Green synthesis of poly(lactic acid)-based nitrogen-doped carbon quantum dots and their application as multifunctional fluorescent probes for the detection of environmental pollutants

Green synthesis of PLA-CQDs as PLA-based N-doped carbon quantum dots is developed. • PLA-CQDs can exhibit quick fluorescence quenching for Fe 3+ and three NAC explosives. • PLA-CQDs probe can have lower LODs, e.g., 57.9 nM (for PA, a typical NAC explosives). • Mechanistic studies show that the quenching reason of Fe 3+ and three NACs is different. • Detection in real water samples and visual sensing with test strips can be achieved. In this study, biobased polymer material poly(lactic acid) (PLA) was used as a green carbon source and ethylenediamine as a nitrogen source to successfully prepare nitrogen-doped carbon quantum dots PLA-CQDs with excellent performance via a one-step hydrothermal method. The morphology, structure, and optical properties of the carbon quantum dots were characterized by using transmission electron microscopy, X-ray photoelectron spectroscopy, FT-IR, and fluorescence spectroscopy. The results show that the PLA-CQDs exhibit a uniform particle size distribution with an average diameter of 4.81 ± 0.89 nm, being rich in amino, hydroxyl, and other functional groups on their surface. Under 365 nm UV lamp irradiation, they can emit bright blue fluorescence with a fluorescence quantum yield of 11.09%. Experimental results demonstrate that the carbon quantum dots have a highly selective fluorescence quenching response to Fe 3+ within 10 s, while also showing excellent recognition ability towards three nitro aromatic compounds (NACs), namely picric acid, p -nitrophenol, and 2,4-dinitrophenol. However, when two types of target analytes coexist, the fluorescence signal overlap occurs, thus the probe is currently only suitable for the detection of a single target analyte. The lower detection limits can reach 3.92 × 10 −7  M (for Fe 3+ ), 5.79 × 10 −8  M (for picric acid), 5.56 × 10 −7  M (for p -nitrophenol), and 1.79 × 10 −7  M (for 2,4-dinitrophenol), respectively. The probe has been applied to the detection of target analytes in real water samples, with spiked recoveries ranging from 94.9% to 104.9% and relative standard deviations below 2.5%, indicating good accuracy and reliability. This study not only achieves high-value utilization of biomass resources by using PLA as a carbon source to prepare multifunctional fluorescent probes, but also provides a new technical approach for the rapid detection of environmental pollutants such as heavy metal ions and NACs in water. Download: Download high-res image (346KB) Download: Download full-size image