Sustainable synthesis of doped blue-emissive carbon nanoparticles for environmental sensing applications

Carbon nanoparticles (CNPs) have emerged as versatile nanomaterials owing to their unique optical properties, biocompatibility, and environmentally friendly synthesis routes. This study advocates a green chemistry assisted microwave method (800W, 180�C, 3 mins) for development of CNPs using Mangifera Indica leaf extract and then heteroatom doping of Nitrogen and Phosphorus (addressed here as N-CNPs and P-CNPs respectively) using urea and phosphoric acid as dopants, respectively. Both N-CNPs and P-CNPs exhibited blue fluorescence under UV light embarking ?�?* energy transition of the conjugated C=C bonds and suppressing n-?* transitions leading to fluorescence enhancement. The Zeta potential measurement yielded -20.3 mV after exposure to phosphorus dopants which aggregated with time. The FTIR for P-CNPs revealed peaks at 1167 cm-1 corresponding to P=O stretching in phosphate groups, while 1000 cm-1 owing to P�O�C bonds. Whereas, for N-CNPs, the FTIR peak at 1625 cm-1 corresponds to the N-H deformation frequencies, and peak at 1460 cm-1 is ascribed to the vibrations of C-N stretching frequency. The X-ray diffraction (XRD) analysis revealed increased crystallinity for both CNPs as compared to their undoped counterparts because doping not only helped align sp2 domains and enhance graphitization but also reduced structural disorders and thus acted as strong nucleation centers. The UV-Vis spectroscopy further confirmed the optical improvements, emphasizing the modulation of the electronic structure achieved through doping. The fluorescence sensing was performed on known concentrations of metal ions and CNPs which yielded Limit of Detection (LOD) as 0.297 ppm and 0.345 ppm for N-CNPs and P-CNPs respectively. These green-synthesized, doped CNPs hold substantial promise for sustainable applications across multiple domains including photocatalysis, environmental remediation, biosensing, and renewable energy. Importantly, their potential as eco-friendly biosensors for detecting heavy metals in contaminated water systems has been explored in our study, contributing to global efforts in environmental monitoring and sustainable water resource management.