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Inorganic Nanostructures Decorated Graphene

Written By

Hong Ngee Lim, Nay Ming Huang, Chin Hua Chia and Ian Harrison

Submitted: 27 August 2012 Published: 20 February 2013

DOI: 10.5772/54321

From the Edited Volume

Advanced Topics on Crystal Growth

Edited by Sukarno Olavo Ferreira

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1. Introduction

1.1. Why use graphene for the assembly of nanostructures?

Graphene, with zero energy gap between the highest occupied molecular orbit and the lowest unoccupied molecular orbit (HOMO-LUMO), offers a unique two-dimensional (2-D) environment for fast electron transport and has potential applications in electronic devices [1, 2]. Other consequences of the band structure is the opacity which is wavelength independent [3], and thermal conductivity [4]. The four edges of a graphene sheet provide significant number of centres for fast heterogeneous electron transfer [1], when compared to single-walled carbon nanotubes (SWCNTs) for which heterogeneous electron transfer occurs only at the two ends of the nanotube [5]. Consequently, graphene sheets may have wider applicability in electrochemistry [6]. While graphite is brittle, graphene’s flexibility is beneficial for use in electromechanical devices [7] and energy storage devices [8]. In the energy storage devices, its weight is of extremely important and the specific area per unit weight is an important figure of merit. Graphene exhibits a theoretical surface area of 2630 m2 g-1, which is ~ 260 times greater than graphite and twice that of CNTs [9]. Thus, graphene provides a way of enhancing the electrochemical catalytic activity of materials by greatly increasing the high surface area [10]. The intriguing electronic, optical, electrochemical, mechanical and thermal properties of graphene make it an indispensable material in various kinds of synthesis processes.

Various inorganic nanostructures have been prepared over the last two decades due to the special properties of nanostructured materials. Previously, 2-D ZnO nanoplates [11], 1-D PbS nanorods [12], 0-D semiconductor materials [13] and core-shell magnetic nanoparticles have been produced [14]. However, heavy aggregation of the nanostructures, resulted by van der Waals forces between the particles, may limit their special properties and cause structural instability, thus reduce their applicability. To prevent this clustering from occurring, nanocomposites, consisting of the nanoparticles embedded within a matrix compound, can be used. These nanocomposites preserve the unique properties of the nanoparticles whilst often having the additional performance benefits of the matrix compound itself.

With large surface area and the unique properties given above, graphene is an attractive choice as the matrix for inorganic nanostructures [15]. Functionalization of graphene sheets with various nanostructures can further enhance the properties of graphene. Heterostructures consisting of nanostructures distributed on the surface of graphene could potentially display not only the unique properties of nanostructures [16] and those of graphene [2, 17, 18], but also additional novel functionalities and properties due to the interaction between them. Moreover, the growth of the nanostructures can take place easily when graphene is used as a matrix due to the planar structure of graphene, in comparison to the hollow tubal-shaped CNTs. The particle size and size distribution of nanostructures are small and narrow when graphene is used as a support for the growth of nanostructures [19-21].


2. Inorganic nanostructures decorated graphene

Graphene nanocomposites can be made from graphene oxide (GO) which is essentially a graphene sheet containing oxy-functional groups, such as epoxy, hydroxyl, carbonyl, and carboxylic, on the surface. The reactive functional groups provide a means of attaching the nanoparticles to the graphene sheet [22, 23]. The GO starting material can be simply and economically synthesized using chemical oxidation of graphite [24]. Graphene manufactured using this highly scalable synthesis route is also popularly known as reduced GO (rGO). Using GO as a support for metallic ions, many types of different nanocomposites have been made. The overview of the types of materials and synthesis methods pertaining to the graphene-based nanostructures are presented in Table 1 along with the potential application for the nanocomposites.

InorganicNanostructure Morphology and Dimension Synthesis Method Potential Application Reference
Ag 16.9±3.5 nm Rapid thermal treatment Antibacterial agent, nanofluids for cooling technology, water treatments, surface-enhanced Raman scattering (SERS), transparent and conductive film, electrochemical immunosensor, and catalysis [25]
Ag ~420 nm Laser assisted photocatalytic reduction Solar energy conversion [26]
AgAu 50–200 nm In situ chemical synthesis Electrochemical immunosensing [27]
Au 30-70 nm Laser assisted photocatalytic reduction Solar energy conversion [26]
Au 30 nm Cyclic voltammetry scanning Detection of mercury [28]
Ni Single-layered Electroless Ni-plating Electrodes, sensors, hydrogen-storage, production of fuel cell [29]
Pd 13±2 nm Electrochemical codeposition An anode catalyst for formic acid electrooxidation [30]
Pd 5–7 nm Laser irradiation CO oxidation [31]
Pt 5–7 nm Laser irradiation CO oxidation [31]
PtRu 2 nm Microwave Electrocatalysts for methanol oxidation [32]
Metal oxide
Ag2O 45 nm In situ oxidation route Supercapacitor [33]
CoO 5–7 nm Laser irradiation CO oxidation [31]
CuO < 20 nm In situ chemical synthesis Glucose biosensor [34]
CuO 30 nm Hydrothermal Anode for lithium-ion batteries [21]
Fe3O4 20, 30 and 40 nm In situ chemical synthesis Sensors, supercapacitors, drug delivery systems, waste water treatment [20]
Fe3O4 12.5 nm Gas/liquid interface reaction Anode for lithium-ion batteries [35]
Mn3O4 10 nm Ultrasonication Supercapacitors [36]
NiO 32 nm Hydrothermal Anode for lithium-ion batteries [37]
PbO image not shown Electrochemical route Detection of trace arsenic [38]
SnO2 10 nm Microwave Detection of mercury(II) [19]
SnO2 4-5 nm One-step wet chemical method Detection of cadmium(II), lead(II), copper(II), and mercury(II) [39]
SnO2 2–3 nm Microwave Supercapacitor [32]
SnO2 4–5 nm Microwave autoclave Anode for lithium-ion batteries [40]
SnO2 2–6 nm Gas/liquid interface reaction Anode for lithium-ion batteries [41]
SnO2 4–6 nm In situ chemical synthesis Anode for lithium-ion batteries [42]
TiO2 ~20 nm Hydrothermal Detection of mercury [43]
TiO2 4–5 nm Sonochemical Photocatalyst [44]
TiO2 (P25) ~30 nm Hydrothermal Photocatalyst [45]
TiO2 (P25) ~30 nm Hydrothermal Photoelectrocatalytic degradation [46]
ZnO nanorods, an approximated
diameter of ~90 nm and length of ~3 μm
Hydrothermal Solar cells, gas sensors, transparent conductors, catalysis [47]
ZrO2 ~42 nm Electrochemical route Enzymeless methyl parathion sensor [48]
Metal oxides
Bi2WO6 nanoparticles containing square nanoplates, 100−300 nm Reflux Photocatalyst [49]
La2Ti2O7 nanosheets, comprehensively integrated Expansion and UV irradiation Photocatalyst [50]
NiFe2O4 6.5 nm Hydrothermal Anode for lithium-ion batteries [51]
Pd-CoO 5–7 nm Laser irradiation CO oxidation [31]
Ag/TiO2 TiO2 layer coexists with Ag Dipping-lifting in sol-gel solution, reducing process and interface reaction Photoelectrochemical conversion [52]
CdS 7.5–20 nm Solvothermal Photocatalyst [53]
Core-shell Fe@Fe2O3@ Si-S-O mean of 22 nm One-pot thermodecomposition Chromium removal [54]
Fe2O3-ZnO Fe2O3 ~50 nm, ZnO <10 nm Hydrothermal Photocatalyst [55]
FeS2 spherical, ~50 nm Hydrothermal Solar energy conversion [56]
SnSb quasi-spherical, 30–40 nm Solvothermal Anode for lithium-ion batteries [57]

Table 1.

