Green synthesis of fluorescent carbon dots from Borassus flabellifer flowers for label-free highly selective and sensitive detection of Fe3+ ions

Utilization of biomass as a renewable and sustainable resource has attracted much attention around the world. For the first time, a new and green method has been developed to synthesize fluorescent carbon dots (CDs) using flowers obtained from Borassus flabellifer (male tree) by thermal pyrolysis. The synthesized CDs were comprehensively characterized by X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy, zeta potential measurements, UV-Vis spectroscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. These studies confirmed that the as-synthesized CDs were functionalized with the (-OH), (C-H), (C-O-C) and (C=O) groups. TEM analysis revealed that the particle sizes of the CDs were in the 3 to 8 +/- 1 nm range. Upon increasing the excitation wavelength from 300 to 400 nm, the emission spectrum shifted from 300 to 403 nm. Furthermore, the interaction between the CDs and metal ions was evaluated by testing with various metal ions and the fluorescence intensity of the CDs was measured under 320 nm excitation. Excellent fluorescence quenching was observed only for Fe3+ ions compared to other metal ions such as Zn2+, Pb2+, Ni2+, Fe2+, Ca2+, Cu2+, Cr3+, Co2+ and Hg2+. The fluorescence intensity decreased after each addition of Fe3+ ions. The CDs were an efficient probe for detection of Fe3+ ions from 0 to 30 nM with a detection limit of 10 nM.