Nitric Acid Assisted Synthesis of Water-Soluble Green Fluorescent Carbon Dots for pH Measurement and Fe³⁺ Ions Detection

A green fluorescent carbon dots (CDs) was synthesized from citric acid, formamide and concentrated nitric acid. The phase compositions, morphologies and fluorescence properties were characterized. The applications of the as.prepared CDs in ion detection and fluorescence imaging were studied as well. The results show that the as. synthesized CDs presented a good water. solubility and emitted bright green fluorescence with an excitation. independent photoluminescence (PL) behavior when the excitation wavelength ranged from 360 to 460 nm. The quantum yield was as high as 44.2%. Meanwhile, the green fluorescent CDs was pH sensitive and the normalized fluorescence intensity was linearly proportional to the pH values of solutions in a range of 4.5 similar to 8.5. Furthermore, the CDs also exhibited excellent selective response to Fe3+ with a good linear relationship between the fluorescence quenching efficiency (I-0/I) and the Fe3+ concentration in a range of 0 similar to 1 000 mu mol.L-1, and the detection limit was calculated to be 9.8 mu mol.L-1.