of quaternary nitrogen doping of graphene oxide.
Conventional thermal annealing, however, comes with some drawbacks, such as hightemperature annealing along with longer process times and structural damage that hinders the applicability of go as a transparent conductor. Additionally, to give a clear evolution from the graphene oxide liquid crystal to longrange ordered graphene fibers, a structure evolution model has been built. Facile thermal annealing of graphite oxide in air for graphene with a. Highly thermally conductive graphene film produced using. Scanning electron microscopy sem and optical images were used to evaluate. The graphene unit cell, marked by dashed lines in figure 1a, contains n 2 carbon atoms. Phonon dispersion of graphene t o understand the thermal properties of graphene, one must.
The degree of oxygen functionalization was controlled by annealing temperature, and an electronic structure evolution was monitored using real. Effect of low oxygen annealing on photoelectrochemical. Raman spectra of the annealed graphene show both the 2d peak and g peak blueshift. Flexible conductive graphene paper obtained by direct and. Comparing effects of thermal annealing and chemical reduction. A collaborative research performed by scientists from uc riverside, moldova state university, and graphenea demonstrates that a method of reducing graphene oxide to graphene via a hightemperature treatment that increases thermal conductivity along the film direction, while decreasing it across the film. Salt rejection and selectivity can be feasibly tuned by mild annealing time. However, the highest defect density is determined after annealing ai go at 500 c r 2d30140 cm1, green dots in figure 2 and partial reconstruction of the graphene lattice can be observed after annealing ai go at c r 2d 12740 cm1, purple dots in figure 2. The role of oxygen during thermal reduction of graphene oxide. Atomicscale investigation of graphene grown on cu foil.
In this study, we demonstrated that bdoped graphene nanoplatelets can be prepared by simple thermal annealing of go nanoplatelets combined with boron oxide b 2 o 3. Go owns rich functionalized oxygen groups, which guarantees excellent water dispersibility. Facile thermal annealing of graphite oxide in air for. Atomic force microscope images showed that almost all the residues could be removed in n 2 h 2 at 400c but only agglomerated in vacuum. Investigation of the thermal stability of the carbon. Catalystfree synthesis of iodinedoped graphene via a. Many attempts have been made to synthesize rgo, either by chemical reduction or thermal annealing of go or a combination of both, to resemble pristinetype graphene, or at least to attain better conducting properties closer to those of pristine graphene. Doping nanoparticles doping nanoparticles onto graphene or go has been done for the following works brenner, 2012. The effects of thermal annealing on the tape residues and edges of graphene are researched. Igraphenes were prepared by annealing graphene oxide go and iodine at 5001100 the anneal treatment was carried out in a tube furnace with high purity argon as protective ambient. Improved performance of graphene in heat dissipation when. Thermal transport in graphene oxide from ballistic. Frontiers mapping of graphene oxide and single layer.
Rapid and scalable fabrication of reduced graphene oxide. Remarkable conversion between n and ptype reduced graphene oxide on varying the thermal annealing temperature article pdf available in chemistry of materials 2721. Pdf remarkable conversion between n and ptype reduced. The degree of oxygen functionalization was controlled by annealing temperature, and an electronic structure evolution was monitored. Mild annealing reduced graphene oxide membrane for nanofiltration. Moreover, go exhibits large specific surface area and remarkable mechanical strength. Interfacemediated extremely low thermal conductivity of. Hojatitalemi, 2010, with solvothermal method tran, 20. Reduction of go with laser irradiation trusovas, 20, rgo from graphite oxide under ultraviolet irradiation ji, 20. Thermal annealing is a process at which the temperature t of the part coated by a coating is at first increased from rt to a maximal operation temperature t max, and later, after finishing the operation e. In this process, the role of trapped water and the evolution of oxygen during annealingarestillnotwellunderstood. Microcrystalline graphene oxide mgo was reduced by thermal annealing to prepare reduced microcrystalline graphene oxide rmgo. Characterization of structural transformation of graphene oxide to reduced graphene oxide during thermal annealing. Thermal annealing of graphene monolayers transferred from cu to sio2si substrate has been investigated to remove polymethyl.
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