Abstract
Few studies have investigated the gas-sensing properties of graphene oxide/titanium dioxide (GO/TiO2) composite combined with photocatalytic effect. Room temperature gas-sensing properties of the GO/TiO2 composite were investigated towards various reducing gases. The composite sensor showed an enhanced gas response and a faster recovery time than a pure GO sensor due to the synergistic effect of the hybridization, such as creation of a hetero-junction at the interface and modulation of charge carrier density. However, the issue of long-term stability at room temperature still remains unsolved even after construction of a composite structure. To address this issue, the surface and hetero-junction of the GO/TiO2 composite were engineered via a UV process. A photocatalytic effect of TiO2 induced the reduction of the GO phase in the composite solution. The comparison of gas-sensing properties before and after the UV process clearly showed the transition from n-type to p-type gas-sensing behavior toward reducing gases. This transition revealed that the dominant sensing material is GO, and TiO2 enhanced the gas reaction by providing more reactive sites. With a UV-treated composite sensor, the function of identifying target gas was maintained over a one-month period, showing strong resistance to humidity.
Highlights
A gas sensor is a device that identifies the presence and amount of target gases
The morphology of the hybridized graphene oxide (GO) nanoflakes and TiO2 nanoparticles was observed by scanning electron microscope (SEM)
The room temperature gas-sensing performance of the GO/TiO2 composite prepared on flexible polymeric film was enhanced by the effect of photocatalysis of TiO2 under UV
Summary
A gas sensor is a device that identifies the presence and amount of target gases. The detection of gas molecules is extremely important for many purposes—such as environmental monitoring, air and water quality control, agricultural condition monitoring, and food safety— to prevent disastrous accidents from gas emission, normally as part of a safety system [1,2,3]. By combining ubiquitous computing and smart textile technology, a high performance sensor with wearability has been developed to be adapted in various applications such as the health care system [6,7]. To advance wearable gas sensors, various chemiresistive materials have been explored. Metal oxides such as SnO2 , ZnO, and TiO2 have been utilized in chemiresistive sensors due to their numerous merits such as low cost, stability, short response time, and long lifetime [8,9]. Since metal oxide sensors operate at high working temperatures, such sensors are improper for wearable electronics [10]. In accordance with wearable applications, Sensors 2018, 18, 3334; doi:10.3390/s18103334 www.mdpi.com/journal/sensors
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