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Original article
13 (
1
); 1633-1640
doi:
10.1016/j.arabjc.2017.12.021

One-step synthesis of reduced graphene oxide/gold nanoparticles under ambient conditions

, , , , ,
a Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-88, 83190 Hermosillo, Sonora, Mexico
b CONACYT-Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-88, 83190 Hermosillo, Sonora, Mexico
c Universidad Autónoma de San Luis Potosí, Facultad de Ingeniería, Dr. Manuel Nava #8, Zona Universitaria, C.P. 78290 San Luis Potosí, S.L.P., Mexico
d Centro Nacional de Metrología, Metrología de Materiales km. 4.5 carretera a Los Cués, El Marqués, Querétaro C.P. 76246, Mexico

⁎Corresponding author. manuelcortez@live.com (M. Cortez-Valadez) jose.cortez@unison.mx (M. Cortez-Valadez)

Received: , Accepted: ,
© The Author(s) 2018
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

This study presents a novel synthesis method for the production of reduced-graphene-oxide functionalized with gold nanoparticles (rGO/Au-NPs) at ambient temperature. Both were obtained simultaneously using sucrose and chloroauric acid as precursors in the formation of the nanocomposite, and ascorbic acid as the reducing and stabilizing agent. Transmission electron microscopy (TEM) showed gold nanoparticles of 15–30 nm interacting with rGO laminates. Raman spectroscopy showed bands D and G centered at 1334 cm−1 and 1577 cm−1, respectively. The optical absorption analysis presented two bands centered at 522 nm and 260 nm, similar to the results reported in literature for Au-NPs and rGO.

Keywords

rGO instant synthesis
rGO/AuNp functionalization
Green synthesis approximation
1

1 Introduction

The study of carbon nanomaterials, such as graphene, graphene oxide and reduced graphene oxide, is growing due to their physicochemical properties and their promising application in nanoscience (Van Pham and Madsuha, 2016; Shen et al., 2015; Powell and Beall, 2015; Mohan et al., 2016; Unnithan et al., 2016). Recent studies report the use of graphene in biomedicine for the treatment of different types of cancer (Tyson et al., 2016; Qin et al., 2016), electrochemical sensors (Martín and Hernández-Ferrer, 2015; Wen et al., 2016), catalysis (Park et al., 2015; Rui Ribeiro et al., 2015), optoelectronics (Jin et al., 2015; Jang et al., 2015), solar cells (Loh et al., 2016; Liu et al., 2015) and surface enhanced Raman scattering (SERS) (Liu and Chen, 2013). Likewise, graphene oxide (GO) and reduced graphene oxide (rGO) show similar properties and applications (Li et al., 2015; Ray, 2015), additionally, both are precursors in the production of graphene (Shang et al., 2016; Zhang et al., 2014). Carbon dioxide reduction (Chakrabarti et al., 2011), chemical vapor deposition (CVD) (Robert Jacobberger et al., 2015), mechanical exfoliation methods (Shinde et al., 2016) and green synthesis (Zang et al., 2016) are some top-down synthesis methods used to obtain these materials, which based on graphite or carbon, use mechanical processes, high temperatures and chemical treatments with oxidizing agents and mixtures made of strong acids to form monolayers, nanobelts or quantum dots made of GO, rGO and graphene.

Moreover, nanocomposites of metallic and bimetallic nanoparticles functionalized with GO and rGO have been implemented in different nanotechnological applications. Among such applications we find: GO/AuAg-NPs with antibacterial properties (Wang et al., 2013), rGO/PtAu-NPs with electrocatalytic properties (Ezhil Vilian et al., 2016), rGO/PtNi-NPs with magnetic properties (Huízar-Félix et al., 2016), GO/Au-NPs used as electrochemical detectors (Karthik et al., 2016; Luo et al., 2016), as SERS substrates (Wen Liang et al., 2013) and in catalytic applications (Wang et al., 2016). It is worth mentioning that the methods reported for the synthesis of GO and RGO functionalized with nanoparticles, use high temperatures in the experimental process, in addition to ultrasonic processes and magnetic stirring for long periods of time. Additionally, the methods use graphite as the base and modify it with the methods mentioned above, or use prefabricated GO and rGO.