A summary of inorganic nanostructures decorated graphene and their potential applications. (Note: If the inorganic nanostructures are nanoparticles, the shape is not mentioned under the column of Morphology and Dimension.)


3. Interaction of nanostructures with graphene

The widely accepted mechanism for the synthesis of inorganic nanostructures decorated graphene is the attraction of the positively-charged metal ions by the polarised bonds of the functional groups on the GO. The attachment of the metal ions to the surface and edges of the GO results in a redox reaction and the formation of nucleation sites, which eventually leads to the growth of nanostructures on the 2-D graphene sheets. An example of this process is the redox hybridization process which occurs between GO and Fe2+ to form Fe3O4/rGO nanocomposite and this is shown in Figure 1 [58]. The Fe2+ ions are first attached to the surface by the functional groups on the surface of the GO sheets (Figure 1a). The GO acts as an oxidizing agent (Equation 1), effectively increasing the oxidation state of the Fe ions from Fe2+ to Fe3+. This is followed by the reaction of the Fe3+ ions, in an alkaline condition, into Fe3O4 nanoparticles (Equation 2) on the surface of the rGO. The complete stoichiometry is depicted by Equation 3. During the redox reaction, the polar oxygenated functional groups on the GO sheets serve as the anchoring sites for the Fe3O4 nanoparticles, consequently preventing serious agglomeration of the magnetic nanoparticles (Figure 1b).

2Fe2++ GO2Fe3++ rGOE1
Fe2++ 2Fe3++ 8OH-Fe3O4+ 4H2OE2
3Fe2++ GO (8OH-)Fe3O4+ 4H2O + rGOE3

Figure 1.

Schematic illustration of the formation of Fe3O4/rGO nanocomposite via a one-step in situ chemical deposition method [20].

In the case of metal/graphene, the nanocomposites are produced through simultaneous reduction of GO and metal ions [29, 31, 32]. In the absence of a reducing environment as in pure water but under the illumination of a radiating energy such as laser, the reduction mechanism of the metal ions (M2+) involving the photogenerated electrons from GO are shown by Equations 4–7, where GO is partially reduced as portrayed by Equations 6 and 7 [26].

GO +hvGO (h++ e)E4
4h++ 2H2OO2+ 4H+E5
M++ GO (e)GO + ME6
GO + 4e+ 4H+rGO + 2H2OE7

In the presence of a reducing agent such as sodium borohydride, NaBH4 used for the synthesis of Ni/graphene, Ni ions and the COOH groups on the surface of the GO sheets were reduced to Ni metal and CH2OH, respectively. The corresponding equation may proceed as represented by Equation 8 [29].


The incorporation of nanoparticles could be through chemisorption, physisorption, electrostatic interaction, van der Waals or covalent bonding with rGO [21, 22]. The attachment of nanostructures onto the surface of the graphene reduces the attractive interactions between the rGO sheets and, minimizes the aggregation and restacking of rGO during the reduction process [53]. Moreover, trace quantity of nanostructures on the basal planes of rGO allows uniform dispersion of the nanocomposite in polar solvents, which is otherwise impossible for rGO [20].


4. A new class of graphene-based inorganic nanostructures

The morphological structure of graphene nanocomposites is varied and depends on the synthesis route. Ag/graphene was synthesized using a thermal expansion method and yielded uniformly distributed Ag nanoparticles on graphene sheets [25] (Figure 2a). Whereas the hydrothermal approach gave an assemble pyrite structured FeS2 nanospheres [56] (Figure 2b), CuO nanospheres [59] (Figure 2c), TiO2 nanoparticles [43] (Figure 2d) and ZnO nanoflowers [60] (Figures 2e and 2f). In the last example, some of the ZnO nanoflowers were brighter in the SEM image than others and seemed to be enveloped by a thin film of graphene. Since the functional groups, such as hydroxyl and epoxy groups, are attached to both sides of GO sheets, the ZnO nanoflowers appear on both sides of the graphene support [61]. Another method based around microwave heating has been used to make SnO2/graphene nanocomposite [19] (Figure 2g). At a higher magnification (Figure 2h), the SnO2 nanoparticles were observed to uniformly adhere on the graphene sheets, with high density [19]. A simple, cost-effective, efficient, and green in situ deposition to synthesize Fe3O4 nanoparticles on graphene [20] (Figure 2i) has also been explored. The magnetic property of the Fe3O4/graphene nanocomposite allows the separation of composite from the solution by applying an external magnetic field (Figure 2j).

Figure 2.

Electron micrographs of various inorganic nanostructures decorating graphene; (a) Ag, (b) FeS2, (c) CuO, (d) TiO2, (e) ZnO, (f) a higher magnification showing flower-like shape ZnO nanoarchitecture, (g) SnO2, (h) a higher magnification revealing SnO2 nanoparticles, and (i) Fe3O4. (j) Photo image of Fe3O4/graphene dispersed uniformly in water and attracted under the external magnetic field.

rGO has proven to be an effective matrix for the adhesion of nanostructures due to the rich content of oxide functional groups on the basal planes and edges of the 2-D material. Good evidence of rGO being an accomplished support is depicted through an FESEM image of Fe3O4/graphene, in which the nanocomposite was prepared at low concentration of Fe2+ ions. The micrograph of the sample shows no evidence for the formation of Fe3O4 nanoparticles (Figure 3a). This is in contrast to the sample prepared using a higher concentration of Fe2+ ions where nanoparticles are apparent (Figure 2i). To investigate this observation further, elemental mapping of C, O, and Fe using energy dispersive x-ray (EDX) analysis (Figure 3b) was undertaken (Figure 3c). The area of bright contrast correlates with the Fe signal map. This result, coupled with the XRD result [20], provides evidence for the presence of Fe3O4 on the surface of the graphene. The exact form of the Fe3O4 cannot be determined. It is possible that a layer of Fe3O4 has formed on the surface of the rGO or more likely that very small nanoparticles have formed.

Figure 3.

Fe3O4/graphene prepared at a low concentration of Fe2+ ions: (a) FESEM image, (b) EDX spectrum, and (c) elemental mapping [20].


5. Growth processes of inorganic nanostructures on graphene sheets

5.1. In situ chemical synthesis

In situ chemical synthesis is a robust route for the formation of graphene decorated with inorganic nanostructures. The attraction of the positively charged metal ions towards the negatively charged electron cloud surrounding the oxygen atoms of the GO sheets is the initial step in the nucleation of the nanostructure on the graphene sheet. Since oxygen atoms are uniformly distributed in the starting graphene oxide sheets, a uniform decoration of nanostructures on the graphene sheets is produced after the reaction. Some metal oxides such as Fe3O4 and SnO2 can grow on the surface of rGO at room temperature [20, 39]. However, by increasing the reaction temperature, the high temperature calcination step may be able to be eliminated e.g. SnO2/graphene [42]. The reduction of GO may not occur during the deposition of the nanostructures on the surface of the GO, for example in the synthesis of MnO2/GO [61]. To ensure the GO is completely reduced, additional reducing agents can be used. For example, in the synthesis of nanocrystal Ag/graphene, hydrazine and ammonia solution in the presence of polyvinyl alcohol were used [27].

