Open Access

Green Approach for the Effective Reduction of Graphene Oxide Using Salvadora persica L. Root (Miswak) Extract

  • Mujeeb Khan1,
  • Abdulhadi H Al-Marri1,
  • Merajuddin Khan1,
  • Mohammed Rafi Shaik1,
  • Nils Mohri2,
  • Syed Farooq Adil1,
  • Mufsir Kuniyil1,
  • Hamad Z Alkhathlan1Email author,
  • Abdulrahman Al-Warthan1Email author,
  • Wolfgang Tremel2,
  • Muhammad Nawaz Tahir2 and
  • Mohammed Rafiq H Siddiqui1Email author
Nanoscale Research Letters201510:281

https://doi.org/10.1186/s11671-015-0987-z

Received: 20 April 2015

Accepted: 23 June 2015

Published: 3 July 2015

Abstract

Recently, green reduction of graphene oxide (GRO) using various natural materials, including plant extracts, has drawn significant attention among the scientific community. These methods are sustainable, low cost, and are more environmentally friendly than other standard methods of reduction. Herein, we report a facile and eco-friendly method for the bioreduction of GRO using Salvadora persica L. (S. persica L.) roots (miswak) extract as a bioreductant. The as-prepared highly reduced graphene oxide (SP-HRG) was characterized using powder X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron (XPS) spectroscopy, and transmission electron microscopy (TEM). Various results have confirmed that the biomolecules present in the root extract of miswak not only act as a bioreductant but also functionalize the surface of SP-HRG by acting as a capping ligand to stabilize it in water and other solvents. The dispersion quality of SP-HRG in deionized water was investigated in detail by preparing different samples of SP-HRG with increasing concentration of root extract. Furthermore, the dispersibility of SP-HRG was also compared with chemically reduced graphene oxide (CRG). The developed eco-friendly method for the reduction of GRO could provide a better substitute for a large-scale production of dispersant-free graphene and graphene-based materials for various applications in both technological and biological fields such as electronics, nanomedicine, and bionic materials.

Keywords

GrapheneGraphene oxideNatural productGreen chemistrySpectroscopy

Background

Among various carbonaceous materials, graphene has attracted tremendous attention of scientists and technologists, due to its stable 2D morphology and exceptional electronic properties related to its crystal structure [13]. Indeed, graphene has revolutionized the field of nanotechnology and has emerged as a promising new nanomaterial for a variety of exciting applications, despite being discovered recently. Remarkable thermal, electrical, and mechanical properties of graphene have been extensively exploited in various fields, including sensors [4], solar cells [5], nanoelectronics [6], energy storage [7], functional nanocomposites [8], biomedicine [9], and catalysis [10, 11]. Commonly, graphene is obtained from graphite [12], which is a naturally occurring material and has been in use for centuries [13]. The free-standing single-layer of graphene was first obtained in 2004 by the isolation of graphene from graphite via micromechanical cleavage [14]. This fascinating approach of peeling off graphene layers from graphite can only be useful for fundamental science, and is not suitable for the large-scale production of graphene [15]. Therefore, tremendous attention is being paid to explore various alternative approaches for the low-cost and bulk production of graphene.

Several methods, including chemical vapor deposition (CVD) [16], arc discharge [17], epitaxial growth on SiC [18], chemical conversion, liquid phase exfoliation, and sequential oxidation reduction of graphite, have been reported [19]. Among all these methods, sequential oxidation and reduction of graphite has attracted significant attention, because it is benign, less expensive, and is more suitable for the bulk production of graphene [20, 21]. Although, the flakes of graphene-like sheets obtained from such methods are not defect free, these nanosheets are highly processable, described as highly reduced graphene oxide (HRG), and have been extensively applied for the preparation of various graphene-based functional bio- and nanocomposites [22].

Among various reduction methods (thermal, electrochemical, or chemical) [2325] of graphite oxide (GO) or graphene oxide (GRO), chemical reduction is the most promising method and is extensively applied for the large-scale production of HRG [26]. Several reducing agents, such as hydrazine [27], ammonia borane complex [28], sodium hydride [29], and hydrohalic acid [30], have been used for the reduction of GRO to obtain HRG [31]. However, despite several advantages, the chemically reduced HRG has limited applications, as it tends to agglomerate strongly due to interlayer attractive van der Waals forces [32]. Therefore, further chemical stabilizers, such as porphyrins and pyrenebutyric acid, are frequently required to prevent these kinds of agglomerations [33]. Majority of the chemicals involved in the reduction and functionalization of GRO are highly toxic in nature, hazardous, and harmful to both environment and human life [34]. In addition, the presence of trace amount of highly toxic reducing agents on the surface of HRG could seriously alter several properties of HRG and has adverse effects on its biological applications [35].

