Facile bulk production of highly blue fluorescent graphitic carbon nitride quantum dots and their application as highly selective and sensitive sensors for the detection of mercuric and iodide ions in aqueous media

Highly blue fluorescent graphitic carbon nitride quantum dots (g-CNQDs) were synthesized by a simple microwave mediated method from formamide (HCONH2). The fluorescence emission of g-CNQDs is found to be strongly dependent on solvent, pH as well as on excitation wavelengths; the life time of the emission decreases with increasing polarity of the solvent. These quantum dots are highly sensitive and selective florescent probes for mercuric ions in aqueous media due to the "superquenching" of fluorescence. The complex formation of Hg2+ ions with the CNx sheet involving pi delocalized electron moieties of the latter, in fact, is responsible for the quenching of fluorescence. The addition of iodide ions abstracts the bound Hg2+ forming HgI2 and gives back the fluorescence characteristic of g-CNQDs. Thus, g-CNQDs can play a dual role for selective and sensitive detection of mercuric ions as well as iodide ions in aqueous media via "ON-OFF-ON" fluorescence response.