Hair fiber as a precursor for synthesizing of sulfur- and nitrogen-co-doped carbon dots with tunable luminescence properties

A novel one-step approach was developed for the large-scale synthesis of sulfur- and nitrogen-co-doped carbon dots (S-N-C-dots) by using sulfuric acid carbonization and etching of hair fiber. It was found that S and N can form different binding configurations in S-N-C-dots framework, such as -C-S- covalent bond of the thiophene-S and -C-SOx- (x = 2, 3, 4, sulfate or sulfonate) for S-doped, pyridinic N and pyrrolic N for N-doped, respectively. Moreover, higher reaction temperature was in favor of the formation of S-N-C-dots with smaller size, higher S content, and longer wavelength of photoluminescence emissions. The resulting S-N-C-dots also exhibited good luminescence stability, low toxicity, good biocompatibility, and high solubility. This approach may provide an efficient strategy for synthesizing heteroatom-co-doped carbon dots.