Comprehensive review on synthesis and adsorption behaviors of graphene-based materials
Comprehensive review on synthesis and adsorption behaviors of graphene-based materials
Carbon letters. 2012. Apr, 13(2): 73-87
Copyright ©2012, Korean Carbon Society
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
  • Received : January 01, 2012
  • Accepted : March 03, 2012
  • Published : April 30, 2012
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About the Authors
Seul-Yi Lee
Korea CCS R&D Center, Korea Institute of Energy Research, 152 Gajeongro, Yuseoung-gu, Daejeon 305-343, South Korea
Soo-Jin Park
Department of Chemistry, Inha University, 100 Inharo, Nam-gu, Incheon 402-751, South Korea
Graphene is the thinnest known materials in the universe and the strongest ever measured. Graphene has emerged as an exotic material of the 21st century and received world-wide attention due to its exceptional charge transport, thermal, optical, mechanical, and adsorptive properties. Recently, graphene and its derivatives are considered promising candidates as adsorbent for H 2 storage, CO 2 capture, etc. and as the sensors for detecting individual gas molecule. The main purpose of this review is to comprehensive the synthesis method of graphene and to brief the adsorption behaviors of graphene and its derivatives.
1. Introduction
The discovery of graphene has been one of the most outstanding recent achievements [1,2]. Graphene is one of the most promising materials in nanotechnology because of its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. In particular, the promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into various functional groups or materials.
As Fig. 1 demonstrates, the optimism about graphene is validated by the number of publications related to graphene, which dramatically increased after 2004 [3] .
Importantly, graphene and its derivatives have been explored for a wide range of applications
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Number of publication on graphene in the past 20 years (from ISI Web of Knowledge).
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Schematic representation of graphene: which is the fundamental starting material for a variety of fullerene materials, buckyballs, carbon nanotubes, and graphite [7].
in such fields as electronic and photonic devices, clean energy, and sensors [4 - 6] . Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced on a large scale from the mother of all graphitic materials, as presented in Fig. 2 [7] . Graphene, one of the allotropes (such as carbon nanotubes, fullerene, diamond, and so on) of elemental carbon, is a planar monolayer of carbon atoms arranged in a two-dimensional (2D) honeycomb lattice with a C-C bond length of 0.142 nm [8] . Graphene is the thinnest of known materials in the universe and the strongest ever measured.
Its extended hexagonal monolayer network is the basic building block of other important allotropes, which can be stacked to form 3D graphite, rolled to form 1D nanotubes, and wrapped to form 0D fullerenes. As can be seen in Table 1 , it has demonstrated a variety of intriguing properties, including high electron mobility at room temperature (250 000 cm 2 /[V·s]) [7] , high specific surface area [8] , superior mechanical properties with Young’s modulus of 1 TPa [10] , and exceptional thermal conductivity (5000 W/[m·K]) [11] .
These potential characteristics are applied to single molecule gas detection, transparent conducting electrodes, composites, and energy storage devices, such as supercapacitors and lithium ion batteries [12 - 16] . Furthermore, a distinct band gap can be formed as the dimensions of graphene are reduced to narrow ribbons with a width of 1-2 nm, producing semi-conductive graphene with potential applications in transistors [17] .
More recently, the adsorption behavior of graphene and graphene- based materials (its derivatives) has also been of interest due to graphene’s high specific surface area and newly created textural properties.
After a general introduction to graphene and its derivatives, this review will demonstrate that graphene is not confined to only single-layer graphene nanosheets; it can have two-, three-, or multi-layer nanosheets. This will even include the graphenebased materials (its derivatives). Because adsorption behavior is mainly studied with graphene and its derivative-based materials, the purpose of this review is to look at, in a brief way, what is re-
Physical properties of single-layer graphene at room temperature
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Physical properties of single-layer graphene at room temperature
ferred to as graphene in the literature and the adsorption behavior of graphene and graphene-related materials for gas sensors, hydrogen storage, carbon dioxide capture, and so on.
2. Synthesis of Graphene
- 2.1. Introduction
Graphene with varying number of layers can be synthesized using different strategies, such as the growth of carbon nanotubes producing graphite with 100 layers of graphene, chemical vapor deposition in metal surfaces (a few layers of graphene), the thermal decomposition of SiC, micromechanical exfoliation cleavage, chemical reduction of graphene oxide, and so on. Although, these various approaches did not produce perfect monolayer graphene, some studies showed that the chemical vapor deposition method has been optimized and become a major technique to produce graphene in large quantities [18] . Now, we briefly overview the various synthetic methods and the properties of the graphene produced by each synthetic method.
- 2.2. Epitaxial growth and chemical vapor deposition technique
For the development of large-scale synthesis of grown graphene, several methods have been studied by many researchers, including graphitization of SiC surfaces [19 , 20] and chemical vapor deposition (CVD) on transition metals [21 - 24] .
At first, epitaxial graphene research evolved out of work on carbon nanotubes. It is well known the carbon nanotubes have superior electronic properties. However, the inability to manufacture well-controlled tubes and scale them up from singletube transistors to large-scale integrated circuits has prevented expanded technological applications. It is presented in Fig. 3 .
De Heer et al. [25 , 26] realized that two-dimensional graphene, essentially unrolled nanotubes, would have many of the same properties as carbon nanotubes, and this idea opened the way to a new approach to carbon electronics. With an epitaxial method, ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization at high temperature. The material can be patterned using standard nanolithography methods [24 - 26] .
Recently, Bae et al. [27] reported a roll-to-roll production of 30-inch graphene films using the CVD method. Their fabrica
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Scanning tunneling microscope topographs (0.8 V sample bias, 100 pA) of nominally 1 mL epitaxial graphene on SiC(0001). Top: image showing large flat regions of 6√3 × 6√3 reconstruction and regions where the reconstruction has not fully formed. Next-layer islands are also seen. Bottom: a region of 6√3 × 6√3 reconstruction, imaged through the overlying graphene layer (detailed information is presented in [19]).
tion process including three steps after the synthesis of graphene on copper substrates: (i) adhesion of polymer supports to the graphene on the copper foil; (ii) etching of the copper layers; and (iii) release of the graphene layers and transfer onto a target substrate ( Fig. 4 ).
Epitaxially grown graphite has a number of differences related to physical properties in comparison with mechanically exfoliated graphene [28] due to the influence of interfacial effects in epitaxial graphene, which are strongly dependant on both the silicon carbide substrate and some growth parameters.
The second method involves substrate-based growth of single layers by a CVD technique. It has been reported that large and predominantly monolayer graphene of excellent quality can be synthesized by CVD on polycrystalline Ni, Cu, Co, Ru, and other transition metals [29 , 30] , with the flow of a hydrocarbon gas, such as methane, ethylene, acetylene, and benzene. In this procedure, the substrate is subjected to electron bombardment in an ultrahigh vacuum at 1000℃ to remove oxide contaminants and then heated to temperatures ranging from 1250℃ to 1450℃ for a few minutes. Blakely et al. [31 , 32] reported the formation of carbon films by the cooling of Ni foils saturated with carbon at high temperatures.
This is known to be relatively simple and economical, and has been used to produce graphene that can reach impressive sizes and can be easily transferred to other substrates [33 , 34] .