This study presents a novel bottom-up synthesis method, of low cost and toxicity, in which Au and rGO nanostructures are obtained simultaneously in a colloidal solution at ambient temperature. The nanoparticles show high stability and are produced in 5 min, using sucrose as the precursor of rGO, and HAuCl4 as the precursor of metallic nanoparticles, which are reduced and stabilized with ascorbic acid.

2

2 Materials and methods

This method is similar to that used by R. Britto H et al. for the synthesis of gold nanoparticles (Britto Hurtado et al., 2016; Navarro-Badilla et al., 2017), but in this case we modified the concentration of sugar as a carbon precursor. We used 0.25 gr of sucrose diluted in 40 ml of H2O + 40 ml of ascorbic acid at 0.05 M (solution S1). For the precursor ions of gold nanoparticles, we used the solution Gold (III) chloride trihydrate (HAuCl4) 0.01 M in deionized water (solution S2). A solution made of 1 ml of S2 diluted in 20 ml of H2O was incorporated to a solution of 0.5 ml of S1 diluted in 10 ml of H2O, which was kept under magnetic stirring for 20 min. The whole process was done under ambient temperature. The change of tone of the solution, from an opaque yellow to a “blueish” purple, indicates the formation of Au nanoparticles functionalized with rGO, see Fig. 1. The characterizations obtained by UV/VIS spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR), were measured with the spectrophotometer Perkin Elmer Lambda 19, a microscope JEOL JEM2010F, Micro Raman X’plora BX41TF OLYMPUS HORIBA Jobin IVON, argon laser 3B from 20 to 25 mW at 532 nm and Perkin Elmer FTIR 1600 respectively.

Schematic representation of the synthesis process of Au NPs functionalized with rGO.
Fig. 1 Schematic representation of the synthesis process of Au NPs functionalized with rGO.

3

3 Results and discussions

Fig. 2 shows the TEM images of rGO functionalized with Au nanoparticles. The metallic nanostructures show different geometrical shapes (pentagonal-bipyramidal, spherical, triangular) with sizes from 15 to 30 nm. The nanostructures are surrounded by rGO laminates, see Fig. 2A. The interplanar distances for Au and Graphene were measured with the algorithm Fast Fourier transformation (FFT) in different areas of the high resolution TEM images, where we found an interplanar distance of 0.240 nm for Au-NPs that corresponds to the crystal plane (1 1 1) and 0.215 nm that corresponds to the crystal plane (1 0 1) of the graphene, see Fig. 2B and C. These results are similar to those reported by other authors (Torres-Mendieta et al., 2016; Dutkiewicz et al., 2015). Furthermore, we corroborated the presence of graphene and gold in a specific region by energy dispersive X-ray spectroscopy (EDS).

(A) TEM images of rGO functionalized with Au nanoparticles. (B) HRTEM images that show a hexagonal diffraction pattern with an interplanar distance of 0.215 nm and (C) interplanar distance of 0.240 nm associated to lattice (1 1 1) for gold. The EDS spectrum of Fig. 2(B) and (C) shows the existence of carbon and gold in the nanocomposite. The presence of Cu is due to the copper grill in the measurements.
Fig. 2 (A) TEM images of rGO functionalized with Au nanoparticles. (B) HRTEM images that show a hexagonal diffraction pattern with an interplanar distance of 0.215 nm and (C) interplanar distance of 0.240 nm associated to lattice (1 1 1) for gold. The EDS spectrum of Fig. 2(B) and (C) shows the existence of carbon and gold in the nanocomposite. The presence of Cu is due to the copper grill in the measurements.

