Concentration-dependent emission of nitrogen-doped carbon dots and its use in hazardous metal-ion detection

Abstract

Nitrogen-doped carbon dots (CDts) with tunable fuorescence properties in aqueous media were synthesized hydrothermally. The excitation wavelength variation to obtain the maximum emission produced a blue shift in the emission peaks upon dilution in an aqueous solution. The shift can be explained by a re-absorption phenomenon in a concentrated solution. The interparticle interaction within was responsible to show dilution-dependent optical behavior. The as-synthesized solution of CDts did not show any prominent absorption peak over a wide range. However, upon dilution, two peaks became predominant. The concentration-dependent behavior was observed during the interaction with metal cations. Cationic salts of Co(II) and Hg(II) caused quenching at diferent dilutions of CDts. This might be explained by the exposure of diferent surface functional groups during dilution and metal-ion?CDts charge transfer. The quenched fuorescence of CDts was rescued using ascorbic acid. Therefore, the one-pot detection of Co(II)/Hg(II) and ascorbic acid was designed through a ‘Turn Of/On’ phenomenon.