Covalently Interconnected Polymer Dot-WS₂Nanosheet 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 WS₂nanosheets with the COOH and SH functional group polymer dots named P-dots-COOH and P-dots-SH, respectively, we have developed P-dots-COOH/WS₂and P-dots-SH/WS₂heterostructure composites. The P-dots-COOH/WS₂80% heterostructure composite demonstrated a slightly higher current density (∼2.6 mA/cm²) than the individual P-dots (∼1.8 mA/cm²) and exfoliated WS₂nanosheets (∼2.0 mA/cm²). However, the P-dots-SH/WS₂80% 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 WS₂nanosheet (∼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 WS₂nanosheets 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 WS₂valence band position. These results indicate that photogenerated electrons can be transferred from the conduction band of WS₂to 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.