Preparation of fluorescent carbon dots from mint leaves and its performance of photocatalytic degradation of organic dyes

The green fluorescent N-doped carbon dots （N-CDs） and （B，N）-doped carbon dots （B，N-CDs） were prepared from mint leaves by one-step hydrothermal method. The morphology structure， elementary composition，surface functional groups， and fluorescence properties of CDs were characterized by TEM， XRD，FT-IR，XPS， UV-Vis， and XRF. The results show that CDs are uniform in size and have hydrophilic groups such as —OH and —COOH on the surface. N-CDs and B，N-CDs are typical aromatic systems， with the maximum fluorescence emission peaks at 490 nm and 440 nm， respectively， exhibiting excitation light-dependent characteristics. After 120 min of simulated solar light， the degradation rate of methylene blue by N-CDs and B， N-CDs are 84% and 67%. The capture experiment result shows that h+，·O2-，and e- are the main active substances produced by N-CDs， and h+ and ·O2- are the main active substances produced by B，N-CDs in the photocatalytic process. The type and intensity of reactive oxygen species are verified using electron spin resonance （ESR） spectroscopy， and ·O2- is detected in both carbon dots. The photocatalytic process of N-CDs also produced more 1O2 than B， N-CDs， which resulted in a higher efficiency of N-CDs in photocatalytic degradation of MB than that of B， N-CDs.