In situ chemical synthesis has also been described as a one-pot thermodecomposition route. When graphene sheets are directly used, a stabilizing agent such as sodium dodecylbenzenesulfonate (SDBS) is required along with a high reaction temperature to encourage the assembly of the nanostructure. The formation of Fe nanostructures on graphene is an example of this. [54]. Similarly, CuO/graphene was synthesized through the stabilization of graphene sheet with ethylene glycol at a high temperature [34]. For some materials, however, the high reaction temperature is not required to promote the assembly. Ag2O/graphene nanocomposites are an example and these were prepared in the presence of N-Methyl-2-pyrrolidone (NMP) under ambient conditions [33]. The stabilizing agents also function as a size- and shape-controlling agent and a reducing agent. In FeS2/graphene, the stabilization agent constraints the growth of FeS2 to a gelatin micelles geometry, resulting in well-formed nanoparticles [56]. Variations of the in situ chemical synthesis include the electrode-less Ni-plating on graphene sheets [29] and the attachment of Bi2WO6 nanoparticles and nanoplates onto GO by refluxing [49].

5.2. Hydrothermal

Hydrothermal synthesis is an efficient inorganic synthesis approach for the formation of a variety of nanomaterials, catalysts, ion-conductors, and zeolites [62] under controlled temperature and pressure. This synthesis route overcomes the drawbacks of high processing temperatures and long reaction times compared to conventional aqueous chemical processing conditions [63]. It has been recognized as an environmentally friendly process because the reaction uses aqueous solutions as a reaction medium and it is carried out in an autoclave, which is a closed system. This method can also be used for the preparation of high-purity, highly crystalline, ultrafine and homogeneous powders of various single and multi-component powders [64, 65]. The autoclave used in the hydrothermal synthesis, as mentioned previously, is a closed system and so raising its temperature increases the pressure inside the vessel above the critical pressure for water which enhances the dissolution of thermodynamically unstable compounds. The high heat energy and pressure in the autoclave facilitates fracture of the macronucleus to form nano-sized particles [66]. This method has been used for the synthesis of CuO/graphene [21], NiO/graphene [37], ZnO/graphene [47], and FeS2/graphene nano-composites [56].

The hydrothermal systhesis methology is not restricted to pure aqueous solutions. The addition of other solvents like ethanol can be used to enhance the dispersion of gel-like GO [43]. For example, TiO2 nanoparticles could be chemically bonded to the surface of rGO [45, 46]. Likewise, a one pot synthesis of Fe2O3 nanoparticles, Zn salt and GO produced Fe2O3-ZnO/graphene nanocomposites, in which the Fe2O3 nanoparticles were chemically bonded to the graphene sheets. The 50 nm sized Fe2O3 nanoparticles were covered with ZnO nanoparticles that are less than 10 nm in size [55].

If the solutions are not aqueous based, the method is known as the solvothermal process, for instance absolute ethanol was used as a medium for the synthesis of SnSb/graphene [57]. For the synthesis of CdS/graphene, dimethyl sulfoxide (DMSO) not only acted as a reaction medium but also the source of sulphide and a reducing agent [67]. SnO2/graphene was prepared via a gas–liquid interfacial reaction, in a process similar to hydrothermal method. During the reaction, a two-phase liquid was vaporized, which allowed the Sn4+ to react with the ammonia at gas/liquid interface to produce Sn(OH)4 along with in situ deposited onto the graphene sheets. The Sn(OH)4 subsequently decomposed to SnO2 on the graphene sheets [41]. Fe3O4/graphene has also been prepared using the same process [35].

5.3. Microwave heating

Microwave heating is believed to be more depending on the molecular properties and the reaction conditions than conventional heating [68]. Microwave syntheses have been increasingly used in the preparation of high monodispersity nanoparticles of oxides such as SnO2, CeO2 and ZrO2 [69]. Utilizing microwave energy for the thermal treatment generally leads to very fine particles in the nanocrystalline regime mainly caused by the shorter synthesis time and a highly focused localised heating. The particle size often falls in the range of 15 nm – 35 nm [70]. Microwave heating also has been widely used for the fabrication of inorganic nanostructure/graphene where the particles were less than 10 nm with a narrow size distribution. In this synthesis, the graphene sheets obviously played an important role in constraining the growth of nanostructures [32, 71]. Hydrothermal method has also been combined with microwave heating to ensure a complete reduction of GO [40].

5.4. Electrodeposition

Electrodeposition provides a facile procedure and offers precise control of the thickness of the resulting film [72]. In addition to the speed of polymerization, which can be controlled by the current density [73], this method also enables mild processing conditions at room temperature [74], without toxic or excess chemicals [75]. GO is coated on the surface of a glassy carbon electrode (GCE) before being immersed into a salt solution. By cycling the potential, the metal salt is oxidized to metal oxide and the GO is reduced to graphene. This synthesis methodology has been used in the preparation of PbO/graphene [38] and ZrO2/graphene [48].

Although it is known to be hydrophilic, GO does not peel off from the GCE surface when it is placed in aqueous electrolytes because of the interaction of hydrophobic regions of GCE and the unoxidized portions of GO [38]. It does, however, swell in an aqueous solution as water molecules bond to the GO.

The formation of the actual graphene based GCE is problematic because it is difficult to obtain a uniform dispersion of graphene in a solvent. The graphene sheets when in solution tend to form irreversible agglomerates or even restack to graphite through strong π-π stacking and van der Waals interaction. If graphene is to be used for the modification of GCE, it must first be dispersed in a stabilizer to form a homogenous dispersion before being dropped cast on the GCE surface. The inorganic nanostructures on graphene are formed by cyclic voltammetry in the appropriate salt solution. An example of this method is the synthesis Ag/graphene [28].

Electrochemical co-deposition is another route to prepare inorganic nanostructure/graphene. Pd/graphene is an example, where a solution containing GO and a metal salt underwent voltammetry cycling simultaneously [30].

5.5. Other unusual strategic routes

There have been several novel processing routes that have been reported. A Ag precursor was physically grounded with dry GO before the product was heated at 1000oC for 20s to produce Ag/graphene [25]. This method produced high purity nanocomposite because the process did not require any reducing or stabilizing agents. The extreme condition spontaneously reduced the Ag ion to Ag metal, and GO to rGO. Inorganic nanostructure/graphene has also been prepared using irradiation (lasers [31], [26], and exposure to UV [50]). Layer-by-layer inorganic structure/graphene can be prepared by dipping-lifting in sol-gel solution [52]. Finally, ultrasonication of the starting solution was able to generate of Mn3O4/graphene nanocomposites [36].


6. Recent advances in the applications of inorganic nanostructure decorated graphene

6.1. Anode for lithium-ion batteries

Graphite-based lithium-ion batteries suffer from poor charge–discharge performance and consequently have poor power performance. In many applications like electric or hybrid cars, there will be periods of high power demand, for example accelerating to overtake a car, and this leads to increased heat dissipation in the cell and accelerated aging of the battery. The use of graphene electrodes significantly improves the power performance of the battery and has resulted in a significant number of papers. The versatility of graphene to accommodate lithium ions on both sides of its single atomic sheet provides high energy storage capacity above 600 mAhg–1, which is higher than the theoretical capacity of graphite (372 mAhg–1). Recently, the use of metal oxides and metal alloys graphene nanocomposite has improved the energy storage of graphene based electrodes even more (700–4000 mAhg–1) [37]. The extra capacity has been attributed to the synergistic effect between the nanoparticles and graphene sheets in the nanocomposite, providing extra sites for the storage of lithium ions [35].

