Room temperature pH-dependent ammonia gas sensors using graphene quantum dots

We report a simple solution-process route to realize ammonia (NH3) gas sensor based on graphene quantum dots (GQDs). Transmission electron microscopy analysis confirmed that the 8-10 nm GQDs were formed from multi-walled carbon nanotubes by using ultrasonication treatment. The as-fabricated gas sensor showed promising selectivity response when expose to NH3 ambient at room temperature. It is indicated that by adjusting the pH value of the aqueous GQDs in acidic and neutral, two types of gas sensors with contrary current responses could be obtained, which might be resulted from quantum confinement, edge effects and presence of functional groups on GQDs.