Cellulose acetate and reduced graphene oxide (rGO)-based flexible humidity sensor for monitoring human respiration

Humidity plays a vital role in our daily life and various agro-industrial productions, and humidity sensors have been widely applied in various fields. In this study, flexible, rapid-response, and directly readable composite humidity sensing films were fabricated, employing cellulose (water-soluble cellulose acetate (WSCA)) as moisture sensing layers and reduced graphene oxide (rGO) as resistive conductive layers. The rGO/WSCA composite film can be used as a new type of humidity-sensitive material for the development of humidity sensors. It has been confirmed that abundant hydroxyl groups in WSCA provided abundant adsorption sites and made the composite film highly sensitive to moisture. In addition, WSCA also be used as the dispersant, which could efficiently reduce lamellar accumulation of rGO during the reduction to form a tightly ordered brick-mortar microstructure of rGO/WSCA composite film. The ordered microstructure makes the composite films exhibit a satisfactory mechanical strength (339.5 MPa). Moreover, the rGO/WSCA film sensor could respond quickly within seconds and exhibited low hysteresis towards changes in RH from 23 % to 97 %, and the repeatable error was less than 2.3 % after 6 cycles. Further, the rGO/WSCA humidity sensor could monitor and recognize human respiratory frequency in different states, indicating its potential application in versatile noncontact humidity sensing fields.