为提高碳点对汞离子光化学识别的选择性及检测方法的可行性, 以柠檬酸和磺胺为原材料采用热解法制备一种新型氮、 硫共掺杂碳点(NS-CDs)。 用红外光谱仪、 紫外-可见光吸收光谱仪、 透射电镜、 元素分析仪和荧光光谱仪等对其结构和光学性能进行表征。 结果表明: 该量子点水溶性和分散性高, 平均粒径4.78 nm左右, 具有类石墨结构; 其在3 446和3 261 cm-1处存在N—C和O—H键振动吸收峰; 2 966和2 923 cm-1处为C—H键振动吸收带; 1 630和1 570 cm-1处吸收峰归属于苯环骨架CC双键振动; 1 388 cm-1处为—CH3剪式振动峰; 1 268, 1 192, 1 146及1 071 cm-1处的振动吸收峰表明存在为C—N, C—S, C—O, C—O—C及—SO-3键, 912 cm-1处为环氧基的特征吸收峰, 739 cm-1处吸收带归属于N—H键变形振动, 可见, 该碳点不仅含有苯环骨架结构, 还有N和S等元素参与的成键结构存在。 其在21.4°处出现一个明显且宽的(002)晶面衍射特征峰, 晶格间距为0.41 nm, 稍大于石墨晶格间距(0.34 nm)。 NS-CDs的C, N, S和O元素含量分别为68.72%, 7.37%, 6.24%及17.67%, 与红外分析结果吻合。 NS-CDs在309 nm处有一个由CC键的π→π*电子跃迁产生的较强吸收峰, 且在可见光区域内有一个很长的拖尾; 同时在335 nm处出现了一个由CO键的n→π*电子跃迁而产生的吸收肩峰。 当激发波长小于390 nm时, NS-CDs原液荧光发射峰值随激发波长增大而逐渐增大, 且在390 nm时, 荧光强度最强; 大于390 nm时, 随激发波长增大而逐渐减弱。 同时发现随激发波长增加, 发射峰逐渐红移。 当NS-CDs溶液逐渐稀释时, 其最佳激发峰也由390 nm蓝移至360 nm; 当pH值＜11.0时, NS-CDs的荧光强度变化很小, 在pH值为7.0时荧光峰最强; 在pH＞12.0时, 荧光强度急剧下降, 故选用PBS缓冲溶液(pH 7)进行金属离子检测实验。 在16种金属离子中只有Hg2+对NS-CDs荧光强度具有极其显著的影响, 使碳点荧光完全猝灭, 基于NS-CDs对Hg2+具有高选择性及Hg2+对NS-CDs强荧光猝灭作用, 建立了其对Hg2+的荧光化学识别方法。 该识别方法的线性方程为y=5.559 02x-13.860 39, 其线性范围为1×10-3~1×10-9 mol·L-1, R2为0.9947, 检出限为7.11×10-3 nmol·L-1, 相对标准偏差小于2.5%, 对实际样品检测精度和回收率高, 可用于实际水样中Hg2+的检测, 在生物和环境分析领域具有良好的应用前景。

To improve the selectivity of carbon dots to the photochemical recognition of mercury ions and the feasibility of its detection methods, a new kind of Nitrogen-Sulfur codoped carbon dots(NS-CDs)material with high fluorescence was prepared by thermal decomposition method and using citric acid and sulfanilamide as raw materials. Its structure and optical properties were characterized by infrared spectrometer, UV-Vis absorption spectrometer, transmission electron microscope, elemental analyzer, fluorescence spectrometer, etc. The results showed the quantum dot had graphite like structure, high water solubility and dispersibility, and its average particle size was about 4.78 nm. There are the following absorption peaks in the infrared spectra of NS-CDs: N—C and O—H bond vibrational absorption peaks at 3 446 and 3 261 cm-1, C—H bond vibrational absorption bands at 2 966 and 2 923 cm-1, the CC double bond vibrational absorption peak of the benzene ring skeleton at 1 630 and 1 570 cm-1, shear vibration peak of —CH3 at 1 388 cm-1, the vibrational absorption peaks of C—N, C—S, C—O, C—O—C and —SO-3 bonds at 1 268, 1 192, 1 146 and 1 071 cm-1, characteristic absorption peak of epoxy group at 912 cm-1 and the absorption band of N—H bond deformed vibration absorption band at 739 cm-1. It can be seen that the carbon dot contains not only the skeleton structure of benzene ring, but also the bonding structure in which N, S and other elements participate. An obvious and wide diffraction characteristic peak of (002) crystal plane appeared at 21.4° in NS-CDs. Its lattice distance (0.41 nm) was slightly larger than that of graphite (0.34 nm). The C, N, S and O element content of NS-CDs is 68.72%, 7.37%, 6.24% and 17.67%, respectively, which are consistent with the results of IR analysis. NS-CDs has a strong absorption peak at 309 nm, due to π→π* electron transition of CC bond, and a long tail in the visible region, and an absorption shoulder peak caused by the n→π* electron transition of the CO bond at 335 nm. When the excitation wavelength is less than 390 nm, the fluorescence emission peak of NS-CDs increases gradually with the increase of excitation wavelength, and the fluorescence intensity is the strongest at 390 nm, and weakens with the increase of excitation wavelength when the excitation wavelength is greater than 390 nm. At the same time, it is found that the emission peak gradually shifts red with the increase of excitation wavelength. When NS-CDs solution is diluted gradually, the optimal excitation peak shifts blue from 390 to 360 nm. When pH<11.0, the fluorescence intensity of NS-CDs varies very little, and it is the strongest at pH value 7.0. When pH>12.0, the fluorescence intensity of NS-CDs decreases sharply, so PBS buffer solution (pH7) was used to detect metal ions. Of the 16 metal ions, only Hg2+ has an extremely significant effect on the fluorescence intensity of NS-CDs, which completely quenches its fluorescence. Due to the high selectivity of NS-CDs to Hg2+ and the strong fluorescence quenching effect of NS-CDs by Hg2+, a new fluorescent chemical recognition method for Hg2+ by NS-CDs was established. The linear equation of the recognition method is y=5.559 02x-13.860 39, with a linear concentration range of 1×10-3~1×10-9 mol·L-1, R2 of 0.994 7 and the detection limit of 7.11×10-3 nmol·L-1. Its relative standard deviation is less than 9%, and it has high detection precision and recovery rate for practical samples, so it can be used for the detection of Hg2+ in real water samples with a good application prospect in the field of biological and environmental analysis.