The use of S2O8 2- and H2O2 as novel specific masking agents for highly selective "turn-on" fluorescent switching recognition of CN- and I- based on Hg2+-graphene quantum dots.

In this study, we report that both CN- and I- can enhance the fluorescent intensity of Hg2+-graphene quantum dots (Hg2+-GQDs). However, the selectivity of the sensor was poor. Accordingly, simple specific masking agents can be directly used to solve this problem. Here, for the first time, we report the use of persulfate ion (S2O8 2-) as a turn-on fluorescent probe of Hg2+-GQDs for selective CN- detection, while hydrogen peroxide (H2O2) was selected for its sensing ability towards I- ion detection. Interestingly, the signal was immediately measured after addition of the masking agent to Hg2+-GQDs and the sample because its interaction was very fast and efficient. The method had a linear response in the concentration ranges of 0.5-8 µM (R 2 = 0.9994) and 1-12 µM (R 2 = 0.9998) with detection limits of 0.17 and 0.20 µM for CN- and I-, respectively. The sensor was successfully used for the dual detection of both CN- and I- in real water samples with satisfactory results. In conclusion, the specific masking agents in a Hg2+-GQDs system appeared to be good candidates for fluorometric "turn-on" sensors for CN- and I- with excellent selectivity over other ions.