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1205-L01-05

Generation and Capture of CO2 and CO in Graphite Oxide Stacks during Thermal Reduction Muge Acik, Rodolfo Guzman and Yves J. Chabal* Laboratory for Surface and Nanostructure Modification, Department of Materials Science and Engineering, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080-3021, U.S.A.

ABSTRACT Infrared spectroscopy is used to monitor the evolution of CO2 (2330-2350 cm-1) and CO (2050-2200 cm-1) generated during thermal reduction of graphite oxide. The appearance of CO2 at low temperatures (≤200°C) is associated with oxygen removal in species such as anhydrides, esters, lactols, carboxylic acids and lactones either at the edges or in the distorted basal plane of the GO sheets. At higher temperatures (250°C-750°C), release of CO is observed and may be due to decomposition of CO2 or oxygen-containing species like ethers, carbonyls, phenols or quinones. Observation of these gases is possible in multilayer GO because they are trapped in between the interlayer spacing of GO stacks for a time sufficient for detection.

INTRODUCTION The gap between graphitic plates (3.35 Å) allows insertion and intercalation of a wide range of species such as ions [1], nanoparticles [2], metals [3] and polymers [4] either chemically [5] or electrochemically [6]. For instance, natural graphite can be exfoliated to graphene stacks by supercritical CO2 processing technique, which forms CO2-intercalated graphite and the expansion of graphitic layers due to the thermal expansion of trapped CO2 in between the layers [7]. Modeling and simulation results of Tenney et.al have shown that there is an increase in CO2 adsorption when the surface density of oxygen containing species is increased. They have also shown that CO2 is adsorbed preferably above defective sites [8]. Release of CO2 is exothermic and more favorable at low temperatures during oxidation of CO species (e.g. carbonyls) at graphene edges, as shown by Paul et.al using a combination of statistical thermodynamics and density functional theory calculations [9]. Carboxylic acids, esters, lactols, lactones, anhydrides, peroxides evolve as CO2 while phenols, hydroquinones, carbonyls, quinones and ethers evolve in the form of CO [10]. Evolution of CO2 and CO species was also observed by Boudou et.al from surface treatment of carbon fibers with oxygen plasma [11]. Walker et.al has also described a Langmuir-Hinshelwood two-step mechanism for the decomposition of CO2 to chemisorbed species and CO during natural graphite gasification [12]. Mechanically milled FeO powder (wustite) decomposes CO2 into graphite producing non-equilibrium state and amorphous carbon at 773K while unmilled FeO powder reduced CO2 to CO upon 180 minute heating on an alumina boat [13].

The interaction of CO2 with carbon has also been studied for sensing applications, by functionalizing carbon nanotubes for instance [14]. Sensing of CO2 is crucial for especially biological applications due to significant production of CO2 in reactions and the necessity of its remova