In any battery application, the degradation of the storage capacity with repeated charge-discharge cycles is extremely important. The cycling performance of graphene inorganic nanostructures far exceeds that of their individual counterparts [21, 35]. Moreover, graphene inorganic nanostructures also displayed excellent reversible specific capacities at a broad range of current densities [40-42]. The good lithium cycling performance is ascribed to the structural integrity of the composite electrodes. The nanocystals located on the surface of graphene prevented the agglomeration of graphene sheets. Likewise, the graphene sheets hindered the direct contact among the adjacent nanocrystals. Minimizing the aggregation of nanocrystals and graphene sheets during discharge/charge cycling gives rise to high surface area, excellent electronic conductivity of the electrodes by forming an efficient electrically conductive network, and high carrier mobility. This heterogeneous construction also provides buffering spaces against the volume changes of nanocrystals during the lithium insertion/extraction processes.

Regardless of the type of inorganic nanocrystal, the graphene nanocomposites have generally displayed a large irreversible capacity in the first cycle [51, 57]. It is widely reported that this phenomenon may be attributed to electrolyte decomposition and formation of solid electrolyte interface (SEI) film [76-78]. Irreversible capacity is the occurrence of naturally non-recoverable charge capacity, in which the kinetics will vary depending on the battery chemistry, electrode composition and design, electrolyte formulation and impurities, and on the storage temperature [79].

6.2. Supercapacitors

With the increase in affluence in developing countries, the energy needs are increasing and energy sustainability is of significant concern especially when the depletion of fossil fuels is also factored in [61]. Supercapacitors, also known as ultracapacitors or electrochemical supercapacitors, have several important characteristics, including prolonged life cycle [80, 81], higher power density than batteries [82] and higher energy density [83] than conventional capacitors which have driven their use in pulse power and power backup applications [84]. According to the mechanism of charge storage, supercapacitors can be classified as i) electric double layer capacitors (EDLCs) where charge is stored at the electrode/electrolyte interface, and ii) pseudocapacitors where the charge is stored mainly by Faradaic reactions on the surface of the electrode materials [85, 86].

Carbon-based materials are commonly used in EDLCs as electrodes because of its high electrical conductivity and outstanding long-term electrochemical stability as a result of the extraordinary chemical stability of carbon [87]. Carbon-based materials such as activated carbon [88], xerogels [89], carbon nanotubes [90], mesoporous carbon [91] and carbide-derived carbons [92] have all been investigated for use as electrodes in EDLC. However, the limited charge accumulation in electrical double layer restricts the specific capacitance of EDLCs to a relatively small range of values between 90 and 250 F/g [93]. Meanwhile, pseudocapacitors like metal oxides such as RuO2 [94-96], NiO [96, 97], Co3O4 [98], MnO2 [99], or conducting polymers including polypyrole [100] and polyaniline [101, 102] usually show poor capacitance behavior.

Recently, graphene has been used as a supercapacitor electrode material due to its high surface area, excellent stability and good conductivity [103-106]. To effectively overcome the shortage of low specific capacitance, the 2-D structured graphene has been hybridized with pseudocapacitors for the preparation of supercapacitors [32, 107-109]. The specific capacitance and electrochemical stability of graphene inorganic structures is enhanced tremendously in comparison to their individual counterparts [33, 36]. The improvement of the supercapacitive behaviour is attributable to the different double-layer and pseudocapacitive contributions.

6.3. Photocatalysts

Organic effluents from industries, agricultural activities and the rapid increase in human waste as a result of the rapid population increase represents some of the most serious environmental pollutants. It is estimated that around four billion people worldwide have no or little access to clean and sanitized water supply, resulting in death, by severe waterborne diseases, of millions of people annually [110]. Photodegradation of organic pollutants has attracted increasing attention during the past decade as it appears to be a viable decontamination process with widespread application, regardless of the state (gas or liquid) or chemical nature of the process target [45, 111]. Photocatalytic oxidation is an economical process owing to the fact that it involves only a photocatalyst and light source [112]. This process does not yield toxic intermediate product, making it suitable for cleaning water environment that contains low to medium contaminants concentration [113].

When a photocatalyst is illuminated with the light of sufficient energy, electrons in the valence band of the photocatalyst are excited into the conduction band, therefore, creating the negative electron-positive hole pairs (eh+). When the photocatalyst is in contact with water, the eh+ pairs will initiate a series of reactions and produce hydroxyl radicals, HO and superoxide radical anions, O+, on the photocatalyst surface. Any organic contaminants at or near to the photocatalyst surface are oxidized by the generated radicals [114, 115]. The most commonly used photocatalysts are titanium dioxide and zinc oxide, which are semiconductors. The drawback of these photocatalysts is the quick electron-hole recombination on the surface of semiconductors, which hampers the hydrogen evolution efficiency.

To manipulate the rate of electron-hole recombination, the presence of non-metal species like carbon, nitrogen, boron and fluorine are targeted to minimize photogenerated electron-hole recombination rate, thus improving quantum efficiency and expanding their useful range of operation into visible light wavelengths [116, 117]. Graphene, a uniform and thin transparent conducting material, is a potential carbon source.

Nanocrystals are not stable and prone to aggregate, which results in a reduced surface area and so limits the likelihood of the photoinduced electron–hole pairs interacting with water molecules to produce the radicals thereby decreasing the application efficiency. This can be overcome by using graphene as a supporting matrix for the photocatalyst particles, as well as an electron acceptor, to improve the efficiency of the degradation of organic pollutants [67] and durability for consecutive photodegradation cycling [45, 49]. In addition, the giant π-conjugation of graphene and two-dimensional planar structure are the driving forces for the non-covalent adsorption between aromatic molecules and aromatic regions of the graphene [45].

Many photocatalysts have a wide band gap and so require UV light for operation. Since ultraviolet (UV) light accounts for only a small fraction (5%) of the Sun’s energy as compared to visible light (45%); any shift in the optical response of a photocatalyst from the UV to the visible spectral range will have a profound positive effect on the photodegradation efficiency of a photocatalyst [118]. Incorporation of carbon is known to be able to reduce the band gap energy of a photocatalyst [116]. Photocatalysis using graphene inorganic structure could take place under the irradiation of visible light due to zero band semiconductor with symmetric K and K’ [49].

On the other hand, the photoelectrocatalytic process takes advantage of the photocatalytic process by applying a biased voltage across a photo-electrode on which the photocatalysts are supported. An enhancement of the photocurrents using graphene nanocomposite electrodes is attributed to the enhanced migration efficiency of the photo-induced electrons and enhanced adsorption activity of the aromatic molecules [46]. Photoelectrocatalytic activity is dependent on the optimal value of graphene content, as superfluous graphene will reduce the absorption efficiency of light by a photocatalyst. Experiments have shown an increase in the degradation of the aromatic molecules by the graphene nanocomposite as the applied potential was increased relative to a reference electrode [119-124]. This was explained by the potential causing band bending close to the electrode surface reducing the potential barriers and improving the mobility of the carrier across the electrode, and hence minimizing the probability of recombination of electrons and holes and elevating the photoelectrocatalysis efficiency [124].

The overall excellent photocatalytic performance of graphene inorganic nanostructures is reportedly attributed to enhanced adsorptivity, extended light absorption range, efficient charge separation and transportation [45].