However, in comparison to chemical reduction, the green reduction of GRO involves biocompatible ingredients under physiological conditions of temperature and pressure [36, 37]. To date, several green reductants extracted from microorganisms, marine organisms, or plant extracts have been applied for the preparation of HRG, including gallic acid, fluorescent protein, melatonine, ascorbic acid, and wild carrot roots [3842]. Among these green reductants, plant extracts have been significantly exploited due to their low cost, bulk availability, and biocompatibility [4346]. Recently, extracts of various plants were used both as reducing and stabilizing agents during the preparation of metallic nanoparticles and in some cases for the reduction of GRO [4751].

In this study, we have applied Salvadora persica (SP) L. (miswak) extract as a bioreductant. ‘Miswak’ is an Arabic word which literally means ‘tooth-cleaning stick or chewing stick’ [52]. It is widely used as an oral hygiene tool in most parts of the world. Approximately, 182 plant species have been used as chewing sticks; however, roots of S. persica L. are the most common one and frequently used for this purpose. Salvadora persica L. is a glabrous tree or shrub belonging to family Salvadoraceae [5355]. S. persica L. is found in many parts of the world. In Saudi Arabia; it is very widely spread, especially in the southern regions of Saudi Arabia. Because of the Sunnah (practices of prophet MuhammadPBUH) of prophet of Islam MuhammadPBUH, use of miswak obtained from roots of S. persica L. is very common and popular in the Muslim world. Besides having several benefits for oral hygiene, various parts of S. persica L. are also used in folk medicine for the treatment of several diseases. For example, it is reported to have diuretic, antiscorbutic, anthelmintic, and analgesic properties [56].

The entire plant of S. persica L. is considered to be edible, and it is reported that leaves of the plant are sometimes used in salad [57]. S. persica L. has been reported to have several important biological activities, such as antimicrobial, cytotoxic, hypoglycemic, antiulcer, antiplasmodial, and anti-inflammatory activities. Moreover, various classes of phytomolecules including terpenoids, alkaloids, flavonoids, saponins, and tannins have been isolated from this plant [56]. Thorough and detailed literature survey revealed that the use of S. persica L. as a bioreducing agent for the synthesis of nanomaterials has not yet been reported in literature. Thus, as part of our ongoing research on Saudi Arabian plants [5860], we reported the green synthesis of HRG via the reduction of GRO using S. persica L. root (miswak) extract (cf. Scheme 1). The SP-HRG was characterized using various microscopic and analytical techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). During this study, a detailed analysis on the effect of plant extract (PE) on the dispersibility of HRG in various solvents was investigated by preparing HRG with different amounts of PE, and the dispersibility of HRG was compared with that of chemically reduced graphene oxide (CRG).
Scheme 1

UV-vis absorption spectra of graphene oxide (GRO, blue line), highly reduced graphene oxide (SP-HRG, green line) reduced with PE, chemically reduced graphene oxide (CRG, purple line) and pure root extract (SP, red line). Although the concentration of CRG was the same as that of SP-HRG, it exhibits a much lower absorption coefficient due to its poor dispersibility in water

Methods

Materials

The roots of S. persica L. growing in Jizan, Southern region of Saudi Arabia were purchased from a local herbal market at Batha, Riyadh, Saudi Arabia. The identity of the plant material was confirmed by a plant taxonomist from the Herbarium Division of the College of Science, King Saud University, Riyadh, Saudi Arabia. A voucher specimen was retained in our laboratory with the voucher specimen number KSUHZK-302. Graphite powder (99.999 %, _200 mesh) was purchased from Alfa Aesar (USA). Concentrated sulfuric acid (H2SO4 98 %), potassium permanganate (KMnO4 99 %), sodium nitrate (NaNO3 99 %) and hydrogen peroxide (H2O2 30 wt %) and all organic solvents were obtained from Aldrich Chemicals (USA) and used without further purification.

Preparation of S. Persica L. Root (Miswak) Extract

First, fresh roots of S. persica L. were cut into small pieces. The resultant pieces (1.3 kg) were soaked in deionized water (3000 mL) and refluxed for 4 h. Then, the aqueous solution obtained after reflux was filtered and dried at 50 °C under reduced pressure in a rotary evaporator to give a dark brownish gummy extract (30.0 g) which was stored at 0–4 °C for further use.

Preparation of Highly Reduced Graphene Oxide (SP-HRG)

Graphite oxide (GO) required for the preparation of SP-HRG was synthesized according to our previously reported method [61]. Initially, as-prepared graphite oxide or GO (200 mg) was dispersed in 40 mL of DI water and sonicated for 30 min to obtain graphene oxide (GRO) sheets. The resulting suspension was taken in a round bottom flask mounted with a cooling condenser, which is heated to 100 °C. Subsequently, 10 mL of an aqueous solution of the root extract (0.1 g mL−1) was added to the suspension, which was then allowed to stir for 24 h at 98 °C. After this, black powder of highly reduced graphene oxide (PE-HRG-1) was collected by filtration, which was further washed with DI water several times to remove the excess root extract residue and redistributed into water for sonication. This suspension was centrifuged at 4000 rpm for another 30 min. Subsequently, the supernatant was thrown out and the precipitate was collected and dried in vacuum.

