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

Abstract

Novel TiO₂ nanosheets co-modified with MoS₂ quantum dots (MQDs) and N-doped carbon dots (NCDs), designated MQDs/NCDs/TiO₂, were synthesized through a simple and mild process. The MQDs/NCDs/TiO₂ nanocomposites exhibited significantly improved efficiency in the photocatalytic degradation of RhB compared to pure TiO₂, mainly attributed to the synergy of excellent photoconversion by NCDs and efficient separation and transfer of photogenerated electron–hole pairs induced by the two heterojunctions formed in MQDs/NCDs/TiO₂. More interestingly, 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 due to the excellent collaboration between the photocatalysis and persulfate activation, in which the persulfate was effectively activated by photogenerated electrons to generate abundant sulfate radicals (SO₄˙⁻) and hydroxyl radicals (˙OH); meanwhile, the electron consumption caused by the persulfate effectually restrained surface electron–hole 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 the MQDs/NCDs/TiO₂–PS system. This work may provide guidance for employing dual quantum dots as co-catalysts, cooperating with activated persulfate, to enhance photocatalytic performance in contaminant degradation.