Enhancing fluorescence sensing of metal species by g-C3N4 prepared by co-polymerization of melamine and urea precursors

Abstract

In this work, several g-C3N4 samples have been synthesized by thermal co-polymerization of melamine and urea precursors, analyzing the impact and advantages of the combination of both precursors, and finally choosing the sample with the highest fluorescent emission to study the detection of Ag+, Fe3+, and Cr(VI) species. The g-C3N4 samples were characterized by several techniques such as XRD, FTIR, DRS, SEM, and PL where the excitation wavelength (λexc) was set at 250 nm for monitoring the quenching of the emission band centered at 371 nm. In this sense, the 10U-g-C3N4 sample was examined for the detection of metal species in aqueous media, showing excellent correlation coefficients (R2 > 0.988) and limits of detection (LOD) of 7.2, 8.4, and 1.9 μmol/L for Fe3+, Ag+, and Cr(VI), respectively. The sensing of Ag+ and Fe3+ ions can be related to a photoinduced electron transfer (PET) mechanism, while the detection of Cr(VI) species is associated with an inner filter effect (IFE). The results show that the graphitic carbon nitride obtained by a co-polymerization route yields better results than g-C3N4 obtained by the calcination of single precursors. This approach enhances the fluorescence sensing of different metal species with a simple synthetic procedure and avoids complex, harmful, or expensive processes.