Humidity sensor based on reduced graphene oxide/lignosulfonate composite thin-film

Lignosulfonate (LS), an aromatic polymer with massive hydrophilic groups from biomass, has been firstly developed as sensitive material for detecting environmental humidity. Using LS as moisture sensing layers and additive reduced graphene oxide (rGO) as resistant transduction layers, an rGO/LS composite thin-film has been prepared as humidity sensor through a cost-effective approach. Here we demonstrate that the three-dimensional molecular structure and amphiphilic behavior of LS enable ultrahigh sensitivity to the degree of moisture. The maximum response of 3 wt% rGO/LS thin-film reaches up to 298% for 97% relative humidity, which is nearly 4 orders of magnitude than that of pure rGO thin-film. Moreover, the rGO/LS thin-film can be used as a humidity sensor with large response, low hysteresis and stable repeatability in broad relative humidity ranging from 22% to 97%. This opens the door to various applications, such as flexible touchless interfaces, which we presented with a respiratory frequency transducer. The low cost, simple designed and portable used humidity sensor highlights the potential application of lignin as high-valued materials.