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Nano Progress
Research Article
Reduced Graphene Oxide Decorated Au Nanoparticles as an Efficient Electrode for the Determination of Hydroquinone
Selvamani Arumugam,a Babu Cadiam Mohan,b Ramkumar Vanaraj c and B. Sundaravel*d
*Corresponding author E-mail address: sundar.chem.bala@gmail.com (B. Sundaravel)
DOI: 10.36686/Ariviyal.NP.2019.01.01.002
Abstract: Herein, we report a simple preparation of reduced graphene oxide (rGO) supported gold nanoparticle (AuNPs) composite (rGO-AuNPs) with different RGO weight percentage (2, 5 and 8 wt %). The rGO-AuNPs was used as an electrode for the determination of hydroquinone (HQ). Initially, the prepared rGO-AuNPs was extensively analyzed by various characterization techniques such as HRTEM, XRD, DRUV-Vis and FT-IR. The results confirmed that the uniform dispersion of AuNPs on rGO surface with good metal-support interaction. The rGO-AuNPs was used as a working electrode (rGO(x)-AuNPs/GCE) (where x – weight percentage of rGO) for the determination of HQ. Electrochemical measurements were carried out by using rGO(x)-AuNPs/GCE as a working electrode and cyclic voltammetry curves were recorded. The electrochemical behaviors of HQ were thoroughly investigated with a pair of redox peaks. Results demonstrated that the rGO(x)-AuNPs/GCE with 5 wt% of rGO has higher electrocatalytic ability when compared to the rGO(x)-AuNPs/GCE with 2 and 8 wt% of rGO. The high surface area and high electron conductibility of rGO(x)-AuNPs/GCE, and the fine dispersion of AuNPs on rGO surface are the main reason for the better activity. A linear response between peak current and HQ concentration was exhibited in the range of 0.2 to 800.0 μmol L-1, and also detection limit of HQ was found to be 8.85×10-8 mol L-1.
Keywords: Graphene; Au-nanoparticles; Hydroquinone; Cyclic voltammetry; Redox peaks
Publication details: Received: 7th February 2019; Revised: 13th February 2019; Accepted: 14th February 2019; Published: 18th February 2019
1. Introduction
Graphene is a two-dimensional sheet of carbon atoms bonded in sp2 hybridization structure.[1-2] It has been demonstrated as a potential candidate for various applications in many emerging fields such as nanoelectronics, engineering materials, energy technology, sensors and catalysis.[3-4] In particular, graphene based nanocomposite materials have been tremendously employed as electrocatalysts in various field such as sensor and energy. In fact, the unique properties such as high surface area, conductive nature, high mechanical and thermal stability, high porosity and unique 2D structure are the main reason for its better performance. The graphene nanocomposites, rGO supported Ag, ZnO, CuO, TiO2, and Fe3O4 are exclusively used for sensor application due to its huge surface area and high electron conductibility.[4-5] One of the promising chemical routes for the preparation of graphene-based nanocomposite are chemical reduction method includes functionalization of rGO with metal nanoparticles.[6] The method is simple, cost-effective and more importantly the targeted composite materials can be prepared in a large scale manner using the chemical reduction method. Hence, the development of unique graphene-based hybrid nanomaterials by using simultaneous chemical reduction method has gained huge interest. To date, there are several papers published on the preparation, characterization and applications of unique graphene-based nanocomposite.[5] Recently, rGO-anchored Au nanoparticles composite was prepared by simultaneous reduction method by using different reducing agents.[7-9]
Among various applications such as catalysis, energy and biomedical, rGO-based nanocomposites have been found to be superior in sensors application.[10-11] In particular, the records showed that the combination of rGO and Au nanoparticle was often worked well in the senor applications. This is may be due to the excellent textural and chemical properties of rGO in which the speed of electron transport and high electron conductibility are the key factors.[4,5] Similarly, Au NPs could increase the current response of sensor material to a great extent, which is due to its high surface reactivity and good conductibility.[12-13] Hence, we believe that the decoration of Au NPs on rGO would yield an excellent nano-hybrid material which is highly suitable as a novel working electrode for sensor applications.
