氧化石墨烯-亚甲基蓝体系荧光光度法灵敏测定铋(Ⅲ)离子

在水溶液中，氧化石墨烯(Go)对亚甲基蓝(CMB)的荧光可产生猝灭作用，加入适量Bi3+可使体系的荧光增强，且增强程度与Bi3+的加入量有关。氧化石墨烯含有大量的含氧官能团使之表面带负电荷，易于分散在水中。带正电荷的荧光染料亚甲基蓝通过静电引力和π—π堆积作用吸附在GO表面，形成了GO-MB复合物，从而产生荧光猝灭。使用改进的Hummers制备了氧化石墨烯，应用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对制备的GO进行了表征。利用紫外可见吸收光谱验证了石墨烯与亚甲基蓝的作用过程，结果表明亚甲基蓝的荧光猝灭后，其两个主要吸收峰强度明显降低，而且GO的吸收光谱与MB的发射光谱完全不同，重叠度太小，不能发生能量转移，因此，GO与MB发生的荧光猝灭属于静态猝灭过程。当向亚甲基蓝氧化石墨烯络合体系加入Bi3+后，由于Bi3+体积小，带正电荷多从而取代了亚甲基蓝致使亚甲基蓝脱离氧化石墨烯，荧光恢复，荧光恢复的程度随Bi3+量的增加而增强，据此建立了氧化石墨烯-亚甲基蓝荧光光度法测定Bi3+的新方法。考察了亚甲基蓝、氧化石墨烯浓度，酸度以及试剂加入顺序对体系荧光恢复的影响，该络合体系的激发波长为667 nm，发射波长为690 nm，在优化条件下，Bi3+的浓度在0.5～100 μmol·L-1范围内与荧光强度呈良好的线性关系，相关系数为0.995 5。方法的检出限为1.0×10-8 mol·L-1(S/N=3)。评价了该方法的选择性，结果表明当共存离子为1 000倍的K+，Ca2+，Na+，Mg2+，Cu2+;100倍的Fe3+，Be2+，SiO2-₃，Al3+，Ni2+，Sb3+，NO-₃，Cl-，F-;20倍的Pb2+，Hg2+，Cd2+不干扰Bi3+的测定，新方法具有灵敏度高、快速、成本低等优点，将提出的方法用于环境水样的分析，回收率为93.4%～105.2%。

Sensitive Determination of Bi3+ by Spectrofluorimetry Based on Graphene Oxide-Methylene Blue System

Graphene oxide was prepared by the modified Hummers method and characterized by field emission scanning electron microscopy. The interaction of graphene with methylene blue was studied by UV absorption, the intensity of two main absorption peaks of methylene blue decreased significantly after the fluorescence was quenched, and the energy transfer didn’t occur because the overlap of the absorption spectrum of GO and the emission spectrum of MB is too small. Therefore, the fluorescence quenching of MB and GO was static. When adding a certain amount of Bi3+ in the graphene-methylene blue system, Bi3+ replaces the methylene blue from the graphene-methylene blue complexes because Bi3+ has the smaller volume and is more positively charged. The methylene blue therefore dissociates from the GO-MB complexes, resulting in the recovery of fluorescence of the system. Furthermore, the fluorescence of the system increases with the increase in the amount of Bi3+ due to the enhanced amount of MB in the system. A novel spectrofluorimetric method was therefore developed for the sensitive determination of Bi3+. Some parameters including the concentration of methylene blue, the amount of graphene oxide, the amount of nitric acid and the sequence of reagent adding were optimized to obtain higher sensitivity. The fluorescence of the system was detected at an emission wavelength of 667 nm with excitation at 690 nm. Under the optimized conditions, the concentration of Bi3+ showed good linear relationships with the fluorescence intensity in the range of 0.5～100 μmol·L-1, with correlation coefficients of r=0.995 5. The limits of detection for Bi3+ was 1.0×10-8 mol·L-1 (S/N=3). The selectivity of the proposed method was evaluated and the results showed that 1 000-fold K+, Ca2+, Na+, Mg2+, Cu2+; 100-fold Fe3+, Be2+, SiO2-_, Al3+, Ni2+, Sb3+, NO-₃, Cl-, F-, and 20-fold Pb2+, Hg2+, Cd2+ had negligible interference with the determination of Bi3+. The method has advantages of sensitivity, rapidness and low cost. It was used for the determination of Bi3+ in environmental water samples including pond water, rain water and sewage water with recoveries of 93.4%～105.2%.