Characterization

UV-vis Spectroscopy

A PerkinElmer lambda 35 (USA) UV-vis spectrophotometer was used for the optical measurements. The analysis was performed in quartz cuvettes using DI water as a reference solvent. Stock solutions of SP-HRG and GRO for the UV measurements were prepared by dispersing 5 mg of sample in 10 mL of DI water and sonicating for 30 min. The UV samples of GRO and SP-HRG were prepared by diluting 1 mL of stock solution with 9 mL of water.

X-ray Diffraction

XRD diffractograms were collected on a Altima IV (Rigaku, Japan) X-ray powder diffractometer using Cu Kα radiation (λ = 1.5418 °A).

Transmission Electron Microscopy

TEM was performed on a JEOL JEM 1101 (USA) transmission electron microscope. The samples for TEM were prepared by placing a drop of primary sample on a holey carbon copper grid and drying for 6 h at 80 °C in an oven.

Fourier Transform Infrared Spectrometer

FT-IR spectra were measured on a PerkinElmer 1000 (USA) Fourier transform infrared spectrometer. In order to remove any free biomass residue or unbound extract to the surfaces of SP-HRG sheets, the SP-HRG nanosheets were repeatedly washed with distilled water, and then the product was centrifuged at 9000 rpm for 30 min and dried. The purified SP-HRG nanosheets were mixed with KBr powder and pressed into a pellet for measurement. Background correction was made using a reference blank KBr pellet.

X-ray Photoelectron Spectroscopy

XPS spectra were measured on a PHI 5600 Multi-Technique XPS (Physical Electronics, Lake Drive East, Chanhassen, MN) using monochromatized Al Kα at 1486.6 eV. Peak fitting was performed using the CASA XPS Version 2.3.14 software.

Results and Discussion

Reduction of GRO was carried out at an elevated temperature under reflux conditions using the root extract of miswak. Upon completion of reduction process, the brown color of GRO dispersion changed to dark black, which indicated the formation of SP-HRG. It is worth mentioning that no color change was observed in the absence of miswak root extract, under similar conditions. Although, 10 mL aqueous root extract (100 mg/mL) was found to be sufficient for the complete reduction of GRO, three different samples of SP-HRG (prepared by increasing the concentration of root extract) were also used to further investigate the effect of concentration of root extract on the dispersion quality of SP-HRG. The dispersion quality of the as-prepared samples of SP-HRG was also compared with chemically reduced GRO (CRG) using hydrazine as a reducing agent. The samples of SP-HRG were synthesized by using 10 mL (100 mg/mL) (SP-HRG-1), 20 mL (SP-HRG-2), and 50 mL (SP-HRG-3) of miswak root extract with concentration (100 mg/mL) while the amount of GRO was kept constant.

GRO reduction was initially monitored by recording UV-vis absorption spectra of both GRO and SP-HRG as shown in Fig. 1. GRO exhibited absorption peak at 230 nm which was attributed to the ππ* transitions of the aromatic C–C bonds and a weak shoulder at 301 nm due to nπ* transitions of C=O bonds present in GRO. However, on reduction of GRO to HRG, the characteristic absorption band at 301 nm disappeared and the absorption band at 230 nm in GRO spectrum is redshifted to 280 in SP-HRG, which confirms the reduction of GRO and the partial restoration of π network of SP-HRG. The absorption maximum in case of CRG appeared at 271 nm instead of 280 nm, which is considerably lower than that of SP-HRG. The higher redshift in case of SP-HRG is attributed to the superior degree of reduction in SP-HRG, as compared to CRG [61].
Fig. 1

Schematic illustration of the green reduction of graphene oxide (GRO) using Salvadora persica L. (S. persica L.) roots (miswak) extract as a bioreductant

The phytomolecules of miswak root extract not only reduce the GRO but also functionalize the surface of SP-HRG. This was confirmed in our previous study by the UV analysis of HRG obtained via reduction of GRO using Pulicaria glutinosa plant extract [61]. In order to investigate this, the UV spectrum of pure miswak root extract was measured, where the absorption maximum appeared at ~282 nm, which overlapped with the characteristic peak of SP-HRG (~280 nm). However, on further increasing the amount of plant extract and keeping the GRO amount constant, notably, the intensity of the absorption band at ~282 nm in these samples also increased (cf. Fig. 2). This clearly indicates the presence of phytomolecules of miswak root extract on the surface of SP-HRG.
Fig. 2

UV-vis absorption spectra of pure root extract (SP, blue line), SP-HRG-1 prepared with 10 mL root extract (red line), SP-HRG-2 prepared with 20 mL root extract (green line), and SP-HRG-3 prepared with 50 mL root extract (purple line)

