The synthesis of graphene materials is typically carried out by oxidizing graphite to graphite oxide followed by a reduction process. Numerous methods exist for both the oxidation and reduction steps, which causes unpredictable contamination from metallic impurities into the final material. These impurities are known to have considerable impact on the properties of graphene materials. We synthesized several reduced graphene oxides from extremely pure graphite using several popular oxidation and reduction methods and tracked the concentrations of metallic impurities at each stage of synthesis. We show that different combinations of oxidation and reduction introduce varying types as well as amounts of metallic elements into the graphene materials, and their origin can be traced to impurities within the chemical reagents used during synthesis. These metallic impurities are able to alter the graphene materials' electrochemical properties significantly and have wide-reaching implications on the potential applications of graphene materials.

Central Analytical Laboratory Institute of Organic Chemistry and Biochemistry of the Academy of Sciences of the Czech Republic 166 10 Prague 6 Czech Republic

Department of Inorganic Chemistry Institute of Chemical Technology 166 28 Prague 6 Czech Republic;

Department of Nuclear Spectroscopy Nuclear Physics Institute of the Academy of Sciences of the Czech Republic 250 68 Řež Czech Republic; and

Division of Chemistry and Biological Chemistry School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371;

Zobrazit více v PubMed

Geim AK, Novoselov KS. The rise of graphene. Nat Mater. 2007;6(3):183–191. PubMed

Novoselov KS, et al. Electric field effect in atomically thin carbon films. Science. 2004;306(5696):666–669. PubMed

Pumera M. Graphene-based nanomaterials and their electrochemistry. Chem Soc Rev. 2010;39(11):4146–4157. PubMed

Gomez De Arco L, et al. Continuous, highly flexible, and transparent graphene films by chemical vapor deposition for organic photovoltaics. ACS Nano. 2010;4(5):2865–2873. PubMed

Pumera M. Graphene-based nanomaterials and their electrochemistry. Energy Environ Sci. 2010;4(3):668–674. PubMed

Stoller MD, Park S, Zhu Y, An J, Ruoff RS. Graphene-based ultracapacitors. Nano Lett. 2008;8(10):3498–3502. PubMed

Stankovich S, et al. Graphene-based composite materials. Nature. 2006;442(7100):282–286. PubMed

Liu Z, Robinson JT, Sun X, Dai H. PEGylated nanographene oxide for delivery of water-insoluble cancer drugs. J Am Chem Soc. 2008;130(33):10876–10877. PubMed PMC

Feng L, Liu Z. Graphene in biomedicine: Opportunities and challenges. Nanomedicine (Lond) 2011;6(2):317–324. PubMed

Rogers JA. Electronic materials: Making graphene for macroelectronics. Nat Nanotechnol. 2008;3(5):254–255. PubMed

IUPAC . Compendium of Chemical Terminology (The “Gold Book”) 2nd Ed. Oxford: Blackwell; 1997.

Lee S, Eom SH, Chung JS, Hur SH. Large-scale production of high-quality reduced graphene oxide. Chem Eng J. 2013;233:297–304.

Brodie BC. On the atomic weight of graphite. Philos Trans R Soc Lond B Biol Sci. 1859;149:249–259.

Staudenmaier L. Verfahren zur Darstellung der Graphitsäure. Ber Dtsch Chem Ges. 1898;31(2):1481–1487.

Hofmann U, König E. Untersuchungen über Graphitoxyd. Z Anorg Allg Chem. 1937;234(4):311–336.

Hofmann U, Holst R. Über die Säurenatur und die Methylierung von Graphitoxyd. Ber Dtsch Chem Ges. 1939;72(4):754–771.

Hummers WS, Jr, Offeman RE. Preparation of graphitic oxide. J Am Chem Soc. 1958;80(6):1339.

Zhou M, et al. Controlled synthesis of large-area and patterned electrochemically reduced graphene oxide films. Chemistry. 2009;15(25):6116–6120. PubMed

Kumar P, Subrahmanyam KS, Rao CNR. Graphene produced by radiation-induced reduction of graphene oxide. Int J Nanosci Ser. 2011;10(04n05):559–566.

Stankovich S, et al. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon. 2007;45(7):1558–1565.