6.4. Sensing platform

Many analytical methods with high sensitivity and low detection limit have been established for determination of organic and inorganic matters [125]. However, they are time consuming, expensive, require complicated instruments and a skilled operator, which are unsuitable for on-line or in-field monitoring [126]. In contrast, electrochemical analysis, which has the advantages of quick response, cheap instrumentation, low power consumption, simplified operation, time-saving, high sensitivity and selectivity, is widely applied in applications such as gas sensing, chemical sensing and biosensing [27, 127-129].

Direct detection using bare electrode yields poor sensitivity to the target material [128]. Inorganic nanoparticles are versatile and sensitive tracers because of their high surface area, high mechanical strength but ultra-light weight, rich electronic properties, and excellent chemical and thermal stability [130] and when coupled with graphene, they provided an attractive nanocomposite for the fabrication of electrochemical sensors [33, 131]. In this regard, inorganic nanostructure decorated graphene has been proven to be an effective tool to detect low amounts of biomarker [27], pesticide [48], heavy metals [28, 38, 39], and glucose [34], with high sensitivity, selectivity, stability and reproducibility.

6.5. Other interesting applications

Besides the four major applications stated above, graphene inorganic nanostructures have also been investigated for other purposes. These include direct formic acid fuel cells, which are widely considered to be one of the most attractive power sources [30]; providing a favourable catalytic pathway for the formation of CO2 [31] to form CO [132]; and producing electrocatalytic activity for methanol oxidation [32]. Other uses of the structures is to produce a photocurrent under UV light or visible light illumination to meet the demand of renewable and clean energy source [52], assisting the conversion of solar energy into hydrogen via the water splitting process [133], and removing chromium(IV) in water through adsorption [54].


7. What does the future hold for inorganic nanostructure decorated graphene?

The significant potential of graphene-based inorganic nanostructure in solving many of today’s problems is evident from the amount of effort that has been devoted to exploring the synthesis of the materials and the investigation of the materials in real-life applications. The cutting-edge research on graphene-based nanoinorganic materials has yet to mature. Drawing comparisons to silicone research, the interest will continue to grow until commercial products using graphene are realized. The simple and scalable production of GO, a derivative of graphene, that is rich in oxygenous functional groups, is encouragement for researchers to modify the surface of the one-atom thick carbon layers with a variety of inorganic nanostructures to cater for the commercial demands and needs. The quality of inorganic nanostructure decorated graphene at atomic level is assured by systematic characterization using state-of-the-art instruments. The graphene research offers novel and exciting opportunities for the scientific community and industrialists who seek new partnerships and advances.



This work was supported by the Exploratory Research Grant Scheme (ER016-2011A), High Impact Research Grants from the University of Malaya (UM.C/625/1/HIR/030) and High Impact Research Grants from the Ministry of Higher Education of Malaysia (UM.C/625/1/HIR/MOHE/05).