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(a) Schematic of the roll-based production of graphene films grown on a copper foil. The process includes adhesion of polymer supports, copper etching (rinsing) and dry transfer-printing on a target substrate. A wet-chemical doping can be carried out using a setup similar to that used for etching. (b) Roll-to-roll transfer of graphene films from a thermal release tape to a positron emission tomography (PET) film at 120℃. (c) A transparent ultra large-area graphene film transferred on a 35-in. PET sheet. (d) An assembled graphene/PET touch panel showing outstanding flexibility [27].
Both epitaxial synthesis and CVD techniques take advantage of specially chosen platforms to encourage high-quality growth. They also have the prospect of producing a single sheet of graphene over an entire wafer.
Meanwhile, the following solution-based synthetic schemes by chemical reduction or exfoliation have no need for support substrates.
- 2.3. Micromechanical exfoliation technique
The micromechanical exfoliation technique is a simple peeling process. Fig. 5 show how a commercially available highly oriented pyrolytic graphite sheet was dry etched in oxygen plasma into many 5 μm deep mesas.
Novoselov et al. [1] first observed single-layer graphene in 2004, as presented in Fig. 6 . They isolated two-dimensional crystals from three-dimensional graphite using the mechanical exfoliation technique. As a result, single- and few-layer flakes are locked up substanding by only van der Waals forces and can be made free-standing by etching the substrate [35 - 38] . This attracted tremendous attention.
To exfoliate a single layer using mechanical exfoliation, the key is to overcome the van der Waals attraction [39 , 40] between exactly the first and second layers without disarranging any subsequent layers. However, this method is a typical top-down approach of graphene, which requires manual effort and produces unreliable results, while small areas hinder practical applications of graphene [41 , 42] .
Meanwhile, it is interesting note that mechanical exfoliation with cellophane tape from graphite is still considered best for producing the highest performing samples [39] , among the various methods.
- 2.4. Chemical reduction and thermal exfoliation
In 1958, Hummers and Offeman [43] reported a method of preparing graphene oxide, which readily forms a stable colloidal
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Micromechanical exfoliation of graphene using scotch tape from highly oriented pyrolytic graphite.
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Novoselov et al. [1] were the first to observe a single layer graphene; (a) photograph (in normal white light) of a relatively large multilayer graphene flake with a thickness of about 3 nm on top of an oxidized Si wafer, (b) atomic force microscope (AFM) image of 2 μm by 2 μm area of this flake near its edge (colors: dark brown, SiO2 surface; orange, 3 nm height above the SiO2 surface), (c) AFM image of single-layer graphene (colors: dark brown, SiO2 surface; brown-red (central area), 0.8 nm height; yellow-brown (bottom left), 1.2 nm; orange (top left), 2.5 nm. Notice the folded part of the film near the bottom, which exhibits a differential height of about 0.4 nm).
suspension in water. This graphene oxide suspension is used to facilitate production of single-layer graphene oxide by ultrasonic treatment (under the hundreds of W and tens of kHz) [44 - 46] .
By modifying the Hummers’ methods, a tremendous number of studies on the synthetic method of graphene production have been published, and the produced graphene has been applied in a variety of applications. With improvement, gram quantities of graphene can also be obtained by a solvothermal procedure for preparing graphene oxide using sodium, potassium, ethanol, and so on [47 , 48] .
To synthesize graphene, the reduction of graphene oxide by chemical methods has been carried out using reducing agents, such as hydrazine [49 - 52] , dimethylhydrazine [53] , hydroquinone [54] , and NaBH 4 [55 , 56] . A proposed reaction pathway for epoxide reduction with hydrazine is presented in Fig. 7 .
The chemical reduction method by graphene oxide in solu-
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A proposed reaction pathway for epoxide reduction with hydrazine [49].
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Aberration-corrected transmission electron microscope image of a single sheet of suspended graphene oxide; (a) the oxidized region of the material, (b) the graphitic region, and (c) the atomic structure of graphite oxide’s region [57].
tion allows easy manipulation and transfer of graphene onto substrates.
Erickson et al. [57] have investigated the local chemical structures on graphene oxide and reduced graphene oxide using the transmission electron microscopy (TEM) measurement (a monochromated aberration-corrected instrument operated at 80 keV). The TEM image of graphene oxide clearly shows the oxidized area ( Figs. 8 a and b) and unoxidized graphene crystal area ( Fig. 8 c). As explained in the figure caption, hydroxyl groups and epoxy were presented on the graphene oxide basal plane. On the other hand, the TEM image of reduced graphene oxide shows the disordered regions ( Fig. 8 a) that is believed to result from the oxidized area being reduced by hydrazine and thermal annealing, and the unoxidized graphene regions.
An important method to synthesize graphene is thermal exfoliation of graphene oxide at high temperatures [58 - 60] . In this method, chemically prepared graphene oxide is placed in a well-sealed long-type quartz tube and then purged with inert gas. Then, the tube containing graphene oxide is quickly inserted into a muffle or tubular furnace preheated to 1050℃ and
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Schematic representation of the mechanisms involved in “gasothermal” exfoliation techniques [60].
maintained at that temperature for around 10 min. This is usually called exfoliated graphene.
Kaniyoor et al. [60] investigated that the effect of different exfoliation conditions on the synthesis of graphene from graphite oxide, for example, Ar at 1050℃ , vacuum at 200℃ , H 2 + Ar mixture at 200℃ , and H 2 at 200℃. They found that these results showed conclusively that the atmosphere for exfoliation of graphite oxide plays a critical role in low temperature synthesis of graphene. It was observed that exfoliationreduction of graphite oxide in pure hydrogen atmosphere at 200℃ results in the highest quality of a few layered graphene sheets. These schematic representation of the mechanisms are presented in Fig. 9 .
- 2.5. Others
Few-layer graphene is synthesized by microwave treatment, conversion of nanodiamonds, and arc discharge of graphite. The method of preparing graphene by microwave treatment is just a post-process using chemically synthesized graphene oxide in large quantities in a short time [61 - 63] . Andersson et al. [64] and Prasad et al. [65] reported that graphene can be synthesized by heating nanodiamonds in an inert or reducing atmosphere. Nanodiamond particles are treated by soaking them in concentrated hydrochloric acid to avoid contamination by magnetic impurities. Then, they are annealed in a graphite container in a graphite furnace in a helium atmosphere at temperatures ranging from 1600 to 2500℃.
Subrahmanyam et al. [66] reported that arc discharge of graphite in a hydrogen atmosphere yields graphenes exclusively containing 2 to 3 layers, although the flakes are relatively small (100 to 200 nm). It has been found that this process depends on the presence of hydrogen gas during the arc discharge which terminates the dangling carbon bonds with hydrogen, which prevents the formation of closed structures [67] . To prepare graphene by the arc discharge method, direct current arc discharge of graphite evaporation is carried out in a water-cooled stainless steel chamber filled with a mixture of hydrogen and helium without any catalyst [68] . It has been reported that the best transition characteristics are exhibited by graphene synthesized by arc discharge of graphite in hydrogen.
