From spruce packaging waste to fluorescent carbon quantum dots/formaldehyde detection probe: performance and mechanism.

Formaldehyde (FA) is widely present in drinking water and industrial wastewater and is extremely harmful to human health. Biosensing probes based on biomass carbon quantum dots (CQDs) represent a novel FA detection technique; however, the existing CQDs/FA probes still face technical bottlenecks, such as the inability to achieve visual detection, which seriously restrict its on-site application. In this study, undoped CQDs (S-CQDs), urea-doped CQDs (U-CQDs), O-phenylenediamine-doped CQDs (O-CQDs) and urea/o-phenylenediamine co-doped CQDs (NN-CQDs) were synthesized by a hydrothermal method (180 °C, 10 h) using the waste wood of spruce packaging as a carbon source. The structure and properties of the CQDs, the performance of CQDs/FA probes, the formation mechanism of CQDs and the mechanism of CQDs/FA were discussed. When excited at 365 nm, S-CQDs, U-CQDs, O-CQDs and NN-CQDs emit blue, blue, yellow and white fluorescence, respectively. The detection limit (LOD) of S-CQDs/FA, U-CQDs/FA, O-CQDs/FA and NN-CQDs/FA probe is 0.045, 0.046, 0.026 and 0.0016 mM, respectively. Especially, the NN-CQDs/FA fluorescent probe may have a potentially broad application prospect in the detection of fluoride in water bodies. Its LOD is far lower than the exposure limit set by the World Health Organization (0.00333 mM), as well as the upper limit requirement stipulated in the Hygienic Standard for Drinking Water (GB 5749-2022, China) and the Hygienic Specification for Secondary Water Supply Facilities (GB 17051-1997, China) (0.02997 mM). When FA concentration gradually increases from 0 to 80 mM, the fluorescence of the probe under 365 nm excitation gradually changes from white to blue, cyan, green and yellow.