Thermal stability of GRO, SP-HRG-1, SP-HRG-2, SP-HRG-3, and miswak root extract were evaluated via TGA (cf. Fig. 3). Pure graphite does not exhibit any weight loss in the temperature range of 0–900 °C; however, GRO exhibited significant weight loss in several steps, due to the presence of various oxygen-containing functional groups [61]. The degradation of GRO involves two prominent steps, initial and relatively faster weight loss of up to ~40 % occurs between 100 and 300 °C, due to the loss of adsorbed water and labile oxygen-containing functional groups, such as hydroxyl and epoxy functional groups. Subsequently, in the second step, a gradual weight loss of ~20 % was observed between 300 and 900 °C (cyan line in Fig. 3), which is attributed to the pyrolysis of remaining oxygen-containing functional groups and burning of carbon skeleton [61].
Fig. 3

TGA traces of root extract (SP), graphene oxide (GRO), SP-HRG-1, SP-HRG-2, and SP-HRG-3

Similarly, pure miswak root extract also exhibited up to ~80 % rapid weight loss between 100 and 900 °C in various steps (orange line in Fig. 3). However, SP-HRG exhibited only ~12–15 % weight loss between this temperature range, which was much lower than that of pure GRO and miswak root extract (purple line in Fig. 3). This is attributed to the significant decrease of oxygen-containing functional groups, which clearly indicates the reduction of GRO. Notably, with increasing concentration of miswak root extract, the weight loss of SP-HRG also increased, for instance, SP-HRG-1 showed a weight loss of ~12–15 % (purple line), SP-HRG-2 exhibited 22–25 % (green line), where as in SP-HRG-3 up to ~45 % of weight loss was observed (red line). This points towards the presence of phytomolecules of miswak root extract on the surface of SP-HRG.

The dual role of the miswak root extract as a bioreductant and capping agent was also confirmed by FT-IR analysis (cf. Fig. 4). FT-IR spectra of GRO (blue line), pure miswak root extract (purple line), SP-HRG (green line), and CRG (red line) were measured. The presence of intense bands at ~1740 cm−1 (for C=O stretching), ~1630 cm−1 (for C=C stretching), ~1209 cm−1 (for C–O–C stretching), ~1050 cm−1 (for C–O stretching), and a broad band at around 3440 cm−1 for hydroxyl groups indicated the presence of various oxygen-containing functional groups, such as carbonyl, carboxylic, epoxy, and hydroxyl groups in GRO. The removal of such oxygen-containing groups of GRO in the samples of SP-HRG and CRG was clearly indicated by the disappearance of some of the bands in their respective FT-IR spectra, such as the band at ~1740 and ~1630 cm−1. Also the relative decrease in the intensity of some of the other bands, like the decrease in intensity of broad band at 3440 cm−1 belonging to the hydroxyl groups of GRO, points towards the reduction of GRO. A relatively small decrease in the intensity of FT-IR signals in case of SP-HRG, when compared to CRG and also the presence of some additional bands in its IR spectrum, is attributed to the phytomolecules bound to the surface of SP-HRG post in-situ functionalization. This was further confirmed by comparing the IR spectra of SP-HRG and the pure miswak root extract. Most of the absorption bands of the miswak root extract also appear in the FT-IR spectrum of SP-HRG, either at same position or with slight shifts, such as the bands at ~3790, ~2329, 1636, and 1005 cm−1. The appearance of these bands in SP-HRG and their absence in CRG spectrum strongly suggests that the phytomolecules of miswak root extract act not only as bioreductant but also as stabilizers on the surface of the SP-HRG sheets.
Fig. 4

FT-IR spectra of graphene oxide (GRO, blue line), root extract-mediated highly reduced graphene oxide (SP-HRG, green line), and chemically reduced graphene oxide (CRG, red line) prepared with hydrazine hydrate and the pure root extract (SP, purple line)

Furthermore, the reduction of GRO was also monitored using XRD analysis. The XRD patterns of pristine graphite (blue line), GRO (red line), CRG (purple line), and SP-HRG (green line) are shown in Fig. 5. The pristine graphite exhibits a very intense and narrow reflection at 2θ = 26.4°, which is considerably shifted to lower Bragg angles at 2θ = 10.9° and slightly broadened in GRO, due to the formation and intercalation of oxygen-containing functional groups between the layers of carbon nanosheets. However, after the reduction, the reflection of GRO at 10.9° disappeared in both SP-HRG and CRG, and their interlayer distance also decreased due to the removal of oxygen-containing functional groups. Moreover, a broad reflection centered at 2θ = 22.4° in their diffraction patterns indicated the formation of graphene nanosheets with a thickness of few layers [30].
Fig. 5

XRD diffractograms of graphite, graphene oxide (GRO), root extract-mediated highly reduced graphene oxide (SP-HRG), and chemically reduced graphene oxide (CRG)

The Raman spectra of graphene comprise two main features: the G and D bands at 1575 and 1350 cm−1, respectively. Figure 6 demonstrates the Raman spectra of GRO and SP-HRG. The G and the D bands of GRO are shifted and appear at 1602 and 1340 cm−1, respectively, due to the destruction of the sp 2 character and the formation of defects in the sheets caused by the extensive oxidation. However after reduction, the G band in SP-HRG is slightly narrower and shifted to 1592 cm−1, and the D band is centered at 1336 cm−1. A comparison of the Raman spectra of both GRO and SP-HRG showed that the G band of SP-HRG is shifted by 10 cm−1 from 1602 to 1592 cm−1, whereas a slight shift was observed in the D band from 1340 to 1336 cm−1. The shifts in the bands of SP-HRG after the reduction towards the ideal positions of the G band (1575 cm−1) and D band (1350 cm−1) of graphene is a clear indication towards the restoration of the sp 2 character of SP-HRG, and it is well-suited with a high degree of reduction.
Fig. 6

