Fig. 1. Synthesis and size characterization of N/Al co-doped carbon dots. (a) Flow chart of synthesis ; (b) AFM image (height profile along mark lines shown in inset); (c) size distribution

Fig. 2. Optical properties of N/Al co-doped carbon dots. (a) UV-vis absorption spectrum; (b) fluorescence emission spectra

Fig. 3. FTIR characterization of N/Al co-doped carbon dots

Fig. 4. XPS characterization of as-prepared carbon dots. (a) Full spectra; (b) Al2p; (c) N1s; (d) C1s

Fig. 5. Environmental adaptability of N/Al co-doped carbon dots. (a) UV-irradiation; (b) salt ion(Na⁺); (c) temperature; (d) pH value

Fig. 6. Influence of H₂O₂ on fluorescence of N/Al co-doped carbon dots under different response time. (a)UV-Vis absorption spectra; (b) fluorescence emission spectra

Fig. 7. Response of carbon dot fluorescence to H₂O₂. (a) Fluorescence intensity of carbon dots versus concentration of H₂O₂; (b) quenching efficiency of carbon dots versus concentration of H₂O₂

Fig. 8. Detecting mechanism of H₂O₂ for carbon dots