  1. 1. ChenFTaoN. JElectron transport in single molecules: From benzene to graphene. Accounts of Chemical Research 200942342938
  2. 2. NovoselovK. SGeimA. KMorozovS. VJiangDZhangYDubonosS. VGrigorievaI. VFirsovA. AElectric field effect in atomically thin carbon films. Science 200430656966669
  3. 3. Nair, R. R, Blake, P, Grigorenko, A. N, Novoselov, K. S, Booth, T. J, Stauber, T. Peres NMR, & Geim AK. Fine structure constant defines visual transparency of graphene. Science (2008). , 320(5881): 1308.
  4. 4. YuARameshPItkisM. EBekyarovaEHaddonR. CGraphite nanoplatelet-epoxy composite thermal interface materials. Journal of Physical Chemistry C 20071112175659
  5. 5. PumeraMThe electrochemistry of carbon nanotubes: Fundamentals and applications. Chemistry- A European Journal 2009152049708
  6. 6. StollerM. DParkSZhuYAnJRuoffR. SGraphene-based ultracapacitors. Nano Letters 20088103498502
  7. 7. BunchJ. SVan Der ZandeA. MVerbridgeS. SFrankI. WTanenbaumD. MParpiaJ. MCraigheadH. GMceuenP. LElectromechanical resonators from graphene sheets. Science 200731558114903
  8. 8. PumeraMElectrochemistry of graphene: New horizons for sensing and energy storage. The Chemical Record 20099421123
  9. 9. ChenX. MWuG. HJiangY. QWang YRC, X. Graphene and graphene-based nanomaterials: The promising materials for bright future of electroanalytical chemistry. Analyst 2011136463140
  10. 10. LiangRDengMCuiSChenHQiuJDirect electrochemistry and electrocatalysis of myoglobin immobilized on zirconia/multi-walled carbon nanotube nanocomposite. Materials Research Bulletin 20104512185560
  11. 11. ChiuW. SKhiewP. SIsaDClokeMRadimanSAbd-shukorRAbdullahM. HHuangN. MSynthesis of two-dimensional ZnO nanopellets by pyrolysis of zinc oleate. Chemical Engineering Journal 200814233743
  12. 12. HuangN. MRadimanSLimH. NYeongS. KKhiewP. SChiuW. SKongS. NSaeed GHM. Synthesis and characterization of ultra small PbS nanorods in sucrose ester microemulsion. Materials Letters 2009635003
  13. 13. HuangN. MRadimanSLimH. NYeongS. KKhiewP. SChiuW. SSaeed GHM, Nadarajah K. Gamma-ray assisted synthesis of Ni3Se2 nanoparticles stabilized by natural polymer. Chemical Engineering Journal 2009147399404
  14. 14. ChiuW. SKhiewP. SClokeMIsaDLimH. NTanT. KHuangN. MRadimanSAbd-shukorRHamid MAA, Chia CH. Heterogeneous seeded growth: Synthesis and characterization of bifunctional Fe3O4/ZnO core/shell nanocrystals. The Journal of Physical Chemistry C 20101141882128
  15. 15. ZhouXHuangXQiXWuSXueCBoey FYC, Yan Q, Chen P, Zhang H. In situ synthesis of metal nanoparticles on single-layer graphene oxide and reduced graphene oxide surfaces. The Journal of Physical Chemistry C 200911325108426
  16. 16. AlivisatosA. PSemiconductor clusters, nanocrystals, and quantum dots. Science 199627152519337
  17. 17. GeimA. KGraphene: Status and prospects. Science 2009324593415304
  18. 18. GeimA. KNovoselovK. SThe rise of graphene. Nature Materials 20076318391
  19. 19. LimH. NNurzulaikhaRHarrisonILimS. STanW. TYeoM. CYarmoM. AHuangN. MPreparation and characterization of tin oxide, SnO2 nanoparticles decorated graphene. Ceramics International 2012385420916
  20. 20. TeoP. SLimH. NHuangN. MChiaC. HHarrisonIRoom temperature in situ chemical synthesis of Fe3O4/graphene. Ceramics International 20123864116
  21. 21. MaiY. JWangX. LXiangJ. YQiaoY. QZhangDGuC. DTuJ. PCuO/graphene composite as anode materials for lithium-ion batteries. Electrochimica Acta 2011565230611
  22. 22. SinghVJoungDZhaiLDasSKhondakerS. ISealSGraphene based materials: Past, present and future. Progress in Materials Science 2011561178271
  23. 23. BaiSShenXGraphene-inorganic nanocomposites. RSC Advances 201226498
  24. 24. HuangN. MLimH. NChiaC. HYarmoM. AMuhamadM. RSimple room-temperature preparation of high-yield large-area graphene oxide. International Journal of Nanomedicine 2011634438
  25. 25. ZainyMHuangN. MVijay Kumar S, Lim HN. Simple and scalable preparation of reduced graphene oxide-silver nanocomposite via rapid thermal treatment. Materials Letters 2012891803
  26. 26. MoussaSAtkinsonGEl-ShallM. SShehataAAbouZeid KM, Mohamed MB. Laser assisted photocatalytic reduction of metal ions by graphene oxide. Journal of Materials Chemistry 201121960819
  27. 27. SuBTangDLiQTangJChenGGold-silver-graphene hybrid nanosheets-based sensors for sensitive amperometric immunoassay of alpha-fetoprotein using nanogold-enclosed titania nanoparticles as labels. Analytica Chimica Acta 201169211624
  28. 28. GongJZhouTSongDZhangLMonodispersed Au nanoparticles decorated graphene as an enhanced sensing platform for ultrasensitive stripping voltammetric detection of mercury(II). Sensors and Actuators B: Chemical 20101504917
  29. 29. HuQ. HWangX. TChenHWangZSynthesis of Ni/graphene sheets by an electroless Ni-plating method. New Carbon Materials 20122713541
  30. 30. JiangY. YLuY. ZLiF. HWuT. SNiuLChenWFacile electrochemical codeposition of “clean” graphene-Pd nanocomposite as an anode catalyst for formic acid electrooxidation. Electrochemistry Communications 201219214
  31. 31. MoussaSAbdelsayedVEl-ShallM. SLaser synthesis of Pt, Pd, CoO and Pd-CoO nanoparticle catalysts supported on graphene. Chemical Physics Letters 2011
  32. 32. WangSJiangS. PWangXMicrowave-assisted one-pot synthesis of metal/metal oxide nanoparticles on graphene and their electrochemical applications. Electrochimica Acta 2011569333844
  33. 33. ChenSZhuJWangXAn in situ oxidation route to fabricate graphene nanoplate-metal oxide composites. Journal of Solid State Chemistry 2011184613939
  34. 34. HsuY. WHsuT. KSunC. LNienY. TPuN. WGerM. DSynthesis of CuO/graphene nanocomposites for nonenzymatic electrochemical glucose biosensor applications. Electrochimica Acta 2012821527
  35. 35. LianPZhuXXiangHLiZYangWWangHEnhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries. Electrochimica Acta 201056283440
  36. 36. WangBParkJWangCAhnHWangGMnOnanoparticles embedded into graphene nanosheets: Preparation, characterization, and electrochemical properties for supercapacitors. Electrochimica Acta 2011552268127
  37. 37. Kottegoda IRM, Idris NH, Lu L, Wang JZ, Liu HK. Synthesis and characterization of graphene-nickel oxide nanostructures for fast charge-discharge application. Electrochimica Acta 20115616581522
  38. 38. RameshaG. KSampathSIn-situ formation of graphene-lead oxide composite and its use in trace arsenic detection. Sensors and Actuators B: Chemical 201116030611
  39. 39. Wei Y, Gao C, Meng FL, Li HH, Wang L, Liu JH, Huang XJ. SnO2/reduced graphene oxide nanocomposite for the simultaneous electrochemical detection of cadmium(II), lead(II), copper(II), and mercury(II): An interesting favorable mutual interference. Journal of Physical Chemistry C 2011;116: 1034-41.
  40. 40. Zhong C, Wang J, Chen Z, Liu H.SnO 2-graphene composite synthesized via an ultrafast and environmentally friendly microwave autoclave method and its use as a superior anode for lithium-ion batteries. The Journal of Physical Chemistry C 2011;115: 25115-20.
  41. 41. LianPZhuXLiangSLiZYangWWangHHigh reversible capacity of SnO2/graphene nanocomposite as an anode material for lithium-ion batteries. Electrochimica Acta 2011561245329
  42. 42. YaoJShenXWangBLiuHWangGIn situ chemical synthesis of SnO2-graphene nanocomposite as anode materials for lithium-ion batteries. Electrochemistry Communications 20091110184952
  43. 43. Chang BYS, Huang NM, An’amt MN, Marlinda AR, Norazriena Y, Muhamad MR, Harrison I, Lim HN, Chia CH.Facile hydrothermal preparation of titanium dioxide decorated reduced graphene oxide nanocomposite. International Journal of Nanomedicine 20127337987
  44. 44. GuoJZhuSChenZLiYYuZLiuQLiJFengCZhangDSonochemical synthesis of TiO2 nanoparticles on graphene for use as photocatalyst. Ultrasonics Sonochemistry 2011185108290
  45. 45. ZhangHLvXLiYWangYLiJ.P25-graphene composite as a high performance photocatalyst. ACS Nano 2010413806