Hydroquinone (HQ) is a common toxic pollutant existed in most environmental samples and, the degradation of HQ is quite difficult due to it high stability.[14-15] Hence, analytical approaches which allow effective sensing of such types of pollutant are highly required. There are various common analytical approaches such as spectrophotometry,[16] HPLC[17] and electroanalysis[18] have been developed. Among them, electrochemical method is extensively employed for the HQ analysis with the merits of facile operation, high sensitivity, economic equipments (such as cyclic voltammetry) and with suitably modified working electrode.[19-20] Hence, herein we prepared highly suitable electro materials (rGO-AuNPs) by a simple chemical reduction method. The prepared rGO-AuNPs was extensively analyzed by various characterization techniques such as HRTEM, XRD, DRUV-Vis and FT-IR. The prepared rGO-AuNPs was used as a working electrode for sensing of HQ.
2. Experimental Section
2.1. Materials and Methods
All the reagents and chemicals are analytical grade and used without further purification to synthesize the rGO decorated Au NPs (rGO-AuNPs). Sulfuric acid (H2SO4, > 98.0%), potassium permanganate (KMnO4, > 99.0%), sodium nitrate (NaNO3, > 99.0%), hydrogen peroxide (H2O2, > 30%), gold(III) chloride trihydrate (AuCl4. 3H2O, > 99.9%) and Hydrazine monohydrate (N2H2.H2O > 50-60%) were used without purification.
X-ray diffraction (XRD) patterns of the prepared rGO-AuNPs was recorded using PANalytical X’pert PRO diffractometer equipped with a CuKα=1.54 Å as the radiation source, the samples were scanned in 2θ range 5-80o with the step scan of 0.02 Å and count time of 5s at each point. The diffuse reflectance ultraviolet visible spectral (DR-UV-Vis) analysis was carried out to identify the coordination of constituent element present in the prepared rGO-AuNPs by using Shimadzu UV-2450 instrument. High-resolution transmission electron microscopy (HRTEM, TECNAI G2 (model T-30) S-twin HRTEM) images were taken for the prepared rGO-AuNPs to study the morphology. Field emission gun was operated at 300 kV. FTIR spectra were recorded on a PerkinElmer FTIR spectrophotometer using KBr technique. The pellet was scanned at 4 cm−1 resolution in the range of 4000–400 cm−1. CHI-1130A electrochemical workstation (USA) was employed for all the electrochemical experiments in HQ determination.
2.2. Preparation of rGO
The graphene oxide was prepared by modified Hummer’s method. In a typical procedure, 1 gm of graphite powder was dispersed in 40 ml Conc. H2SO4 and followed by addition of 1 gm of NaNO3 at constant stirring for 30 minutes. Subsequently, 6 gm of solid KMnO4 was added with constant stirring and the obtained mixture was maintained at 5 áµ’C for 30 minutes. The resulting solution was stirred for 3 hours and treated with 6 ml of 30% of aqueous H2O2. It was further stirred for 15 minutes and then aged for 1 hour. The resultant precipitate was filtered and washed well with double distilled water and 5% of dil. HCl for several times until the pH reaches 7. Finally, it was dried at 100 áµ’C in vacuum oven for 24 hours to form graphene oxide (GO) powder. To get rGO, calculative amount of prepared GO powder was dispersed in distilled water and the pH of solution was adjusted to 10 using KOH solution. Hydrazine monohydrate (1 mL) was added to the solution and which was stirred for 24 h at 90 áµ’C. The black precipitate was filtered and washed several times with distilled water to remove the excess hydrazine. The black powder was dried at 80 áµ’C under vacuum to obtain reduced graphene oxide (rGO).
2.3. Preparation of rGO-AuNPs
In order synthesis the rGO-AuNPs, a certain volume of the olive leaf extract and HAuCl4.3H2O was taken in 10 ml de-ionized water and stirred until color of the solution was changed from yellow to violet to dark pink. Consequently, obtained mixture was collected by centrifugation and washed with ultrapure water several times, further which was dried to form rGO-AuNPs. Mass of the rGO was varied (x = 2, 5 and 8 wt%) to obtain rGO(x)-AuNPs.
