Preparation of protonated, two-dimensional graphitic carbon nitride nanosheets by exfoliation, and their application as a fluorescent probe for trace analysis of copper(II)

Bulk graphitic carbon nitride (g-C3N4) was obtained by pyrolysis of urea at 600 A degrees C. The material was then subjected to protonation and exfoliation to obtain strongly fluorescent g-C3N4 nanosheets. These nanosheets are representing a two-dimensional layered material that emits strong blue fluorescence peaking at 434 nm, and their quantum yield of up to 10.3 % is much higher than that of bulk g-C3N4 (6.0 %). It was found that Cu(II) ions quench the fluorescence of the nanosheets due to photo-induced electron transfer (PET), probably the result of the stronger binding affinity between Cu(II) and the nitrogen and oxygen functional groups of the nanosheets. The probe responds to Cu(II) in the 0.01 to 0.4 nM concentration range, with a 8 pM detection limit. The method was applied to the determination of Cu(II) in spiked water samples.