A new humidity sensor based upon graphene quantum dots prepared via carbonization of citric acid

A new humidity sensor was fabricated using graphene quantum dots (GQDs), synthesized via controlled carbonization of citric acid. The synthesized GQDs showed an outstandingly sensitivity to the variation of environment humidity. The sensor exhibited two sensing regions situating between 0%-52% and 52%-97% of the relative humidity, indicating the dominance of two different sensing mechanisms. However, increasing of the relative humidity from 0% to 97% led to about 1387-fold variation in sensor response. Based on the results obtained, a sensing mechanism was proposed for the developed GQD-based humidity sensor. The response time of the sensor was about 10 s. However, the recovery time was found to be somewhat longer, compared to the response time. The sensor showed appropriate durability and reversibility as well as negligible hysteresis, responding to the change in relative humidity of the environment.