Covalently Interconnected Polymer Dot–WS₂ Nanosheet Heterostructure for Visible Light-Driven Hydrogen Production

Photocatalytic hydrogen evolution is a promising solution to energy and environmental crises. The aim is to design an effective and strong photocatalyst that makes perfect use of solar energy. This is possible when catalysts have a good visible absorption ability, wide band gap, slow electron–hole pair recombination rate, and a large amount of active surface area. Considering the important properties of an excellent photocatalyst, in this work, by mixing variable amounts of chlorophyll-assisted exfoliated WS₂ nanosheets with the COOH and SH functional group polymer dots named P-dots-COOH and P-dots-SH, respectively, we have developed P-dots-COOH/WS₂ and P-dots-SH/WS₂ heterostructure composites. The P-dots-COOH/WS₂ 80% heterostructure composite demonstrated a slightly higher current density (∼2.6 mA/cm²) than the individual P-dots (∼1.8 mA/cm²) and exfoliated WS₂ nanosheets (∼2.0 mA/cm²). However, the P-dots-SH/WS₂ 80% heterostructure composite demonstrated almost 200% (∼4.6 mA/cm²) enhanced photocurrent density and low charge transfer resistance compared to P-dots-SH (∼2.0 mA/cm²) and WS₂ nanosheet (∼2.0 mA/cm²) materials. This was due to the coordination of the thiol functional group of P-dots-SH with the defect interface site of the chlorophyll-assisted exfoliated WS₂ nanosheets that reduced the charge transfer resistance, increased the number of electron–hole pairs, and reduced the electron–hole pair recombination rate. We discussed the possible photocatalytic hydrogen evolution mechanism in which the P-dots-SH valence band position was lower than the WS₂ valence band position. These results indicate that photogenerated electrons can be transferred from the conduction band of WS₂ to the conduction band of P-dots-SH, which reduces the possibility of recombination of electrons and holes and is more conducive to the transfer of electrons resulting in the hydrogen reduction potential, that is, the hydrogen production.