N- and S-doped CQDs were prepared using L-cysteine as a precursor. Different NS-CQDs/g-C3N4 composite photocatalysts were formed by modifying graphite-phase carbon nitride with different contents of NS-CQDs using a hydrothermal method. The morphology, constituent elements and functional groups of the composite photocatalysts were analyzed by SEM, EDS, TEM, Mapping, XRD and FT-IR as a proof of its successful preparation. Meanwhile, it was characterized by PL, UV-Vis DRS and electrochemical impedance, which proved that the CQDs could be used as an electronic memory in the composite system to accelerate the electron transfer induced by the photo-excitation of g-C3N4 and effectively inhibit the recombination of e--h+ improvement of the photocatalytic activity of g-C3N4. The stability of the composite photocatalysts under different conditions and the photodegradation activity of Rh B under visible light were investigated. It was found that the photocatalytic degradation efficiency of rhodamine B by NS-CQDS-modified g-C3N4 was significantly higher than that of pure g-C3N4, which could reach 90.82%, and its degradation rate was 3.5 times higher than that of pure g-C3N4. It was demonstrated by free radical trapping experiments that ·OH and ·O2- were the main active species in the photocatalytic degradation process, in which ·O2- played a guiding role.
Keywords: CQDs/g-C3N4; photocatalytic activity; rhodamine B.