High-response humidity sensing with graphene oxide/lignosulfonate and laser-induced graphene for respiratory health†

Abstract

Most current commercial humidity sensors rely on precious metals and chemicals. In this study, alkali lignin produced in the paper industry was utilized to form a film with hydroxyethyl cellulose to generate laser-induced graphene (LIG) as an electrode material for a sensor by the laser-induction technique. LIG exhibits excellent conductivity, and the experimental results demonstrate that its resistivity can be adjusted by laser power without the necessity for additional conductive materials. A solution comprising a blend of graphene oxide and sodium lignosulfonate was introduced to the LIG surface in a dropwise manner, thereby establishing a sensing surface. This process resulted in the introduction of hydrophilic groups, including carboxyl, phenolic hydroxyl, and sulfonic acid. The integration of these hydrophilic groups enhanced the surface's sensitivity to humidity, thereby facilitating the precise capture of alterations in ambient air humidity. The humidity sensor, which employs alkali lignin and lignin laser-induced graphene as electrodes and graphene oxide (GO) as the humidity-sensitive layer, exhibits an exceptionally high degree of sensitivity to humidity. The response reached 42.74 (R_RH/R₀) at 80% relative humidity and 133.96 (R_RH/R₀) at 90% humidity with a sensitivity of 147.73%/% RH. Moreover, the sensor displays an impressively brief recovery period, which remains unaltered even after multiple cycles. Additionally, the humidity sensor exhibits excellent stability for a period of up to 30 days. This study has successfully developed a simple and efficient method for preparing graphene, and has produced a flexible resistive sensor with high sensitivity, repeatability, and stability, thereby opening up new avenues for the high-value utilisation of lignin.