Nitrogen self-doped desiccated coconut–derived carbon dots as optical nanoprobe sensor for the detection of heavy metal ion Hg²⁺

This work describes the novel synthesis of nitrogen self-doped desiccated coconut–derived carbon dots (N-DCCDs) from the desiccated coconut powder as a natural precursor through the hydrothermal method. The prepared N-DCCDs present bright blue fluorescence under UV light of 365 nm due to electron–hole pair localization by obtaining the quantum efficiency of ~ 32%. Structural and morphological studies of prepared N-DCCDs carried out by HRXRD and HRTEM analysis, confirming the non-crystalline graphitic texture and uniform spherical morphology having particles averaging 10 nm in size. Photoluminescence emission spectra demonstrate the excitation-dependent emission of synthesized N-DCCDs in the visible spectrum, confirming the existence of common fluorescent carbon dots due to the quantum confinement effect. Synthesized N-DCCDs have been used as a nanoprobe optical sensor using the quenching mechanism for the efficient sensitive and selective detection of hazardous heavy metal (Hg²⁺) in the aqueous solution. The stability of fabricated sensor is monitored under the effect of different ionic concentrations, pH values, and incubation time. The fabricated nanoprobe sensor shows the low limit of detection (2.4 nM), indicates that N-DCCDs-based optical sensor can be an eminent contributor to study the regulating concentrations of Hg²⁺ ion.