Raman spectra of graphene oxide (GRO) and highly reduced graphene oxide (SP-HRG) using root extract

Figure 7 shows a comparison of the XPS spectra of GRO and SP-HRG. The graphene sample (GRO) exhibits the typical peaks at 284.0, 286.2, 288.0, and 289.2 eV resulting from sp 3 and sp 2 C–C, C–O, C=O, and O–C=O groups, respectively (cf. Fig. 7a) [62]. Applying the same boundary conditions to the fit of the reduced sample (SP-HRG) results in a deviation at 285.9 and 287.7 eV originating from C–C and C–O groups of the root extract (cf. Fig. 7c). The additional shoulder in the O1s peak of SP-HRG (cf. Fig. 7d), which is missing in the GRO spectrum (cf. Fig. 7b), confirms the presence of root extract residues on the surface of the sample. Calculation of the atomic concentrations shows the amount of C–O and C=O groups on SP-HRG to be reduced significantly (35.74 to 7.11 % and 6.83 to 4.33 %, respectively), while maintaining the amount of C–C groups (56.24 to 57.83 %), representing the high degree of reduction on the surface of the sample. The peak at 289.2 eV increases after reduction (1.19 to 5.14 %), which points to an additional peak originating from C=O groups of the plant extract, which was not added due to the low intensity.
Fig. 7

XPS spectra of graphene oxide (GRO): C1s (a) and O1s peak (b) and highly reduced graphene oxide with root extract (SP-HRG): C1s (c) and O1s peak (d)

Figure 8a, b illustrates the morphology and layer thickness of the SP-HRG, which were determined by transmission electron microscopy (TEM). The TEM images revealed the transparent and sheet-like structure of SP-HRG. An enormous number of scrolls and wrinkles were observed on the surface of the SP-HRG sheet, which remained stable under the high-energy electron beam. It has been noticed that the edges of the suspended graphene layers were folded back, and few layer thickness of SP-HRG was observed in the high-resolution TEM.
Fig. 8

TEM images (a and b) of as-prepared SP-HRG at different resolutions

The large-scale production of graphene obtained via solution-based sequential oxidation-reduction processes usually suffer from poor dispersibility in water and other organic solvents, due to their strong hydrophobic nature [63]. The irreversible agglomeration of graphene nanosheets is usually prevented by the addition of various external surfactants and stabilizers, including polymers and dendrimers [64], which have undesirable effects on the properties of graphene. However, during the green reduction of GRO using plants extracts, additional surfactants or stabilizers are not required, wherein the plant extracts themselves act as both reducing as well as stabilizing agents [61]. The dispersion quality of HRG obtained using root extract of miswak (SP-HRG) is investigated and also compared with chemically obtained HRG (CRG). For this purpose, various samples of SP-HRG are prepared by increasing the concentration of miswak root extract. For instance, SP-HRG-1, SP-HRG-2, and SP-HRG-3 are prepared by using 10, 20, and 50 mL of miswak root extract (100 mg/mL), respectively.

The dispersions of these samples and CRG are prepared by sonicating 5 mg of each sample in 10 mL of DI water. Superior dispersions were obtained for the bioreduced SP-HRG as compared to CRG. Notably, the dispersion quality of SP-HRG samples improved with increasing the concentration of miswak root extract. For example, SP-HRG-3 demonstrated an excellent dispersion, which remained stable even after 2 weeks compared to relatively lower stability SP-HRG-1. However, after 2 weeks, the CRG suspension became completely unstable, whereas all the samples of SP-HRG demonstrated excellent dispersibility in water as shown in Fig. 9.
Fig. 9

Digital images of the dispersions of CRG, SP-HRG-1 prepared with 10 mL of plant extract, SP-HRG-2 prepared with 20 mL of plant extract, and SP-HRG-3 prepared with 50 mL of plant extract and CRG (prepared with hydrazine hydrate)

Conclusions

Graphene oxide is reduced using an eco-friendly route, i.e., root extract of S. persica (miswak) as both a bioreductant and stabilizer. The as-prepared bioreduced SP-HRG exhibited excellent dispersibility compared to the chemically reduced graphene oxide (CRG). The concentration of S. persica (miswak) root extract played a critical role in the dispersibility of SP-HRG, whereas SP-HRG prepared using a high concentration of miswak root extract (SP-HRG-3) demonstrated superior dispersion in DI water. This clearly indicates that the miswak root extract acted not only as a bioreductant but also as a capping ligand, which was confirmed by various spectroscopic techniques. Therefore, the protocol presented here for the bioreduction of GRO can be potentially applied for the large-scale production of dispersant-free graphene nanosheets. Indeed, the highly oxidized nature, abundancy, and low cost of miswak root extract can be further exploited for the up-scaling of graphene and graphene-based materials for various technological and biological applications.