The Raman bands located in 1334 cm−1 (band D) and 1577 cm−1 (band G) confirm the presence of a graphite-like material in the colloidal solution obtained (Fig. 3). Band D is associated to the breathing mode present in the carbon rings with hybridization sp2. Therefore, an increase in the intensity of band D represents a higher presence of sp2 domains. In other words, the presence of double bonds (C⚌C). Band G is associated with doubly degenerate sp2 carbon atoms and with the first-order of phonon dispersion E2g. Additionally, the absence of band 2D and the relation between the relative intensities (ID/IG ≈ 1.6), confirmed the formation of rGO.

Raman spectra of rGO/Au-NPs at an excitation wavelength of 532 nm.
Fig. 3 Raman spectra of rGO/Au-NPs at an excitation wavelength of 532 nm.

The optical absorption spectrum showed a contribution of Au-NPs in 522 nm and a second band in 260 nm for rGO (Fig. 4). Other authors report absorption bands of rGO in 260 nm (Muthoosamy et al., 2015), 265 nm (Yang et al., 2012) and 270 nm (Huang et al., 2011). Hussain et al. (2014) in the synthesis of rGO/AuNPs, reported two absorption bands in 265 nm and 537 nm for rGO and Au-NPs, respectively. Therefore, the results of this study are similar to those reported in the literature. Additionally, we observe slightly the presence of an absorption band close to 375 nm (de-convoluted of the UV-Vis spectra), located approximately between the absorption bands associated with rGO and AuNP. Chen et al. show an absorption band near 390 nm in ternary compounds of Ag-C-Au (Chen et al., 2013). This absorption band may be evidence of the interaction between AuNPs and the rGO laminates as observed in the TEM image in Fig. 2B.

Optical absorption spectrum of rGO/Au-NPs.
Fig. 4 Optical absorption spectrum of rGO/Au-NPs.

The Fourier transform infrared spectroscopy (FTIR) spectroscopy was used to characterize the functional groups and investigate the changes in chemical compositions of the mixtures (Fig. 5). Fig. 5a shows the FTIR spectrum for the solution S1, indicating the presence of peaks that are attributed to dehydroascorbic acid and sucrose according to registration numbers (CAS) 490-83-5 and 57-50-1 respectively. Fig. 5b shows the FTIR spectrum after of reaction of the solution S1 with HAuCl4. We observed that some peaks disappeared and the sample presented a spectrum similar to that reported by other authors for rGO (Gurunathan et al., 2015; Yang et al., 2015; Thangaraju et al., 2015). The FTIR peak of rGO showed stretching vibrations can be assigned to —OH hydroxyl groups (3420 cm−1), the peaks at 1645 cm−1 and 1260 cm−1 correspond to C—C groups and the asymmetric and symmetric stretching vibration of C—O—C respectively (Gao et al., 2013; Gong et al., 2014).

(a) FTIR of Sucrose and ascorbic acid solution (b) FTIR of rGO/AuNPs nanocomposite.
Fig. 5 (a) FTIR of Sucrose and ascorbic acid solution (b) FTIR of rGO/AuNPs nanocomposite.

