“…It was observed that the blue emission of N-GQDs could be strongly quenched in the presence of Cr(VI), likely through the interaction between the -OH group and/or -NH group on the N-GQDs and the aqueous Cr(VI) anions. 23 Some other common ions, including Fe 3+ , Ca 2+ , Ni 2+ , Cr 3+ , Cd 2+ , Cu 2+ , Pb 2+ , Zn 2+ , Mg 2+ , Mn 2+ , Al 3+ , Na + , K + , Au 3+ , Ba 2+ , Co 2+ , Hg 2+ , NO 3…”