Declarations

Acknowledgements

This project was supported by NSTIP Strategic technologies programs, number (11NAN1860-02) in the Kingdom of Saudi Arabia.

Authors’ Affiliations

(1)
Department of Chemistry, College of Science, King Saud University
(2)
Institute for Inorganic and Analytical Chemistry, University of Mainz

References

  1. Geim AK, Novoselov KS. The rise of graphene. Nat Mater. 2007;6:183–91.View ArticleGoogle Scholar
  2. Rao CNR, Sood AK, Subrahmanyam KS, Govindaraj A. Graphene: the new two‐dimensional nanomaterial. Angew Chem Int Ed. 2009;48:7752–77.View ArticleGoogle Scholar
  3. Allen MJ, Tung VC, Kaner RB. Honeycomb carbon: a review of graphene. Chem Rev. 2009;110:132–45.View ArticleGoogle Scholar
  4. Ambrosi A, Chua CK, Bonanni A, Pumera M. Electrochemistry of graphene and related materials. Chem Rev. 2014;114:7150–88.View ArticleGoogle Scholar
  5. Chabot V, Higgins D, Yu A, Xiao X, Chen Z, Zhang J. A review of graphene and graphene oxide sponge: material synthesis and applications to energy and the environment. Energ Environ Sci. 2014;7:1564–96.View ArticleGoogle Scholar
  6. Fiori G, Bonaccorso F, Iannaccone G, Palacios T, Neumaier D, Seabaugh A, et al. Electronics based on two-dimensional materials. Nat Nanotechnol. 2014;9:768–79.View ArticleGoogle Scholar
  7. Xiong G, Meng C, Reifenberger RG, Irazoqui PP, Fisher TS. A review of graphene‐based electrochemical microsupercapacitors. Electroanal. 2014;26:30–51.View ArticleGoogle Scholar
  8. Cong H-P, Chen J-F, Yu S-H. Graphene-based macroscopic assemblies and architectures: an emerging material system. Chem Soc Rev. 2014;43:7295–325.View ArticleGoogle Scholar
  9. Wang XM, Zhang WH. Application of graphene derivatives in cancer therapy: a review. Carbon. 2014;67:795.View ArticleGoogle Scholar
  10. Jiao Y, Zheng Y, Jaroniec M, Qiao SZ. Origin of the electrocatalytic oxygen reduction activity of graphene-based catalysts: a roadmap to achieve the best performance. J Am Chem Soc. 2014;136:4394–403.View ArticleGoogle Scholar
  11. Navalon S, Dhakshinamoorthy A, Alvaro M, Garcia H. Carbocatalysis by graphene-based materials. Chem Rev. 2014;114:6179–212.View ArticleGoogle Scholar
  12. Fasolino A, Los J, Katsnelson MI. Intrinsic ripples in graphene. Nat Mater. 2007;6:858–61.View ArticleGoogle Scholar
  13. Chung D. Review graphite. J Mater Sci. 2002;37:1475–89.View ArticleGoogle Scholar
  14. Novoselov KS, Geim AK, Morozov S, Jiang D, Zhang Y, Dubonos S, et al. Electric field effect in atomically thin carbon films. Sci. 2004;306:666–9.View ArticleGoogle Scholar
  15. Loh KP, Bao Q, Ang PK, Yang J. The chemistry of graphene. J Mater Chem. 2010;20:2277–89.View ArticleGoogle Scholar
  16. Hussain S, Iqbal MW, Park J, Ahmad M, Singh J, Eom J, et al. Physical and electrical properties of graphene grown under different hydrogen flow in low pressure chemical vapor deposition. Nanoscale Res Lett. 2014;9:546.View ArticleGoogle Scholar
  17. Shen B, Ding J, Yan X, Feng W, Li J, Xue Q. Influence of different buffer gases on synthesis of few-layered graphene by arc discharge method. Appl Surf Sci. 2012;258:4523–31.View ArticleGoogle Scholar
  18. Huang Q, Kim JJ, Ali G, Cho SO. Width‐tunable graphene nanoribbons on a SiC substrate with a controlled step height. Adv Mater. 2013;25:1144–8.View ArticleGoogle Scholar
  19. Wei D, Xie L, Lee KK, Hu Z, Tan S, Chen W, et al. Controllable unzipping for intramolecular junctions of graphene nanoribbons and single-walled carbon nanotubes. Nat Commun. 2013;4:1374.View ArticleGoogle Scholar
  20. Chua CK, Pumera M. Chemical reduction of graphene oxide: a synthetic chemistry viewpoint. Chem Soc Rev. 2014;43:291–312.View ArticleGoogle Scholar
  21. Feng H, Cheng R, Zhao X, Duan X, Li J. A low-temperature method to produce highly reduced graphene oxide. Nat Commun. 2013;4:1539.View ArticleGoogle Scholar
  22. Bai S, Shen X. Graphene–inorganic nanocomposites. RSC Adv. 2012;2:64–98.View ArticleGoogle Scholar
