Carboxyl Graphene Oxide Functionalized Cotton Textile with Superwettable Patterns for Humidity Sensing

In this study, a carboxyl-modified graphene oxide (GO–COOH) was prepared and deposited into flexible superwettable patterned cotton (SPC) for humidity sensing. The morphology of the as-prepared electronic-SPC (ESPC) was characterized by field emission scanning electron microscopy (FESEM). The carboxylation process was investigated by comparing the chemical properties of GO–COOH and the unmodified GO via X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, and Raman. The as-prepared ESPC was then applied for humidity sensing for the first time, whereby the GO–COOH impregnated into the superwettable patterns of SPC played an important role. The as-prepared ESPC processed a high sensitivity for humidity sensing with a quite short response time (less than 1 s at ΔRH of 60%) and the output current increased with increasing relative humidity (ΔRH). The output current was affected by the thickness of the GO–COOH layer, which could be controlled by varying the effective area (diameter of the dots) as well as the loading amount (concentration of GO–COOH). The as-prepared ESPC showed high stability and durability whereby the output current did not show a significant change after overnight washing. Meanwhile, the high flexibility of ESPC was confirmed by the bending test, and results showed that it could maintain an output current of 25 nA even after 2000 bending cycles. The high performance noncontact ESPC was further applied in human breathing sensing test and the results showed that the ESPC could be a promising material for wearable health monitoring.