3. Adsorption Behaviors
- 3.1. Introduction
The unique chemical properties of graphene affecting its adsorption behavior have only recently attracted the attention of many researchers; thus, it has not yet been studied in sufficient detail. Therefore, we will attempt to elucidate the adsorption behaviors of graphene and graphene-based materials.
Adsorption behavior depends significantly on the unique structure and concentration of chemical species created by a process of preparing graphene. It is possible to possess a large high surface area, sufficient porosity, superior conductivity, broad potential window, and rich surface chemistry. In addition, the extended polyaromatic π-electron system and coordinatively unsaturated terminal carbon atoms have a decisive effect on the reactivity of graphene. The readily polarizable π-electron system of graphene is equally reactive with electro- and nucleophilic species, and this makes the system sensitive even to radical species.
- 3.2. Water physisorption
A water cluster adsorbed on a graphite surface is a prototypical weakly bound van der Waals π-system that involves watergraphite and water-water interactions. Zhang and Sarkar [69] investigated that the binding energy of water clusters interacting with graphite is dependent on the number of water molecules that form hydrogen bonds, but is independent of the water cluster size, as presented in Fig. 10 .
Furthermore, Lin et al. [70] found that these physically adsorbed or physisorbed water clusters show little change in their IR peak position and leave an almost perfect planar graphite surface. This is shown in Fig. 11 .
- 3.3. Hydrogen storage
The US Department of Energy’s revised gravimetric capacity target for hydrogen storage systems for 2015 is 5.5 wt%. These targets have not yet been reproducibly met by any available storage technology. Solid carbon adsorbents, such activated carbons [71 , 72] , fullerenes [73 , 74] , carbon nanotubes [75 - 78] , graphites, carbon nanofibers [79 - 81] , ordered porous carbon [82 , 83] , and carbon-based hybrid composites [84 , 85] , and so on, had previously been considered to be promising candidates for hydrogen storage due to their large surface area, structural stability, and light mass. In particular, the adsorption mode of H 2 on carbon nanomaterials is reversible weak physisorption, which is a key factor in the operation of hydrogen/fuel-cell-powered systems.
To satisfy the increasing need for hydrogen storage, graphene has been attracting much attention as the newest carbon materials. It appears to be composed of a monolayer of carbon atoms packed into a dense honeycomb crystal structure. Single-layer graphene is theoretically predicted to have a large surface area of 2600 m 2 /g, while the specific surface area of few-layer graphenes prepared by various methods is in the range from 250 to 1500 m 2 /g.
Furthermore, recently, graphene-like nanosheets (in some cases, it has contained some oxygen functionalities; therefore,
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Geometry structures of a booklike water hexamer (a) and that of different orientations (b, d) on the graphite surface, as well as the optimized adsorption structures (c, e, and f ).
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Calculated infrared spectra of a free water hexamer and its adsorbed cases on a graphite surface: (a) prism (H2O)6, (b) (fbz)37-(H2O)6 prism a, (c) bag (H2O)6, and (d) (fbz)37-(H2O)6 prism b.
all of these graphene-like nano-materials are called “graphene oxide”) have been studied in relation to the adsorption of hydrogen. They are produced relatively easily by oxidative treatment of graphitic materials with strong oxidizing agents. Graphene oxide is a stacked structure similar to graphite but with a wider spacing between graphene oxide nanosheet layers with diverse range of 6 to 15 Å [86] .
Srinivas et al. [87] studied graphene oxide prepared by the reduction of a colloidal suspension of exfoliated graphite oxide for hydrogen storage capacity. The nitrogen/77 K adsorptiondesorption isotherms and TEM/SEM images of synthesized
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Nitrogen/77 K adsorption-desorption isotherms of graphene oxide prepared from Srinivas et al. [87].
graphene oxide are presented in Figs. 12 and 13 , respectively. As can be seen in Figs. 14 and 15 , the sample was found to be in a highly agglomerated state with many wrinkles, and it had a specific surface area of 640 m 2 /g as measured by nitrogen adsorption at 77 K.
The isotherms exhibited a typical type-I curve at low relative pressure and a hysteresis loop at relative pressure from 0.4, indicating the presence of microporosity, mesoporosity, and some macroporosity [88] . They explained that the overlap and stacking of the exfoliated layers influenced the significant low textural characteristic.
In the Srinivas study, it was shown that the highest hydrogen storage capacities of a prepared sample were about 1.2 wt% and 0.1 wt% at pressures up to 10 bar under the temperatures
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Transmission electron microscope (a) and scanning electron microscope (b) images of graphene oxide prepared from Srinivas et al. [87].
of 77 K and 298 K, respectively. Furthermore, they predicted the adsorption capacities at 100 bar of ~3 wt% and 0.72 wt% at 77 K and 298 K, respectively, obtained by linear extrapolation using the model LangmuirEXT2 expression. The room temperature hydrogen adsorption capacity was higher than other recent experimental results on hydrogen storage in a pristine graphene sample [89] , which might be attributable to the higher isosteric heat of adsorption values. Ma et al. [89] reported that 0.4 wt% and ~0.2 wt% hydrogen uptake of graphene oxide were obtained at 77 K under 1 bar and 298 K under 60 bar, respectively.
Ghosh et al. [90] found that high hydrogen adsorption capacity on graphene oxide obtained by thermal exfoliation or conversion of nanodiamond was 3.1 wt% (in case of single-layer graphene) at 298 K and 100 bar. As shown in Fig. 14 , the hydrogen uptake varied linearly with the specific surface area, and the presence of more than one layer of graphene oxide in this study caused a decrease in the hydrogen uptake. In addition, the specific surface area of graphene oxide depends on the number of layers, not the pore effect [91 , 92] .
It is interesting to note that the H 2 -graphene interaction energies obtained in their study satisfy the optimum conditions for adsorptive storage of hydrogen [93] . They also expected that higher values for hydrogen storage should be possible by preparing better samples and by reducing the average number of graphene layers.
The transition metal loaded/graphene oxide composites for hydrogen storage are being extensively researched. Wang et al. [94] have investigated the structural properties of graphene oxide and the feasibility of using graphene oxide to anchor Ti for hydrogen storage with first-principles computations. They reported that on graphene oxide there exist stable structural motifs as the basic function units of oxygen functionalities. It is consid-
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The multi-binding hydrogen adsorption model of Ti-anchored graphene oxide [94].
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Linear relationship between the specific surface area and the hydrogen storage capacity at 77 K and 1 bar.
ered that graphene oxide could be an excellent substrate for Ti, but for hydrogen storage, it requires the hydrogenation of epoxy and open sp 2 sites. Upon hydrogenated graphene oxide, the Ti binding energy is increased to a level that is high enough to prevent Ti clustering. Dihydrogen binding energy is also favorable for room temperature storage. The theoretical gravimetric density was 4.9 wt%. Thus, Ti-anchored graphene oxide may offer a feasible solution for hydrogen storage.
Kim and Park [95] have reported nickel/graphite hybrid materials which are produced by mixed acid treatment of graphite flakes for hydrogen storage. The graphene oxide samples were prepared by dipping graphite flake into a mixed acid solution (H 2 SO 4 and H 2 O 2 ) in a range of from 10:1 to 5:5 at room temperature. The experimental conditions of mixed acid treatments and textural properties of produced graphene oxides are listed in Table 2 .
