Fabrication of 3D Graphene and 3D Graphene Oxide Devices for Sensing VOCs
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Fabrication of 3D Graphene and 3D Graphene Oxide Devices for Sensing VOCs So Matsuyama, Tomoaki Sugiyama, Toshiyuki Ikoma, and Jeffrey S. Cross Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan ABSTRACT Detection of volatile organic compounds (VOCs) emitted from cancerous tumor cells in exhaled human breath allows for early diagnosis of various types of cancers. 3D graphene with a large surface area is considered a suitable material for creating novel sensitive VOCs sensors. In this study, 3D graphene and 3D graphene oxide were synthesized from graphene oxide suspension, hydroquinone and formaldehyde by employing polymerization and reduction. The capability of VOC gas sensing was evaluated by measuring the electrical current response in flowing N2 gas over a range of concentrations of acetone or 1-butanol at room temperature. It was observed that the device current correlated well with the VOC concentration. The adsorption of acetone decreased the current, but the adsorption of 1-butanol increased the current during sensing. 3D graphene oxide device was more sensitive than 3D graphene device because of the high concentration of oxygen-containing functional groups on the surface. These results indicated that 3D graphene and 3D graphene oxide may be the suitable materials for VOCs sensing devices. INTRODUCTION Graphene is two-dimensional (2D), one-atom-thick planar sheet with a honeycomb lattice composed of carbon atoms binding with sp2 hybridized orbital. Numerous research studies have been carried out in the fields of electronics, batteries, and sensors [1] due to its superior electric conductivity and high specific surface area-to-volume ratio. In particular, the gas sensing based on graphene and its derivatives have been widely investigated [2]. The adsorption of gas molecules on the surfaces changes its electrical conductivity due to variation of the local carrier densities. The adsorbates can be electron donors or acceptors, resulting in detectable changes in electrical conductivity [3]. For example, NH3, NO2, acetone and ethanol were employed for sensing gases [4-5]. However, it is difficult to improve sensitivity due to the limitation of contact surface area of gas molecules on a single layer of graphene. Three-dimensional (3D) graphene and its derivatives have been fabricated by a chemical vapor deposition method [6-7] and from graphene oxide (GO) as a precursor [8-10], since graphene has a limited surface area per a volume. 3D graphene has complex porous structures and high electric conductivities, of which properties are applicable for not only gas sensor, but also solar cells without Pt based electrodes [11]. The interconnected pores in the aerogel structure act as a diffusion path of gas molecules, which has been applicable for NO2 gas sensing [12-13]. Volatile organic compounds (VOCs) emitted from the human body have been identified by ion flow tube mass spectrometry [14] and gas chromatography mass spectrometry [15]. There are
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