Carbon Nanotubes/Graphene Oxide Composite Applications in Fiber RH Sensor

We propose a high-sensitivity optical fiber relative humidity (RH) sensor based on multiwalled carbon nanotubes (MWCNTs)/graphene oxide (GO) composite, which functions as the humidity-sensitive film. The optical component of this demonstrated sensor is a single-mode fiber-solid core fiber-single-mode fiber-based multimode interference structure. For the composite sensitive film, GO is used as a dispersant for two types of MWCNTs with different lengths. Subsequently, GO-dispersed MWCNT hybrid films are formed on fiber surfaces by the dip-coating method. Herein, the hydroxylated MWCNTs can function as supporting structures to avoid the formation of layer-by-layer stacked GO, and this destacking humidity-sensitive film is beneficial to enhance water molecules' absorptive capacity. To clarify the principle, the interaction between composite humidity-sensitive film and water molecules is investigated. The experimental results reveal that the interference fringe shows a redshift with the increase in RH. When RH changing from 40% to 90%, the sensor probe with long-range MWCNT-based film has higher sensitivity than that with short-range MWCNT-based film, which demonstrates the effect of the supporting action of MWCNTs. Besides, a larger specific surface area and pore size of long-range GO-MWCNTs benefit sensitivity enhancement. In addition, this proposed sensor has good repeatability, stability, and a large linear measurement range (40% RH-90% RH).