Nitrogen-doped carbon dot impregnated g-C3N4/SnS2 nanocomposite as an efficient mediator and co-catalyst for enhanced photocatalytic degradation and water splitting

Noble metal electron mediators and co-catalysts have prevented further development of indirect Z-scheme systems for photocatalytic applications. Carbonaceous candidates have been one of the best alternatives to address this issue. For this purpose, in the present study, a novel nitrogen-doped carbon dot (N-DCD) impregnated g-C3N4/SnS2 heterostructure has been successfully synthesized with optimized contents of N-DCDs and SnS2 ultra-thin nanoflakes through thermal-impregnation and reflux methods. The most efficient nanocomposite containing 0.25 wt% N-DCDs and 2 wt% SnS2 exhibited methylene blue (MB) degradation rate constant of 0.032 min−1 and hydrogen (H2) production efficiency of 1622.2 μmol/g.h after 120 and 180 min visible light irradiation. The photodegradation rate constant was almost 32, 8, and 2, and H2 production efficiency was 16, 30, and 5 fold higher than g-C3N4, SnS2, and g-C3N4/2 wt% SnS2 (without N-DCDs), respectively. The photodegradation and H2 production efficiencies are enhanced by impregnated N-DCDs, which act as an electron mediator and noble metal-free co-catalyst. Through N-DCDs impregnation, the synergistic effect between SnS2 and up-conversion properties of N-DCDs was observed, resulting in the reduction of the band gap energy from 2.97 eV in g-C3N4 to 2.80 eV in the optimized ternary nanocomposite, as well as reductions in PL intensity and onset potential. The major active species throughout photocatalytic degradation reactions were superoxide and hydroxyl radicals, proposing a Z-scheme mechanism for charge transfer. The optimized ternary nanocomposite also exhibited outstanding photostability after recycling tests. This work highlighted the role of N-DCDs as a highly effective noble metal-free co-catalyst and electron mediator in photocatalytic applications. The raw/processed data required to reproduce these findings cannot be shared at this time due to legal or ethical reasons. •g-C3N4/ N-DCD/SnS2 heterostructure was prepared for photocatalytic applications.•N-DCDs and SnS2 nanoflakes were impregnated and grown on the g-C3N4 nanosheets.•Main active species in photodegradation were superoxide and hydroxyl radicals.•The role of N-DCDs as noble metal-free co-catalyst for H2 production was discussed.•A synergistic effect between N-DCDs up-conversion and SnS2 was observed.