Search

The antioxidant activity of graphene quantum dots (GQD) with different chemical composition and sp 2 -hybridized carbon content has been evaluated and compared to that of a standard antioxidant, ascorbic acid. GQD were prepared by top down and bottom up synthetic approaches from three different precursors (carbon black, glucose and pyrene) in order to vary significantly the chemical composition, electron density and sp 2 -hybridized carbon content. For a given radical, the three types of GQD exhibited very different radical scavenging activity (RSA). Moreover, the RSA varied with the type of free radical and reactive oxygen species (ROS) tested, indicating different radical inhibition mechanisms. Overall, GQD with strong hydrogen donor behavior and large content of sp 2 –hybridized carbon domains were the most effective radical scavengers. Thus, highly graphitic GQD with abundant edge functional groups produced from pyrene exhibited an extraordinary high antioxidant activity, with inhibition effective concentrations much lower than those of ascorbic acid. The great potential of highly antioxidant GQD as protective films against organic dye decoloration by ROS was demonstrated with two model target molecules, methylene blue and rhodamine B.

A simple and versatile method to produce filtration membranes with graphene quantum dots (GQD) and their excellent performance as turn-off fluorescence sensing platforms for Cr (VI) detection in water is presented. Suitably functionalized GQD were immobilized on various types of membranes (nylon, cellulose and glass fiber) and the resulting GQD-modified membranes exhibited the characteristic fluorescence fingerprint of the GQD probes. The membrane fluorescence was quenched by highly toxic Cr (VI) ions due to selective coordination to GQD functional groups. The analytical performance of membranes was comparable to that of dispersed GQD fluorescent probes, displaying a fast and linear response to Cr (VI) concentration in the 1–500 μM range, a low detection limit of 190 nM, high sensitivity, reproducibility and selectivity. Moreover, the membranes can be regenerated by simple washing with deionized water and reused, preserving their good sensing response after several Cr (VI) detection-washing cycles. Membrane sensing performance was very stable after being immersed in water for several days and filtering water through them.