  46. 46. WangPAoYWangCHouJQianJEnhanced photoelectrocatalytic activity for dye degradation by graphene-titania composite film electrodes. Journal of Hazardous Materials 2012
  47. 47. MarlindaA. RHuangN. MMuhamadM. RAn’amt MN, Chang BYS, Yusoff N, Harrison I, Lim HN, Vijay Kumar S. Highly efficient preparation of ZnO nanorods decorated reduced graphene oxide nanocomposites. Materials Letters 201280912
  48. 48. GongJMiaoXWanHSongDFacile synthesis of zirconia nanoparticles-decorated graphene hybrid nanosheets for an enzymeless methyl parathion sensor. Sensors and Actuators B: Chemical 20121623417
  49. 49. MinY. LZhangKChenY. CZhangY. GEnhanced photocatalytic performance of Bi2WO6 by graphene supporter as charge transfer channel. Separation and Purification Technology 20128698105
  50. 50. WuC. HZhangY. ZLiSZhengH. JWangHLiuJ. BLiK. WYanHSynthesis and photocatalytic properties of the graphene-La2Ti2O7 nanocomposites. Chemical Engineering Journal 201117846874
  51. 51. FuYWanYXiaHWangXNickel ferrite-graphene heteroarchitectures: Toward high-performance anode materials for lithium-ion batteries. Journal of Power Sources 201221333842
  52. 52. LiGWangTZhuaYZhangSMaoCWuJJinBTianYPreparation and photoelectrochemical performance of Ag/graphene/TiO2 composite film. Aplied Surface Science 2011257656872
  53. 53. XWangX, HTianH, YYangY, HWangH, SWangS, WZhangW, YLiuY. Reduced graphene oxide/CdS for efficiently photocatalystic degradation of methylene blue. Journal of Alloys and Compounds 2012524512
  54. 54. ZhuJWeiSGuHRapoleS. BWangQLuoZHaldolaarachchigeNYoungD. PGuoZOne-pot synthesis of magnetic graphene nanocomposites decorated with core@double-shell nanoparticles for fast chromium removal. Environmental Science and Technology 20124697785
  55. 55. Vijay Kumar, S, Huang, NM, Yusoff, N, Lim, HN. High performance magnetically separable graphene/zinc oxide nanocomposite. Materials Letters (2012). , 93, 411-4.
  56. 56. GolsheikhA. MHuangN. MLimH. NChiaC. HHarrisonIMuhamadM. ROne-pot hydrothermal synthesis and characterization of FeS2 (pyrite)/graphene nanocomposite. Chemical Engineering Journal 2012DOI:
  57. 57. XieJSongWZhengYLiuSZhuTCaoGZhaoXPreparation and Li-storage properties of SnSb/graphene hybrid nanostructure by a facile one-step solvothermal route. International Journal of Smart and Nano Materials 20112426171
  58. 58. XueYChenHYuDWangSYardeniMDaiQGuoMLiuYLuFQuJDaiLOxidizing metal ions with graphene oxide: The in situ formation of magnetic nanoparticles on self-reduced graphene sheets for multifunctional applications. Chemical Communication 201147168991
  59. 59. Yusoff, N, Huang, NM, Muhamad, MR, Kumar, SV, Lim, HN, Harrison, I. Hydrothermal synthesis of copper oxide/functionalized graphene nanocomposites for dye degradation. Materials Letters (2012). , 93: 393-6.
  60. 60. HuangN. MMarlindaA. RLimH. Ninventors; Efficient fabrication of flower-like ZnO/reduced functionalized graphene oxide nanocomposites for gas sensing applications. Patent filed. 2012
  61. 61. ChenSZhuJWuXHanQWangXGraphene oxide-MnO2 nanocomposites for supercapacitors. ACS Nano 2010452822930
  62. 62. LimH. NKassimALimS. PRastamNizar NS, Huang NM. Microstructural changes of carbonaceous monoliths synthesized via hydrothermal. Journal of the Chilean Chemical Society 20115615846
  63. 63. ZakaryaS. AKassimALimH. NAnwarN. SHuangN. MSynthesis of titanium dioxide microstructures via sucrose ester microemulsion-mediated hydrothermal method. Sains Malaysiana 20103969759
  64. 64. AnwarN. SKassimALimH. NZakaryaS. AHuangN. MSynthesis of titanium dioxide nanoparticles via sucrose ester micelle-mediated hydrothermal processing route. Sains Malaysiana 20103922615
  65. 65. LimH. NKassimAHuangN. MPreparation and characterization of calcium phosphate nanorods using reverse microemulsion and hydrothermal processing routes. Sains Malaysiana 201039226773
  66. 66. HawC. YMohamedFRadimanSChiaC. HHuangN. MLimH. NHydrothermal synthesis of magnetite nanoparticles as MRI contrast agents. Ceramics International 2010364141722
  67. 67. WangXTianHYangYWangHWangSZhangWLiuYReduced graphene oxide/CdS for efficiently photocatalystic degradation of methylene blue. Journal of Alloys and Compounds 2012524512
  68. 68. DressenMMicrowave heating in fine chemical applications: Role of heterogeneity. Thesis 2009
  69. 69. WangYLeeJ. YMicrowave-assisted synthesis of SnO2-graphite nanocomposites for Li-ion battery applications. Journal of Power Sources 20051442205
  70. 70. SubramanianVBurkeW. WZhuHWeiBNovel microwave synthesis of nanocrystalline SnO2 and its electrochemical properties. Journal of Physical Chemistry C 200811245506
  71. 71. Zhang, M, Lei D, Du Z, Yin X, Chen L, Li Q, Wang Y, Wang T. Fast synthesis of SnO2/graphene composites by reducing graphene oxide with stannous ions. Journal of Materials Chemistry (2010). , 21, 1673-6.
  72. 72. TullyEHigsonS. POKennedyR. The development of a’labeless’ immunosensor for the detection of Listeria monocytogenes cell surface protein, Internalin B. Biosensors and Bioelectronics 20082390612
  73. 73. ZhangJKongLWangBLuoYKangLIn-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors. Synthetic Metals 20091592606
  74. 74. TorresSNeculqueoGMartinezFMorphological and structural characterization of poly(3-decylthiophene) prepared by electropolymerization using 1-butyl-3-methyl-imidazoliumtetrafluorborate as solvent. Journal of the Chilean Chemical Society 200752312356
  75. 75. TsaiMChenPDoJPreparation and characterization of Ppy/Al2O3/Al used as a solid state capacitor. Journal of Power Sources 200413330211
  76. 76. LiYLvXLuJLiJPreparation of SnO2-nanocrystal/graphene-nanosheets composites and their lithium storage ability. Journal of Physical Chemistry C 2010114217704
  77. 77. HeYHuangLCaiJ. SZhengX. MSunS. GStructure and electrochemical performance of nanostructured Fe3O4/carbon nanotube composites as anodes for lithium ion batteries. Electrochimica Acta 20105511404
  78. 78. MuraliganthTMuruganA. VManthiramAFacile synthesis of carbon-decorated single-crystalline Fe3O4 nanowires and their application as high performance anode in lithium ion batteries. Chemical Communication 20094773602
  79. 79. YazamiRReynierY. FMechanism of self-discharge in graphite-lithium anode. Electrochimica Acta 200247121723
  80. 80. RanLSeung lC, Sang BL. Poly(3,4ethylenedioxythiophene) nanotubes as electrode materials for a high-powered supercapacitor. Nanotechnology 2008pp).
  81. 81. RuizVBlancoCGrandaMSantamariaREnhanced life-cycle supercapacitors by thermal treatment of mesophase-derived activated carbons. Electrochimica Acta 20085430510
  82. 82. PortetCTabernaP. LSimonPFlahautELaberty-robertCHigh power density electrodes for carbon supercapacitor applications. Electrochimica Acta 200550417481
  83. 83. HuXDengZSuoJPanZA high rate, high capacity and long life (LiMn2O4 + AC)/Li4Ti5O12 hybrid battery-supercapacitor. Journal of Power Sources 20091876359
  84. 84. JayalakshmiMBalasubramaniamKSimple capacitors to supercapacitors- An overview. International Journal of Electrochemistry 200831196217
  85. 85. SimonPGogotsiYMaterials for electrochemical capacitors. Nature Materials 2008784554
  86. 86. LangXHirataAFujitaTChenMNanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors. Nature Nanotechnology 201162326
  87. 87. LiQLiZLinLWangX. YWangYZhangCWangHFacile synthesis of activated carbon/carbon nanotubes compound for supercapacitor application. Chemical Engineering Journal 20101565004
  88. 88. FrackowiakEBeguinFCarbon materials for the electrochemical storage of energy in capacitors. Carbon 20013993750
  89. 89. MayerS. TPerkalaR. WKaschmitterJ. LThe aerocapacitor: An electrochemical double-layer energy-storage device. Journal of the Electrochemical Society 1993140244651
  90. 90. KaempgenMChanC. KMaJCuiYGrunerGPrintable thin film supercapacitors using single-walled carbon nanotubes. Nano Letters 2009918726