Shin HJ, et al. Efficient reduction of graphite oxide by sodium borohydride and its effect on electrical conductance. Adv Funct Mater. 2009;19(12):1987–1992.

Ambrosi A, Chua CK, Bonanni A, Pumera M. Lithium aluminum hydride as reducing agent for chemically reduced graphene oxides. Chem Mater. 2012;24(12):2292–2298.

Zhu C, Guo S, Fang Y, Dong S. Reducing sugar: New functional molecules for the green synthesis of graphene nanosheets. ACS Nano. 2010;4(4):2429–2437. PubMed

Wang Y, Shi Z, Yin J. Facile synthesis of soluble graphene via a green reduction of graphene oxide in tea solution and its biocomposites. ACS Appl Mater Interfaces. 2011;3(4):1127–1133. PubMed

Chua CK, Pumera M. Chemical reduction of graphene oxide: A synthetic chemistry viewpoint. Chem Soc Rev. 2014;43(1):291–312. PubMed

Hu FM, Ma T, Lin H-Q, Gubernatis JE. Magnetic impurities in graphene. Phys Rev B Condens Matter. 2011;84(7):075414.

Krasheninnikov AV, Nieminen RM. Attractive interaction between transition metal atom impurities and vacancies in graphene: A first-principles study. Theor Chem Acc. 2011;129(3-5):625–630.

Ambrosi A, et al. Metallic impurities in graphenes prepared from graphite can dramatically influence their properties. Angew Chem Int Ed Engl. 2012;51(2):500–503. PubMed

Ambrosi A, et al. Chemically reduced graphene contains inherent metallic impurities present in parent natural and synthetic graphite. Proc Natl Acad Sci USA. 2012;109(32):12899–12904. PubMed PMC

Sljukić B, Banks CE, Compton RG. Iron oxide particles are the active sites for hydrogen peroxide sensing at multiwalled carbon nanotube modified electrodes. Nano Lett. 2006;6(7):1556–1558. PubMed

Banks CE, Crossley A, Salter C, Wilkins SJ, Compton RG. Carbon nanotubes contain metal impurities which are responsible for the “electrocatalysis” seen at some nanotube-modified electrodes. Angew Chem Int Ed Engl. 2006;45(16):2533–2537. PubMed

Batchelor-McAuley C, Wildgoose GG, Compton RG, Shao L, Green MLH. Copper oxide nanoparticle impurities are responsible for the electroanalytical detection of glucose seen using multiwalled carbon nanotubes. Sens Actuators B Chem. 2008;132(1):356–360.

Dai X, Wildgoose GG, Compton RG. Apparent ‘electrocatalytic’ activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: Occluded copper nanoparticles. Analyst (Lond) 2006;131(8):901–906. PubMed

Ambrosi A, Pumera M. Regulatory peptides are susceptible to oxidation by metallic impurities within carbon nanotubes. Chemistry. 2010;16(6):1786–1792. PubMed

Pumera M, Ambrosi A, Chng ELK. Impurities in graphenes and carbon nanotubes and their influence on the redox properties. Chem Sci. 2012;3:3347–3355.

Guo L, et al. Iron bioavailability and redox activity in diverse carbon nanotube samples. Chem Mater. 2007;19(14):3472–3478.

Liu X, et al. Bioavailability of nickel in single-wall carbon nanotubes. Adv Mater. 2007;19(19):2790–2796.

Tian X, et al. Metal impurities dominate the sorption of a commercially available carbon nanotube for Pb(II) from water. Environ Sci Technol. 2010;44(21):8144–8149. PubMed

Hou P-X, Liu C, Cheng H-M. Purification of carbon nanotubes. Carbon. 2008;46(15):2003–2025.

Pumera M. Carbon nanotubes contain residual metal catalyst nanoparticles even after washing with nitric acid at elevated temperature because these metal nanoparticles are sheathed by several graphene sheets. Langmuir. 2007;23(11):6453–6458. PubMed

International Union of Pure and Applied Chemistry Isotopic and nuclear analytical techniques in biological systems: A critical study. Part IX. Neutron activation analysis. Pure Appl Chem. 1995;67(11):1929–1941.

