Fluorescence Mechanism Of Carbon Dots And Their Application In Ion Detection

Carbon dots(CDs)can be synthesized from various source materials and possess properties such as high quantum yield,broad fluorescence range,low toxicity and good resistance to photobleaching.CDs have been applied in areas such as bioimaging,chemical sensing,biosensing,photocatalysis and drug loading,etc.However,the fluorescence mechanism of CDs is still unclear.The mainstream researches focus on the surface defect states of CDs,while some other research demonstrated that the fluorescence of CDs synthesized from citric acid originates from fluorescent molecules.Potassium ferricyanide is applied in gold cyanidation,munition and photographic processing industries.Although the toxicity of ferricyanide([Fe(CN)3]-)is relatively low,highly toxic cyanide(CN-)can be released if ferricyanide reacts to other chelators that exists in nature.The existing methods for ferricyanide detection are not satisfactory due to their low sensitivity.To further elucidate the fluorescence mechanism of CDs and explore facile and sensitive ferricyanide detection method,the following study are proposed:(1)Seven kinds of CDs were synthesized with bottom-up synthesis methods,namely hydrothermal,solvothermal and microwave synthesis.Comparisons of absorption and fluorescence peak locations and excitation dependence of fluorescence between CDs and corresponding dialysate shows their fluorescence homogeneity.Analysis of mass spectra of dialysates and comparisons of quantum yield,photobleaching,signal to noise ratio of absorption peaks between CDs and corresponding dialysates demonstrate the universality of the existence of fluorophores and their contribution to CDs’ fluorescence.(2)CDs exhibiting green fluorescence are synthesized via microwave treatment of mixed citric acid and urea solution.The as-synthesized CDs possess high quantum yield and good stability.The existence of fluorophores in the dialysate of CDs is demonstrated by the mass spectrum.By the comparison between CDs and dialysate with different surface oxidation states,it can be established that the CDs’ fluorescence can be attributed to the existence of fluorophores and surface defect states.Since the absorption peaks of CDs and ferricyanide overlap,ferricyanide will quench the fluorescence of CDs solution.Combining the change of the fluorescence and absorption spectra of CDs solution in the presence of ferricyanide,sensitive and selective detection of ferricyanide is achieved.