2.4. Electrochemical Measurement: Determination of HQ
All electrochemical experiments were carried out with a CHI 1130A electrochemical workstation (USA). The three–electrode system consists of glassy carbon (3 mm dia) as a working electrode, Ag/AgCl with 3 M KCl as a reference electrode and Pt wire as a counter electrode with 30 mL working volume. The surface of GCE was first cleaned mechanically by polishing with 0.05 and 1.0 µm Al powder on a polishing cloth (Buehler) followed by sonication in DD water for 10 min. The pre-treatment of GCE was performed electrochemically by cyclic voltammetry for 20 cycles in the potential window of -1 to 1v Vs Ag/AgCl in phosphate buffer solution at a potential in various scan rate. The modified working electrode was prepared as follows: At first, a required amount of rGO-AuNPs was dispersed in 5 wt% of nafion and methanol (1:2) to form colloidal sol and which was coated on carbon paper containing an area and thickness of 1 x 1 cm and 0.02 cm, respectively. The obtained modified electrode (rGO(x)-AuNPs-GCE) was dried at ambient temperature and subjected further for CV analysis.
HQ solution in 0.1 mol L-1 pH 2.0 PBS was taken into a 10 mL electrochemical cell and the three-electrode system was immersed into the solution. Cyclic voltammetry was investigated for electrochemical behavior of HQ in the potential range from -0.2 to 0.8 V with scan rate of 100 mV s-1. Differential pulse voltammetric (DPV) measurements were further measured for quantitative analysis of HQ with instrumental parameters step up such as increment potential of 0.004 V, pulse amplitude of 0.05 V, pulse width of 0.05 s, ample width of 0.017 s and pulse period of 0.2 s.
3. Results and Discussions
3.1. XRD Pattern of rGO-AuNPs
In order to confirm the presence of AuNPs in rGO-AuNPs and the crystalline property and crystalline size of AuNPs, XRD patterns were recorded for fresh AuNPs and rGO(5)-AuNPs. Fig. 1 shows the characteristic diffraction peaks of the AuNPs and the prepared rGO-AuNPs. The appearance of diffraction peaks around 2θ = 38.20°, 44.41° and 64.54° are respect to the (111), (200) and (220) planes corresponding to standard cubic phase of Au.[21] The crystalline size of AuNPs was found to be 8.4 nm calculated from Scherrer’s equation using (111) plane. In addition, the presence of a broad diffraction peak at 23° is a representation of stacked graphene layers structure in the prepared rGO-AuNPs composite.[22]
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%201.png)
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3.2. HRTEM Results of rGO(5)-AuNPs
Surface morphology of the prepared rGO(5)-AuNPs was investigated by using high resolution transmission electron microscope (HR-TEM), and the recorded images with different magnifications were given in Fig. 2.The HRTEM images clearly show that the AuNPs was uniformly decorated on the surface of rGO. The AuNPs supported on the rGO surface were spherical in shape with average particle size of 8.2 nm (Fig. 2). This HRTEM result is in good agreement with the XRD results of rGO(5)-AuNPs.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%202.png)
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3.3. N2 Adsorption-Desorption
The surface area of rGO(x)-AuNPs was determined by BET analysis. Fig. 3 shows the N2 adsorption desorption isotherms of rGO(x)AuNPs, the presence of hysteresis loop at relative pressure between 0.7-1 is indicating that the rGO(x)-AuNPs samples have high amount of mesoporous structure. The surface area of rGO was found to be 348 m2/g, whereas the fresh AuNPs shows the surface area of 113 m2/g. However, in comparison to the fresh rGO and AuNPs, the rGO(x)-AuNPs showed slightly lower surface area which may be due to the blocking of pores by the AuNPs (Table 1). The surface area ofrGO(x)-AuNPs was found to be not significantly changed even after the weight of rGO was increased from 5 to 8 wt %. The result clearly suggests that 5 wt% of rGO is the optimum one for the synthesis of rGO(x)-AuNPs with high surface area. The textural properties of rGO(x)-AuNPs are provided in Table 1.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%203.png)