  23. Qiu Y, Guo F, Hurt R, Külaots I. Explosive thermal reduction of graphene oxide-based materials: mechanism and safety implications. Carbon. 2014;72:215–23.View ArticleGoogle Scholar
  24. Kuila T, Mishra AK, Khanra P, Kim NH, Lee JH. Recent advances in the efficient reduction of graphene oxide and its application as energy storage electrode materials. Nanoscale. 2013;5:52–71.View ArticleGoogle Scholar
  25. Xu X, Huang D, Cao K, Wang M, Zakeeruddin SM, Grätzel M. Electrochemically reduced graphene oxide multilayer films as efficient counter electrode for dye-sensitized solar cells. Sci Rep 2013, 3, Article number: 1489:1-7.Google Scholar
  26. Chua CK, Pumera M. Reduction of graphene oxide with substituted borohydrides. J Mater Chem A. 2013;1:1892–8.View ArticleGoogle Scholar
  27. Park S, Ruoff RS. Chemical methods for the production of graphenes. Nat Nanotechnol. 2009;4:217–24.View ArticleGoogle Scholar
  28. Pham VH, Hur SH, Kim EJ, Kim BS, Chung JS. Highly efficient reduction of graphene oxide using ammonia borane. Chem Commun. 2013;49:6665–7.View ArticleGoogle Scholar
  29. Mohanty N, Nagaraja A, Armesto J, Berry V. High‐throughput, ultrafast synthesis of solution‐dispersed graphene via a facile hydride chemistry. Small. 2010;6:226–31.View ArticleGoogle Scholar
  30. Pei S, Cheng H-M. The reduction of graphene oxide. Carbon. 2012;50:3210–28.View ArticleGoogle Scholar
  31. Tung VC, Allen MJ, Yang Y, Kaner RB. High-throughput solution processing of large-scale graphene. Nat Nanotechnol. 2008;4:25–9.View ArticleGoogle Scholar
  32. Luo D, Zhang G, Liu J, Sun X. Evaluation criteria for reduced graphene oxide. The J Phy Chem C. 2011;115:11327–35.View ArticleGoogle Scholar
  33. Quintana M, Vazquez E, Prato M. Organic functionalization of graphene in dispersions. Acc Chem Res. 2012;46:138–48.View ArticleGoogle Scholar
  34. Tran DN, Kabiri S, Losic D. A green approach for the reduction of graphene oxide nanosheets using non-aromatic amino acids. Carbon. 2014;76:193–202.View ArticleGoogle Scholar
  35. Gurunathan S, Han JW, Kim E, Kwon D-N, Park J-K, Kim J-H. Enhanced green fluorescent protein-mediated synthesis of biocompatible graphene. J Nanobiotechnol. 2014;12:41.View ArticleGoogle Scholar
  36. Dhillon GS, Brar SK, Kaur S, Verma M. Green approach for nanoparticle biosynthesis by fungi: current trends and applications. Crit Rev Biotechnol. 2012;32:49–73.View ArticleGoogle Scholar
  37. Husen A, Siddiqi KS. Plants and microbes assisted selenium nanoparticles: characterization and application. J Nanobiotechnol. 2014;12:28.View ArticleGoogle Scholar
  38. Li C, Fu R, Yu C, Li Z, Guan H, Hu D, et al. Silver nanoparticle/chitosan oligosaccharide/poly (vinyl alcohol) nanofibers as wound dressings: a preclinical study. Int j Nanomedcine. 2013;8:4131–45.Google Scholar
  39. Pavlidis IV, Patila M, Bornscheuer UT, Gournis D, Stamatis H. Graphene-based nanobiocatalytic systems: recent advances and future prospects. Trends Biotechnol. 2014;32:312–20.View ArticleGoogle Scholar
  40. Esfandiar A, Akhavan O, Irajizad A. Melatonin as a powerful bio-antioxidant for reduction of graphene oxide. J Mater Chem. 2011;21:10907–14.View ArticleGoogle Scholar
  41. Zhang J, Yang H, Shen G, Cheng P, Zhang J, Guo S. Reduction of graphene oxide via L-ascorbic acid. Chem Communi. 2010;46:1112–4.View ArticleGoogle Scholar
  42. Kuila T, Bose S, Khanra P, Mishra AK, Kim NH, Lee JH. A green approach for the reduction of graphene oxide by wild carrot root. Carbon. 2012;50:914–21.View ArticleGoogle Scholar
  43. Rodríguez-León E, Iñiguez-Palomares R, Navarro RE, Herrera-Urbina R, Tánori J, Iñiguez-Palomares C, et al. Synthesis of silver nanoparticles using reducing agents obtained from natural sources (Rumex hymenosepalus extracts). Nanoscale Res Lett. 2013;8:318.View ArticleGoogle Scholar
  44. Hussain MA, Shah A, Jantan I, Tahir MN, Shah MR, Ahmed R, et al. One pot light assisted green synthesis, storage and antimicrobial activity of dextran stabilized silver nanoparticles. J Nanobiotechnol. 2014;12:53.View ArticleGoogle Scholar
