Carbon dots as solid-state electron mediator and electron acceptor in S-scheme heterojunction for boosted photocatalytic hydrogen evolution

Nowadays, it is still an attracting work to photocatalytic water splitting into hydrogen production using solar energy owing to its ecological and sustainable development significance. Herein, a ternary ZnIn2S4/carbon dots/g-C3N4 (ZIS/CDs/CN) S-scheme heterojunction photocatalyst with solid-state electron mediator and electron acceptor dual roles of CDs (∼5 nm) as a co-catalyst are designed via a calcination method follow-up water bath process for boosted photocatalytic H2 evolution. Compared to individual ZIS and pure CN, the photocatalytic efficiency of H2 evolution over ZIS/CDs/CN is enhanced by about 2 and 10 times, respectively. Combined with density functional theory (DFT) calculations, the heterojunction type between ZIS and CN is determined to be S-scheme heterojunction. In order to corroborate the role of CDs in S-scheme heterojunction, ZnIn2S4/g-C3N4 (ZIS/CN) was synthesized for comparative experiments and characterization, and its promotion of S-scheme heterojunction was confirmed. Furthermore, ZIS/CDs/CN S-scheme heterojunction photocatalyst still express excellent practicality in seawater environment and structural stability after four successive cycling reactions for photocatalytic H2 evolution. In addition, this bi-functional CDs is also applicable to S-scheme heterojunction constructed from other two different semiconductors, which enrich the construction method of later S-scheme heterojunctions and advance the development of S-scheme heterojunctions.