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Sample | Surface area m2/g* |
rGO | 348 |
AuNPs | 113 |
rGO(2)-AuNPs | 286 |
rGO(5)-AuNPs | 253 |
rGO(8)-AuNPs | 251 |
*Surface area measured by using BET analysis
3.4. DRUV-Vis Spectra
DRUV-Vis spectra were recorded for rGO and rGO(x)-AuNPs and the results are provided in Fig. 4. Chemical coordination between Au NPs and rGO was studied. According to previous literature reports, rGO would show absorbance maximum at around 230 nm and 306 nm respect to á´« -á´«* transitions for aromatic C-C bonds and n-á´«* transitions for C=O bonds, respectively.[23-24] However, reduce graphene oxide (rGO) showed shift in á´« -á´«* from 230 nm to 265 nm which indicates that surface of GO was reduced and conjugated structure was restored.[25] The plasmonic band of Au and red shift in the characteristic peak for rGO confirmed the presence of absorbance maximum at 530 nm, which is in good accordance with literature.[26]
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%204.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.4..png)
3.5. FT-IR Spectra
FTIR spectra were studied to identify the possible molecules for the capping and stabilization of Au- rGO nanoparticles and result are illustrated in Fig. 5. FT-IR spectrum of GO exhibited a intense band at 3290 cm-1 corresponding to stretching vibration of -OH presented in water or carboxylic acid group. The peaks around 2930 and 2853 cm-1 are respect to stretching vibrations of C-C bonds. The signal present at 1740 cm-1 is characteristic of C=O stretching vibrations for carbonyl and carboxylic groups. In addition, the presence of band approximately at 1590 cm-1 is responds for the stretching vibrations of C=C. The disappearance of peak corresponding to hydroxyl vibrations and carbonyl/carboxyl group is also illustrates that deoxygenation of graphene surface to form the rGO.[27] The presence of blue shift and increase in characteristic bands of respective functional groups in rGO(x)-AuNPs suggest that the successful formation of stable gold nanoparticles on reduced graphene oxide.[28]
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%205.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.5..png)
4. Electrochemical measurement
4.1. Analysis of HQ on rGO(x)-AuNPs
The voltammetric response on GCE and rGO(x)-AuNPs/GCE (x=2, 5 and 8 wt%) for the determination of 5.0×10−4 mol L-1 concentration of HQ in 0.1 mol L-1 pH 2.0 PBS at the scan rate of about 100 mV s-1 was illustrated in Fig. 6. A pair of broad redox peaks was observed on bare GCE, whereas rGO(x)-AuNPs/GCE shows sharp peaks with higher current. From these results, we can understand that the rGO(5)-AuNPs/GCE shows sharper peak with higher current compared to that of rGO(x)-AuNPs/GCE with 2 and 8 wt% of rGO. This is may be due to the fine dispersion of Au NPs on rGO, high surface area (Table 1) and high conductivity associated with easy transfer of electrons.[4-5,12] Also, presence of hydroxyl group in HQ enhances the electrochemical reaction at selected potential range.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%206.png)
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Table 2 clearly elucidates the electrochemical data of cyclic voltammgrams, the ratio of anodic peak current to cathodic peak current (Ipa/Ipc) was smaller than that of bare GCE which may be due to more reversible electrochemical process were taken place on rGO(x)-AuNPs/GCE by tremendous electrocatalytic activity of AuNPs. The presence of AuNPs in rGO showed excellent electrocatalytic activity with interaction of aromatic ring of HQ, which may greatly enhances the electron transfer property of the analyte. Hence, rGO(5)-AuNPs/GCE showed lesser value of (Ipa/Ipc= 1.01) compared to others.
