Applied Surface Science 301 (2014) 183–188 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Pulsed laser irradiation for environment friendly reduction of graphene oxide suspensions Ehsan Ezzatpour Ghadim a , Nasim Rashidi b , Salimeh Kimiagar b , Omid Akhavan c,d,∗ , Firouzeh Manouchehri e , Elham Ghaderi f a Young Researchers and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran 13185-768, Iran b Department of Physic, Azad University, Central Tehran Branch (IAUCTB), Tehran 14676-6831, Iran c Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Iran d Institute for Nanoscience and Nanotechnology, Sharif University of Technology, P.O. Box 14588-89694, Tehran, Iran e Department of Chemistry, Azad University, Central Tehran Branch (IAUCTB), Tehran 14676-6831, Iran f Nanobiotechnology Research Lab., Division of Advanced Materials, Azadi Ave., Tehran, Iran a r t i c l e i n f o Article history: Received 5 November 2013 Received in revised form 4 February 2014 Accepted 8 February 2014 Available online 18 February 2014 Keywords: Graphene Nanostructures Pulsed laser irradiation Green synthesis a b s t r a c t Graphene oxide (GO) sheets were synthesized through a modified Hummers’ method. Using high resolu- tion transmission electron microscopy the thickness of the GO sheets in a multilayer structure of stacked GO sheets was found ∼0.8 nm. A nanosecond pulsed laser (with wavelength of 532 nm and average power of 0.3 W) was applied for effective and environment friendly reduction of the GO sheets in an ammonia solution (pH ∼9) at room temperature conditions. The deoxygenation of the GO sheets by the pulsed laser reduction method was confirmed by using UV–visible, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS) and thermo gravimetric analysis. Based on XPS analysis, the O/C ratio of the GO sheets decreased from 49% to 21% after 10 min laser irradiation. This reduction efficiency was comparable with the efficiency achieved by hydrazine which yielded the O/C ratio of 15% at 80 ◦ C after 10 min. Using Raman spectroscopy it was found that the pulsed laser reduction method resulted in nearly no aggregation of the reduced GO sheets in the ammonia solution. These results can help to further promotion and application of pulsed lasers in environment friendly reduction of GO. © 2014 Elsevier B.V. All rights reserved. Introduction Graphene (as a single atomic layer with sp 2 -hybridized carbon atoms in a perfect hexagonal lattice structure) has opened up the possibility of enormous progresses in various fundamental [1–6] and technological [7–13] areas. Hence, environment friendly mass production [14] and consequently high consumption of graphene (especially in bio-nanotechnological fields such as nanomedicine [15,16]) is highly demanded in soon future. One of the most usual methods for mass production of graphene is chemical exfolia- tion of graphite followed by reduction of the obtained graphene oxide (GO) sheets into reduced graphene oxide (rGO) ones [17–21]. In fact, the graphene oxide synthesized by this method usually contains epoxide and hydroxyl groups on their basal plane, and car- bonyl as well as carboxyl groups on their edges [22]. Although, the ∗ Corresponding author at: Department of Physics, Sharif University of Technol- ogy, P.O. Box 11155-9161, Tehran, Iran. Tel.: +98 21 66164566; fax: +98 21 66022711. E-mail address: oakhavan@sharif.edu (O. Akhavan). chemically synthesized GO sheets show high water-dispersibility, we often require a subsequent reduction to obtain rGO sheets with, e.g., much better electrical conductivity (∼five orders of magni- tude [23]). At first, GO sheets were reduced by strong chemical reductants such as hydrazine (N 2 H 4 ) [24] and sodium borohy- dride (NaBH 4 ) [25] and/or heating in a reducing ambient [26,27]. However, the high temperatures needed in the thermal reductions (usually >500 ◦ C) restrict applications of this method. On the other hand, the strong chemical reductants, e.g. hydrazine, are known as hazardous agents for human’s life and environment. For instance, hydrazine exhibits highly corrosive, explosive and toxic properties [28]. In addition, reduction by hydrazine resulted in formation of sp 3 C–N bonds as disorders on surface of the reduced sheets. Such disorders prevent obtaining graphene sheets with high electrical conductivities [29]. Therefore, achieving environment friendly as well as effective low-temperature methods for reduction of GO is highly demanded, especially in mass production of graphene. So far, some environment friendly methods for reduction of GO such as flash photo reduction [30], hydrothermal dehydration [31], solvothermal reduction [32], catalytic [33] and photocatalytic http://dx.doi.org/10.1016/j.apsusc.2014.02.036 0169-4332/© 2014 Elsevier B.V. All rights reserved.