Quick transformation of polymeric waste into high valuable N-self doped carbon quantum dot for detection of heavy metals from wastewater

[Display omitted] •N-CQDs was synthesized using a waste melamine sponge and lemon juice as green precursors.•N-CQDs was quickly synthesized by a facile method within 10 min without any sophisticated instruments.•As prepared N-CQDs possessed superior performance in the heavy metal sense.•The N-CQDs probe is used to quantitatively detect the harmful Hg2+ and S2− based on a “turn-off-on” mechanism.•The detection limit was 1.04 µM for Hg2+ and 1.62 µM for S2−. Preparing carbon dots (CDs) from waste materials is essential in the current scenario. Herein, we converted non-disposable environmental pollutants into multifaceted, robust, and cost-effective sensing nitrogen-doped fluorescent CDs (N-CQDs) to quickly detect analytes in a wide range of samples. Herein, we studied the simple and efficient way for large-scale synthesis of the N-CQDs from waste melamine sponge (WMS) and lemon juice (LJ) by the treatment of concentrated sulphuric acid (H2SO4) within 10 min and the yield of 60.9 wt% obtained, much higher than those from traditional processes. As-prepared N-CQDs showed bright blue fluorescence and were significantly quenched with Hg2+ (turn off) completely regained by S2− (turn on) due to higher affinity S2− towards Hg2+. The detection limit was 1.04 µM for Hg2+ and 1.62 µM for S2−. This study provides a new perspective for developing N-CQDs and selective sensing Hg2+ and S2− from wastewater.