Additionally, the composite was mixed with F9 zeolite (a porous material with several applications, optics, biological, catalysis, water treatment, etc.). Subsequently, the vibrational properties of the material were analyzed by Raman spectroscopy before and after incorporating the RGO/AuNp composite (Fig. 6). The F9 have three characteristic bands located approximately in 290, 380 and 509 cm−1. Bending vibrations present in 6-membered rings are associated with bands located at 290 and 380 cm−1. These rings are formed by T—O—T bonds, with (T⚌Al o T⚌Si). The Raman band detected at 509 cm−1 is the main characteristic band in the Raman spectrum of the F9 and associated with bending vibrations type in 4-membered rings. (Yu et al., 2001) After the incorporation of the composite, the enhancement in the Raman intensities located at low wavenumbers is not representative. However, for higher wavenumbers a well-defined band located at 2128 cm−1 is observed with a low intensity for the cases with 0.15 and 0.30 ml of RGO/AuNp. In addition, when using 0.50 ml of RGO/AuNps composite, it is observed that the band has a considerably enhanced intensity. This band could be associated with presence of Si-H2 bond type (Yoshigoe et al., 1995; Nodaa, 2000; Saleh and Nickel, 2003). These modes are usually not detected in conventional Raman spectroscopy for F9. Two mechanisms are responsible for the SERS effect, Electromagnetic Enhancement Mechanism (EM) y Chemical Enhancement Mechanism (CE). The first is associated with superficial effects of metallic nanoparticles and the second associated with a rearrangement of the energy levels in the molecular orbitals and/or generation of new electronic states. Both cases could be increase and occurrence of Raman bands not detectable by conventional Raman spectroscopy. Both effects can be originated by the nanocomposite given the semiconductor/metal constitution (rGO/Au). This result can be used for a quantitative analysis of the Si–H relationship in solid cavities and surfaces (Volodin and Koshelev, 2013), as well as to study the behavior of the hydrogen adsorption in zeolites (Langmi et al., 2003), OH groups and secondary chemical reactions (Kotrel et al., 2001), etc.

Raman spectroscopy before and after incorporating the RGO/AuNp composite in Zeolite F9.
Fig. 6 Raman spectroscopy before and after incorporating the RGO/AuNp composite in Zeolite F9.

Table 1 shows some studies that report the manufacture of graphene, GO and rGO functionalized with Au-NPs. In most of these studies the Hummer method is used with graphite to obtain GO, which afterwards is treated under thermic processes, magnetic or ultrasonic stirring with HAuCL4 for the production of the nanocomposite. In general, the precursors mostly used in these studies for the production of graphene nanomaterials with Au-NPs are GO and HAuCL4. However, in this study we used sucrose as the precursor of rGO. We consider that the sucrose solution follows a dehydration process when combined with the acid solution of gold, the metallic ions are reduced into metallic agglomerates at the same time as graphene oxide is formed due to the presence of the nanostructures and ascorbic acid. Our assumptions are based on the current studies that use sucrose to obtain graphene and graphene dioxide. Zhengsong Sun, et al., were able to produce graphene monolayers using sucrose at 800 °C (Sun et al., 2010); Libin Tang et al. reported a novel bottom-up method to obtain nanolaminates of graphene dioxide using glucose, sugar and fructose by Hydrothermal self-assembly (Tang et al., 2012); Hargreaves and Cooper synthesized nanographite at room temperature with a method of sucrose and concentrated sulfuric acid microemulsion (Hargreaves and Cooper, 2016). On the other hand, hydrochloric acid (HCI) was used for the reduction of graphene oxide (Coleman et al., 2008). Ascorbic acid is also reported as the reducing agent of GO (Zhang et al., 2010; Paredes et al., 2011). In addition, metallic nanoparticles are used as catalysts to obtain rGO from GO at ambient temperature (Zhuo et al., 2013). Therefore, in our experimental process we consider the acid solution of gold in magnetic stirring with gold and ascorbic acid to allow the simultaneous formation of GO and Au-NPs, where gold nanoparticles and the presence of ascorbic acid play a similar role to catalyzers and reducing agents potentialized to obtain the nanocomposite. With the above mentioned in mind, there are five important points: (1) it is possible to obtain graphene with sucrose, using thermic treatments at high temperatures. (2) Chlorhydric acid (HCI) is used to obtain rGO from graphite and/or GO. (3) Metallic nanoparticles work as catalysts to obtain rGO from GO. (4) Nanographite can be obtained with sucrose and concentrated sulfuric acid at ambient temperature. (5) Lastly, we emphasize that by the simple synthesis method at ambient temperature presented in this study, it is possible to simultaneously obtain a nanocompound of rGO/Au-NPs with sucrose and chloroauric acid (HAuCl4) as precursors.

