摘要
以碱木质素(Alkali lignin,AL)为碳源、乙二胺(Ethanediamine,EDA)为钝化剂、双氧水(H2O2)为氧化剂,利用简单、绿色、高效的水热法制备碱木质素碳点(ALE-CDs)。以荧光性能为指标,通过单因素实验优选出ALE-CDs的最佳制备工艺。结果表明,ALE-CDs表面存在大量的羟基(—OH)、羧基(—COOH)和氨基(—NH2)等官能团,在水中具有优良的分散性和稳定性,荧光量子产率及寿命分别为19.20%和6.03 ns。利用ALE-CDs为荧光探针检测不同金属离子,发现ALE-CDs对F
碳点(Carbon dots,CDs),又称碳量子点或者碳纳米点,是一类尺寸在10 nm以内的碳基零维材料,具有独特的光学性能、良好的水溶性、高稳定性、低毒性、优良的生物相容性和低环境影响等特性,被认为是一种新颖而极具应用前景的荧光碳材料而备受瞩
木质素是一种含量仅次于纤维素的芳香族天然高分子化合物,其储量大、来源广、无毒廉价、易分解,且具有较高的碳含量和丰富的芳香结
另一方面,随着社会经济的快速发展,金属离子的快速准确检测在环境、食品和医疗领域显得尤为重要。铁离子(F
碱木质素(Alkali lignin,AL),购自北京索莱宝科技有限公司;透析袋(截留分子质量3500),美国。乙二胺(Ethanediamine,EDA)、质量分数30% H2O2,均为分析纯,购于国药集团化学试剂有限公司。
UAT-02型暗箱式紫外分析仪,山东普创工业科技有限公司;F-280型荧光分光光度计,天津港东科技股份有限公司;UV-6300型双光束紫外可见分光光度计,上海美谱达仪器有限公司;Quantaurus-QY plus型绝对量子产率测量仪,日本滨松公司;TECNAI G2 F20型场发射透射电子显微镜,美国FEI公司;D8 advance型X射线衍射仪,德国Bruker公司;VERTEX 70型傅里叶变换红外光谱仪,德国Bruker公司;Invia Reflex型激光拉曼光谱仪,英国Renishaw公司。
称取0.5 g AL,超声搅拌溶解于50 mL去离子水中,随后加入一定量的EDA,再加入10 mL H2O2,磁力搅拌30 min。将分散均匀的溶液转移到100 mL聚四氟乙烯内衬,密闭于不锈钢釜中,放入恒温干燥箱反应,随后自然冷却至室温,即获得棕黄色ALE-CDs溶液。
取稀释后的ALE-CDs溶液20 mL,向其中添加各金属阳离子(B
本研究采用单因素实验法,以碳点的荧光强度为指标,通过对水热温度、AL∶EDA质量比、水热时间这3个因素的对比研究,来确定ALE-CDs的最佳制备工艺。




图1 工艺条件对ALE-CDs荧光强度的影响及其UV-Vis吸收光谱、荧光激发和发射光谱、荧光图像
Fig. 1 Effect of process conditions on the fluorescence intensity of ALE-CDs and the UV-Vis absorption spectra, fluorescence excitation and emission spectra, and fluorescence images of ALE-CDs
AL∶EDA质量比对ALE-CDs荧光强度的影响如
进一步研究了ALE-CDs荧光发射性能与激发波长之间的关系,结果如

图2 ALE-CDs激发依赖的荧光发射光谱和荧光发射归一化光谱
Fig. 2 Excitation-dependent fluorescence emission spectra and fluorescence emission normalized spectra of ALE-CDs

图3 ALE-CDs的时间分辨光谱
Fig. 3 Time-resolved spectrum of ALE-CDs
(1) |
式中,R为荧光强度;A1、A2为常数,分别为670.20、502.23;t为时间;τ1、τ2为各指数成分寿命,分别为1.59、7.76。
(2) |
此外,通过量子产率测量仪(Quantaurus-QY plus)直接测定ALE-CDs的绝对量子产率为19.20%,此方法具有精准、快捷、高效、无需标样、测试数值稳定、可重复性较好等优势。
通过透射电子显微镜(TEM)和高分辨率透射电子显微镜(HRTEM)观察了ALE-CDs的粒径大小、分布和石墨化程度,结果见

图4 ALE-CDs的TEM图(插图:HRTEM图)和粒径分布图
Fig. 4 TEM image (Inset: HRTEM image) and particle size distribution diagram of ALE-CDs
采用红外光谱仪对AL、EDA和ALE-CDs表面功能团进行分析,结果如

图5 AL、EDA和ALE-CDs的红外光谱图
Fig. 5 Infrared spectra of AL, EDA and ALE-CDs
利用X射线衍射仪(XRD)分析了AL及冷干后ALE-CDs的晶型结构,见


图6 AL、ALE-CDs的XRD谱图和ALE-CDs的拉曼光谱图
Fig. 6 XRD patterns of AL and ALE-CDs, Raman spectrum of ALE-CDs
利用拉曼光谱进一步研究了ALE-CDs的石墨化程度。
利用暗箱式紫外分析仪和荧光光谱仪研究了17种阳离子(浓度均为50 mmol/L)对ALE-CDs的荧光猝灭行为,见


图7 ALE-CDs溶液在紫外光照射下(λ= 365 nm)的照片和不同离子存在时ALE-CDs的荧光强度
Fig. 7 Photo of ALE-CDs solution under ultraviolet light (λ = 365 nm) and fluorescence intensity of ALE-CDs in the presence of different ions
进一步研究了F
(3) |
式中,δ为信号的标准偏差;S是直线的斜率。


图8 不同 F
Fig. 8 Fluorescence intensity of ALE-CDs under different F
计算求得F
本研究选用价格低廉、来源广泛的碱木质素作碳源、以含氮量丰富的乙二胺为钝化剂,在双氧水的氧化作用下,通过一步水热法合成具有高荧光的碱木质素基碳点(ALE-CDs),实现了碱木质素的高附加值转化。
3.1 以荧光强度为碳点性能指标,通过单因素实验优化ALE-CDs的合成工艺,获得的最佳工艺条件为:水热温度190℃、AL∶EDA质量比1∶4、水热时间12 h;合成的ALE-CDs荧光量子产率及寿命分别为19.20%和6.03 ns,碳点粒径集中在1.6~2.8 nm。
3.2 将ALE-CDs作为荧光纳米探针来检测金属离子,结果表明,ALE-CDs对F
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