Color-Tunable Fluorescent Nitrogen-doped Graphene Quantum Dots Derived from Pineapple Leaf Fiber Biomass to detect Hg2+

Abstract In this study, nitrogen-doped graphene quantum dots (N-GQDs) exhibiting high water solubility were produced based on the hydrothermal approach. Ethylenediamine (EDA) was used as the nitrogen dopant and microcrystalline cellulose (MCC), extracted from pineapple leaf fiber (PALF) biomass, used as the carbon source. The as-prepared N-GQDs exhibited an average size of 3.7 nm, 8-10 layers and the excitation wavelength-dependent fluorescence. It was noteworthy that controlling the pH value of the EDA solution in the hydrothermal process could change the fluorescence color of the N-GQDs, exhibiting unique green, cyan and blue light. Besides, because of the effective fluorescence quenching effect of N-GQDs by mercury (II) ions (Hg2+), the as-prepared N-GQDs were successfully employed as the efficient nanosized fluorescence sensors to selectively detect Hg2+ in aqueous solutions with the detection limit of 0.25 nM and a linear range of 0∼30 μM. The selectivity experiments indicated that as-prepared N-GQDs were specific for Hg2+ even with interference by high concentrations of other metal ions. Notably, the N-GQDs could be well adopted to determine Hg2+ in river water samples.