A novel ternary MQDs/NCDs/TiO2 nanocomposite collaborated with activated persulfate for efficient RhB degradation under visible light irradiation

A novel MoS2 quantum dots (MQDs) and N-doped carbon dots (NCDs) co-modified TiO2 nanosheets (MQDs/NCDs/TiO2) were synthesized through a simple and gentle process. The MQDs/NCDs/TiO2 nanocomposites exhibited significantly improved efficiency for photocatalytic degradation of RhB compared to pure TiO2, which is mainly attributed to the synergy of excellent photoconversion function of NCDs and efficient separation and transfer of photogenerated electron-holes induced by two heterojunctions formed in MQDs/NCDs/TiO2. It is more interesting that the degradation rate was further promoted by 2.15 times after adding 2 mmol persulfate to the MQDs/NCDs/TiO2 photocatalytic system. This result is benefited from the excellent collaboration between photocatalysis and persulfate activation, in which the persulfate was effectively activated by photogenerated electrons to generate abundant sulfate radicals (SO4•-) and hydroxyl radicals (•OH), and meanwhile the electrons consumption caused by the persulfate effectually restrained surface electron-holes recombination, inducing more holes (h+) to participate in pollutant degradation. Radical quenching experiments and electron spin resonance spectra show that SO4•-, •OH, •O2- and h+ were all in charge of RhB elimination in MQDs/NCDs/TiO2-PS system. This work may provide a guidance for employing dual quantum dots as co-catalyst and cooperating with activated persulfate to enhance phtocatalytic performance in contaminant degradation.