Chemiluminescence of graphene quantum dots induced by acidic potassium permanganate and its application to quenchometric flow-injection assays of hydroquinone in water

Graphene quantum dots (GQDs) with particle size of 4.5±1.0 nm were prepared and characterized by transmission electron microscopy, UV-vis absorption spectroscopy and fluorescence spectroscopy. It was found that KMnO4 could oxidize GQDs to produce a relatively intense chemiluminescence (CL) emission. The mechanism of CL generation was investigated based on absorption spectra and CL emission spectra. CL emission was attributed to the radiative recombination of oxidant-injected holes and thermally excited electrons in the GQDs. On the other hand, both KMnO4 and ∙O2− could react with GQDs to produce GQDs∙+ and GQDs∙−. The electron-transfer annihilation of GQDs∙+ and GQDs∙− could form excited-state GQDs*, which acted as the final emitter in the system. In order to show the analytic potential of GQDs-KMnO4 CL system, it was applied for the determination of hydroquinone based on its diminishing effect. Under the optimized conditions, the proposed CL system exhibits excellent analytic performance for determination of hydroquinone. Calibration curve in the range of 2.49×10−4-9.96×10−7 g mL−1 was linear with the correlation coefficient (r) of 0.9924. The limit of detection was 8.46×10−8 g mL−1, and the relative standard deviation (RSD) was found to be 1.7% for 11 determinations of 4.98×10−6 g mL−1 hydroquinone. The applicability of the method was verified by applying to real tap water, lake water, and waste water samples. The recoveries were in the range of 89.7-97.1% with RSD of 0.9-2.1%. The proposed method has a good linearity, high sensitivity and good repeatability and can be applied for routine determination of hydroquinone in water.