Carbonized polymer dots (CPDs) have attracted widespread attention owing to their unique properties and are usually prepared from monomers of polymers or polymers. To reduce the waste of high-value petropolymers and environmental pollution, a simple and green method for the preparation of CPDs using a hydrothermal technique based on the cross-linking enhanced emission effect was proposed, in which nylon 66 waste fibers were used as a precursor and glutaraldehyde as a crosslinking agent. The as-prepared CPDs possessed polymer/carbon hybrid structures with a 3.5 nm average diameter, and hydroxyl (−OH), carboxyl (−COOH), and amino (−NH 2 ) groups were present on the surface of CPDs. It can be found that the asprepared CPDs display excitation-dependent photoluminescence emission, which is mainly attributed to the molecular state luminescence center. Because the molecular state fluorescence of CPDs could be affected by the presence of Fe 3+ and the change of pH values, the as-prepared CPDs can be used as a probe for the detection of the concentration of Fe 3+ and the pH variations of solution. The fluorescence intensity of CPDs was selectively quenched by Fe 3+ in the range from 1 to 145 μM. In virtue of the static quenching of CPDs by Fe 3+ , a sensing system was fabricated for the quantitative detection of Fe 3+ , and its limit of detection was 0.1 μM. Based on the electrostatic doping/charging of CPDs, a pH sensor was fabricated. It showed that the fluorescence intensity of CPDs decreased along with the increase of pH from 2.60 to 12.6. What is more, the CPDs were found to be an alternative to traditional fluorescent inks for encryption and information storage.

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Environmentally friendly polyethylene terephthalate-based carbon dots (PET-CDs) with ultrahigh fluorescence quantum yield were prepared with waste PET textiles as raw materials. First, oligomers were prepared from the reaction of waste PET textile and ethylene glycol by the microwave method. Then, the mixture without isolation and purification as well as pyromellitic acid and urea were adopted as precursors for the preparation of PET-CDs by the hydrothermal method. It was found that the as-prepared PET-CDs had a spherical structure with an average particle size of 2.8 nm. The carbon core of PET-CDs was a graphene-like structure doped with nitrogen atoms in the form of pyrrole nitrogen and the surface contained −NH2, which is convenient for modification and functionalization with various materials in the form of chemical bonds. The as-prepared PET-CDs exhibit excitation-independent emission properties in the range from 340 to 440 nm, and the best excitation and emission wavelengths of PET-CDs are 406 and 485 nm, respectively, while the fluorescence quantum yield is 97.3%. In terms of the application, the as-prepared PET-CDs could be adopted as a fluorescence probe for the detection of Fe3+, and the limit of detection is as low as 0.2 μmol/L. The mechanism of PET-CDs by Fe3+ was found to be the static quenching mechanism. In addition, PET-CDs can be used in LEDs and fluorescent anticounterfeiting.

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