Nitrogen/sulfur Co-doping strategy to synthesis green-yellow emitting carbon dots derived from xylose: Toward application in pH sensing

It is still a great challenge to synthesize carbohydrate-derived carbon dots (CDs) with long-wavelength emissions via a green and facile strategy. Herein, novel xylose-derived CDs with green-yellow emission (i.e., GY-CDs) were synthesized due to the doping effect of S and N elements, using a one-pot microwave-assisted hydrothermal method . The maximum emission located at 533 nm under 460 nm excitation, and the absolute quantum yield was as high as 42.44%. To unveil the emission mechanism, green and blue emissive xylose-derived CDs doped with N were also synthesized, respectively. Comparative study and various structural characterizations revealed that introducing protonated amino groups and sulfur-related moieties can narrow the energy gaps within surface states and contribute to the green-yellow emission. Further, the GY-CDs not only displayed transmutation of luminescent centers when the solution pH was above 6, but also exhibited ratiometric fluorescence changes in the pH range of 6–10 under 360 and 460 nm excitation, such distinctive dual-mode response, which together with excellent anti-interference, good water solubility, and outstanding photostability enables the prepared GY-CDs to be potential pH nanosensors .