Table 1 Synthesis method, precursors and application of graphene nanocomposites with Au-NPs.
Nanocomposite Precursors Synthesis Method NPs size (nm) Applications Ref.
G/Au-NPs Graphite, GO and HaAuCl4 Hummer’s method and sonication ∼30 Electrochemical biosensor Daodong et al. (2015)
Hummer’s method and Electrochemical coreduction 25 Electrocatalytic activity Jiao et al. (2013)
Graphene and HAuCl4 Sonication 30–35 Conductivity and biocompability Zhai et al. (2014)
GO/Au-NPs GO and HAuCl4 Hummer’s method and stirring and heating process ∼30 Biosensors Nayak et al. (2015)
Hummer’s method, stirring and hydrothermally treated 10–20 SERS Qin et al. (2014)
GO and HAuCl4 Magnetic stirring ∼10–18 Solar cells Cong Chen et al. (2016)
GO/AuNanorod Graphite, GO and HAuCl4 Hummer’s method and stirring ∼60 and 35 SERS Vianna et al. (2016)
rGO/Au-NPs Graphite, GO and HAuCl4 Hummer’s and Offerman method and stirring 28 ± 4 Electrocatalytic activity Wang et al. (2016)
Hummer’s and low temperature refluxing method 10–20 Electrochemical sensors Johra and Jung (2016)
Hummer’s method and Solvothermal process ∼27.4 Nanocatalysts Ghosh et al. (2016)
Hummer’s method and Slovothermal process ∼20 Electrochemical oxidation Sahoo et al. (2015)
Hummer’s method and UV irradiation ∼15 ± 2 Sensing electrode Li et al. (2015)
Hummer’s method and ultrasonic treatments 10–20 Electrochemical sensor Guo et al. (2015)
Hummer’s method and hydrothermal reduction ∼31.6 Catalytic activity Cao et al. (2016)
GO and AU choloride Electrochemical reduction ∼8.2 Electrocatalytic activity Govindhan et al. (2015)
This work Sucrose, Asorbic acid and HAuCl4 New method ∼15–30 nm SERS –

4

4 Conclusions

We presented a method similar to green synthesis with which, for the first time at room temperature, we obtained reduced graphene oxide functionalized with gold nanoparticles (rGO/Au-NPs) simultaneously with SERS applications, in a highly stable in time colloidal suspension, using sucrose and chloroauric acid (HAuCl4) as precursors and ascorbic acid as the reducing and stabilizing agents of the nanocompound. The high resolution TEM images facilitated the identification of the diffraction planes associated to carbon and to Au-NPs in relation to planes (1 0 1) and (1 1 1), respectively. The images also evidenced the existence of rGo/AuNPs nanocompounds. Raman spectroscopy facilitated the clear detection of bands D and G in the graphite materials. Nevertheless, the relative intensity between the bands ID/IG ≈ 1.6 corroborated the presence of rGO in the synthesized material. The FTIR showed stretching vibrations associated with —OH hydroxyl groups and C—C groups presents in rGO. Additionally, two absorption bands were observed, one associated to the presence of rGO located at 260 nm and the other located at 522 nm associated to the transverse surface plasmon resonance in AuNPs. Additionally, an absorption band at 375 nm approximately is slightly observed, possibly evidencing the interparticle interaction of rGO/AuNPs. The synthesis method presented in this work represents a highly efficient method, easy to use, and with low cost for the production of a rGO/AuNPs nanocompound. Due to the simplicity of production of this material, it facilitates the accessibility for the study of different applications such as antibacterial, electrical properties, SERS, catalysts and biosensors, among others.

Acknowledgements

The computational resources for this investigation was facilitated by UNISON/Acarus. Special thanks to supporting given by Laboratory of Transmission Electron Microscopy in the Universidad de Sonora. We appreciate the support given by PRODEP through C.A. UNISON-CA-188 project and appreciate the support given by the DCEN through USO315001053 and USO315000709 projects.

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