Gas Sensing Behaviors of Combinatorial Structures of Graphene Oxide and ZnO

Nanoscale materials are outstanding candidates for gas-sensing elements due to extremely high surface-to-volume ratio [1]. Their unique and attractive properties can lead to novel sensors that have advantages of fast reaction speed and sensitivity, ease of miniaturization, minimum power consumption, and low cost. Recently, the expansion of gas sensor applications to medical diagnosis, wearable electronics would demand operation at room temperature and convenient fabrication of the sensors on various substrates [2].

Nanostructured metal oxides such as tin oxide, zinc oxide, and graphene oxide have been demonstrated as gas sensing materials with their excellent semiconducting properties. However, the sensitivity and selectivity of the metal oxide-based gas sensors may not be sufficient for a wide range of applications. To overcome the limitations, combined graphene oxide and ZnO based sensor has been attempted by making ZnO as catalyst nanoparticles [3,4]. Such hybrid structure may present potential benefits, but the methods to construct combined structure of graphene oxide and ZnO are rarely found in the literature. Therefore, we investigate the design and fabrication of the combinatorial structure from two nanomaterials of graphene oxide and ZnO.

Combinatorial structures of graphene oxide and ZnO have been performed via chemical and physical deposition methods to form layer by layer structure. Hierarchical oxide nanostructures consisting of graphene oxide flakes and ZnO nanorods were also fabricated by using electrochemical deposition. Gas sensing performance of individual graphene oxides and ZnO nanorods was shown in Fig. 1. Graphene oxide can sense various gases at room temperature, but ZnO nanorods can perform at room temperature with an aid of external energy such as UV. Thus chemical modification of ZnO nanorods was performed to achieve room temperature operation. It was also found that sensing performance of graphene oxide was strongly dependent on surface conditions or reduction of graphene oxide. Thermal reduction of deposited graphene oxide resulted in the change of reduction degree. The increase of thermal reduction temperature enabled transformation from graphene oxide (GO) to reduced graphene oxide (r-GO) as confirmed by FTIR and Raman in Fig.2. Such change also showed n-p transition of sensing behaviors. This study will present systematic investigation of nanostructured graphene oxide and ZnO for combinatorial structure. The strategies to construct combinatorial structures and their sensing behaviors in conjunction with sensing mechanisms are discussed in detail.

This research was supported by Agency for Defense Development (ADD) as global corporative research for direct urine fuel cell and a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology.

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