Tohamy Hebat-Allah S
Cellulose and Paper Department, National Research Centre, 33 El Bohouth Str., P.O. 12622, Dokki, Giza, Egypt.
Sci Rep. 2025 Jun 2;15(1):19335. doi: 10.1038/s41598-025-03982-w.
The observed fluorescence behavior of the sulfur, nitrogen-doped carbon dots (S, N-CDs) ink which derived from onion peel wastes (OW) demonstrates its pH-sensitive nature, making it suitable for applications where visual or fluorescent changes upon pH variation are desired. The initial lack of fluorescence under UV light suggests that the S, N-CDs in the ink are in a non-fluorescent state. However, upon treatment with acid, the ink exhibits a faint yellow color under light and fluoresces under UV light. This indicates a shift in the electronic structure of the S, N-CDs, likely due to protonation. The return to non-fluorescence after re-treatment with alkaline solution suggests that the de-protonation process reverses the effect of acid, restoring the S, N-CDs to their original non-fluorescent state. This reversible pH-sensitivity is a valuable asset for various applications. The synthesized S, N-CDs exhibited a reversible change in fluorescence intensity under acidic and alkaline conditions, transitioning from non-fluorescent to fluorescent under acidic conditions and back to non-fluorescent in alkaline media. Density Functional Theory (DFT) calculations revealed that S, N-doping resulted in a narrower energy gap (0.2779 eV compared to 0.3199 eV for N-CDs) and a higher dipole moment (2.640 Debye), enhancing their reactivity towards protons and leading to more pronounced color and fluorescence changes across different pH conditions. The S, N-CDs displayed dual fluorescence emission peaks at 443.00 nm and 502.00 nm upon excitation at 350 nm, and fluorescence contour maps (FCM) confirmed their multicolor emission capabilities. The calculated quantum yield for the S, N-CDs was notably high at 37.76%. Fourier Transform Infrared (FTIR) spectroscopy confirmed the successful incorporation of sulfur (S-H at 2368 cm⁻, C-S at 750 cm⁻) and nitrogen (N-H at 3552 cm⁻, C-N at 989 cm⁻) functionalities into the carbon dot structure. Furthermore, Molecular Electrostatic Potential (ESPM) mapping indicated regions of high negative potential around S, OH, and C=O groups, particularly pronounced under acidic and basic conditions, supporting the observed pH sensitivity.
从洋葱皮废料（OW）中提取的硫、氮共掺杂碳点（S，N-CDs）墨水所观察到的荧光行为表明其具有pH敏感性，这使其适用于需要在pH变化时产生视觉或荧光变化的应用。在紫外光下最初缺乏荧光表明墨水中的S，N-CDs处于非荧光状态。然而，用酸处理后，墨水在光照下呈现淡黄色，并在紫外光下发出荧光。这表明S，N-CDs的电子结构发生了变化，可能是由于质子化。用碱性溶液重新处理后恢复为非荧光状态，这表明去质子化过程逆转了酸的作用，使S，N-CDs恢复到原来的非荧光状态。这种可逆的pH敏感性对于各种应用来说是一项宝贵的资产。合成的S，N-CDs在酸性和碱性条件下荧光强度呈现可逆变化，在酸性条件下从非荧光转变为荧光，在碱性介质中又变回非荧光。密度泛函理论（DFT）计算表明，硫、氮共掺杂导致能隙变窄（与N-CDs的0.3199 eV相比为0.2779 eV）和偶极矩增大（2.640德拜），增强了它们对质子的反应性，并导致在不同pH条件下颜色和荧光变化更明显。在350 nm激发下，S，N-CDs在443.00 nm和502.00 nm处显示出双荧光发射峰，荧光等高线图（FCM）证实了它们的多色发射能力。计算得出的S，N-CDs的量子产率高达37.76%。傅里叶变换红外（FTIR）光谱证实硫（2368 cm⁻处的S-H、750 cm⁻处的C-S）和氮（3552 cm⁻处的N-H、989 cm⁻处的C-N）官能团成功地掺入了碳点结构中。此外，分子静电势（ESPM）图谱表明在S、OH和C=O基团周围存在高负电势区域，在酸性和碱性条件下尤为明显，这支持了所观察到的pH敏感性。
