Facile Synthesis of Photoluminescent Graphitic Carbon Nitride Quantum Dots for Hg²⁺ Detection and Room Temperature Phosphorescence

Carbon nitride materials have become highly explored carbon based nanomaterials since their rediscovery in the 1990s due to their semiconductor like behavior. Here, we report a facile one pot synthesis of sulfur and oxygen doped carbon nitride quantum dots (SCNQDs) from thiourea and ethylenediaminetetraacetic acid disodium salt by a thermal method. The SCNQDs prepared are characterized by UV–visible, FT-IR, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction, and transmission electron microscopy (TEM) imaging. We have demonstrated the Hg²⁺ sensing ability of SCNQDs in solution as well as in the solid phase, i.e. SCNQDs loaded onto filter paper. The Hg²⁺ sensing capability of the SCNQDs in the solution phase is the same for Hg²⁺ ion in double distilled water as well as in tap water, which gives the method a practical applicability in real conditions. The sensitivity of SCNQDs with Hg²⁺ follows a linear relationship in the range from 10 nM to 1 μM. The minimum detection limit is found to be 0.01 nM, which is lower than previous reports. Similarly the SCNQDs loaded onto filter paper also showed same sensing capability with Hg²⁺ spiked tap water as Hg²⁺ in double distilled water solutions. Thus, we have devised a ready to use system for Hg²⁺ detection with SCNQDs loaded filter paper to be used in biological fluids as well as in environmental samples, which is not available now, to the best of our knowledge. Further we have also made a composite of SCNQDs with poly­(vinyl alcohol) (PVA) to observe room temperature phosphorescence (RTP) in SCNQDs. Therefore, RTP in SCNQDs, which is reported for the first time, will add to the exploration and development of high efficiency optoelectronic devices involving SCNQDs.