Fig. 16 is a schematic of the pore development of a graphite flake using the acidic method. The layer distance of each graphite sheet is nearly 0.354 nm, and it is impossible for hydrogen molecules to be adsorbed at this dimension. However, after the expansion of the layers, the layer distance widens and new adsorption sites become exposed for hydrogen molecules.
Furthermore, Ni nanoparticles were loaded onto graphene ox-
Specific surface area and pore volumes of graphene oxide as a function of the mixed acid ratio
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Specific surface area and pore volumes of graphene oxide as a function of the mixed acid ratio
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A schematic of hydrogen storage sites on graphite surfaces: (a) as-received graphite and (b) graphene oxide manufactured by mixed acid treatments in this study.
ide surfaces as a function of Ni content in an effort to increase the final hydrogen uptake. In Fig. 17 , the highest hydrogen storage result of the 8:2/Ni-0.05 sample was 4.48 wt%, which was prepared by 0.05 wt% of NiSO 4 per 1 g of graphene oxide.
However, it is important to note that the 10:1 sample showed lower hydrogen uptake the 8:2 sample, though the former had a higher specific surface area. This result indicates that the 8:2 samples may have a more suitable pore dimension for the adsorption of hydrogen molecules. Though the 10:1 sample had a high specific surface area, it was checked by a nitrogen molecule, indicating that the area was not suitable for hydrogen molecules.
Park et al. [95] suggested the newly a dipole-induced mechanism for hydrogen storage. As shown in Fig. 18 , the first hydrogen molecules introduced can be reacted with metal particles due to the high oxidation power of metals on graphite surfaces due to the Kubas reaction [96 , 97] .
Here, unlike the chemical binding of hydrogen atoms to transition metal on carbon surfaces, lone transition metal atoms bind hydrogen via the so-called “Kubas interaction,” in which the
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Hydrogen storage behavior of graphene oxide as a function of mixed acid ratio and nickel content.
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A schematic of the hydrogen storage mechanism on metal/ carbon surfaces: (a) the accumulation of hydrogen molecules on metal/ carbon surfaces, (b) the dispersion of hydrogen molecules from metals to carbon surfaces by dipole-induced effects [95].
H-H bond undergoes some elongation rather than complete dissociation into atoms.
However, the amount of this initial reaction is very small. The binding energy and bond distance in this case are 85 kJ/mol and 0.2 nm, respectively, because the binding energy and bond distance of metal hydride are normally close to 85 kJ/mol and 0.2 nm, respectively. The second group of hydrogen molecules introduced cannot chemically react due to a site limitation caused by the initially introduced hydrogen molecules; however, they are physically adsorbed by dipole-induced effects. The hydro-
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Fourier transform infrared spectrum of molecular adsorption of CO2 in graphene oxide sample.
gen molecules are basically non-polar, but the strong interaction of the metal particles leads to the dipole inducing effects of the hydrogen molecules. The third group and any remaining hydrogen molecules are adsorbed by the same mechanism of high gas pressure, but this equilibrium can be broken when the interaction of oxidized graphite surfaces and dipole-induced hydrogen molecules is stronger than metal-hydrogen interactions [98 - 102] . This mechanism can be applied only under higher pressure, and when graphite supports are charged strong electron acceptors.
These unique characteristics of graphene oxide can play a leading part in enhancing hydrogen storage capacity.
- 3.3. Carbon dioxide capture
Mishra and Ramaprabhu [103] suggested graphene oxide for CO 2 adsorption, which is prepared by hydrogen-induced thermal exfoliation of graphene oxide at 200℃ for possible large-scale production of graphene [104] . They confirmed the physical adsorption of CO 2 in graphene oxide using Fourier transform infrared spectroscopy.
In Fig. 19 , the band corresponding to –OH groups at 3435 cm-1 is quite prominent compared by the insignificant ratios of
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Carbon capture geometry optimized structure obtained; (a) pristine graphene, (b) Ca/graphene at 12.5%, and (c) Ca/graphene at 16.67%.
anti-symmetric and symmetric =CH 2 vibrations for graphene oxide in this work. Furthermore, the intense peaks correspond to the carboxylic and carbonyl groups at 1726 (>C=C), 1563 (=CH-), and 1173 cm -1 (>C=O). An additional peak of 2324 cm -1 corresponds to the adsorbed molecular CO 2 in graphene oxide resulting from physical CO 2 adsorption. They reported that the maximum adsorption capacity was 21.6 mmol/g at 298 K and 11 bar. This value is higher than that of other adsorbents. In addition, they compared the CO 2 adsorption capacity of graphene oxide with those of other usual adsorbents, such as, carbon materials, MOF, zeolite, and so on, as mentioned below.
Before everything else, Mishra and Ramaprabhu [105] reported CO 2 adsorption capacity, obtained by study of multiwalled carbon nanotubes, was observed to be 11.7, 8.3, and 7.0 mmol/g at 11 bar and 25℃ , 50℃, and 100℃, respectively. Also, Siriwardane et al. [106] and Gensterblum et al. [107] reported 7 mmol/g and 6 mmol/g, respectively, of CO 2 adsorption in activated carbon at 45℃ and 11 bar. Zhang et al. [108] reported enhancement of around 20% in CO 2 uptake, which was achieved by modifying the AC with nitrogen at 298 K, and adsorption capacity was about 16 mmol/g adsorption capacity at 11 bar. Cavenati et al. [109] reported 3.2 mmol/g of CO 2 adsorption in 13X zeolite at 298 K and 12 bar. A high-pressure CO 2 adsorption study on various metal organic frameworks by Millward and Yaghi [110] achieved CO 2 adsorption capacity ranging from 2 to 8 mmol/g under similar conditions.
In addition, Wang et al. [94] reported CO 2 adsorption by graphene oxide. They studied the CO 2 adsorption of graphene oxide at 195 K and 1 bar, which conditions showed somewhat variable values of CO 2 uptake in the range from 10 to 38 wt%. It is possible that low CO 2 uptake values can occur in graphene samples containing large particulates.
Next, we will discuss metal-loaded graphene composites for CO 2 adsorption. As shown in Fig. 20 , Cazorla et al. [111] performed a first-principles study of CO 2 adsorbent materials consisting of calcium atoms and carbon-based nanostructures.
They found that Ca-decorated graphene possesses unusually large CO 2 uptake capacities in the range from 0.1 to 0.4 g CO 2 /g sorbent under a low-gas-pressure regime as a result of their unique topology and a strong interaction between the metal nanoparticles and CO 2 molecules. It is also reported that the strength of the Ca metal and CO 2 molecule interactions can be efficiently tuned as a function of the Ca loading content ( Table 3 ).
Enhancement of the CO 2 reactivity properties of carbons in the presence of Ca atoms can be understood in terms of electronic structure, that is, overlapping of s,d-metallic and p-molecular states in the region near the Fermi level. Thus, by use
Binding energy (per CO2molecule) and corresponding gas-adsorption capacities of Ca/graphene as a function of Ca content
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Binding energy (per CO2 molecule) and corresponding gas-adsorption capacities of Ca/graphene as a function of Ca content
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CO2 adsorption onto Ti-graphene (C2Ti). The final configuration shows the dissociation of the molecule in CO and O. The initial orientation of the molecule has no influence on the result.
of first-principles simulation techniques, Guo et al. [111] confidently proposed that these Ca metal/carbon-based nanomaterial composites exhibit characteristics of suitable adsorbents for CO 2 capture and sequestration applications.
