This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Carbon quantum dots (CQDs) are fluorescent carbon nanomaterials with potential applications in sensing, optoelectronics, displays, anticounterfeiting and environmental technologies. Their optical properties can be adjusted by modifying the carbon structure and surface chemistry, particularly through defect states and the incorporation of heteroatoms.
However, achieving predictable and continuous tuning of photoluminescence from a single carbon precursor remains difficult. Many previous approaches rely on different starting materials, synthesis routes or postsynthetic treatments, making it challenging to determine how individual chemical modifications alter the electronic states responsible for light emission. Waste polyamide offers an attractive starting material for addressing this challenge.
Widely used in textiles, packaging, automotive components, fishing gear and consumer products, polyamide contributes to substantial postconsumer plastic waste. Converting this material into functional carbon nanomaterials could therefore combine waste valorization with the production of high-value optical materials. A research team comprising Dr.
Christian Ebere Enyoh and Professor Emeritus Qingyue Wang of the Graduate School of Science and Engineering at Saitama University investigated whether the photoluminescence of carbon quantum dots could be systematically controlled using waste polyamide as a single carbon precursor. The researchers prepared eight chemically distinct CQD variants through dry pyrolysis and hydrothermal or solvothermal synthesis, progressively modifying their surface chemistry through oxidation and the introduction of boron-, nitrogen-, sulfur- and phosphorus-containing functionalities. Using fluorescence spectroscopy, UV–visible spectroscopy, Fourier-transform infrared spectroscopy, optical transition-energy analysis and colorimetric characterization, the team continuously shifted the emission wavelength from 308 nm in the ultraviolet region to 552 nm in the yellow-green region—a total tuning range of 244 nm—while using the same polyamide precursor throughout.
In doing so, the researchers demonstrated that controlled defect-state engineering can systematically regulate the optical emission of waste-polyamide-derived CQDs. The study was published online in Journal of Luminescence, under the title "Defect state engineering in polyamide-derived carbon quantum dots enables continuous photoluminescence tuning." The results revealed a progressive change in both surface chemistry and optical behavior across the eight CQD variants. As chemical modification proceeded, the effective optical transition energy decreased from 4.32 to 2.50 eV, in parallel with the shift toward longer-wavelength emission.
The B,O co-functionalized CQDs achieved the highest photoluminescence quantum yield of 62.74%, while an S,N-containing variant reached 59.06%. The P,S,N-modified CQDs produced the longest-wavelength emission at 552 nm and achieved a color purity of 95.20%. Together, the spectroscopic and photophysical results support a progressive transition from predominantly carbon-core-associated emission toward increasing contributions from surface-defect and heteroatom-associated emissive states.
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