Electrode | Ipa(μA) | Ipc(μA) | Ipa/Ipc |
GCE | 28.74 | 8.46 | 3.39 |
rGO(2)-AuNPs/GCE | 40.08 | 38.13 | 1.05 |
rGO(5)-AuNPs/GCE | 59.45 | 58.86 | 1.01 |
rGO(8)-AuNPs/GCE | 53.74 | 52.43 | 1.02 |
4.2. Effect of pH
The influence of buffer pH on voltammetric behavior of 5.0×10-4 mol L-1 HQ on rGO(5)-AuNPs/GCE was studied in the pH range of 1.5 to 5.5 and the results are presented in Fig. 7. The pH of buffer was found to be greatly influenced the cyclic voltammograms with gradual deformation. In addition, the redox peak potential shifted towards negative side when the pH of buffer solution was increased; this is due to the participation of protons in the electrode reaction. This result confirms that the redox peak shifted to negative region after the pH of 2.0 and the pH of 2.0 was fixed as a suitable condition for the further experiments.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%207.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.7..png)
4.3. Effect of rGO Mass
The effect of rGO mass on cyclic voltammetric curves of HQ were studied with rGO(x)-AuNPs/GCE in different wt% of rGO. Fig. 8 clearly showed that the cyclic voltammetric curves of HQ were significantly affected by rGO wt%. However, 5 wt. % of rGO is a most suitable amount and produced the better activity than the 2 and 8 wt% of rGO as shown in Fig. 8.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%208.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.8..png)
4.4. Effect of Scan Rate
The effect of scan rate on electrochemical behavior of HQ on rGO(5)-AuNPs/GCE was studied in range from 20~500 mV s-1 as shown in Fig. 9. This result indicating that increase of scan rate was influence the grown in regular movement in redox potentials for the currents of two peaks, which established a quasi-reversible electrode process. It is also clearly indicating that current was gradually increased with scan rate.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%209.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.9..png)
4.5. Differential Pulse Voltammetry (DPV) Analysis
The DPV analysis was carried out for the quantitative determination of HQ using rGO(x)-AuNPs /GCE and the results are shown in Fig. 10. A linear relationship was founded between Ipa and concentrations of HQ in the range of 2.0×10-7 ~ 8.0×10-4 mol L-1 (insert Fig. 10). From the DPV analysis, it is clearly observed that rGO(5)-AuNPs/GCE is greatly facilitated the lower oxidation potential compared to that of modified electrodes. The linear regression equation was obtained as Ipa (μA) = 0.031 C (μmol L-1)-0.0283 (γ = 0.9965) accompanied by a detection limit of 8.85×10-8 mol L-1. The reproducibility of rGO(x)-AuNPs/GCE was evaluated by recording 10 successive detections of 5.0×10-4 mol L-1 HQ due to the catalytic effect of rGO(x)-AuNPs/GCE.
![](/webadmin/ckeditor_html/kcfinder/upload/images/AP-NP-2019-02-004%20(R1)/Fig%2010.png)
![](/webadmin/ckeditor_html/kcfinder/upload/images/Fig.10..png)
5. Conclusions
In summary, rGO(x)-AuNPs was prepared by a simple chemical reduction method and it was used as an electrode material for the determination of hydroquinone. Facile preparation, good stability, sensitive, selective and low cost of the prepared rGO(x)-AuNPs/GCE is highly beneficial. The excellent electrocatalytic activity towards the determination of hydroquinone analysis is due to high specific surface area and rapid electron transfer of AuNPs. The linear detection range of HQ was from 2.0×10-7 to 8.0×10-4 mol L-1 and detection limit was found to be 8.85×10-8 mol L-1. In addition, the present method showed excellent anti-interference ability and reproducibility for detection of HQ. Overall, the rGO(5)-AuNPs is a potential candidate for the electrocatalytic determination of hydroquinone.
Acknowledgements
The authors V.R and A.S are greatly acknowledge the DST-SERB-NPDF/2017, New Delhi for providing National Post-Doctoral Fellowship (NPDF) to carry out the research work.
Conflicts of Interest
The authors declare no conflict of interest.
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