Influência da composição química do óxido de grafeno nas propriedades de detecção de sensores de umidade

Abstract

Graphene oxide (GO), a two-dimensional carbon nanomaterial with a highly functionalized and defect-free structure, has attracted great interest for the development of relative humidity (RH) sensors due to the abundant presence of oxygenated groups (OFGs) in its structure. GO characteristics, such as degree of oxidation, flake size, basal plane defects, and chemical composition, directly influence its sensing properties. In this study, resistive RH sensors fabricated with three GO variations (GO-I, GO-II, and GO-III) were analyzed. These sensors were obtained by different modifications of the Hummers method, resulting in distinct functional group distributions and levels of structural disorder. The GO samples were extensively characterized by spectroscopic (UV-Vis, FTIR, Raman, XPS), morphological (SEM and AFM), structural (XRD), and electrical techniques, allowing the correlation between structure, OFGs, and sensory performance. The devices were fabricated by depositing GO suspensions onto thermally evaporated aluminum interdigitated electrodes (IDEs) on glass substrates. Among the sensors analyzed, the GOII-based device showed the best performance, with a sensitivity of 2113 ± 2%, surpassing that based on GO-I (1592 ± 1%) and GO-III (388.1 ± 0.1%). All sensors demonstrated fast response and recovery times, on the order of 2 and 3 seconds, respectively. The results indicate that the high concentration of highly polar OFGs, such as carbonyl and hydroxyl groups, together with permanent structural defects in GO-II, was decisive for the significant improvement in the humidity response. Furthermore, the sensors can operate at low voltage (0.1 V) and exhibit high linearity (>95), highlighting their potential for applications in systems that demand both energy savings and accurate measurements.