Accelerated Thermal Decomposition of Graphene Oxide Films in Air via in Situ X‑ray Diffraction Analysis Qin Pan, † Ching-Chang Chung, ‡ Nanfei He, † Jacob L. Jones,* ,‡ and Wei Gao* ,† † Department of Textile Engineering, Chemistry & Science, College of Textiles, and ‡ Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States * S Supporting Information ABSTRACT: Thermal decomposition of graphene oxide (GO) has been extensively investigated in the past decade, but the detailed reaction kinetics remains elusive so far. Here we employ an in situ X-ray diffraction (XRD) analysis to clarify the kinetics of GO decomposition in different atmospheres and sample morphologies. The XRD peak (002), which is the major diffraction peak corresponding to the interlayer distance in GO samples, shifted from 11.5° to 23° along with significant decrease in intensity when samples were heated from 25 to 350 °C. The decomposition in air exhibits a higher reaction rate compared with that in pure nitrogen gases because the O 2 molecules in air facilitate the oxidation of carbon atoms, leading to the evolution of CO and CO 2 . Free-standing films of GO also decompose significantly faster than GO powders, owing to their slower heat dissipation into the environment and higher thermal conductivity within the well-stacked lamella. This study has provided new insights into the reaction kinetics of GO thermal decomposition and offered a novel perspective on kinetic analysis based on our in situ XRD technique. ■ INTRODUCTION Graphene, a monolayer of sp 2 carbon atoms, has shown excellent performance in transistors, sensors, supercapacitors, and solar cells due to its excellent electrical, optical, thermal, and mechanical properties. 1-6 A lot of effort has been made toward the large-scale production of graphene through various approaches after it was first exfoliated from graphite, among which conversion of graphene oxide (GO) has attracted enormous attention due to its large scale accessibility and versatility. 7-10 GO, typically made via chemical oxidation of graphite, 11 is a nonstoichiometric compound, with oxygenated groups, such as hydroxyl, epoxy, ester, lactol, and carboxyl groups, attached on the surfaces and peripheries of the basal planes. 12,13 When dispersed in water, GO hydrolyzes and bares negative charges on its surface; thus, GO flakes are well exfoliated into single layers. 14 Chemical reduction of GO dispersion along with some surfactants can lead to large quantities of monolayer graphene in water, which is hardly available through any other protocols. 15-17 In addition, thermal conversion of GO back to graphene also attracted considerable attention since it is a facile and nontoxic process with great potential in lowering the cost of graphene production. 18-21 GO decomposes easily upon heating, resulting in the loss of oxygenated groups and the evolution of H 2 O, CO, and CO 2 . 12,22,23 However, all of the reported conversions only result in partial recovery of the sp 2 carbon lattice, and the conversion mechanisms remain elusive. 7,24 The extent of GO conversion to graphene can be characterized by the color, microscale morphology, carbon-to- oxygen (C/O) ratio, electrical conductivity, and dispersibility of the resulted products. 7 These analyses can offer detailed information on structural changes in GO before and after decomposition but are quite limited in providing a dynamic scheme of the reaction. In situ characterization techniques can observe the entire reaction process directly and would therefore be able to collect real-time data for mechanistic and kinetic studies. However, very few studies have been reported to date on GO decomposition via in situ analysis techniques. Sampath Received: May 18, 2016 Revised: June 18, 2016 Article pubs.acs.org/JPCC © XXXX American Chemical Society A DOI: 10.1021/acs.jpcc.6b05031 J. Phys. Chem. C XXXX, XXX, XXX-XXX