Carrillo et al. [112] studied the adsorption of CO 2 on a Tigraphene system with high metal coverage using the density functional theory and molecular dynamics simulation. Positively charged Ti atoms on graphene surfaces attract negatively charged oxygen atoms towards the graphene surfaces. This force is stronger than the initial repulsion on the C atom by the Ti atoms. When a CO 2 molecule approaches the graphene surfaces, the CO 2 molecule cannot be linear any longer. The O atoms in a bent CO 2 molecule are under different force fields. Thus, one O atom traps an electronic charge from the Ti atoms of the upper plane and ends bonded to four Ti atoms, resulting in the CO 2 molecule interacting very strongly with the Ti atoms of the upper plane, as can be seen in Fig. 21 .
To complete the discussion of Carrillo et al. [112] mentioned above, it is essential to place mono-dispersed Ti atoms on a graphene surface. Ma and Resenberg [113] reported that their experiments showed that adsorbed Ti atoms on a clean graphite surface tend to form islands or some clusters. Meanwhile, Zhang et al. [114] showed that not only the Ti coating atoms can be dispersed along single-walled carbon nanotubes; Al and Au nanoparticles are also uniformly deposited on the pre-treated nanotubes, which means that this procedure could facilitate the dispersion of Ti atoms on graphene surfaces.
NH3on graphene: the adsorption energy (Ea) and the charge transfer (ΔQ) from graphene to the molecule for various adsorption sites and orientations
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NH3 on graphene: the adsorption energy (Ea) and the charge transfer (ΔQ) from graphene to the molecule for various adsorption sites and orientations
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The density of states (DOS) of graphene with adsorbed NH3 molecule calculated with a 60 × 60 × 1 MP grid and a Gaussian smearing of 0.14 eV. The dotted vertical lines show the molecular orbitals of NH3.
- 3.4. Ammonia adsorption
Hugo et al. [115] reported studies of the interaction of NH 3 with a graphene field-effect transistor (FETs) supported on Si/ SiO 2 substrates to provide further insight into the nature of the molecule-graphene interaction mechanism. Here, SiO 2 is used as a gate dielectric, and the heavily doped Si substrate is used as the bottom gate electrode. From the study, they elucidated that graphene FETs initially behave as a p-type system due to exposure to air, while these FETs can be rendered n-type by longterm vacuum-degassing at 200℃ .
Leenaerts et al. [116] investigated the adsorption process of NH 3 molecules on graphene through first-principle calculations and showed the presence of two main charge transfer mechanisms. They considered two different orientations of NH 3 molecules with respect to the graphene surface: (i) the H atoms pointing away from the surface ( u ) and (ii) the H atoms pointing toward the surface ( d ). They showed the calculated adsorption energies and charge transfers ( Table 4 ). It was found that the charge transfer is only determined by the orientation of the molecule and not by the adsorption sites. There is a small charge transfer of 0.03 e from the molecule to the graphene surface in the u orientation; there is almost no charge transfer in the d orientation.
Fig. 22 shows this dependence on the orientation can be understood in terms of the highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) of the molecule and the total density of states of the system. The HOMO and LUMO are both close enough to the Dirac point to cause some charge transfer through orbital mixing (hybridization) with the graphene orbital. In the u orientation, the NH 3 molecule acts as a donor, because the HOMO is the only orbital that can have a significant overlap with the graphene orbitals, and as a consequence, acts as a donor in this orientation. Meanwhile, in the d orientation, both the HOMO and LUMO of the NH 3 molecule are able to interact with graphene. This leads to competing charge transfers to and away from graphene, resulting in a total charge transfer close to zero. As observed experimentally in their study, the u orientation is energetically favored, which explains the donor character of NH 3 molecules.
4. Summary
The field of graphene-related research has grown at a spectacular pace since a single-layer flake was first isolated in 2004. The Nobel Prize in Physics 2010 was awarded to Andre Geim and Konstantin Novoselov for ground breaking experiments. Graphene and graphene-based materials are promising candidates as components in various applications due to their superior properties. Recently, the development of various methods for producing these materials has stimulated a vast amount of research, for example, epitaxial growth and chemical vapor deposition techniques, micromechanical exfoliation, chemical reduction, and thermal exfoliation, microwave treatments, and conversion of nanodiamonds. A proper understading of the growth and properties of graphene is a must for its optimal utilization.
The main purpose of this review was to comprehensive the synthesis method of graphene and to brief the adsorption behaviors of graphene and graphene-based materials. We have also reported not only the nature of adsorption sites for various gases on their surfaces for high H 2 storage capacity and CO 2 capture, but the sensor ability for detecting individual gas molecules. The superior adsorption behaviors of graphene and graphene-based materials might be attributable to their large specific surface area and special interaction between electron-donor and acceptor molecules.
We acknowledge the financial support by grants from Korea CCS R&D Center, funded by the Ministry of Education, Science and Technology of Korean government.
