Chemical Reduction of GO

Hydrazine is widely used in chemical reduction of GO [11]. Mechanisms for epoxide reduction was first studied [79]. Two possible processes have been considered the direct Eley-Rideal (ER) process and the intermediate anchored Langmuir-... 

Each reduction method has their advantages and disadvantages. The most common method for rGO production is by chemical reduction of GO using different reducing agents of which the most... 

Because GO is a poor conductor, the electrical conductivity of ECP-GO can he increased hy the reduction of GO to RGO in the composite film. Despite of the large variety of available chemical reduction methods for GO, the electrochemical reduction is a quick, clean, practical, and safe method for the reduction of GO to RGO [78]. For the electro-chemical reduction of GO in ECP-GO composites, they are exposed to sufficiently negative potentials resulting in irreversible reduction of GO to RGO [79], whereas the ECP can be brought back to the electrically conducting state by appl5dng a positive potential to the film. 

Successful usage of hydrohalic acid to achieve chemical reduction of GO has recently been reported (Moon et al., 2011 Pei et al., 2010). A few samples of GOl and G02 films were dispersed in HBr for 24 h, and improvement in electrical conductivity values of these samples affirmed the effectiveness of the process. To understand the effect of the chemical process parameters and optimize the value of electrical... 

Therefore, it can be concluded that significant restoration of electrical conductivity can be achieved by partial chemical reduction of GO with strong hydrohalic acids at atmospheric temperature employing shorter periods of exfoliation through ultrasonica-tion and chemical reaction. 

As noted in the previous section, the maximum value of conductivity attained through chemical reduction of GO sheets was 39,000 S/m and that for PMMA— GO-cast films was 18.5 S/m. The thickness of the GO films and PMMA—GO-cast films were 0.1 and 0.15 mm, respectively. The predicted values of EMI SE for thin GO films as well as PMMA—GO-cast films are presented in Table 8.26. 

Exceptionally fascinating work (exploring the oxidation of methanol for use within fuel cells) investigated the structure, composition and morphology of support materials, which were found to significantly affect the catalytic characteristics of Pt-based nanocatalysts [115]. Considering the effects of different carbon supports of graphene (produced via chemical reduction of GO), SWCNTs and Vulcan XC-72 carbon upon the electrocatalytic characteristics of the... 

GO was prepared from graphite powder through the modified Hummers method [183]. Graphene was synthesized via the chemical reduction of GO by sodium acetate trihydrate. A typical procedure was 1.10 g CH3C00Na 3H20 dispersed into 55 mL of GO dispersion (1 mg/mL). 

Liquid-phase chemical reduction is suitable for the formation of metal and metal oxide NPs on nanocarbons. Careful consideration is required in designing the nanocarbon-precursor interaction and choosing the reduction/oxidation method. The synthetic process is often quite time consuming and a number of filtering/washing steps are often required. As discussed, the concurrent liquid phase reduction of GO and precursor is a simple, efficient way to produce a hybrid but the lack of control of GO reduction may affect further applications. 

Reduction of GO provides a promising way for large scale production of graphene. Many methods have been used for the reduction process, such as chemical reduction [9-11], thermal reduction [12, 13], flash reduction [14], electrochemical reduction [15], photocatalytic reduction [16, 17], and direct laser-writing [18]. 

Figure 8.5 Schematic illustration of the procedure for one-pot hydrothermal synthesis of RGO-supported PtPd alloy nanocubes. Stage 1 The reduction of GO and the nucleation of nanocrystals. Stage 2 The growth process of alloy nanocubes. Reprinted with permission from reference [51]. Copyright 2013 American Chemical Society.

Figure 8.8 Scheme of protein-based decoration and reduction of GO, leading to a general nanoplatform for nanoparticle assembly. Reprinted with permission from reference [57]. Copyright 2010 American Chemical Society. 

The most widely preparation procedure for G suspensions consists in performing deep chemical oxidation of graphite to GO followed by high-efficient GO exfoliation and final reduction of GO to G (Scheme 3.3). 

The chemical reduction of 26 has not been successful, but electrochemical studies reveal that 26 undergoes a two-electron reduction to yield Pd3(GO)(dppm)3, z/(GO) = 1,761 cm Density functional calculations on [Pd3(GO)(PH3)6] and Pd3(GO)(PH3)6 as models for the products of one-electron and two-electron reduction show increases in the Pd-Pd distances in both cases, as expected due to occupation of the LUMO by reduction. For Pd3(GO)(PH3)6, the Pd-Pd distances are predicted to be 3A, indicative of homolytic cleavage of the Pd-Pd bonds.The fact that the cluster does not break up upon reduction reflects the role dppm and GO play in holding... 

An efficient chemical reduction method to produce graphene from GO is one of the prime areas of research today. Apart from that, tuning the physical and chemical properties of GO for engineering usage as nanofiller also requires controlling the extent of reduction. Several papers report that a wide variety of chemical and/or thermal routes have been published in recent years (Lin et al., 2010), as summarized in succeeding sections. 

Electrical conductivity is the attribute of the carbon-based nanofiUers that makes them highly suitable for electronic applications. GO is intrinsically insulating due to the presence of oxygen-containing functional groups, but the removal of such groups makes GO suitable to manufacture of conducting nanocomposites. From the different methods discussed previously for reduction of GO, the chemical and thermal routes are most commonly used to restore the electrical conductivity of GO nanofillers before their incorporation into a polymer matrix. Polymer composites with chemically and/ or thermally reduced GO were reported to display electrical percolation thresholds as low as 0.2% vol. in various studies as depicted in Table 8.4. 

---