Sustainable clove-derived nitrogen-doped carbon dots with programmable multimodal fluorescence for metal ion and fluoride sensing.

The development of sustainable fluorescent nanomaterials from renewable biomass represents a promising strategy for environmentally benign chemical sensing. In this work, nitrogen-doped carbon dots (N-CDs) were synthesized from clove biomass using glycine as a nitrogen source through a rapid microwave-assisted pyrolysis route, providing a greener and significantly more energy-efficient alternative to conventional hydrothermal synthesis by reducing the overall reaction and cooling time (by approximately 75%), thereby lowering the overall energy requirements through rapid and volumetric heating while providing an efficient route for the synthesis of highly fluorescent N-CDs. The resulting N-CDs exhibited a quasi-spherical morphology with an average particle size of 7.20 nm, excitation-dependent fluorescence, excellent water dispersibility, outstanding photostability, and a high quantum yield of 29.42%. Structural characterization by XPS, FTIR, and Raman spectroscopy confirmed successful nitrogen incorporation and abundant surface functional groups responsible for their favorable optical properties. The N-CDs functioned as a highly selective fluorescent nanoprobe for Fe(iii) and Cr(vi) ions via fluorescence quenching, achieving low detection limits of 73.93 nM and 49.16 nM, respectively. Notably, the Fe(iii)-quenched system exhibited selective fluorescence recovery upon the addition of F- ions, whereas no recovery was observed for the Cr(vi)-quenched system, enabling differential discrimination between the two analytes and subsequent F- detection with a detection limit of 1.69 µM. This work demonstrates a sustainable biomass-derived fluorescent nanoprobe that integrates rapid green synthesis with selective dual-mode sensing, providing an efficient platform for the sensitive monitoring of environmentally relevant metal ions and fluoride in aqueous media.