Novoselov KS , Geim AK , Morozov SV , Jiang D , Zhang Y , Dubonos SV , Grigorieva IV , Firsov AA (2004) Electric field effect in atomicallythin carbon films. Science 306 666 -
Tkachev S , Buslaeva E , Gubin S (2011) Graphene: a novel carbon nanomaterial. Inorg Mater 47 1 -
Singh V , Joung D , Zhai L , Das S , Khondaker SI , Seal S (2011) Graphenebased materials: past, present and future. Prog Mater Sci 56 1178 -
Novoselov KS , Jiang Z , Zhang Y , Morozov SV , Stormer HL , Zeitler U , Maan JC , Boebinger GS , Kim P , Geim AK (2007) Room-temperature quantum Hall effect in graphene. Science 315 1379 -
Ritter KA , Lyding JW (2009) The influence of edge structure on the electronicproperties of graphene quantum dots and nanoribbons. Nat Mater 8 235 -
Ubbelohde AR , Lewis FA (1960) Graphite and its Crystal Compounds Clarendon Press Oxford
Geim AK , Novoselov KS (2007) The rise of graphene. Nat Mater 6 183 -
Chung DDL (2002) Review graphite. J Mater Sci 37 1475 -
Stoller MD , Park S , Zhu Y , An J , Ruoff RS (2008) Graphene-based ultracapacitors. Nano Lett 8 3498 -
Bunch JS , van der Zande AM , Verbridge SS , Frank IW , Tanenbaum DM , Parpia JM , Craighead HG , McEuen PL (2007) Electromechanical resonators from graphene sheets. Science 315 490 -
Balandin AA , Ghosh S , Bao W , Calizo I , Teweldebrhan D , Miao F , Lau CN (2008) Superior thermal conductivity of single-layer graphene. Nano Lett 8 902 -
Li X , Wang X , Zhang L , Lee S , Dai H (2008) Chemically derived, ultrasmoothgraphene nanoribbon semiconductors. Science 319 1229 -
Shenderova OA , Zhirnov VV , Brenner DW (2002) Carbon nanostructures. Crit Rev Solid State Mater Sci 27 227 -
Krishnan A , Dujardin E , Treacy MMJ , Hugdahl J , Lynum S , Ebbesen TW (1997) Graphitic cones and the nucleation of curved carbonsurfaces. Nature 388 451 -
Nagashima A , Nuka K , Itoh H , Ichinokawa T , Oshima C , Otani S (1993) Electronic states of monolayer graphite formed on TiC(111)surface. Surf Sci 291 93 -
Forbeaux I , Themlin JM , Debever JM (1998) Heteroepitaxial graphiteon 6H-SiC(0001): interface formation through conduction-bandelectronic structure. Phys Rev B 58 16396 -
Wu J , Becerril HA , Bao Z , Liu Z , Chen Y , Peumans P (2008) Organicsolar cells with solution-processed graphene transparentelectrodes. Appl Phys Lett 92 263302 -
Ohta T , Bostwick A , Seyller T , Horn K , Rotenberg E (2006) Controlling the electronic structure of bilayer graphene. Science 313 951 -
de Heer WA , Berger C , Wu X , First PN , Conrad EH , Li X , Li T , Sprinkle M , Hass J , Sadowski ML , Potemski M , Martinez G (2007) Epitaxial graphene. Solid State Commun 143 92 -
Emtsev KV , Bostwick A , Horn K , Jobst J , Kellogg GL , Ley L , McChesney JL , Ohta T , Reshanov SA , Rohrl J , Rotenberg E , Schmid AK , Waldmann D , Weber HB , Seyller T (2009) Towards wafersizegraphene layers by atmospheric pressure graphitization of siliconcarbide. Nat Mater 8 203 -
Kim KS , Zhao Y , Jang H , Lee SY , Kim JM , Kim KS , Ahn JH , Kim P , Choi JY , Hong BH (2009) Large-scale pattern growth of graphene filmsfor stretchable transparent electrodes. Nature 457 706 -
Reina A , Jia X , Ho J , Nezich D , Son H , Bulovic V , Dresselhaus MS , Kong J (2008) Large area, few-layer graphene films on arbitrarysubstrates by chemical vapor deposition. Nano Lett 9 30 -
Yu Q , Lian J , Siriponglert S , Li H , Chen YP , Pei S-S (2008) Graphenesegregated on Ni surfaces and transferred to insulators. Appl Phys Lett 93 113103 -
Li X , Cai W , An J , Kim S , Nah J , Yang D , Piner R , Velamakanni A , Jung I , Tutuc E , Banerjee SK , Colombo L , Ruoff RS (2009) Large-areasynthesis of high-quality and uniform graphene films on copperfoils. Science 324 1312 -
Berger C , Song Z , Li X , Wu X , Brown N , Naud C , Mayou D , Li T , Hass J , Marchenkov AN , Conrad EH , First PN , de Heer WA (2006) Electronic confinement and coherence in patterned epitaxial graphene. Science 312 1191 -
Hass J , Heer WAd , Conrad EH (2008) The growth and morphology ofepitaxial multilayer graphene. J Phys: Condens Matter 20 323202 -
Bae S , Kim H , Lee Y , Xu X , Park JS , Zheng Y , Balakrishnan J , Lei T , Ri Kim H , Song YI , Kim YJ , Kim KS , Ozyilmaz B , Ahn JH , Hong BH , Iijima S (2010) Roll-to-roll production of 30-inch graphenefilms for transparent electrodes. Nat Nanotechnol 5 574 -
Berger C , Song Z , Li T , Li X , Ogbazghi AY , Feng R , Dai Z , Marchenkov AN , Conrad EH , First PN , de Heer WA (2004) Ultrathin epitaxialgraphite: 2D electron gas properties and a route toward graphenebasednanoelectronics. J Phys Chem B 108 19912 -
Jauregui LA , Cao H , Wu W , Yu Q , Chen YP (2011) Electronic propertiesof grains and grain boundaries in graphene grown by chemicalvapor deposition. Solid State Commun 151 1100 -
Cao H , Yu Q , Jauregui LA , Tian J , Wu W , Liu Z , Jalilian R , Benjamin DK , Jiang Z , Bao J , Pei SS , Chen YP (2010) Electronic transportin chemical vapor deposited graphene synthesized on Cu: quantumHall effect and weak localization. Appl Phys Lett 96 122106 -
Eizenberg M , Blakely JM (1979) Carbon monolayer phase condensationon Ni(111). Surf Sci 82 228 -
Isett LC , Blakely JM (1976) Segregation isosteres for carbon at the(100) surface of nickel. Surf Sci 58 397 -
Somani PR , Somani SP , Umeno M (2006) Planer nano-graphenes fromcamphor by CVD. Chem Phys Lett 430 56 -
Chen YP , Yu Q (2010) Nanomaterials: graphene rolls off the press. Nat Nanotechnol 5 559 -
Meyer JC , Geim AK , Katsnelson MI , Novoselov KS , Booth TJ , Roth S (2007) The structure of suspended graphene sheets. Nature 446 60 -
Bolotin KI , Sikes KJ , Jiang Z , Klima M , Fudenberg G , Hone J , Kim P , Stormer HL (2008) Ultrahigh electron mobility in suspended graphene. Solid State Commun 146 351 -
Bolotin KI , Sikes KJ , Hone J , Stormer HL , Kim P (2008) Temperature-dependent transport in suspended graphene. Phys Rev Lett 101 096802 -
Novoselov KS , Jiang D , Schedin F , Booth TJ , Khotkevich VV , Morozov SV , Geim AK (2005) Two-dimensional atomic crystals. Proc Natl Acad Sci USA 102 10451 -
Park SJ (2006) van der Waals interaction at surfaces. In: Somasundaran P,ed. Encyclopedia of Surface and Colloid Science. 2nd ed. Taylor& Francis New York 5570 -