  45. Khan M, Khan M, Kuniyil M, Adil SF, Al-Warthan A, Alkhathlan HZ, et al. Biogenic synthesis of palladium nanoparticles using Pulicaria glutinosa extract and their catalytic activity towards the Suzuki coupling reaction. Dalton Trans. 2014;43:9026–31.View ArticleGoogle Scholar
  46. Khan M, Khan M, Adil SF, Tahir MN, Tremel W, Alkhathlan HZ, et al. Green synthesis of silver nanoparticles mediated by Pulicaria glutinosa extract. Int J Nanomed. 2013;8:1507–16.Google Scholar
  47. Shameli K, Ahmad MB, Zamanian A, Sangpour P, Shabanzadeh P, Abdollahi Y, et al. Green biosynthesis of silver nanoparticles using Curcuma longa tuber powder. Int J Nanomed. 2012;7:5603–10.View ArticleGoogle Scholar
  48. Ghosh S, Patil S, Ahire M, Kitture R, Gurav DD, Jabgunde AM, et al. Gnidia glauca flower extract mediated synthesis of gold nanoparticles and evaluation of its chemocatalytic potential. J Nanobiotechnol. 2012;10:17.View ArticleGoogle Scholar
  49. Akhtar MS, Panwar J, Yun Y-S. Biogenic synthesis of metallic nanoparticles by plant extracts. Acs Sustain Chem Eng. 2013;1:591–602.View ArticleGoogle Scholar
  50. Mhamane D, Ramadan W, Fawzy M, Rana A, Dubey M, Rode C, et al. From graphite oxide to highly water dispersible functionalized graphene by single step plant extract-induced deoxygenation. Green Chem. 2011;13:1990–6.View ArticleGoogle Scholar
  51. Thakur S, Karak N. Green reduction of graphene oxide by aqueous phytoextracts. Carbon. 2012;50:5331–9.View ArticleGoogle Scholar
  52. Hattab F. Meswak: the natural toothbrush. J Clin Dent. 1996;8:125–9.Google Scholar
  53. Halawany HS. A review on miswak (Salvadora persica) and its effect on various aspects of oral health. Saudi Dent J. 2012;24:63–9.View ArticleGoogle Scholar
  54. Hyson Jr JM. History of the toothbrush. J Hist Dent. 2003;51:73–80.Google Scholar
  55. Migahid AM. Migahid and Hammouda's Flora of Saudi Arabia. 1978.Google Scholar
  56. Akhtar J, Siddique KM, Bi S, Mujeeb M. A review on phytochemical and pharmacological investigations of miswak (Salvadora persica Linn). J Pharm Bioallied Sci. 2011;3:113–7.View ArticleGoogle Scholar
  57. Collenette S. Illustrated guide to the flowers of Saudi Arabia. 1985.Google Scholar
  58. Alkhathlan HZ, Khan M, Abdullah MMS, Al-Mayouf AM, Mousa AA, Al-Othman ZAM. Launaea nudicaulis as a source of new and efficient green corrosion inhibitor for mild steel in acidic medium: a comparative study of two solvent extracts. Int J Electrochem Sci. 2014;9:870–89.Google Scholar
  59. Khan M, Al-Mansour MA, Mousa AA, Alkhathlan HZ. Compositional characteristics of the essential oil of Myrtus communis grown in the central part of Saudi Arabia. J Essen Oil Res. 2014;26:13–8.View ArticleGoogle Scholar
  60. Khan M, Mousa AA, Syamasundar KV, Alkhathlan HZ. Determination of chemical constituents of leaf and stem essential oils of Artemisia monosperma from central Saudi Arabia. Nat Prod Commun. 2012;7:1079–82.Google Scholar
  61. Khan M, Al-Marri AH, Khan M, Mohri N, Adil SF, Al-Warthan A, et al. Pulicaria glutinosa plant extract: a green and eco-friendly reducing agent for the preparation of highly reduced graphene oxide. RSC Adv. 2014;4:24119–25.View ArticleGoogle Scholar
  62. Dreyer DR, Todd AD, Bielawski CW. Harnessing the chemistry of graphene oxide. Chem Soc Rev. 2014;43:5288–301.View ArticleGoogle Scholar
  63. Ayan-Varela M, Paredes J, Villar-Rodil S, Rozada R, Martinez-Alonso A, Tascon J. A quantitative analysis of the dispersion behavior of reduced graphene oxide in solvents. Carbon. 2014;75:390–400.View ArticleGoogle Scholar
  64. Roppolo I, Chiappone A, Bejtka K, Celasco E, Chiodoni A, Giorgis F, et al. A powerful tool for graphene functionalization: benzophenone mediated UV-grafting. Carbon. 2014;77:226–35.View ArticleGoogle Scholar

Copyright

© Khan et al. 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

Advertisement