Near-infrared carbon quantum dots from PEG-based deep eutectic solvents for high-accuracy quantitative analysis of naphthenic acids in wastewater

Naphthenic acids (NAs) are toxic components in refinery wastewater and in oil sands process water. The presence of NAs in aqueous environments would cause serious environmental problems. Development of a rapid method for screening and determination of trace NAs is urgent. In this work, a near-infrared fluorescence carbon quantum dots (CQDs) was successfully synthesized with p-phenylenediamine (PPD) and polyethylene glycol 400 (PEG 400) by the hydrothermal method. It showed a good fluorescence response to NAs with good detectability. The limit of detection was calculated to be 0.16 mmol‧L−1, with a linear range from 0.5 to 15 mmol‧L−1. The detection mechanism of NAs and CQDs was also proposed with in situ infrared spectrometer. This work provides new insights into the fluorescence detection of CQDs in the petrochemical industry, broadening the application of CQDs in the detection of environmental organic pollutants.