Park SJ (1999) Long-range force contributions to surface dynamics. In:Hsu JP, ed. Interfacial Forces and Fields: Theory and Applications Marcel Dekker New York 385 -
Li X , Cai W , Colombo L , Ruoff RS (2009) Evolution of graphene growthon Ni and Cu by carbon isotope labeling. Nano Lett 9 4268 -
Park SJ , Seo MK (2011) Interface Science and Composites Academic Press Boston
Hummers WS Jr , Offeman RE (1958) Preparation of graphitic oxide. J Am Chem Soc 80 1339 -
Allen MJ , Tung VC , Kaner RB (2009) Honeycomb carbon: a review ofgraphene. Chem Rev 110 132 -
Hernandez Y , Nicolosi V , Lotya M , Blighe FM , Sun Z , De S , Mc-Govern IT , Holland B , Byrne M , Gun’Ko YK , Boland JJ , Niraj P , Duesberg G , Krishnamurthy S , Goodhue R , Hutchison J , Scardaci V , Ferrari AC , Coleman JN (2008) High-yield production of grapheneby liquid-phase exfoliation of graphite. Nat Nanotechnol 3 563 -
Lotya M , Hernandez Y , King PJ , Smith RJ , Nicolosi V , Karlsson LS , Blighe FM , De S , Wang Z , McGovern IT , Duesberg GS , Coleman JN (2009) Liquid phase production of graphene by exfoliation ofgraphite in surfactant/water solutions. J Am Chem Soc 131 3611 -
Marcano DC , Kosynkin DV , Berlin JM , Sinitskii A , Sun Z , Slesarev A , Alemany LB , Lu W , Tour JM (2010) Improved synthesis of grapheneoxide. ACS Nano 4 4806 -
Kim KS , Park SJ (2011) Influence of multi-walled carbon nanotubeson the electrochemical performance of graphene nanocompositesfor supercapacitor electrodes. Electrochim Acta 56 1629 -
Nakajima T , Mabuchi A , Hagiwara R (1988) A new structure modelof graphite oxide. Carbon 26 357 -
Stankovich S , Dikin DA , Piner RD , Kohlhaas KA , Kleinhammes A , Jia Y , Wu Y , Nguyen ST , Ruoff RS (2007) Synthesis of graphenebasednanosheets via chemical reduction of exfoliated graphiteoxide. Carbon 45 1558 -
Lomeda JR , Doyle CD , Kosynkin DV , Hwang WF , Tour JM (2008) Diazonium functionalization of surfactant-wrapped chemically convertedgraphene sheets. J Am Chem Soc 130 16201 -
Tung VC , Allen MJ , Yang Y , Kaner RB (2009) High-throughput solution processing of large-scale graphene. Nat Nanotechnol 4 25 -
Ren PG , Yan DX , Ji X , Chen T , Li ZM (2011) Temperature dependenceof graphene oxide reduced by hydrazine hydrate. Nanotechnology 22 055705 -
Stankovich S , Dikin DA , Dommett GHB , Kohlhaas KM , Zimney EJ , Stach EA , Piner RD , Nguyen ST , Ruoff RS (2006) Graphenebased composite materials. Nature 442 282 -
Wang G , Yang J , Park J , Gou X , Wang B , Liu H , Yao J (2008) Facile synthesis and characterization of graphene nanosheets. J Phys Chem C 112 8192 -
Si Y , Samulski ET (2008) Synthesis of water soluble graphene. Nano Lett 8 1679 -
Erickson K , Erni R , Lee Z , Alem N , Gannett W , Zettl A (2010) Determinationof the local chemical structure of graphene oxide and reducedgraphene oxide. Adv Mater 22 4467 -
McAllister MJ , Li JL , Adamson DH , Schniepp HC , Abdala AA , Liu J , Herrera-Alonso M , Milius DL , Car R , Prud’homme RK , Aksay IA (2007) Single sheet functionalized graphene by oxidation and thermalexpansion of graphite. Chem Mater 19 4396 -
Schniepp HC , Li J-L , McAllister MJ , Sai H , Herrera-Alonso M , Adamson DH , Prud’homme RK , Car R , Saville DA , Aksay IA (2006) Functionalized single graphene sheets derived from splittinggraphite oxide. J Phys Chem B 110 8535 -
Kaniyoor A , Baby TT , Arockiadoss T , Rajalakshmi N , Ramaprabhu S (2011) Wrinkled graphenes: a study on the effects of synthesis parameterson exfoliation-reduction of graphite oxide. J Phys Chem C 115 17660 -
Subrahmanyam KS , Vivekchand SRC , Govindaraj A , Rao CNR (2008) A study of graphenes prepared by different methods: characterization,properties and solubilization. J Mater Chem 18 1517 -
Rao CNR , Sood AK , Subrahmanyam KS , Govindaraj A (2009) Graphene:the new two-dimensional nanomaterial. Angew Chem IntEd 48 7752 -
Morales GM , Schifani P , Ellis G , Ballesteros C , Martínez G , Barbero C , Salavagione HJ (2011) High-quality few layer graphene producedby electrochemical intercalation and microwave-assistedexpansion of graphite. Carbon 49 2809 -
Andersson OE , Prasad BLV , Sato H , Enoki T , Hishiyama Y , Kaburagi Y , Yoshikawa M , Bandow S (1998) Structure and electronic propertiesof graphite nanoparticles. Phys Rev B 58 16387 -
Prasad BLV , Sato H , Enoki T , Hishiyama Y , Kaburagi Y , Rao AM , Eklund PC , Oshida K , Endo M (2000) Heat-treatment effect on the nanosizedgraphite π-electron system during diamond to graphite conversion. Phys Rev B 62 11209 -
Subrahmanyam KS , Panchakarla LS , Govindaraj A , Rao CNR (2009) Simple method of preparing graphene flakes by an arc-dischargemethod. J Phys Chem C 113 4257 -
Rao CNR , Subrahmanyam KS , Matte HSSR , Abdulhakeem B , Govindaraj A , Barun D , Prashant K , Anupama G , Dattatray JL (2010) A studyof the synthetic methods and properties of graphenes. Sci Technol Adv Mater 11 054502 -
Seshadri R , Govindaraj A , Aiyer HN , Sen R , Subbanna GN , Raju AR , Rao CNR (1994) Investigations of carbon nanotubes. Curr Sci 66 839 -
Zhang RQ , Sarkar AD (2011) Theoretical studies on formation, property,tuning and adsorption of graphene segments. In: Mikhailov S, ed.Physics and Applications of Graphene--Theory, InTech Openbook,Chapter 1
Lin CS , Zhang RQ , Lee ST , Elstner M , Frauenheim T , Wan LJ (2005) Simulation of water cluster assembly on a graphite surface. J Phys Chem B 109 14183 -
Kim BJ , Lee YS , Park SJ (2008) Novel porous carbons synthesized frompolymeric precursors for hydrogen storage. Int J Hydrogen Energy 33 2254 -
Yoo HM , Lee SY , Kim BJ , Park SJ (2011) Influence of phosphoric acidtreatment on hydrogen adsorption behaviors of activated carbons. Carbon Lett 12 112 -
Saha D , Deng S (2011) Hydrogen adsorption on Pd- and Ru-doped C60fullerene at an ambient temperature. Langmuir 27 6780 -
Chen J , Wu F (2004) Review of hydrogen storage in inorganic fullerene-like nanotubes. Appl Phys A 78 989 -
Lee SY , Park SJ (2010) Effect of temperature on activated carbon nanotubesfor hydrogen storage behaviors. Int J Hydrogen Energy 35 6757 -
Park SJ , Lee SY (2010) Hydrogen storage behaviors of platinum-supportedmulti-walled carbon nanotubes. Int J Hydrogen Energy 35 13048 -
Lee SY , Park SJ (2010) Influence of CO2activation on hydrogen storagebehaviors of platinum-loaded activated carbon nanotubes. J Solid State Chem 183 2951 -