IAEA . Use of Research Reactors for Neutron Activation Analysis (IAEA-TECDOC-1215) Vienna: IAEA; 2001.

Panich AM, Shames AI, Aleksenskii AE, Dideikin A. Magnetic resonance evidence of manganese–graphene complexes in reduced graphene oxide. Solid State Commun. 2012;152(6):466–468.

Paratala BS, Jacobson BD, Kanakia S, Francis LD, Sitharaman B. Physicochemical characterization, and relaxometry studies of micro-graphite oxide, graphene nanoplatelets, and nanoribbons. PLoS ONE. 2012;7(6):e38185. PubMed PMC

Panich AM, Shames AI, Sergeev NA. Paramagnetic impurities in graphene oxide. Appl Magn Reson. 2013;44(1-2):107–116.

Wang L, Ambrosi A, Pumera M. “Metal-free” catalytic oxygen reduction reaction on heteroatom- doped graphene is caused by trace metal impurities. Angew Chem Int Ed Engl. 2013;52(51):13818–13821. PubMed

Kumar R, Suresh VM, Maji TK, Rao CNR. Porous graphene frameworks pillared by organic linkers with tunable surface area and gas storage properties. Chem Commun (Camb) 2014;50(16):2015–2017. PubMed

Sil S, Kuhar N, Acharya S, Umapathy S. Is chemically synthesized graphene ‘really’ a unique substrate for SERS and fluorescence quenching? Sci Rep. 2013;3:3336. PubMed PMC

Park S, et al. Hydrazine-reduction of graphite- and graphene oxide. Carbon. 2011;49(9):3019–3023.

Wong CHA, Chua CK, Khezri B, Webster RD, Pumera M. Graphene oxide nanoribbons from the oxidative opening of carbon nanotubes retain electrochemically active metallic impurities. Angew Chem Int Ed Engl. 2013;52(33):8685–8688. PubMed

Adekunle AS, Ozoemena KI. Insights into the electro-oxidation of hydrazine at single-walled carbon-nanotube-modified edge-plane pyrolytic graphite electrodes electro-decorated with metal and metal oxide films. J Solid State Electrochem. 2008;12(10):1325–1336.

Abbaspour A, Khajehzadeh A, Ghaffarinejad A. Electrocatalytic oxidation and determination of hydrazine on nickel hexacyanoferrate nanoparticles-modified carbon ceramic electrode. J Electroanal Chem (Lausanne Switz) 2009;631(1-2):52–57.

Ohta T, Bostwick A, Seyller T, Horn K, Rotenberg E. Controlling the electronic structure of bilayer graphene. Science. 2006;313(5789):951–954. PubMed

Xue M, et al. Superconductivity in potassium-doped few-layer graphene. J Am Chem Soc. 2012;134(15):6536–6539. PubMed

Lv YA, Zhuang GL, Wang JG, Jia YB, Xie Q. Enhanced role of Al or Ga-doped graphene on the adsorption and dissociation of N2O under electric field. Phys Chem Phys. 2011;13(27):12472–12477. PubMed

Ao ZM, Yang J, Li S, Jiang Q. Enhancement of CO detection in Al doped graphene. Chem Phys Lett. 2008;461(4-6):276–279.

Cohen-Tanugi D, Grossman JC. Water desalination across nanoporous graphene. Nano Lett. 2012;12(7):3602–3608. PubMed

WHO . Guidelines for Drinking-Water Quality. 4th Ed. Geneva: WHO; 2011.

De Corte F, Simonits A. Vade Mecum for k0 Users. Geleen, The Netherlands: DMS Research; 1994.

Kubešová M, Kučera J, Fikrle M. A new monitor set for the determination of neutron flux parameters in short-time k0-NAA. Nucl Instrum Methods Phys Res A. 2011;656(1):61–64.

Kubešová M, Krausová I, Kučera J. Verification of k0-NAA results at the LVR-15 reactor in Řež with the use of Au+Mo+Rb(+Zn) monitor set. J Radioanal Nucl Chem. 2014;300(2):473–480.

MacDonald AMG. The oxygen flask method. A review. Analyst. 1961;86(1018):3–12.