  91. 91. Prabaharan SRS, Vimala R, Zainal Z.Nanostructured mesoporous carbon as electrodes for supercapacitors. Journal Power Sources 20061617306
  92. 92. ChmiolaJYushinGDashRGogotsiYEffect of pore size and surface area of carbide derived carbons on specific capacitance. Journal Power Sources 200615876572
  93. 93. LuXWangGZhaiTYuMGanJTongYLiYHydrogenated TiO2 nanotube arrays for supercapacitors. Nano Letters 20121216906
  94. 94. WuZWangDRenWZhaoJZhouGLiFChengHAnchoring hydrous RuO2 on graphene sheets for high-performance electrochemical capacitors. Advanced Functional Materials 2010203595602
  95. 95. WangHRobinsonJ. TLiXDaiHSolvothermal reduction of chemically exfoliated graphene sheets. Journal of the American Chemical Society 200913199101
  96. 96. WangHLiangYMirfakhraiTChenZCasalongueHDaiHAdvanced asymmetrical supercapacitors based on graphene hybrid materials. Nano Research 2011472936
  97. 97. ZhaoBSongJLiuPXuWFangTJiaoZZhangHJiangYMonolayer graphene/NiO nanosheets with two-dimension structure for supercapacitors. Journal of Materials Chemistry 201121187928
  98. 98. ZhouWLiuJChenTTanK. SJiaXLuoZCongCYangHLiC. MYuTFabrication of Co3O4-reduced graphene oxide scrolls for high-performance supercapacitor electrodes. Physical Chemistry Chemical Physics 201113144625
  99. 99. ChengQTangJMaJZhangHShinyaNQinLGraphene and nanostructured MnO2 composite electrodes for supercapacitors. Carbon 201149291725
  100. 100. SiPDingSLouXKimDAn electrochemically formed three-dimensional structure of polypyrrole/graphene nanoplatelets for high-performance supercapacitors. RSC Advances 201111271127
  101. 101. ZhangKZhangL. LZhaoX. SWuJGraphene/polyaniline nanofiber composites as supercapacitor electrodes. Chemistry of Materials 2010221392401
  102. 102. WangHHaoQYangXLuLWangXA nanostructured graphene/polyaniline hybrid material for supercapacitors. Nanoscale 20102216470
  103. 103. WangYShiZHuangYMaYWangCChenMChenYSupercapacitor devices based on graphene materials. Journal of Physical Chemistry C 2009113131037
  104. 104. LiuCYuZNeffDZhamuAJangB. ZGraphene-based supercapacitor with an ultrahigh energy density. Nano Letters 20101048638
  105. 105. KimT. YLeeH. WStollerMDreyerD. RBielawskiC. WRuoffR. SSuhK. SHigh-performance supercapacitors based on poly(ionic liquid)-modified graphene electrodes. ACS Nano 2011543642
  106. 106. StollerM. DParkSZhuYAnJRuoffR. SGraphene-based ultracapacitors. Nano Letters 200883498502
  107. 107. DongXXuHWangXHuangYChan-parkMZhangHWangLHuangWChenP3D Graphene-cobalt oxide electrode for high-performance supercapacitor and enzymeless glucose detection. ACS Nano 20126320613
  108. 108. RakhiR. BChenWChaDAlshareefH. NHigh performance supercapacitors using metal oxide anchored graphene nanosheet electrodes. Journal of Materials Chemistry 20112116197204
  109. 109. SuHWangTZhangSSongJMaoCNiuHJinBWuJTianYFacile synthesis of polyaniline/TiO2/graphene oxide composite for high performance supercapacitors. Solid State Sciences 20121467781
  110. 110. ChongM. NJinBChow CWK, Saint C. Recent developments in photocatalytic water treatment technology: A review. Water Research 2010441029973027
  111. 111. HeYWuYGuoHShengTWuXVisible light photodegradation of organics over VYO composite catalyst. Journal of Hazardous Materials 200916985560
  112. 112. JiangRZhuHLiXXiaoLVisible light photocatalytic decolourization of C. I. Acid Red 66 by chitosan capped CdS composite nanoparticles. Chemical Engineering Journal 200915253742
  113. 113. FatinS. OLimH. NTanW. THuangN. MComparison of photocatalytic activity and cyclic voltammetry of zinc oxide and titanium dioxide nanoparticles toward degradation of methylene blue. International Journal of Electrochemical Science 20127907484
  114. 114. KroppRTompkinsDBarryTZeltnerWPeppingGAndersonMBarryTA device that converts aqueous ammonia into nitrogen gas. Aquacultural Engineering 20094112834
  115. 115. SoltaninezhadMAAminifarA. Study nanostructures of semiconductor zinc oxide (ZnO) as a photocatalyst for the degradation of organic pollutants. International Journal of Nanodimension 2011213745
  116. 116. ImJ. SYunS. MLeeY. SInvestigation of multielemental catalysts based on decreasing the band gap of titania for enhanced visible light photocatalysis. Journal of Colloid and Interface Science 20093361838
  117. 117. GeorgievaJArmyanovSPouliosISotiropoulosSAn all-solid photoelectrochemical cell for the photooxidation of organic vapours under ultraviolet and visible light illumination. Electrochemistry Communications 200911816436
  118. 118. ZhangXJingDGuoLEffects of anions on the photocatalytic H2 production performance of hydrothermally synthesized Ni-doped Cd0.1Zn0.9S photocatalysts. International Journal of Hydrogen Energy 2010351370517
  119. 119. TrykD. AFujishimaAHondaKRecent topics in photoelectrochemistry: Achievements and future prospects. Electrochimica Acta 200045236376
  120. 120. WaldnerGKrysaJPhotocurrents and degradation rates on particulate TiO2 layers: Effect of layer thickness, concentration of oxidizable substance and illumination direction. Electrochimica Acta 2005504498504
  121. 121. Carneiro, P. A, Osugi, M. E, Sene, J. J, & Anderson, M. A. Zanoni MVB. Evaluation of color removal and degradation of a reactive textile azo dye on nanoporous TiO2 thin film electrodes. Electrochimica Acta (2004). , 49(22-23), 3807-20.
  122. 122. SolarskaRRutkowskaIMorandRAugustynskiJPhotoanodic reactions occurring at nanostructured titanium dioxide films. Electrochimica Acta 2006511122306
  123. 123. Hepel, M, & Hazelton, S. Photoelectrocatalytic degradation of diazo dyes on nanostructured WO3 electrodes. Electrochimica Acta (2005).50(25-26): 5278-91.
  124. 124. Hepel, M, & Hazelton, S. Photoelectrocatalytic degradation of diazo dyes on nanostructured WO3 electrodes. Electrochimica Acta (2005). , 50(25-26): 5278-91.
  125. 125. Ballesteros-gómezARubioSPérez-benditoDAnalytical methods for the determination of bisphenol A in food. Journal of Chromatography A 20091216344969
  126. 126. YinHCuiLChenQShiWAiSZhuLLuLAmperometric determination of bisphenol A in milk using PAMAM-Fe3O4 modified glassy carbon electrode. Food Chemistry 201112531097103
  127. 127. LimH. NNurzulaikhaRHarrisonILimS. STanW. TYeoM. CSpherical tin oxide, SnO2 particles fabricated via facile hydrothermal method for detection of mercury (II) ions. International Journal of Electrochemical Science 20116432940
  128. 128. WangFYangJWuKMesoporous silica-based electrochemical sensor for sensitive determination of environmental hormone bisphenol A. Analytica Chimica Acta 20096381238
  129. 129. MatinB. MMortazaviYKhodadadiA. AAbbasiAFiroozA. AAlkaline- and template-free hydrothermal synthesis of stable SnO2 nanoparticles and nanorods for CO and ethanol gas sensing. Sensors and Actuators B: Chemicals 20101511405
  130. 130. SiangprohWDungchaiWRattanaratPChailapakulONanoparticle-based electrochemical detection in conventional and miniaturized systems and their bioanalytical applications: A review. Analytica Chimica Acta 20116901025
  131. 131. YangMJavadiAGongSSensitive electrochemical immunosensor for the detection of cancer biomarker using quantum dot functionalized graphene sheets as labels. Sensors and Actuators B: Chemical 201115535760
  132. 132. Ligthart DAJM, van Santen RA & Hensen EJM. Supported rhodium oxide nanoparticles as highly active CO oxidation catalysts. Angewandte Chemie International Edition 201150530610
  133. 133. BiswalNDasD. PMarthaSParidaK. MEfficient hydrogen production by composite photocatalyst CdS-ZnS/zirconium-titanium phosphate (ZTP) under visible light illumination. International Journal of Hydrogen Energy 2011361345260

Written By

Hong Ngee Lim, Nay Ming Huang, Chin Hua Chia and Ian Harrison

Submitted: 27 August 2012 Published: 20 February 2013