Lee SY , Park SJ (2010) Effect of chemical treatments on hydrogen storagebehaviors of multi-walled carbon nanotubes. Mater Chem Phys 124 1011 -
Jung MJ , Im JS , Jeong E , Jin H , Lee YS (2009) Hydrogen adsorption ofpan-based porous carbon nanofibers using MgO as the substrate. Carbon Lett 10 217 -
Sharon M , Sharon M , Kalita G , Mukherjee B (2011) Hydrogen storageby carbon fibers synthesized by pyrolysis of cotton fibers. Carbon Lett 12 39 -
Im JS , Kwon O , Kim YH , Park SJ , Lee YS (2008) The effect of embeddedvanadium catalyst on activated electrospun CFs for hydrogenstorage. Microporous Mesoporous Mater 115 514 -
Lee SY , Park SJ (2011) Preparation and characterization of orderedporous carbons for increasing hydrogen storage behaviors. J Solid State Chem 184 2655 -
Jiang J , Gao Q , Zheng Z , Xia K , Hu J (2010) Enhanced room temperaturehydrogen storage capacity of hollow nitrogen-containing carbonspheres. Int J Hydrogen Energy 35 210 -
Lee SY , Park SJ (2011) Effect of platinum doping of activated carbonon hydrogen storage behaviors of metal-organic frameworks-5. Int J Hydrogen Energy 36 8381 -
Park SJ , Lee SY (2009) Hydrogen storage behaviors of carbon nanotubes/metal-organic frameworks-5. Carbon Lett 10 19 -
Tylianakis E , Psofogiannakis GM , Froudakis GE (2010) Li-doped pillaredgraphene oxide: a graphene-based nanostructured materialfor hydrogen storage. J Phys Chem Lett 1 2459 -
Srinivas G , Zhu Y , Piner R , Skipper N , Ellerby M , Ruoff R (2010) Synthesisof graphene-like nanosheets and their hydrogen adsorptioncapacity. Carbon 48 630 -
Bourlinos AB , Steriotis TA , Karakassides M , Sanakis Y , Tzitzios V , Trapalis C , Kouvelos E , Stubos A. (2007) Synthesis, characterization andgas sorption properties of a molecularly-derived graphite oxidelikefoam. Carbon 45 852 -
Ma LP , Wu ZS , Li J , Wu ED , Ren WC , Cheng HM (2009) Hydrogenadsorption behavior of graphene above critical temperature. Int J Hydrogen Energy 34 2329 -
Ghosh A , Subrahmanyam KS , Krishna KS , Datta S , Govindaraj A , Pati SK , Rao CNR (2008) Uptake of H2and CO2by graphene. J Phys Chem C 112 15704 -
Peigney A , Laurent C , Flahaut E , Bacsa RR , Rousset A (2001) Specificsurface area of carbon nanotubes and bundles of carbon nanotubes. Carbon 39 507 -
Kaneko K , Ishii C , Ruike M , kuwabara H (1992) Origin of superhighsurface area and microcrystalline graphitic structures of activatedcarbons. Carbon 30 1075 -
Bhatia SK , Myers AL (2006) Optimum conditions for adsorptive storage. Langmuir 22 1688 -
Wang L , Lee K , Sun YY , Lucking M , Chen Z , Zhao JJ , Zhang SB (2009) Graphene oxide as an ideal substrate for hydrogen storage. ACS Nano 3 2995 -
Kim BJ , Park SJ (2011) Optimization of the pore structure of nickel/graphite hybrid materials for hydrogen storage. Int J Hydrogen Energy 36 648 -
Kubas GJ , Ryan RR , Swanson BI , Vergamini PJ , Wasserman HJ (1984) Characterization of the first examples of isolable molecular hydrogencomplexes, M(CO)3(PR3)2(H2) (M = molybdenum or tungsten;R = Cy or isopropyl). Evidence for a side-on bonded dihydrogen ligand. J Am Chem Soc 106 451 -
Kubas GJ (1988) Molecular hydrogen complexes: coordination of a.sigma. bond to transition metals. Acc Chem Res 21 120 -
Hoang TKA , Antonelli DM (2009) Exploiting the Kubas interaction inthe design of hydrogen storage materials. Adv Mater 21 1787 -
Singh AK , Sadrzadeh A , Yakobson BI (2010) Metallacarboranes: towardpromising hydrogen storage metal organic frameworks. J Am Chem Soc 132 14126 -
Skipper CVJ , Hamaed A , Antonelli DM , Kaltsoyannis N (2010) Computationalstudy of silica-supported transition metal fragmentsfor Kubas-type hydrogen storage. J Am Chem Soc 132 17296 -
Hamaed A , Hoang TKA , Moula G , Aroca R , Trudeau ML , Antonelli DM (2011) Hydride-induced amplification of performance andbinding enthalpies in chromium hydrazide gels for Kubas-typehydrogen storage. J Am Chem Soc 133 15434 -
Zhu H , Chen Y , Li S , Yang X , Liu Y (2011) Novel sandwich-typedimetallocenes: toward promising candidate media for highcapacityhydrogen storage. Int J Hydrogen Energy 36 11810 -
Mishra AK , Ramaprabhu S (2011) Carbon dioxide adsorption in graphenesheets. AIP Advances 1 032152 -
Kaniyoor A , Baby TT , Ramaprabhu S (2010) Graphene synthesis viahydrogen induced low temperature exfoliation of graphite oxide. J Mater Chem 20 8467 -
Mishra AK , Ramaprabhu S (2011) Nano magnetite decorated multiwalledcarbon nanotubes: a robust nanomaterial for enhancedcarbon dioxide adsorption. Energy Environ Sci 4 889 -
Siriwardane RV , Shen MS , Fisher EP , Poston JA (2001) Adsorption ofCO2on molecular sieves and activated carbon. Energy Fuels 15 279 -
Gensterblum Y , van Hemert P , Billemont P , Busch A , Charriere D , Li D , Krooss BM , de Weireld G , Prinz D , Wolf KHAA (2009) Europeaninter-laboratory comparison of high pressure CO2sorptionisotherms. I: activated carbon. Carbon 47 2958 -
Zhang Z , Xu M , Wang H , Li Z (2010) Enhancement of CO2adsorptionon high surface area activated carbon modified by N2, H2and ammonia. Chem Eng J 160 571 -
Cavenati S , Grande CA , Rodrigues AE (2004) Adsorption equilibriumof methane, carbon dioxide, and nitrogen on zeolite 13X at highpressures. J Chem Eng Data 49 1095 -
Millward AR , Yaghi OM (2005) Metal?organic frameworks with exceptionallyhigh capacity for storage of carbon dioxide at roomtemperature. J Am Chem Soc 127 17998 -
Cazorla C , Shevlin SA , Guo ZX (2011) Calcium-based functionalizationof carbon materials for CO2capture: a first-principlescomputational study. J Phys Chem C 115 10990 -
Carrillo I , Rangel E , Magana LF (2009) Adsorption of carbon dioxideand methane on graphene with a high titanium coverage. Carbon 47 2758 -
Ma Q , Rosenberg RA (1999) Interaction of Ti with the (0001) surface ofhighly oriented pyrolitic graphite. Phys Rev B 60 2827 -
Zhang Y , Franklin NW , Chen RJ , Dai H (2000) Metal coating on suspendedcarbon nanotubes and its implication to metal?tubeinteraction. Chem Phys Lett 331 35 -
Hugo ER , Prasoon J , Awnish KG , Humberto RG , Milton WC , Srinivas AT , Peter CE (2009) Adsorption of ammonia on graphene. Nanotechnology 20 245501 -
Leenaerts O , Partoens B , Peeters FM (2009) Adsorption of small moleculeson graphene. Microelectron J 40 860 -