The detection and control of ethanol found in most consumer goods is essential due to its side effects such as skin irritation and nasal mucous membrane inflammation. Several ethanol detection methods have been applied such as the use of plastic optical fiber sensors which have outperformed traditional sensors. Enhanced interaction between light propagation and the sensing layer in the fiber core is one way to improve the performance of optical fiber sensors. Nanostructured materials such as graphene oxide and carbon nanotubes have been found to improve the sensor performance. Uncladded plastic optical fibers have recently gained interest due to their flexibility and simplicity among other properties. Researchers observe that there are promising opportunities in ethanol sensing applications by examining sensing characteristics of graphene oxide and carbon nanotube coatings on uncladded plastic optical fibers.
Dr. Yaacob and colleagues at Universiti Putra Malaysia developed an ethanol sensor based on uncladded plastic optical fibers coated with carbon nanotubes and graphene oxide, and achieved results at room temperature indicating high efficiency of plastic optical fibers over conventional ethanol sensors. Their work is now published in Optics Express.
The proposed uncladded plastic optical fiber ethanol sensor was fabricated using a fluorinated polymer cladding and a multimode plastic optical fiber. The cladding was removed using sandpaper, acetone, and deionized water. Carbon nanotubes were formed by adding raw carbon nanotubes into sulfuric acid to obtain carbon nanotubes with different carboxyl contents and this layer was deposited onto the uncladded plastic optical fiber through drop-casting technique. For comparison purposes, graphene oxide nanomaterial was formed using Hummer’s method and drop-casted on the uncladded plastic optical fiber.
The authors investigated the optical response towards different ethanol concentrations of the uncladded plastic optical fiber sensor, based on graphene oxide and carbon nanotubes to check on their sensing performances. The research team found out that the dynamic response as well as the recovery times of the carbon nanotube based sensor, increased proportionally with the ethanol concentration, as a result of the interaction between ethanol molecules and adsorbed oxygen ions. On the other hand, the graphene oxide-based sensor exhibited limited response and recovery times at ethanol concentrations below 60 percent.
Further, the authors showed that the carbon nanotube-based sensor exhibited 4 times higher sensitivity as compared with the graphene oxide-based sensor towards ethanol concentrations. The enhancement of the sensitivity of the carbon nanotube-based sensor is as a result of its porous surface that provides a large surface area for the adsorption of ethanol molecules which penetrate its sensing layer to interact with the fleeting wave. This is not the case with the graphene oxide-based sensor because its surface roughness is five times less than that of the carbon nanotube-based sensor.
Carbon nanotube-based sensor attained lower resolution limit as compared with graphene oxide based sensor. Further, the sensitivity of the carbon nanotube-based sensor shows no visible saturation at elevated ethanol concentrations and as such can be regarded as ideal and reliable for practical use. The research team also demonstrated that carbon nanotube-based sensor has significant selectivity to ethanol as compared with other analytes and is therefore recommended for ethanol detection in industrial fields.
A.L. Khalaf, P.T. Arasu, H.N. Lim, S. Paiman, N.A. Yusof, M.A. Mahdi, M.H. Yaacob. Modified plastic optical fiber with CNT and graphene oxide nanostructured coatings for ethanol liquid sensing. Optics Express, 2017, 5, 5509-5520.Go To Optics Express