Facile Synthesis of High Yield Blue-Green Emissive Nitrogen-Doped Carbon Dots for the Detection of Fe3+ Ions and as a Fluorescent Ink.

An N-doped carbon dot was hydrothermally (one-pot) prepared from citric acid (C-source) and isonazid (N-source) in 1:4.2 ratios. It has an amorphous-nanocrystalline turbostratic carbon system consisting of N-disrupt core sp2/sp3 carbon with highly integrated nitrogen, whereas in the outer sp2 carbon shell with excess nitrogen creating densely and multifaceted groups (amine, amide, and pyridinic). The characteristic broad pxrd peak at 22.40° (002) and a hump 44.70° (100) were obtained with particle size ≈8.0-9.0 nm in quasispherical form with distinct lattice d-spacing value. The N-CDs gain highly hydrophilicity and dispersibility in water. The N-CDs possess excellent optical properties with long range (350-600 nm) blue-green fluorescence caused by electron trapping in N-surface states and radiative recombination (Ф = 32%). This fluorescence emission is selectively quenched upon interaction with Fe3+ ions in pool of various metal ions. The quenching mechanism involves the locking of electron trap N-surface states caused by Hard Acid-Hard Base complexation of Fe3+ ions with multifunctional N and O containing groups leading to Photoinduced Electron Transfer. The linear quenching and regression coefficient reveal a highly sensitive (LOD = 99.4 nM), strong binding and static quenching. Practical application in real water sample analysis and anticounterfeiting ink test was demonstrated.