Solvent-free preparation of high synthetic yield carbon dots from sodium ligninsulfonate for on-site detection of formaldehyde in the environment

[Display omitted] •We prepared sodium ligninsulfonate derived CDs via solvent-free reaction method.•The CDs show excellent fluorescent response to FA with a LOD of 79 nM.•The CDs exhibit color change under sunlight and UV light in the detection of FA.•A droplet detection system is developed for indoor actual detection of FA gas.•The device achieves on-site, convenient and visual detection of indoor FA gas. Formaldehyde (FA), as a widespread toxic pollutant in cars, furniture and construction materials, has been implicated in hazardous health effects on the human body. This paper presents a green and large-scale preparation of carbon dots (CDs) using sodium ligninsulfonate and o-phenylenediamine through a solvent-free reaction method. The prepared CDs exhibit a synthetic yield of 43 % and show green fluorescence. In addition, the CDs can be employed as an ideal fluorescent FA probe, exhibiting excellent linearity within the range of 0–50 μM (R2 = 0.998, limit of detection (LOD) = 79 nM). By taking advantage of the obvious color changes in detection, the droplet detection system is investigated for on-site visual detection of indoor FA gas. This work not only contributes to the efficient utilization of agricultural waste but also represents a significant process in the development of FA on-site detection.